An effective medium approach to predict the apparent contact angle of drops on super-hydrophobic randomly rough surfaces.

PubMed

Bottiglione, F; Carbone, G

2015-01-14

The apparent contact angle of large 2D drops with randomly rough self-affine profiles is numerically investigated. The numerical approach is based upon the assumption of large separation of length scales, i.e. it is assumed that the roughness length scales are much smaller than the drop size, thus making it possible to treat the problem through a mean-field like approach relying on the large-separation of scales. The apparent contact angle at equilibrium is calculated in all wetting regimes from full wetting (Wenzel state) to partial wetting (Cassie state). It was found that for very large values of the roughness Wenzel parameter (r(W) > -1/ cos θ(Y), where θ(Y) is the Young's contact angle), the interface approaches the perfect non-wetting condition and the apparent contact angle is almost equal to 180°. The results are compared with the case of roughness on one single scale (sinusoidal surface) and it is found that, given the same value of the Wenzel roughness parameter rW, the apparent contact angle is much larger for the case of a randomly rough surface, proving that the multi-scale character of randomly rough surfaces is a key factor to enhance superhydrophobicity. Moreover, it is shown that for millimetre-sized drops, the actual drop pressure at static equilibrium weakly affects the wetting regime, which instead seems to be dominated by the roughness parameter. For this reason a methodology to estimate the apparent contact angle is proposed, which relies only upon the micro-scale properties of the rough surface.

Contact angle measurement with a smartphone

NASA Astrophysics Data System (ADS)

Chen, H.; Muros-Cobos, Jesus L.; Amirfazli, A.

2018-03-01

In this study, a smartphone-based contact angle measurement instrument was developed. Compared with the traditional measurement instruments, this instrument has the advantage of simplicity, compact size, and portability. An automatic contact point detection algorithm was developed to allow the instrument to correctly detect the drop contact points. Two different contact angle calculation methods, Young-Laplace and polynomial fitting methods, were implemented in this instrument. The performance of this instrument was tested first with ideal synthetic drop profiles. It was shown that the accuracy of the new system with ideal synthetic drop profiles can reach 0.01% with both Young-Laplace and polynomial fitting methods. Conducting experiments to measure both static and dynamic (advancing and receding) contact angles with the developed instrument, we found that the smartphone-based instrument can provide accurate and practical measurement results as the traditional commercial instruments. The successful demonstration of use of a smartphone (mobile phone) to conduct contact angle measurement is a significant advancement in the field as it breaks the dominate mold of use of a computer and a bench bound setup for such systems since their appearance in 1980s.

Contact angle measurement with a smartphone.

PubMed

Chen, H; Muros-Cobos, Jesus L; Amirfazli, A

2018-03-01

In this study, a smartphone-based contact angle measurement instrument was developed. Compared with the traditional measurement instruments, this instrument has the advantage of simplicity, compact size, and portability. An automatic contact point detection algorithm was developed to allow the instrument to correctly detect the drop contact points. Two different contact angle calculation methods, Young-Laplace and polynomial fitting methods, were implemented in this instrument. The performance of this instrument was tested first with ideal synthetic drop profiles. It was shown that the accuracy of the new system with ideal synthetic drop profiles can reach 0.01% with both Young-Laplace and polynomial fitting methods. Conducting experiments to measure both static and dynamic (advancing and receding) contact angles with the developed instrument, we found that the smartphone-based instrument can provide accurate and practical measurement results as the traditional commercial instruments. The successful demonstration of use of a smartphone (mobile phone) to conduct contact angle measurement is a significant advancement in the field as it breaks the dominate mold of use of a computer and a bench bound setup for such systems since their appearance in 1980s.

Microscopic description of a drop on a solid surface.

PubMed

Ruckenstein, Eli; Berim, Gersh O

2010-06-14

Two approaches recently suggested for the treatment of macro- or nanodrops on smooth or rough, planar or curved, solid surfaces, based on fluid-fluid and fluid-solid interaction potentials are reviewed. The first one employs the minimization of the total potential energy of a drop by assuming that the drop has a well defined profile and a constant liquid density in its entire volume with the exception of the monolayer nearest to the surface where the density has a different value. As a result, a differential equation for the drop profile as well as the necessary boundary conditions are derived which involve the parameters of the interaction potentials and do not contain such macroscopic characteristics as the surface tensions. As a consequence, the macroscopic and microscopic contact angles which the drop profile makes with the surface can be calculated. The macroscopic angle is obtained via the extrapolation of the circular part of the drop profile valid at some distance from the surface up to the solid surface. The microscopic angle is formed at the intersection of the real profile (which is not circular near the surface) with the surface. The theory provides a relation between these two angles. The ranges of the microscopic parameters of the interaction potentials for which (i) the drop can have any height (volume), (ii) the drop can have a restricted height but unrestricted volume, and (iii) a drop cannot be formed on the surface were identified. The theory was also extended to the description of a drop on a rough surface. The second approach is based on a nonlocal density functional theory (DFT), which accounts for the inhomogeneity of the liquid density and temperature effects, features which are missing in the first approach. Although the computational difficulties restrict its application to drops of only several nanometers, the theory can be applied indirectly to macrodrops by calculating the surface tensions and using the Young equation to determine the contact angle. Employing the canonical ensemble version of the DFT, nanodrops on smooth and rough solid surfaces could be investigated and their characteristics, such as the drop profile, contact angle, as well as the fluid density distribution inside the drop can be determined as functions of the parameters of the interaction potentials and temperature. It was found that the contact angle of the drop has a simple (quasi)universal dependence on the energy parameter epsilon(fs) of the fluid-solid interaction potential and temperature. The main feature of this dependence is the existence of a fixed value theta(0) of the contact angle theta which separates the solid substrates (characterized by the energy parameter epsilon(fs) of the fluid-solid interaction potential) into two classes with respect to their temperature dependence. For theta>theta(0) the contact angle monotonously increases and for theta

Statistical contact angle analyses; "slow moving" drops on a horizontal silicon-oxide surface.

PubMed

Schmitt, M; Grub, J; Heib, F

2015-06-01

Sessile drop experiments on horizontal surfaces are commonly used to characterise surface properties in science and in industry. The advancing angle and the receding angle are measurable on every solid. Specially on horizontal surfaces even the notions themselves are critically questioned by some authors. Building a standard, reproducible and valid method of measuring and defining specific (advancing/receding) contact angles is an important challenge of surface science. Recently we have developed two/three approaches, by sigmoid fitting, by independent and by dependent statistical analyses, which are practicable for the determination of specific angles/slopes if inclining the sample surface. These approaches lead to contact angle data which are independent on "user-skills" and subjectivity of the operator which is also of urgent need to evaluate dynamic measurements of contact angles. We will show in this contribution that the slightly modified procedures are also applicable to find specific angles for experiments on horizontal surfaces. As an example droplets on a flat freshly cleaned silicon-oxide surface (wafer) are dynamically measured by sessile drop technique while the volume of the liquid is increased/decreased. The triple points, the time, the contact angles during the advancing and the receding of the drop obtained by high-precision drop shape analysis are statistically analysed. As stated in the previous contribution the procedure is called "slow movement" analysis due to the small covered distance and the dominance of data points with low velocity. Even smallest variations in velocity such as the minimal advancing motion during the withdrawing of the liquid are identifiable which confirms the flatness and the chemical homogeneity of the sample surface and the high sensitivity of the presented approaches. Copyright © 2014 Elsevier Inc. All rights reserved.

Drop impact on spherical soft surfaces

NASA Astrophysics Data System (ADS)

Chen, Simeng; Bertola, Volfango

2017-08-01

The impact of water drops on spherical soft surfaces is investigated experimentally through high-speed imaging. The effect of a convex compliant surface on the dynamics of impacting drops is relevant to various applications, such as 3D ink-jet printing, where drops of fresh material impact on partially cured soft substrates with arbitrary shape. Several quantities which characterize the morphology of impacting drops are measured through image-processing, including the maximum and minimum spreading angles, length of the wetted curve, and dynamic contact angle. In particular, the dynamic contact angle is measured using a novel digital image-processing scheme based on a goniometric mask, which does not require edge fitting. It is shown that the surface with a higher curvature enhances the retraction of the spreading drop; this effect may be due to the difference of energy dissipation induced by the curvature of the surface. In addition, the impact parameters (elastic modulus, diameter ratio, and Weber number) are observed to significantly affect the dynamic contact angle during impact. A quantitative estimation of the deformation energy shows that it is significantly smaller than viscous dissipation.

Droplets move over viscoelastic substrates by surfing a ridge

PubMed Central

Karpitschka, S.; Das, S.; van Gorcum, M.; Perrin, H.; Andreotti, B.; Snoeijer, J. H.

2015-01-01

Liquid drops on soft solids generate strong deformations below the contact line, resulting from a balance of capillary and elastic forces. The movement of these drops may cause strong, potentially singular dissipation in the soft solid. Here we show that a drop on a soft substrate moves by surfing a ridge: the initially flat solid surface is deformed into a sharp ridge whose orientation angle depends on the contact line velocity. We measure this angle for water on a silicone gel and develop a theory based on the substrate rheology. We quantitatively recover the dynamic contact angle and provide a mechanism for stick–slip motion when a drop is forced strongly: the contact line depins and slides down the wetting ridge, forming a new one after a transient. We anticipate that our theory will have implications in problems such as self-organization of cell tissues or the design of capillarity-based microrheometers. PMID:26238436

Motion and shape of partially non-wetting drops on inclined surfaces

NASA Astrophysics Data System (ADS)

Puthenveettil, Baburaj A.; Senthilkumar K, Vijaya; Hopfinger, E. J.; IIT Madras-LEGI Collaboration

2011-11-01

We study high Reynolds number (Re) motion of partially non- wetting liquid drops on inclined surfaces using (i) water on Fluoro-Alkyl Silane (FAS) coated glass and (ii) mercury on glass. The high hysteresis (35°) water drop experiments have been conducted for a range of inclination angles 26° < α <62° which give a range of Capillary numbers 0 . 0003 < Ca < 0 . 0075 and 137 < Re < 3142 . For low hysteresis (6°) mercury on glass experiments, 5 .5° < α < 14 .3° so that 0 . 0002 < Ca < 0 . 0023 and 3037 < Re < 20069 . It is shown that when Re >>103 for water and Re >> 19 for mercury, the observed velocities are accounted for by a boundary layer flow model. The dimensionless velocity in the inertial regime, Ca√{ Re } scales as the modified Bond number (Bom), while Ca Bom at low Re . We show that even at high Re , the dynamic contact angles (θd) depend only on Ca , similar to that in low Re drops. Only the model by Shikhmurzaev is consistent with the variation of dynamic contact angles in both mercury and water drops. We show that the corner transition at the rear of the mercury drop occurs at a finite, receding contact angle, which is predicted by a wedge flow model that we propose. For water drops, there is a direct transition to a rivulet from the oval shape at a critical ratio of receding to static contact angles.

Contact angle of sessile drops in Lennard-Jones systems.

PubMed

Becker, Stefan; Urbassek, Herbert M; Horsch, Martin; Hasse, Hans

2014-11-18

Molecular dynamics simulations are used for studying the contact angle of nanoscale sessile drops on a planar solid wall in a system interacting via the truncated and shifted Lennard-Jones potential. The entire range between total wetting and dewetting is investigated by varying the solid-fluid dispersive interaction energy. The temperature is varied between the triple point and the critical temperature. A correlation is obtained for the contact angle in dependence of the temperature and the dispersive interaction energy. Size effects are studied by varying the number of fluid particles at otherwise constant conditions, using up to 150,000 particles. For particle numbers below 10,000, a decrease of the contact angle is found. This is attributed to a dependence of the solid-liquid surface tension on the droplet size. A convergence to a constant contact angle is observed for larger system sizes. The influence of the wall model is studied by varying the density of the wall. The effective solid-fluid dispersive interaction energy at a contact angle of θ = 90° is found to be independent of temperature and to decrease linearly with the solid density. A correlation is developed that describes the contact angle as a function of the dispersive interaction, the temperature, and the solid density. The density profile of the sessile drop and the surrounding vapor phase is described by a correlation combining a sigmoidal function and an oscillation term.

The Dynamics of Oblate Drop Between Heterogeneous Plates Under Alternating Electric Field. Non-uniform Field

NASA Astrophysics Data System (ADS)

Kashina, M. A.; Alabuzhev, A. A.

2018-02-01

The dynamics of the incompressible fluid drop under the non-uniform electric field are considered. The drop is bounded axially by two parallel solid planes and the case of heterogeneous plates is investigated. The external electric field acts as an external force that causes motion of the contact line. We assume that the electric current is alternative current and the AC filed amplitude is a spatially non-uniform function. In equilibrium, the drop has the form of a circular cylinder. The equilibrium contact angle is 0.5 π. In order to describe this contact line motion the modified Hocking boundary condition is applied: the velocity of the contact line is proportional to the deviation of the contact angle and the speed of the fast relaxation processes, which frequency is proportional to twice the frequency of the electric field. The Hocking parameter depends on the polar angle, i.e. the coefficient of the interaction between the plate and the fluid (the contact line) is a function of the plane coordinates. This function is expanded in a series of the Laplace operator eigenfunctions.

Capillary forces exerted by liquid drops caught between crossed cylinders. A 3-D meniscus problem with free contact line

NASA Technical Reports Server (NTRS)

Patzek, T. W.; Scriven, L. E.

1982-01-01

The Young-Laplace equation is solved for three-dimensional menisci between crossed cylinders, with either the contact line fixed or the contact angle prescribed, by means of the Galerkin/finite element method. Shapes are computed, and with them the practically important quantities: drop volume, wetted area, capillary pressure force, surface tension force, and the total force exerted by the drop on each cylinder. The results show that total capillary force between cylinders increases with decreasing contact angle, i.e. with better wetting. Capillary force is also increases with decreasing drop volume, approaching an asymptotic limit. However, the wetted area on each cylinder decreases with decreasing drop volume, which raises the question of the optimum drop volume to strive for, when permanent bonding is sought from solidified liquid. For then the strength of the bond is likely to depend upon the area of contact, which is the wetted area when the bonding agent was introduced in liquid form.

Drop evaporation on superhydrophobic PTFE surfaces driven by contact line dynamics.

PubMed

Ramos, S M M; Dias, J F; Canut, B

2015-02-15

In the present study, we experimentally study the evaporation modes and kinetics of sessile drops of water on highly hydrophobic surfaces (contact angle ∼160°), heated to temperatures ranging between 40° and 70 °C. These surfaces were initially constructed by means of controlled tailoring of polytetrafluoroethylene (PTFE) substrates. The evaporation of droplets was observed to occur in three distinct phases, which were the same for the different substrate temperatures. The drops started to evaporate in the constant contact radius (CCR) mode, then switched to a more complex mode characterized by a set of stick-slip events accompanied by a decrease in contact angle, and finally shifted to a mixed mode in which the contact radius and contact angle decreased simultaneously until the drops had completely evaporated. It is shown that in the case of superhydrophobic surfaces, the energy barriers (per unit length) associated with the stick-slip motion of a drop ranges in the nJ m(-1) scale. Furthermore, analysis of the evaporation rates, determined from experimental data show that, even in the CCR mode, a linear relationship between V(2/3) and the evaporation time is verified. The values of the evaporation rate constants are found to be higher in the pinned contact line regime (the CCR mode) than in the moving contact line regime. This behavior is attributed to the drop's higher surface to volume ratio in the CCR mode. Copyright © 2014 Elsevier Inc. All rights reserved.

Validation of a Novel Technique and Evaluation of the Surface Free Energy of Food

PubMed Central

Senturk Parreidt, Tugce; Schmid, Markus; Hauser, Carolin

2017-01-01

Characterizing the physical properties of a surface is largely dependent on determining the contact angle exhibited by a liquid. Contact angles on the surfaces of rough and irregularly-shaped food samples are difficult to measure using a contact angle meter (goniometer). As a consequence, values for the surface energy and its components can be mismeasured. The aim of this work was to use a novel contact angle measurement method, namely the snake-based ImageJ program, to accurately measure the contact angles of rough and irregular shapes, such as food samples, and so enable more accurate calculation of the surface energy of food materials. In order to validate the novel technique, the contact angles of three different test liquids on four different smooth polymer films were measured using both the ImageJ software with the DropSnake plugin and the widely used contact angle meter. The distributions of the values obtained by the two methods were different. Therefore, the contact angles, surface energies, and polar and dispersive components of plastic films obtained using the ImageJ program and the Drop Shape Analyzer (DSA) were interpreted with the help of simple linear regression analysis. As case studies, the superficial characteristics of strawberry and endive salad epicarp were measured with the ImageJ program and the results were interpreted with the Drop Shape Analyzer equivalent according to our regression models. The data indicated that the ImageJ program can be successfully used for contact angle determination of rough and strongly hydrophobic surfaces, such as strawberry epicarp. However, for the special geometry of droplets on slightly hydrophobic surfaces, such as salad leaves, the program code interpolation part can be altered. PMID:28425932

Hysteresis of Contact Angle of Sessile Droplets on Smooth Homogeneous Solid Substrates via Disjoining/Conjoining Pressure.

PubMed

Kuchin, I; Starov, V

2015-05-19

A theory of contact angle hysteresis of liquid droplets on smooth, homogeneous solid substrates is developed in terms of the shape of the disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all contact angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium contact angle θ ≠ θe, correspond to the state of slow "microscopic" advancing or receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This "microscopic" motion almost abruptly becomes fast "macroscopic" advancing or receding motion after the contact angle reaches the critical values θa or θr, correspondingly. The values of the static receding, θr, and static advancing, θa, contact angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown now that (i) both advancing and receding contact angles of a droplet on a on smooth, homogeneous solid substrate can be calculated based on shape of disjoining/conjoining pressure isotherm, and (ii) both advancing and receding contact angles depend on the drop volume and are not unique characteristics of the liquid-solid system. The latter is different from advancing/receding contact angles in thin capillaries. It is shown also that the receding contact angle is much closer to the equilibrium contact angle than the advancing contact angle. The latter conclusion is unexpected and is in a contradiction with the commonly accepted view that the advancing contact angle can be taken as the first approximation for the equilibrium contact angle. The dependency of hysteresis contact angles on the drop volume has a direct experimental confirmation.

Liquid-bridge stability and breakup on surfaces with contact-angle hysteresis.

PubMed

Akbari, Amir; Hill, Reghan J

2016-08-10

We study the stability and breakup of liquid bridges with a free contact line on surfaces with contact-angle hysteresis (CAH) under zero-gravity conditions. Non-ideal surfaces exhibit CAH because of surface imperfections, by which the constraints on three-phase contact lines are influenced. Given that interfacial instabilities are constraint-sensitive, understanding how CAH affects the stability and breakup of liquid bridges is crucial for predicting the drop size in contact-drop dispensing. Unlike ideal surfaces on which contact lines are always free irrespective of surface wettability, contact lines may undergo transitions from pinned to free and vice versa during drop deposition on non-ideal surfaces. Here, we experimentally and theoretically examine how stability and breakup are affected by CAH, highlighting cases where stability is lost during a transition from a pinned-pinned (more constrained) to pinned-free (less constrained) interface-rather than a critical state. This provides a practical means of expediting or delaying stability loss. We also demonstrate how the dynamic contact angle can control the contact-line radius following stability loss.

The effect of temperature, matrix alloying and substrate coatings on wettability and shear strength of Al/Al2O3 couples

NASA Astrophysics Data System (ADS)

Sobczak, N.; Ksiazek, M.; Radziwill, W.; Asthana, R.; Mikulowski, B.

2004-03-01

A fresh approach has been advanced to examine in the Al/Al2O3 system the effects of temperature, alloying of Al with Ti or Sn, and Ti and Sn coatings on the substrate, on contact angles measured using a sessile-drop test, and on interface strength measured using a modified push-off test that allows shearing of solidified droplets with less than 90 deg contact angle. In the modified test, the solidified sessile-drop samples are bisected perpendicular to the drop/Al2O3 interface at the midplane of the contact circle to obtain samples that permit bond strength measurement by stress application to the flat surface of the bisected couple. The test results show that interface strength is strongly influenced by the wetting properties; low contact angles correspond to high interface strength, which also exhibits a strong temperature dependence. An increase in the wettability test temperature led to an increase in the interface strength in the low-temperature range where contact angles were large and wettability was poor. The room-temperature shear tests conducted on thermally cycled sessile-drop test specimens revealed the effect of chemically formed interfacial oxides; a weakening of the thermally cycled Al/Al2O3 interface was caused under the following conditions: (1) slow contact heating and short contact times in the wettability test, and (2) fast contact heating and longer contact times. The addition of 6 wt pct Ti or 7 wt pct Sn to Al only marginally influenced the contact angle and interfacial shear strength. However, Al2O3 substrates having thin (<1 µm) Ti coatings yielded relatively low contact angles and high bond strength, which appears to be related to the dissolution of the coating in Al and formation of a favorable interface structure.

Investigation of pH response and photo-control of wettability on spiropyran-derivatized surfaces

NASA Astrophysics Data System (ADS)

Park, Choong-Do

2009-12-01

One promising method to control a liquid drop on a surface for microfluidic devices is to use the surface tension gradient on a photo-responsive surface by light irradiation. A photo-switchable spiropyran monolayer was prepared on smooth glass or silicon wafers via 3-aminopropylmethyldiethoxysilane linkages. The pH response of the surface-bound spiropyran was investigated by measuring contact angle as a function of pH, since the pH value of the liquids applied to a microfluidic system can vary widely. Based on the contact angle titration and UV-Vis spectroscopic data, a protonation and deprotonation mechanism of the surface-bound spiropyran was proposed. The advancing contact angles under UV and under visible light irradiation at high pH values were about 100 smaller than those at low pH values. The decrease in contact angle under UV light with decreasing pH value was assigned to the protonation of open merocyanine (MC) to MC-OH+. Meanwhile, the decrease in contact angle under visible light was attributed to the protonation of the closed spiropryan (SP), generating a mixed state of MC-OH+ in equilibrium with N-protonated SP-NH+. In order to examine the possibility of light-induced liquid drop motion on the spiropyran-derivatized smooth surfaces, the light-induced surface tension change between SP and MC was estimated using the contact angle hysteresis (CAH) and the Lifshitz---van der Waals/Acid-Base (LWAB) approaches based on the contact angle data. The average light-induced surface energy change between the two isomers under UV and visible light exposure was 1.4 mJ/m 2, implying that the small change in surface tension is not sufficient to move a liquid droplet on the surface. Liquid drop motion requires that the light-induced switching angle be greater than the contact angle hysteresis. However, the light-induced switching angle of the spiropyran-derivatized surface was significantly smaller than the hysteresis. Thus, in order to achieve liquid drop motion on the spiropyran-derivatized surface, a new surface design which employs a combination of chemical modification of a hydrophobic organosilane and micropatterned rough surface morphology was suggested.

Mixed Cassie-Baxter wetting states on a porous material stabilized by electrowetting

NASA Astrophysics Data System (ADS)

Lambert, Jérôme; Gauchet, Lucien; Crassous, Jérôme

2017-07-01

Electrowetting is used to force imbibition in model porous plates. These porous plates are sintered disordered bronze bead packings that are homogeneously coated with a constant-thickness layer of parylene. Cycles of increasing and decreasing voltage trigger the imbibition of a ionized water sessile drop by changing its contact angle with the porous material from non-wetting to wetting shapes. During a cycle, a drop experiences partial imbibition and a strong hysteresis of its contact angle with the porous plate. Since the imbibition process quickly stabilizes, we adopt an equilibrium description of the wetting properties of the drop on the porous plate. Our model, based on the Cassie-Baxter approach, shows that three different wetting states are experienced by the drop, one of which being made possible only by the modification of the contact angle inside the pores. Our model describes the experimental results very well.

Effect of Spreading Time on Contact Angle of Nanofluid on the Surface of Stainless Steel AISI 316 and Zircalloy 4

NASA Astrophysics Data System (ADS)

Prajitno, D. H.; Trisnawan, V.; Syarif, D. G.

2017-05-01

The solid surface tension plays an important role in the heat and mass transfer system for heat exchanger equipment. In the nuclear power plant industry, the stainless steel AISI 316 and Zircalloy 4 have been used for long time as structure materials. The purpose of the experimental is to study solid state surface tension behavior by measure contact angle Nano fluid contain nano particle alumina on metal surface of stainless steel AISI 316 and Zircalloy 4 by sessile drop method. The experiment is to measure the static contact angle and drop nano fluid contains nano particle alumina on stainless steel 316 and zircalloy 4 with different spreading time from 1 to 30 minute. It was observed that stainless steel 316 and zircalloy 4 lose their hydrophobic properties with increasing elapsed time during drop of nano fluid on the surface of alloy. As a result the contact angle of nano fluid on surface of metal is decrease with increasing elapsed time. While the magnitude diameter of drop nano fluid and wetting surface is increase with increasing elapsed time on the surface of the stainless steel SS 316 and Zircalloy 4.

Simulation of drop movement over an inclined surface using smoothed particle hydrodynamics.

PubMed

Das, Arup K; Das, Prasanta K

2009-10-06

Smoothed particle hydrodynamics (SPH) is used to numerically simulate the movement of drops down an inclined plane. Diffuse interfaces have been assumed for tracking the motion of the contact line. The asymmetric shape of the three-dimensional drop and the variation of contact angle along its periphery can be calculated using the simulation. During the motion of a liquid drop down an inclined plane, an internal circulation of liquid particles is observed due to gravitational pull which causes periodic change in the drop shape. The critical angle of inclination required for the inception of drop motion is also evaluated for different fluids as a function of drop volume. The numerical predictions exhibit a good agreement with the published experimental results.

Spreading of Electrolyte Drops on Charged Surfaces: Electric Double Layer Effects on Drop Dynamics

NASA Astrophysics Data System (ADS)

Bae, Kyeong; Sinha, Shayandev; Chen, Guang; Das, Siddhartha

2015-11-01

Drop spreading is one of the most fundamental topics of wetting. Here we study the spreading of electrolyte drops on charged surfaces. The electrolyte solution in contact with the charged solid triggers the formation of an electric double layer (EDL). We develop a theory to analyze how the EDL affects the drop spreading. The drop dynamics is studied by probing the EDL effects on the temporal evolution of the contact angle and the base radius (r). The EDL effects are found to hasten the spreading behaviour - this is commensurate to the EDL effects causing a ``philic'' tendency in the drops (i.e., drops attaining a contact angle smaller than its equilibrium value), as revealed by some of our recent papers. We also develop scaling laws to illustrate the manner in which the EDL effects make the r versus time (t) variation deviate from the well known r ~tn variation, thereby pinpointing the attainment of different EDL-mediated spreading regimes.

Equilibrium shapes of drops on membranes

NASA Astrophysics Data System (ADS)

Sharma, Ishan; Nair, Vineet; Shankar, Viswanathan

2017-11-01

Equilibrium shapes for axisymmetric sessile and pendant drops placed on / attached to geometrically nonlinear elastic membranes, in horizontal as well as inclined configurations, are obtained. The effective contact angle of the drop with the membrane, its contact radius, the maximum membrane displacement, and the volume of the drop is investigated for various values of Bond Number and membrane tension.

Piling-to-buckling transition in the drying process of polymer solution drop on substrate having a large contact angle.

PubMed

Kajiya, Tadashi; Nishitani, Eisuke; Yamaue, Tatsuya; Doi, Masao

2006-01-01

We studied the drying process of polymer solution drops placed on a substrate having a large contact angle with the drop. The drying process takes place in three stages. First, the droplet evaporates keeping the contact line fixed. Second, the droplet shrinks uniformly with receding contact line. Finally the contact line is pinned again, and the droplet starts to be deformed. The shape of the final polymer deposit changes from concave dot, to flat dot, and then to concave dot again with the increase of the initial polymer concentration. This shape change is caused by the gradual transition from the solute piling mechanism proposed by Deegan to the crust buckling mechanism proposed by de Gennes and Pauchard.

Energy stability of droplets and dry spots in a thin film model of hanging drops

NASA Astrophysics Data System (ADS)

Cheung, Ka-Luen; Chou, Kai-Seng

2017-10-01

The 2-D thin film equation describing the evolution of hang drops is studied. All radially symmetric steady states are classified, and their energy stability is determined. It is shown that the droplet with zero contact angle is the only global energy minimizer and the dry spot with zero contact angle is a strict local energy minimizer.

Equilibrium and stability of axisymmetric drops on a conical substrate under gravity

NASA Astrophysics Data System (ADS)

Nurse, A. K.; Colbert-Kelly, S.; Coriell, S. R.; McFadden, G. B.

2015-08-01

Motivated by recent investigations of toroidal tissue clusters that are observed to climb conical obstacles after self-assembly [Nurse et al., "A model of force generation in a three-dimensional toroidal cluster of cells," J. Appl. Mech. 79, 051013 (2012)], we study a related problem of the determination of the equilibrium and stability of axisymmetric drops on a conical substrate in the presence of gravity. A variational principle is used to characterize equilibrium shapes that minimize surface energy and gravitational potential energy subject to a volume constraint, and the resulting Euler equation is solved numerically using an angle/arclength formulation. The resulting equilibria satisfy a Laplace-Young boundary condition that specifies the contact angle at the three-phase trijunction. The vertical position of the equilibrium drops on the cone is found to vary significantly with the dimensionless Bond number that represents the ratio of gravitational and capillary forces; a global force balance is used to examine the conditions that affect the drop positions. In particular, depending on the contact angle and the cone half-angle, we find that the vertical position of the drop can either increase ("the drop climbs the cone") or decrease due to a nominal increase in the gravitational force. Most of the equilibria correspond to upward-facing cones and are analogous to sessile drops resting on a planar surface; however, we also find equilibria that correspond to downward facing cones that are instead analogous to pendant drops suspended vertically from a planar surface. The linear stability of the drops is determined by solving the eigenvalue problem associated with the second variation of the energy functional. The drops with positive Bond number are generally found to be unstable to non-axisymmetric perturbations that promote a tilting of the drop. Additional points of marginal stability are found that correspond to limit points of the axisymmetric base state. Drops that are far from the tip are subject to azimuthal instabilities with higher mode numbers that are analogous to the Rayleigh instability of a cylindrical interface. We have also found a range of completely stable solutions that correspond to small contact angles and cone half-angles.

Flow visualization and characterization of evaporating liquid drops

NASA Technical Reports Server (NTRS)

Chao, David F. (Inventor); Zhang, Nengli (Inventor)

2004-01-01

An optical system, consisting of drop-reflection image, reflection-refracted shadowgraphy and top-view photography, is used to measure the spreading and instant dynamic contact angle of a volatile-liquid drop on a non-transparent substrate. The drop-reflection image and the shadowgraphy is shown by projecting the images of a collimated laser beam partially reflected by the drop and partially passing through the drop onto a screen while the top view photograph is separately viewed by use of a camera video recorder and monitor. For a transparent liquid on a reflective solid surface, thermocapillary convection in the drop, induced by evaporation, can be viewed nonintrusively, and the drop real-time profile data are synchronously recorded by video recording systems. Experimental results obtained from this technique clearly reveal that evaporation and thermocapillary convection greatly affect the spreading process and the characteristics of dynamic contact angle of the drop.

Modeling, investigation and formulation of hydrophobic coatings for potential self-cleaning applications

NASA Astrophysics Data System (ADS)

Rios, Pablo Fabian

Self-cleaning surfaces have received a great deal of attention, both in research and commercial applications. Transparent and non-transparent self-cleaning surfaces are highly desired. The Lotus flower is a symbol of purity in Asian cultures, even when rising from muddy waters it stays clean and untouched by dirt. The Lotus leaf "self-cleaning" surface is hydrophobic and rough, showing a two-layer morphology. While hydrophobicity produces a high contact angle, surface morphology reduces the adhesion of dirt and water to the surface, thus water drops slide easily across the leaf carrying the dirt particles with them. Nature example in the Lotus-effect and extensive scientific research on related fields have rooted wide acceptance that high hydrophobicity can be obtained only by a proper combination of surface chemistry and roughness. Most researchers relate hydrophobicity to a high contact angle. However, the contact angle is not the only parameter that defines liquid-solid interactions. An additional parameter, the sliding angle, related to the adhesion between the liquid drop and the solid surface is also important in cases where liquid sliding is involved, such as self-cleaning applications. In this work, it is postulated that wetting which is related to the contact angle, and interfacial adhesion, which is related to the sliding angle, are interdependent phenomena and have to be considered simultaneously. A variety of models that relate the sliding angle to forces developed along the contact line between a liquid drop and a solid surface have been proposed in the literature. A new model is proposed here that quantifies the drop sliding phenomenon, based also on the interfacial adhesion across the contact area of the liquid/solid interface. The effects of roughness and chemical composition on the contact and sliding angles of hydrophobic smooth and rough surfaces were studied theoretically and experimentally. The validity of the proposed model was investigated and compared with the existing models. Ultra-hydrophobic non-transparent and transparent coatings for potential self-cleaning applications were produced using hydrophobic chemistry and different configurations of roughening micro and nano-particles, however they present low adhesion and durability. Durability and stability enhancement of such coatings was attempted and improved by different methods.

Motion of Drops on Surfaces with Wettability Gradients

NASA Technical Reports Server (NTRS)

Subramanian, R. Shankar; McLaughlin, John B.; Moumen, Nadjoua; Qian, Dongying

2002-01-01

A liquid drop present on a solid surface can move because of a gradient in wettability along the surface, as manifested by a gradient in the contact angle. The contact angle at a given point on the contact line between a solid and a liquid in a gaseous medium is the angle between the tangent planes to the liquid and the solid surfaces at that point and is measured within the liquid side, by convention. The motion of the drop occurs in the direction of increasing wettability. The cause of the motion is the net force exerted on the drop by the solid surface because of the variation of the contact angle around the periphery. This force causes acceleration of an initially stationary drop, and leads to its motion in the direction of decreasing contact angle. The nature of the motion is determined by the balance between the motivating force and the resisting hydrodynamic force from the solid surface and the surrounding gaseous medium. A wettability gradient can be chemically induced as shown by Chaudhury and Whitesides who provided unambiguous experimental evidence that drops can move in such gradients. The phenomenon can be important in heat transfer applications in low gravity, such as when condensation occurs on a surface. Daniel et al have demonstrated that the velocity of a drop on a surface due to a wettability gradient in the presence of condensation can be more than two orders of magnitude larger than that observed in the absence of condensation. In the present research program, we have begun to study the motion of a drop in a wettability gradient systematically using a model system. Our initial efforts will be restricted to a system in which no condensation occurs. The experiments are performed as follows. First, a rectangular strip of approximate dimensions 10 x 20 mm is cut out of a silicon wafer. The strip is cleaned thoroughly and its surface is exposed to the vapor from an alkylchlorosilane for a period lasting between one and two minutes inside a desiccator. This is done using an approximate line source of the vapor in the form of a string soaked in the alkylchlorosilane. Ordinarily, many fluids, including water, wet the surface of silicon quite well. This means that the contact angle is small. But the silanized surface resists wetting, with contact angles that are as large as 100 degs. Therefore, a gradient of wettability is formed on the silicon surface. The region near the string is highly hydrophobic, and the contact angle decreases gradually toward a small value at the hydrophilic end away from this region. The change in wettability occurs over a distance of several mm. The strip is placed on a platform within a Plexiglas cell. Drops of a suitable liquid are introduced on top of the strip near the hydrophobic end. An optical system attached to a video camera is trained on the drop so that images of the moving drop can be captured on videotape for subsequent analysis. We have performed preliminary experiments with water as well as ethylene glycol drops. Results from these experiments will be presented in the poster. Future plans include the refinement of the experimental system so as to permit images to be recorded from the side as well as the top, and the conduct of a systematic study in which the drop size is varied over a good range. Experiments will be conducted with different fluids so as to obtain the largest possible range of suitably defined Reynolds and Capillary numbers. Also, an effort will be initiated on theoretical modeling of this motion. The challenges in the development of the theoretical description lie in the proper analysis of the region in the vicinity of the contact line, as well as in the free boundary nature of the problem. It is known that continuum models assuming the no slip condition all the way to the contact line fail by predicting that the stress on the solid surface becomes singular as the contact line is approached. One approach for dealing with this issue has been to relax the no-slip boundary condition using the Navier model. Molecular dynamics simulations of the contact line region show that for a non-polar liquid on a solid surface, the no-slip boundary condition is in fact incorrect near the contact line. Furthermore, the same simulations also show that the usual relationship between stress and the rate of deformation breaks down in the vicinity of the contact line. In developing continuum theoretical models of the system, we shall accommodate this knowledge to the extent possible.

Experimental Measurements of Spreading of Volatile Liquid Droplets

NASA Technical Reports Server (NTRS)

Zhang, Neng-Li; Chao, David F.

2001-01-01

Based on the laser shadowgraphic system used by the first author of the present paper, a simple optical system, which combined the laser shadowgraphy and the direct magnified-photography, has been developed to measure the contact angle, the spreading speed, and the evaporation rate. Additionally, the system can also visualize thermocapillary convection inside of a sessile drop simultaneously. The experimental results show that evaporation/condensation and thermocapillary convection in the sessile drop induced by the evaporation strongly affects the wetting and spreading of the drop. Condensation always promotes the wetting and spreading of the drop. Evaporation may increase or decrease the contact angle of the evaporating sessile drops, depending on the evaporation rate. The thermocapillary convection in the drop induced by the evaporation enhances the effects of evaporation to suppress the spreading.

Evaporation of pure liquid sessile and spherical suspended drops: a review.

PubMed

Erbil, H Yildirim

2012-01-15

A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by a contact line and characterized by contact angle, contact radius and drop height. Diffusion-controlled evaporation of a sessile drop in an ambient gas is an important topic of interest because it plays a crucial role in many scientific applications such as controlling the deposition of particles on solid surfaces, in ink-jet printing, spraying of pesticides, micro/nano material fabrication, thin film coatings, biochemical assays, drop wise cooling, deposition of DNA/RNA micro-arrays, and manufacture of novel optical and electronic materials in the last decades. This paper presents a review of the published articles for a period of approximately 120 years related to the evaporation of both sessile drops and nearly spherical droplets suspended from thin fibers. After presenting a brief history of the subject, we discuss the basic theory comprising evaporation of micrometer and millimeter sized spherical drops, self cooling on the drop surface and evaporation rate of sessile drops on solids. The effects of drop cooling, resultant lateral evaporative flux and Marangoni flows on evaporation rate are also discussed. This review also has some special topics such as drop evaporation on superhydrophobic surfaces, determination of the receding contact angle from drop evaporation, substrate thermal conductivity effect on drop evaporation and the rate evaporation of water in liquid marbles. Copyright © 2011 Elsevier B.V. All rights reserved.

Effect of surface texturing on superoleophobicity, contact angle hysteresis, and "robustness".

PubMed

Zhao, Hong; Park, Kyoo-Chul; Law, Kock-Yee

2012-10-23

Previously, we reported the creation of a fluorosilane (FOTS) modified pillar array silicon surface comprising ~3-μm-diameter pillars (6 μm pitch with ~7 μm height) that is both superhydrophobic and superoleophobic, with water and hexadecane contact angles exceeding 150° and sliding angles at ~10° owing to the surface fluorination and the re-entrant structure in the side wall of the pillar. In this work, the effects of surface texturing (pillar size, spacing, and height) on wettability, contact angle hysteresis, and "robustness" are investigated. We study the static, advancing, and receding contact angles, as well as the sliding angles as a function of the solid area fraction. The results reveal that pillar size and pillar spacing have very little effect on the static and advancing contact angles, as they are found to be insensitive to the solid area fraction from 0.04 to ~0.4 as the pillar diameter varies from 1 to 5 μm and the center-to-center spacing varies from 4.5 to 12 μm. On the other hand, sliding angle, receding contact angle, and contact angle hysteresis are found to be dependent on the solid area fraction. Specifically, receding contact angle decreases and sliding angle and hysteresis increase as the solid area fraction increases. This effect can be attributable to the increase in pinning as the solid area fraction increases. Surface Evolver modeling shows that water wets and pins the pillar surface whereas hexadecane wets the pillar surface and then penetrates into the side wall of the pillar with the contact line pinning underneath the re-entrant structure. Due to the penetration of the hexadecane drop into the pillar structure, the effect on the receding contact angle and hysteresis is larger relative to that of water. This interpretation is supported by studying a series of FOTS pillar array surfaces with varying overhang thickness. With the water drop, the contact line is pinned on the pillar surface and very little overhang thickness effect was observed. On the other hand, the hexadecane drop is shown to wet the pillar surface and the side wall of the overhang. It then pins at the lower edge of the overhang structure. A plot of the thickness of the overhang as a function of the static, advancing, and receding contact angles and sliding angle of hexadecane reveals that static, advancing, and receding contact angles decrease and sliding angle increases as the thickness of the overhang increases. A larger overhang effect is observed with octane due to its lower surface tension. The robustness of the pillar array surface against external pressure induced wetting and abrasion was modeled. Surface Evolver simulation (with the hexadecane drop) indicates that wetting breakthrough pressure as high as ~70 kPa is achievable with 0.5-μm-diameter pillar array FOTS surfaces. Mechanical modeling shows that bending of the pillars is the key failure by abrasion, which can be avoided with a short pillar structure. The path to fabricate a superoleophobic surface that can withstand the external force equivalent of a gentle cleaning blade (up to ~30 kPa) without wetting and abrasion failure is discussed.

Experimental studies of contact angle hysteresis phenomena on polymer surfaces – Toward the understanding and control of wettability for different applications.

PubMed

Grundke, K; Pöschel, K; Synytska, A; Frenzel, R; Drechsler, A; Nitschke, M; Cordeiro, A L; Uhlmann, P; Welzel, P B

2015-08-01

Contact angle hysteresis phenomena on polymer surfaces have been studied by contact angle measurements using sessile liquid droplets and captive air bubbles in conjunction with a drop shape method known as Axisymmetric Drop Shape Analysis - Profile (ADSA-P). In addition, commercially available sessile drop goniometer techniques were used. The polymer surfaces were characterized with respect to their surface structure (morphology, roughness, swelling) and surface chemistry (elemental surface composition, acid-base characteristics) by scanning electron microscopy (SEM), scanning force microscopy (SFM), ellipsometry, X-ray photoelectron spectroscopy (XPS) and streaming potential measurements. Heterogeneous polymer surfaces with controlled roughness and chemical composition were prepared by different routes using plasma etching and subsequent dip coating or grafting of polymer brushes, anodic oxidation of aluminium substrates coated with thin polymer films, deposition techniques to create regular patterned and rough fractal surfaces from core-shell particles, and block copolymers. To reveal the effects of swelling and reorientation at the solid/liquid interface contact angle hysteresis phenomena on polyimide surfaces, cellulose membranes, and thermo-responsive hydrogels have been studied. The effect of different solutes in the liquid (electrolytes, surfactants) and their impact on contact angle hysteresis were characterized for solid polymers without and with ionizable functional surface groups in aqueous electrolyte solutions of different ion concentrations and pH and for photoresist surfaces in cationic aqueous surfactant solutions. The work is an attempt toward the understanding of contact angle hysteresis phenomena on polymer surfaces aimed at the control of wettability for different applications. Copyright © 2014 Elsevier B.V. All rights reserved.

Corner wetting during the vapor-liquid-solid growth of faceted nanowires

NASA Astrophysics Data System (ADS)

Spencer, Brian; Davis, Stephen

2016-11-01

We consider the corner wetting of liquid drops in the context of vapor-liquid-solid growth of nanowires. Specifically, we construct numerical solutions for the equilibrium shape of a liquid drop on top of a faceted nanowire by solving the Laplace-Young equation with a free boundary determined by mixed boundary conditions. A key result for nanowire growth is that for a range of contact angles there is no equilibrium drop shape that completely wets the corner of the faceted nanowire. Based on our numerical solutions we determine the scaling behavior for the singular surface behavior near corners of the nanowire in terms of the Young contact angle and drop volume.

Fabrication of a silica aerogel and examination of its hydrophobic properties via contact angle and 3M water repellency tests

NASA Astrophysics Data System (ADS)

Mazrouei-Sebdani, Z.; Javazmi, L.; Khoddami, A.; Shams-Ghahfarokhi, F.; Low, T.

2017-05-01

Aerogels are dry gels with a very high specific pore volume. Aerogels with increased hydrophobicity have significant potential to expand their use as lightweight materials. Considering its special nanostructure and exceptional properties, this paper focuses on the synthesis and hydrophobic evaluation of a silica aerogel. The structural properties were investigated by measuring density, SEM micrographs, and BET analyses. Also, the hydrophobic evaluation was carried out by measuring 3M water repellency and water/alcohol contact angle. The BET analysis showed successful synthesis of the nanoporous silica aerogel with a pore size of 24 nm and porosity of 89%. The synthesized aerogel showed 3M water repellency of 3 and water contact angle of 129.6°. Also, it is worth-mentioning that as the alcohol content of the drops in 3M water repellency test is increased, the drop contact angle is decreased due to its lower surface tension. Thus, the contact angle reaches the zero at 3M water repellency test number of 4 (water/alcohol 60/40).

Contact angle control of sessile drops on a tensioned web

NASA Astrophysics Data System (ADS)

Park, Janghoon; Kim, Dongguk; Lee, Changwoo

2018-04-01

In this study, the influence of the change of tension applied to flexible and thin web substrate on the contact angle of sessile drop in roll-to-roll system was investigated. Graphene oxide and deionized water solutions were used in the experiments. Tension was changed to 29, 49, and 69 N, and the casting distance of the micropipette and the material was set to 10, 20, and 40 mm, and the droplet volume was set to 10, 20, and 30 μL, respectively. Statistical analysis of three variables and analysis of the variance methodology showed that the casting distance was most significant for the contact angle change, and the most interesting tension variable was also affected. The change in tension caused the maximum contact angle to change by 5.5°. The tension was not uniform in the width direction. When the droplet was applied in the same direction in the width direction, it was confirmed that the tension unevenness had great influence on the contact angle up to 11°. Finally, the casting distance, which has a large effect on the contact angle, was calibrated in the width direction to reduce the width direction contact angle deviation to 1%. This study can be applied to fine patterning research using continuous inkjet printing and aerosol jet printing, which are roll-to-roll processes based on droplet handling.

Evaporation of liquid droplets on solid substrates. I. Flat substrate with pinned or moving contact line

NASA Astrophysics Data System (ADS)

Amini, Amirhossein; Homsy, G. M.

2017-04-01

We study the evolution of the profile of a two-dimensional volatile liquid droplet that is evaporating on a flat heated substrate. We adopt a one-sided model with thermal control that, together with the lubrication approximation, results in an evolution equation for the local height of the droplet. Without requiring any presumption for the shape of the drop, the problem is formulated for the two modes of evaporation: a pinned contact line and a moving contact line with fixed contact angle. Numerical solutions are provided for each case. For the pinned contact line case, we observe that after a time interval the contact angle dynamics become nonlinear and, interestingly, the local contact angle goes to zero in advance of total evaporation of the drop. For the case of a moving contact line, in which the singularity at the contact line is treated by a numerical slip model, we find that the droplet nearly keeps its initial circular shape and that the contact line recedes with constant speed.

Diminution of contact angle hysteresis under the influence of an oscillating force.

PubMed

Manor, Ofer

2014-06-17

We suggest a simple quantitative model for the diminution of contact angle hysteresis under the influence of an oscillatory force invoked by thermal fluctuations, substrate vibrations, acoustic waves, or oscillating electric fields. Employing force balance rather than the usual description of contact angle hysteresis in terms of Gibbs energy, we highlight that a wetting system, such as a sessile drop or a bubble adhered to a solid substrate, appears at long times to be partially or fully independent of contact angle hysteresis and thus independent of static friction forces, as a result of contact line pinning. We verify this theory by studying several well-known experimental observations such as the approach of an arbitrary contact angle toward the Young contact angle and the apparent decrease (or increase) in an advancing (or a receding) contact angle under the influence of an external oscillating force.

Directional self-cleaning superoleophobic surface.

PubMed

Zhao, Hong; Law, Kock-Yee

2012-08-14

In this work, we report the creation of a grooved surface comprising 3 μm grooves (height ~4 μm) separated by 3 μm from each other on a silicon wafer by photolithography. The grooved surface was then modified chemically with a fluorosilane layer (FOTS). The surface property was studied by both static and dynamic contact angle measurements using water, hexadecane, and a polyethylene wax ink as the probing liquids. Results show that the grooved surface is both superhydrophobic and superoleophobic. Its observed contact angles agree well with the calculated Cassie-Baxter angles. More importantly, we are able to make a replica of the composite wax ink-air interface and study it by SEM. Microscopy results not only show that the droplet of the wax ink "sits" on air in the composite interface but also further reveal that the ink drop actually pins underneath the re-entrant structure in the side wall of the grooved structure. Contact angle measurement results indicate that wetting on the grooved surface is anisotropic. Although liquid drops are found to have lower static and advancing contact angles in the parallel direction, the drops are found to be more mobile, showing smaller hysteresis and lower sliding angles (as compared to the FOTS wafer surface and a comparable 3-μm-diameter pillar array FOTS surface). The enhanced mobility is attributable to the lowering of the resistance against an advancing liquid because 50% of the advancing area is made of a solid strip where the liquid likes to wet. This also implies that the contact line for advancing is no longer smooth but rather is ragged, having the solid strip area leading the wetting and the air strip area trailing behind. This interpretation is supported by imaging the geometry of the contact lines using molten ink drops recovered from the sliding angle experiments in both the parallel and orthogonal directions. Because the grooved surface is mechanically stronger against mechanical abrasion, the self-cleaning effect exhibited in the parallel direction suggests that groove texturing is a viable approach to create mechanically robust, self-cleaning, superoleophobic surfaces.

Characteristics and self-cleaning effect of the transparent super-hydrophobic film having nanofibers array structures

NASA Astrophysics Data System (ADS)

Lee, Kyungjun; Lyu, Sungnam; Lee, Sangmin; Kim, Youn Sang; Hwang, Woonbong

2010-09-01

Transparent super-hydrophobic films were fabricated using the PDMS method and silane process, based on anodization in phosphoric acid. Contact angle tests were performed to determine the contact angle of each film according to the anodizing time. Transmittance tests also were performed to obtain the transparency of each TPT (trimethylolpropane propoxylate triacrylate) replica film according to the anodizing time. The contact angle was determined by studying the drop shape, and the transmittance was measured using a UV-spectrometer. The contact angle increases with increasing anodizing time, because increasing pillar length can trap more air between the TPT replica film and a drop of water. The transmittance falls with increasing anodizing time because the increasing pillar length causes a scattering effect. This study shows that the pillar length and transparency are inversely proportional. The TPT replica film having nanofibers array structures was better than other films in aspect of self-cleaning by doing quantitative experimentation.

Contact angle of unset elastomeric impression materials.

PubMed

Menees, Timothy S; Radhakrishnan, Rashmi; Ramp, Lance C; Burgess, John O; Lawson, Nathaniel C

2015-10-01

Some elastomeric impression materials are hydrophobic, and it is often necessary to take definitive impressions of teeth coated with some saliva. New hydrophilic materials have been developed. The purpose of this in vitro study was to compare contact angles of water and saliva on 7 unset elastomeric impression materials at 5 time points from the start of mixing. Two traditional polyvinyl siloxane (PVS) (Aquasil, Take 1), 2 modified PVS (Imprint 4, Panasil), a polyether (Impregum), and 2 hybrid (Identium, EXA'lence) materials were compared. Each material was flattened to 2 mm and a 5 μL drop of distilled water or saliva was dropped on the surface at 25 seconds (t0) after the start of mix. Contact angle measurements were made with a digital microscope at initial contact (t0), t1=2 seconds, t2=5 seconds, t3=50% working time, and t4=95% working time. Data were analyzed with a generalized linear mixed model analysis, and individual 1-way ANOVA and Tukey HSD post hoc tests (α=.05). For water, materials grouped into 3 categories at all time-points: the modified PVS and one hybrid material (Identium) produced the lowest contact angles, the polyether material was intermediate, and the traditional PVS materials and the other hybrid (EXA'lence) produced the highest contact angles. For saliva, Identium, Impregum, and Imprint 4 were in the group with the lowest contact angle at most time points. Modified PVS materials and one of the hybrid materials are more hydrophilic than traditional PVS materials when measured with water. Saliva behaves differently than water in contact angle measurement on unset impression material and produces a lower contact angle on polyether based materials. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

A thermodynamic model of contact angle hysteresis.

PubMed

Makkonen, Lasse

2017-08-14

When a three-phase contact line moves along a solid surface, the contact angle no longer corresponds to the static equilibrium angle but is larger when the liquid is advancing and smaller when the liquid is receding. The difference between the advancing and receding contact angles, i.e., the contact angle hysteresis, is of paramount importance in wetting and capillarity. For example, it determines the magnitude of the external force that is required to make a drop slide on a solid surface. Until now, fundamental origin of the contact angle hysteresis has been controversial. Here, this origin is revealed and a quantitative theory is derived. The theory is corroborated by the available experimental data for a large number of solid-liquid combinations. The theory is applied in modelling the contact angle hysteresis on a textured surface, and these results are also in quantitative agreement with the experimental data.

Interpreting contact angle results under air, water and oil for the same surfaces

NASA Astrophysics Data System (ADS)

Ozkan, Orkun; Yildirim Erbil, H.

2017-06-01

Under-water and under-oil superhydropobicity and superhydrophilicity have gained significant attention over the last few years. In this study, contact angles on five flat surfaces (polypropylene, poly(methyl methacrylate), polycarbonate, TEFLON-FEP and glass slide) were measured in water drop-in-air, air bubble-under-water, oil drop-in-air, air bubble-under-oil, oil drop-under-water and water drop-under-oil conditions. Heptane, octane, nonane, decane, dodecane, and hexadecane hydrocarbons were used as oils. Immiscible water/oil pairs were previously mutually saturated to provide thermodynamical equilibrium conditions and their surface and interfacial tensions were determined experimentally. These pairs were used in the two-liquid contact angle measurements. Surface free energies of the solid surfaces in air were determined independently by using the van Oss-Good method, using the contact angle results of pure water, ethylene glycol, formamide, methylene iodide and α-bromonaphalene. In addition, Zisman’s ‘critical surface tension’ values were also determined for comparison. In theory, the summation of contact angle results in a complementary case would give a total of 180° for ideal surfaces. However, it was determined that there are large deviations from this rule in practical cases and these deviations depend on surface free energies of solids. Three complementary cases of (water-in-air with air bubble-under-water); (oil-in-air with air bubble-under-oil); and (oil-under-water with water-under-oil) were investigated in particular to determine the deviations from ideality. A novel approach, named ‘complementary hysteresis’ [γ WA(cosθ 1  -  cosθ 2) and γ OW(cosθ 6  -  cosθ 5)] was developed where γ WA and γ OW represent the interfacial tensions of water/air and oil/water, and θ 1, θ 2, θ 5, and θ 6 were the contact angles of water/air, air bubble/water, oil/water and water/oil respectively. It was experimentally determined that complementary hysteresis varies almost linearly with the surface free energy of the flat solid samples. This is the first report showing the relation of the surface free energy of a solid which is determined under-air with the contact angles obtained on the same solid in different three-phase systems.

Wetting of biopolymer coatings: contact angle kinetics and image analysis investigation.

PubMed

Farris, Stefano; Introzzi, Laura; Biagioni, Paolo; Holz, Torsten; Schiraldi, Alberto; Piergiovanni, Luciano

2011-06-21

The surface wetting of five biopolymers, used as coating materials for a plastic film, was monitored over a span of 8 min by means of the optical contact angle technique. Because most of the total variation was observed to occur during the first 60 s, we decided to focus on this curtailed temporal window. Initial contact angle values (θ(0)) ranged from ∼91° for chitosan to ∼30° for pullulan. However, the water drop profile began to change immediately following drop deposition for all biocoatings, confirming that the concept of water contact angle equilibrium is not applicable to most biopolymers. First, a three-parameter decay equation [θ(t) = θ(0) exp(kt(n))] was fit to the experimental contact angle data to describe the kinetics of the contact angle change for each biocoating. Interestingly, the k constant correlated well with the contact angle evolution rate and the n exponent seemed to be somehow linked to the physicochemical phenomena underlying the overall kinetics process. Second, to achieve a reliable description of droplet evolution, the contact angle (CA) analysis was coupled with image analysis (IA) through a combined geometric/trigonometric approach. Absorption and spreading were the key factors governing the overall mechanism of surface wetting during the 60 s analysis, although the individual quantification of both phenomena demonstrated that spreading provided the largest contribution for all biopolymers, with the only exception of gelatin, which showed two quasi-equivalent and counterbalancing effects. The possible correlation between these two phenomena and the topography of the biopolymer surfaces are then discussed on the basis of atomic force microscopy analyses. © 2011 American Chemical Society

Contact angle hysteresis on superhydrophobic stripes.

PubMed

Dubov, Alexander L; Mourran, Ahmed; Möller, Martin; Vinogradova, Olga I

2014-08-21

We study experimentally and discuss quantitatively the contact angle hysteresis on striped superhydrophobic surfaces as a function of a solid fraction, ϕS. It is shown that the receding regime is determined by a longitudinal sliding motion of the deformed contact line. Despite an anisotropy of the texture the receding contact angle remains isotropic, i.e., is practically the same in the longitudinal and transverse directions. The cosine of the receding angle grows nonlinearly with ϕS. To interpret this we develop a theoretical model, which shows that the value of the receding angle depends both on weak defects at smooth solid areas and on the strong defects due to the elastic energy of the deformed contact line, which scales as ϕS(2)lnϕS. The advancing contact angle was found to be anisotropic, except in a dilute regime, and its value is shown to be determined by the rolling motion of the drop. The cosine of the longitudinal advancing angle depends linearly on ϕS, but a satisfactory fit to the data can only be provided if we generalize the Cassie equation to account for weak defects. The cosine of the transverse advancing angle is much smaller and is maximized at ϕS ≃ 0.5. An explanation of its value can be obtained if we invoke an additional energy due to strong defects in this direction, which is shown to be caused by the adhesion of the drop on solid sectors and is proportional to ϕS(2). Finally, the contact angle hysteresis is found to be quite large and generally anisotropic, but it becomes isotropic when ϕS ≤ 0.2.

Crystalline desiccation patterns and film break up from evaporating drops on hydrophobic oxide surfaces

NASA Astrophysics Data System (ADS)

McBride, Samantha; Dash, Susmita; Khan, Sami; Varanasi, Kripa

2017-11-01

Solute-laden sessile drops evaporating on a substrate will often force crystallization of the solute at the triple phase contact line between the drop, substrate, and air in an effect similar to the ``coffee-ring'' deposition of particles from a particle-laden drop. We report new observations of ring-shaped desiccation patterns of gypsum crystals on hydrophobic oxide substrates; ceria, erbia, and silica. These surfaces have similar contact angles ( 105 degrees), and evaporation of sessile drops proceeds at the same rate and without contact angle hysteresis on all three substrates. However, despite the apparent similarity, the patterns of crystal deposits exhibit large differences across the substrates. The supersaturation and elapsed time at the onset of crystallization also varied across substrates, despite overall evaporation rates being identical. The differences in patterns can be explained in light of the position and morphology of the crystals just prior to completion of evaporation when the sessile drop has transitioned to a thin film spread over the deposit area. Break-up of this film occurs very differently on the different surfaces, and is simultaneously influenced by existing crystals while also influencing final crystalline patterns. This work was supported by the NSF GRFP.

Wettability of Pyrolytic Boron Nitride by Aluminum

NASA Technical Reports Server (NTRS)

Chiaramonte, Francis P.; Rosenthal, Bruce N.

1991-01-01

The wetting of pyrolytic boron nitride by molten 99.9999 percent pure aluminum was investigated by using the sessile drop method in a vacuum operating at approximately 660 micro-Pa at temperatures ranging from 700 to 1000 C. The equilibrium contact angle decreased with an increase in temperature. For temperatures at 900 C or less, the equilibrium contact angle was greater than 90 deg. At 1000 C a nonwetting-to-wetting transition occurred and the contact angle stabilized at 49 deg.

Measuring the force of drag on air sheared sessile drops

NASA Astrophysics Data System (ADS)

Milne, Andrew J. B.; Fleck, Brian; Amirfazli, Alidad

2012-11-01

To blow a drop along or off of a surface (i.e. to shed the drop), the drag force on the drop (based on flow conditions, drop shape, and fluid properties) must overcome the adhesion force between the drop and the surface (based on surface tension, drop shape, and contact angle). While the shedding of sessile drops by shear flow has been studied [Milne, A. J. B. & Amirfazli, A. Langmuir 25, 14155 (2009).], no independent measurements of the drag or adhesion forces have been made. Likewise, analytic predictions are limited to hemispherical drops and low air velocities. We present, therefore, measurements of the drag force on sessile drops at air velocities up to the point of incipient motion. Measurements were made using a modified floating element shear sensor in a laminar low speed wind tunnel to record drag force over the surface with the drop absent, and over the combined system of the surface and drop partially immersed in the boundary layer. Surfaces of different wettabilities were used to study the effects of drop shape and contact angles, with drop volume ranged between approximately 10 and 100 microlitres. The drag force for incipient motion (which by definition equals the maximum of the adhesion force) is compared to simplified models for drop adhesion such as that of Furmidge

Water Drop Evaporation on Mushroom-like Superhydrophobic Surfaces: Temperature Effects.

PubMed

do Nascimento, Rodney Marcelo; Cottin-Bizonne, Cécile; Pirat, Christophe; Ramos, Stella M M

2016-03-01

We report on experiments of drop evaporation on heated superhydrophobic surfaces decorated with micrometer-sized mushroom-like pillars. We analyze the influence of two parameters on the evaporation dynamics: the solid-liquid fraction and the substrate temperature, ranging between 30 and 80 °C. In the different configurations investigated, the drop evaporation appears to be controlled by the contact line dynamics (pinned or moving). The experimental results show that (i) in the pinned regime, the depinning angles increase with decreasing contact fraction and the substrate heating promotes the contact line depinning and (ii) in the moving regime, the droplet motion is described by periodic stick-slip events and contact-angle oscillations. These features are highly smoothed at the highest temperatures, with two possible mechanisms suggested to explain such a behavior, a reduction in the elasticity of the triple line and a decrease in the depinning energy barriers. For all surfaces, the observed remarkable stability of the "fakir" state to the temperature is attributed to the re-entrant micropillar curvature that prevents surface imbibition.

Contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids

NASA Astrophysics Data System (ADS)

Gao, J.; Mendel, N.; Dey, R.; Baratian, D.; Mugele, F.

2018-05-01

Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including lab-on-a-chip devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, short range chemical interactions, viscous oil entrainment, and electrostatic stresses, we find that this observation can be explained by progressive thinning of the oil layer underneath the drop with increasing voltage. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.

Axisymmetric Liquid Hanging Drops

ERIC Educational Resources Information Center

Meister, Erich C.; Latychevskaia, Tatiana Yu

2006-01-01

The geometry of drops hanging on a circular capillary can be determined by numerically solving a dimensionless differential equation that is independent on any material properties, which enables one to follow the change of the height, surface area, and contact angle of drops hanging on a particular capillary. The results show that the application…

Drop dynamics on a thin film: Thin film rupture

NASA Astrophysics Data System (ADS)

Carlson, Andreas; Kim, Pilnam; Stone, Howard A.

2011-11-01

The spreading of a water drop on an oil film that covers a solid substrate is a common event in many industrial processes. We study in experiments the dynamics of a water drop on a thin silicone oil film and quantify its interaction with the solid substrate that supports the film. The oil film becomes unstable and ruptures for solids that are hydrophilic. We determine the ``waiting time,'' the time it takes the water drop to drain the silicone film. This timescale is found to highly depend on how well water wets the solid, illustrating the interplay between intermolecular and hydrodynamic forces in the phenomenon. A phase diagram for the thin film stability is extracted based on waters equilibrium contact angle on the solid, which shows that we can either promote or inhibit de-wetting. As water comes in direct contact with the solid, it spreads and peels off the silicone film. We show the influence of viscosity, equilibrium contact angle and film height on the opening radius of the hole formed as the solid de-wets.

Effect of drop volume and surface statistics on the superhydrophobicity of randomly rough substrates

NASA Astrophysics Data System (ADS)

Afferrante, L.; Carbone, G.

2018-01-01

In this paper, a simple theoretical approach is developed with the aim of evaluating shape, interfacial pressure, apparent contact angle and contact area of liquid drops gently deposed on randomly rough surfaces. This method can be useful to characterize the superhydrophobic properties of rough substrates, and to investigate the contact behavior of impacting drops. We assume that (i) the size of the apparent liquid-solid contact area is much larger than the micromorphology of the substrate, and (ii) a composite interface is always formed at the microscale. Results show apparent contact angle and liquid-solid area fraction are slightly influenced by the drop volume only at relatively high values of the root mean square roughness h rms, whereas the effect of volume is practically negligible at small h rms. The main statistical quantity affecting the superhydrophobic properties is found to be the Wenzel roughness parameter r W, which depends on the average slope of the surface heights. Moreover, transition from the Cassie-Baxter state to the Wenzel one is observed when r W reduces below a certain critical value, and theoretical predictions are found to be in good agreement with experimental data. Finally, the present method can be conveniently exploited to evaluate the occurrence of pinning phenomena in the case of impacting drops, as the Wenzel critical pressure for liquid penetration gives an estimation of the maximum impact pressure tolerated by the surface without pinning occurring.

Normal Forces at Solid-Liquid Interface

NASA Astrophysics Data System (ADS)

Das, Ratul

Adhesion can be defined as the tendency of dissimilar particles or surfaces to cling on to one another. Fields that require knowledge about adhesion interactions at the solid-liquid interface span over a wide spectrum from biotechnological issues such as liquid adhesion to skin tissues, insect feet adhesion to solids, or contact lenses to tear fluid adhesion; filtration issues such as membrane fouling and membrane affinity to different liquids; oil and gas extraction where one needs knowledge of the adhesion of the oil and brine to the rock; fuel cells in which droplets are formed on the electrodes and need to be considered in the system's design; classic chemical engineering industry such as drop adhesion to the mist eliminators in flash drums, or to heat exchangers; and classic surface science such as nano-structured surfaces, self cleaning surfaces, and general wetting phenomena. We execute the Young-Dupre (Y-P) gedanken experiment to establish unique values of work of adhesion rather than a work of adhesion range that the contact angle hysteresis results in. We use the Centrifugal Adhesion Balance (CAB) which allows independent manipulation of normal and lateral forces to induce an increase in the normal force which pulls on a liquid drop while keeping zero lateral force. This method mimics a drop that is subjected to a gravitational force that is gradually increasing. The values obtained for the work of adhesion are independent of drop size and are in agreement with the Y-P estimate. Cyclically varying the normal force, just to prevent the drop flying away from the surface will also enable us to study the Contact Angle Hysteresis for a pendant drop. With this set up, the work of adhesion is not only calculated from experimental normal force measurements, but the found results are also used to provide a venue for calculating the Young equilibrium contact angle, theta0. According to Shanahan and de Gennes, a liquid drop with a non-zero contact angle is associated with a deformation of the solid surface at the three phase contact line, causing the triple line to protrude up and form a rim, this is due to the unsatisfied normal component of the surface tension. Such rims were demonstrated by Care et al, and by Extrand, and the stresses associated with the rims facilitate reorientation of solid molecules at the interface, and therefore result in stronger solid liquid interaction at the rim. This stronger interaction gives rise to retention forces (due to adhesion). Recently, Xu et al, wrote a force equation based on this understanding, we test the validity of this approach and the Furmidge - Dussan model and other, more empirical, retention force approaches. A liquid drop that partially wets a solid surface will slide along the plane when a force beyond a critical value is applied to it. We study the sliding pattern of such a drop. Experiments for identifying the pattern of motion of liquid drops under influence of different normal forces are performed. We use a centrifugal adhesion balance (CAB) to study the pattern of drop motion under different effective gravities. A drop on a solid surface only slides after a certain critical force is applied to it, which is dependent on the drop volume, surface heterogeneities and other factors, even after the application of force the drop doesn't continue to move uniformly, which is the subject matter of this discussion.

Predicting wettability behavior of fluorosilica coated metal surface using optimum neural network

NASA Astrophysics Data System (ADS)

Taghipour-Gorjikolaie, Mehran; Valipour Motlagh, Naser

2018-02-01

The interaction between variables, which are effective on the surface wettability, is very complex to predict the contact angles and sliding angles of liquid drops. In this paper, in order to solve this complexity, artificial neural network was used to develop reliable models for predicting the angles of liquid drops. Experimental data are divided into training data and testing data. By using training data and feed forward structure for the neural network and using particle swarm optimization for training the neural network based models, the optimum models were developed. The obtained results showed that regression index for the proposed models for the contact angles and sliding angles are 0.9874 and 0.9920, respectively. As it can be seen, these values are close to unit and it means the reliable performance of the models. Also, it can be inferred from the results that the proposed model have more reliable performance than multi-layer perceptron and radial basis function based models.

Dynamics of simultaneously impinging drops on a dry surface: Role of inhomogeneous wettability and impact shape.

PubMed

Ashoke Raman, K

2018-04-15

The quality of the printed lines in applications such as ink-jet printing and additive manufacturing is affected by the interactions between the impinging drops. Impact shape and the inhomogeneity in surface wettability govern the spreading and recoiling dynamics of the interacting drops. Hence, understanding the role of these factors on the interaction dynamics is essential to optimize these applications. Phase-field based lattice Boltzmann method solver has been employed to investigate the interaction dynamics of two simultaneously impinging drops onto a dry surface. A geometry-based contact angle scheme is used to model the moving contact line. Numerical simulations reveal that the previously identified interaction modes (Raman et al., 2017) are sensitive to the contact angle hysteresis, resulting in different impact outcomes. Two different interaction mechanisms have been discerned when drops impinge on a surface with a wettability gradient. It is shown that the deviation from the spherical geometry of the impact shape leads to different spreading behaviors and droplet morphology around the connecting region. With the increase in the cross-sectional aspect ratio, the interaction dynamics of oblate-oblate combination is similar to its spherical counterpart, albeit at a faster recoiling rate. Copyright © 2018 Elsevier Inc. All rights reserved.

Water Touch-and-Bounce from a Soft Viscoelastic Substrate: Wetting, Dewetting, and Rebound on Bitumen.

PubMed

Lee, Jae Bong; Dos Santos, Salomé; Antonini, Carlo

2016-08-16

Understanding the interaction between liquids and deformable solid surfaces is a fascinating fundamental problem, in which interaction and coupling of capillary and viscoelastic effects, due to solid substrate deformation, give rise to complex wetting mechanisms. Here we investigated as a model case the behavior of water drops on two smooth bitumen substrates with different rheological properties, defined as hard and soft (with complex shear moduli in the order of 10(7) and 10(5) Pa, respectively, at 1 Hz), focusing both on wetting and on dewetting behavior. By means of classical quasi-static contact angle measurements and drop impact tests, we show that the water drop behavior can significantly change from the quasi-static to the dynamic regime on soft viscoelastic surfaces, with the transition being defined by the substrate rheological properties. As a result, we also show that on the hard substrate, where the elastic response is dominant under all investigated conditions, classical quasi-static contact angle measurements provide consistent results that can be used to predict the drop dynamic wetting behavior, such as drop deposition or rebound after impact, as typically observed for nondeformable substrates. Differently, on soft surfaces, the formation of wetting ridges did not allow to define uniquely the substrate intrinsic advancing and receding contact angles. In addition, despite showing a high adhesion to the soft surface in quasi-static measurements, the drop was surprisingly able to rebound and escape from the surface after impact, as it is typically observed for hydrophobic surfaces. These results highlight that measurements of wetting properties for viscoelastic substrates need to be critically used and that wetting behavior of a liquid on viscoelastic surfaces is a function of the characteristic time scales.

Proposition of stair climb of a drop using chemical wettability gradient

NASA Astrophysics Data System (ADS)

Seerha, Prabh P. S.; Kumar, Parmod; Das, Arup K.; Mitra, Sushanta K.

2017-07-01

We propose a passive technique for a drop to climb along the staircase textured surface using chemical wettability gradients. The stair structure, droplet configuration, and contact angle gradient are modeled using Lagrangian smoothed particle hydrodynamics. The stair climb efficiency of the droplet is found to be a function of wettability gradient strength. Using analytical balance of actuation and resistive forces across droplets, physical reasons behind stair climbing are established and influencing parameters are identified. Evolution of the droplet shape along with the advancing and the receding contact angles is presented from where instantaneous actuation and hysteresis forces are calculated. Using history of Lagrangian particles, circulation at the foot of stairs and progressing development of the advancing drop front are monitored. Higher efficiency in stair climbing in the case of a bigger sized drop than smaller one is obtained from simulation results and realized from force balance. Difficulty in climbing steeper stairs is also demonstrated to delineate the effect of gravitational pull against the actuation force due to the wettability gradient.

Applicability of contact angle techniques used in the analysis of contact lenses, part 1: comparative methodologies.

PubMed

Campbell, Darren; Carnell, Sarah Maria; Eden, Russell John

2013-05-01

Contact angle, as a representative measure of surface wettability, is often employed to interpret contact lens surface properties. The literature is often contradictory and can lead to confusion. This literature review is part of a series regarding the analysis of hydrogel contact lenses using contact angle techniques. Here we present an overview of contact angle terminology, methodology, and analysis. Having discussed this background material, subsequent parts of the series will discuss the analysis of contact lens contact angles and evaluate differences in published laboratory results. The concepts of contact angle, wettability and wetting are presented as an introduction. Contact angle hysteresis is outlined and highlights the advantages in using dynamic analytical techniques over static methods. The surface free energy of a material illustrates how contact angle analysis is capable of providing supplementary surface characterization. Although single values are able to distinguish individual material differences, surface free energy and dynamic methods provide an improved understanding of material behavior. The frequently used sessile drop, captive bubble, and Wilhelmy plate techniques are discussed. Their use as both dynamic and static methods, along with the advantages and disadvantages of each technique, is explained. No single contact angle technique fully characterizes the wettability of a material surface, and the application of complimenting methods allows increased characterization. At present, there is not an ISO standard method designed for soft materials. It is important that each contact angle technique has a standard protocol, as small protocol differences between laboratories often contribute to a variety of published data that are not easily comparable.

Quadricep and hamstring activation during drop jumps with changes in drop height.

PubMed

Peng, Hsien-Te; Kernozek, Thomas W; Song, Chen-Yi

2011-08-01

Compare the muscle activation patterns of the quadricep-hamstring during drop jumps with increasing demands of drop heights. Observational. University biomechanics laboratory. Fifteen male and eight female college physical education students. Electromyographic activity of the rectus femoris (RF) and biceps femoris (BF) during the landing and takeoff phase of drop jumps from 20 to 60-cm heights. The ground contact time, vertical ground reaction force (vGRF), knee flexion angle during ground contact, and jump height after takeoff were also analyzed. The activation of RF was higher in the drop jump from 60-cm than that from 20- and 30-cm (comparing 107.0 ± 45.9 to 82.3 ± 30.8 and 88.9 ± 38.9 %MVIC, P<.05) during the landing phase. Activation of BF remained similar across all drop heights. Drop jump from 60-cm resulted in greater contact time during takeoff phase and peak vGRF, and resulted in greater maximum knee flexion but straighter knee at ground contact than from lower drop heights. At drop height of 60-cm, the altered knee muscular activation and movement patterns may diminish the effectiveness of plyometric training and increase the potential injury risk of knee. Copyright © 2010 Elsevier Ltd. All rights reserved.

Pore-scale Analysis of the effects of Contact Angle Hysteresis on Blob Mobilization in a Pore Doublet

NASA Astrophysics Data System (ADS)

Hsu, Shao-Yiu; Glantz, Roland; Hilpert, Markus

2011-11-01

The mobilization of residual oil blobs in porous media is of major interest to the petroleum industry. We studied the Jamin effect, which hampers the blob mobilization, experimentally in a pore doublet model and explain the Jamin effect through contact angle hysteresis. A liquid blob was trapped in one of the tubes of the pore doublet model and then subjected to different pressure gradients. We measured the contact angles (in 2D and 3D) as well as the mean curvatures of the blob. Due to gravity effects and hysteresis, the contact angles of the blob were initially (zero pressure gradient) non-uniform and exhibited a pronounced altitude dependence. As the pressure gradient was increased, the contact angles became more uniform and the altitude dependence of the contact angle decreased. At the same time, the mean curvature of the drainage interface increased, and the mean curvature of the imbibition interface decreased. The pressure drops across the pore model, which we inferred with our theory from the measured contact angles and mean curvatures, were in line with the directly measured pressure data. We not only show that a trapped blob can sustain a finite pressure gradient but also develop methods to measure the contact angles and mean curvatures in 3D.

Bouncing dynamics of liquid drops impact on ridge structure: an effective approach to reduce the contact time.

PubMed

Li, Tao; Zhang, Lishu; Wang, Zhichao; Duan, Yunrui; Li, Jie; Wang, Junjun; Li, Hui

2018-06-20

Surfaces designed so that liquid metals do not stick to them but instead rebound as soon as possible have received considerable attention due to their significant importance in many practical technologies. We herein design a ridge structure that can induce the drop to rapidly rebound through the combination effect of centre-drawing recoil and the resulting faster retraction velocity. The suitable sharp-angle of the ridge for minimizing the contact time is determined as 20-30°. Further analysis reveals that multi-ridge structure or two-ridge structure with gaps can reduce more contact time. We also highlight the role the impact velocity played in minimizing the contact time, which has been a neglected parameter previously. Our studies would open up a new way to reduce the contact time and control the bouncing dynamics of metal drops, which provides guidance for some potential applications, such as preventing splashing molten drops from depositing on clean surface.

Contact angle of a nanodrop on a nanorough solid surface.

PubMed

Berim, Gersh O; Ruckenstein, Eli

2015-02-21

The contact angle of a cylindrical nanodrop on a nanorough solid surface is calculated, for both hydrophobic and hydrophilic surfaces, using the density functional theory. The emphasis of the paper is on the dependence of the contact angle on roughness. The roughness is modeled by rectangular pillars of infinite length located on the smooth surface of a substrate, with fluid-pillar interactions different in strength from the fluid-substrate ones. It is shown that for hydrophobic substrates the trend of the contact angle to increase with increasing roughness, which was noted in all previous studies, is not universally valid, but depends on the fluid-pillar interactions, pillar height, interpillar distance, as well as on the size of the drop. For hydrophilic substrate, an unusual kink-like dependence of the contact angle on the nanodrop size is found which is caused by the change in the location of the leading edges of the nanodrop on the surface. It is also shown that the Wenzel and Cassie-Baxter equations can not explain all the peculiarities of the contact angle of a nanodrop on a nanorough surface.

A precise goniometer/tensiometer using a low cost single-board computer

NASA Astrophysics Data System (ADS)

Favier, Benoit; Chamakos, Nikolaos T.; Papathanasiou, Athanasios G.

2017-12-01

Measuring the surface tension and the Young contact angle of a droplet is extremely important for many industrial applications. Here, considering the booming interest for small and cheap but precise experimental instruments, we have constructed a low-cost contact angle goniometer/tensiometer, based on a single-board computer (Raspberry Pi). The device runs an axisymmetric drop shape analysis (ADSA) algorithm written in Python. The code, here named DropToolKit, was developed in-house. We initially present the mathematical framework of our algorithm and then we validate our software tool against other well-established ADSA packages, including the commercial ramé-hart DROPimage Advanced as well as the DropAnalysis plugin in ImageJ. After successfully testing for various combinations of liquids and solid surfaces, we concluded that our prototype device would be highly beneficial for industrial applications as well as for scientific research in wetting phenomena compared to the commercial solutions.

Surface tension propellant control for Viking 75 Orbiter

NASA Technical Reports Server (NTRS)

Dowdy, M. W.; Hise, R. E.; Peterson, R. G.; Debrock, S. C.

1976-01-01

The paper describes the selection, development and qualification of the surface tension system and includes results of low-g drop tower tests of scale models, 1-g simulation tests of low-g large ullage settling and liquid withdrawal, structural qualification tests, and propellant surface tension/contact angle studies. Subscale testing and analyses were used to evaluate the ability of the system to maintain or recover the desired propellant orientation following possible disturbances during the Viking mission. This effort included drop tower tests to demonstrate that valid wick paths exist for moving any displaced propellant back over the tank outlet. Variations in surface tension resulting from aging, temperature, and lubricant contamination were studied and the effects of surface finish, referee fluid exposure, aging, and lubricant contamination on contact angle were assessed. Results of movies of typical subscale drop tower tests and full scale slosh tests are discussed.

Filamentary superhydrophobic Teflon surfaces: Moderate apparent contact angle but superior air-retaining properties.

PubMed

Di Mundo, Rosa; Bottiglione, Francesco; Palumbo, Fabio; Notarnicola, Michele; Carbone, Giuseppe

2016-11-15

Micro-scale textured Teflon surfaces, resulting from plasma etching modification, show extremely high water contact angle values and fairly good resistance to water penetration when hit by water drops at medium-high speed. This behavior is more pronounced when these surfaces present denser and smaller micrometric reliefs. Tailoring the top of these reliefs with a structure which further stabilizes the air may further increase resistance to wetting (water penetration) under static and dynamic conditions. Conditions of the oxygen fed plasma were tuned in order to explore the possibility of obtaining differently topped structures on the surface of the polymer. Scanning Electron Microscopy (SEM) was used to explore topography and X-ray Photoelectron Spectroscopy (XPS) to assess chemical similarity of the modified surfaces. Beside the usual advancing and receding water contact angle (WCA) measurements, surfaces were subjected to high speed impacting drops and immersion in water. At milder, i.e. shorter time and lower input power, plasma conditions formation of peculiar filaments is observed on the top of the sculpted reliefs. Filamentary topped surfaces result in a lower WCA than the spherical ones, appearing in this sense less superhydrophobic. However, these surfaces give rise to the formation of a more pronounced air layer when placed underwater. Further, when hit by water drops falling at medium/high speed, they show a higher resistance to water penetration and a sensitively lower surface-liquid contact time. The contact time is as low as previously observed only on heated solids. This behavior may be ascribed to the cavities formed beneath the filaments which, similarly with the salvinia leaf structures, require a surplus of pressure to be filled by water. Also, it suggests a different concept of superhydrophobicity, which cannot be expected on the basis of the conventional water contact angle characterization. Copyright © 2016 Elsevier Inc. All rights reserved.

Motion of a drop driven by substrate vibrations

NASA Astrophysics Data System (ADS)

Brunet, P.; Eggers, J.; Deegan, R. D.

2009-01-01

We report an experimental study of liquid drops moving against gravity, when placed on a vertically vibrating inclined plate, which is partially wet by the drop. Frequency of vibrations ranges from 30 to 200 Hz, and above a threshold in vibration acceleration, drops experience an upward motion. We attribute this surprising motion to the deformations of the drop, as a consequence of an up/down symmetry-breaking induced by the presence of the substrate. We relate the direction of motion to contact angle measurements.

Contact angle measurements of a polyphenyl ether to 190 C on M-50 steel

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1981-01-01

Contact angle measurements were performed for a polyphenyl ether on steel in nitrogen. A tilting plate and a sessile drop apparatus were used. Surface tension was measured with a maximum bubble pressure apparatus. Critical surface energies of spreading were found to be 30.1 and 31.3 dynes/cm. It was concluded that the polyphenyl ether is inherently autophobic and will not spread on its own surface film.

Contact Angle of Drops Measured on Nontransparent Surfaces and Capillary Flow Visualized

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Nengli

2003-01-01

The spreading of a liquid on a solid surface is important for various practical processes, and contact-angle measurements provide an elegant method to characterize the interfacial properties of the liquid with the solid substrates. The complex physical processes occurring when a liquid contacts a solid play an important role in determining the performance of chemical processes and materials. Applications for these processes are in printing, coating, gluing, textile dyeing, and adhesives and in the pharmaceutical industry, biomedical research, adhesives, flat panel display manufacturing, surfactant chemistry, and thermal engineering.

Numerical analysis of moving contact line with contact angle hysteresis using feedback deceleration technique

NASA Astrophysics Data System (ADS)

Park, Jun Kwon; Kang, Kwan Hyoung

2012-04-01

Contact angle (CA) hysteresis is important in many natural and engineering wetting processes, but predicting it numerically is difficult. We developed an algorithm that considers CA hysteresis when analyzing the motion of the contact line (CL). This algorithm employs feedback control of CA which decelerates CL speed to make the CL stationary in the hysteretic range of CA, and one control coefficient should be heuristically determined depending on characteristic time of the simulated system. The algorithm requires embedding only a simple additional routine with little modification of a code which considers the dynamic CA. The method is non-iterative and explicit, and also has less computational load than other algorithms. For a drop hanging on a wire, the proposed algorithm accurately predicts the theoretical equilibrium CA. For the drop impacting on a dry surface, the results of the proposed algorithm agree well with experimental results including the intermittent occurrence of the pinning of CL. The proposed algorithm is as accurate as other algorithms, but faster.

Measurement of an Evaporating Drop on a Reflective Substrate

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Nengli

2004-01-01

A figure depicts an apparatus that simultaneously records magnified ordinary top-view video images and laser shadowgraph video images of a sessile drop on a flat, horizontal substrate that can be opaque or translucent and is at least partially specularly reflective. The diameter, contact angle, and rate of evaporation of the drop as functions of time can be calculated from the apparent diameters of the drop in sequences of the images acquired at known time intervals, and the shadowgrams that contain flow patterns indicative of thermocapillary convection (if any) within the drop. These time-dependent parameters and flow patterns are important for understanding the physical processes involved in the spreading and evaporation of drops. The apparatus includes a source of white light and a laser (both omitted from the figure), which are used to form the ordinary image and the shadowgram, respectively. Charge-coupled-device (CCD) camera 1 (with zoom) acquires the ordinary video images, while CCD camera 2 acquires the shadowgrams. With respect to the portion of laser light specularly reflected from the substrate, the drop acts as a plano-convex lens, focusing the laser beam to a shadowgram on the projection screen in front of CCD camera 2. The equations for calculating the diameter, contact angle, and rate of evaporation of the drop are readily derived on the basis of Snell s law of refraction and the geometry of the optics.

Spreading of blood drops over dry porous substrate: complete wetting case.

PubMed

Chao, Tzu Chieh; Arjmandi-Tash, Omid; Das, Diganta B; Starov, Victor M

2015-05-15

The process of dried blood spot sampling involves simultaneous spreading and penetration of blood into a porous filter paper with subsequent evaporation and drying. Spreading of small drops of blood, which is a non-Newtonian liquid, over a dry porous layer is investigated from both theoretical and experimental points of view. A system of two differential equations is derived, which describes the time evolution of radii of both the drop base and the wetted region inside the porous medium. The system of equations does not include any fitting parameters. The predicted time evolutions of both radii are compared with experimental data published earlier. For a given power law dependency of viscosity of blood with different hematocrit level, radii of both drop base and wetted region, and contact angle fell on three universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and the wetted region inside the porous layer and dynamic contact angle on dimensionless time. The predicted theoretical relationships are three universal curves accounting satisfactorily for the experimental data. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

Complex Contact Angles Calculated from Capillary Rise Measurements on Rock Fracture Faces

NASA Astrophysics Data System (ADS)

Perfect, E.; Gates, C. H.; Brabazon, J. W.; Santodonato, L. J.; Dhiman, I.; Bilheux, H.; Bilheux, J. C.; Lokitz, B. S.

2017-12-01

Contact angles for fluids in unconventional reservoir rocks are needed for modeling hydraulic fracturing leakoff and subsequent oil and gas extraction. Contact angle measurements for wetting fluids on rocks are normally performed using polished flat surfaces. However, such prepared surfaces are not representative of natural rock fracture faces, which have been shown to be rough over multiple scales. We applied a variant of the Wilhelmy plate method for determining contact angle from the height of capillary rise on a vertical surface to the wetting of rock fracture faces by water in the presence of air. Cylindrical core samples (5.05 cm long x 2.54 cm diameter) of Mancos shale and 6 other rock types were investigated. Mode I fractures were created within the cores using the Brazilian method. Each fractured core was then separated into halves exposing the fracture faces. One fracture face from each rock type was oriented parallel to a collimated neutron beam in the CG-1D imaging instrument at ORNL's High Flux Isotope Reactor. Neutron radiography was performed using the multi-channel plate detector with a spatial resolution of 50 μm. Images were acquired every 60 s after a water reservoir contacted the base of the fracture face. The images were normalized to the initial dry condition so that the upward movement of water on the fracture face was clearly visible. The height of wetting at equilibrium was measured on the normalized images using ImageJ. Contact angles were also measured on polished flat surfaces using the conventional sessile drop method. Equilibrium capillary rise on the exposed fracture faces was up to 8.5 times greater than that predicted for polished flat surfaces from the sessile drop measurements. These results indicate that rock fracture faces are hyperhydrophilic (i.e., the height of capillary rise is greater than that predicted for a contact angle of zero degrees). The use of complex numbers permitted calculation of imaginary contact angles for such surfaces. This analysis yielded a continuum of contact angles (real above, and imaginary below, zero degrees) that can be used to investigate relationships with properties such surface roughness and porosity. It should be noted these are preliminary, unreplicated results and further research will be needed to verify them and refine the approach.

Droplet Depinning on Inclined Surfaces at High Reynolds Numbers

NASA Astrophysics Data System (ADS)

White, Edward; Singh, Natasha; Lee, Sungyon

2017-11-01

Contact angle hysteresis enables a sessile liquid drop to adhere to a solid surface when the surface is inclined, the drop is exposed to gas-phase flow, or the drop is exposed to both forcing modalities. Previous work by Schmucker and White (2012.DFD.M4.6) identified critical depinning Weber numbers for water drops subject to gravity- and wind-dominated forcing. This work extends the Schmucker and White data and finds the critical depinning Weber number obeys a two-slope linear model. Under pure wind forcing at Reynolds numbers above 1500 and with zero surface inclination, Wecrit = 8.0 . For non-zero inclinations, α, Wecrit decreases proportionally to A Bo sinα where A is the drop aspect ratio and Bo is its Bond number. The same relationship holds for α < 0 when gravity resists depinning by wind. Above We 4 , depinning is dominated by wind forcing; at We < 4 , depinning is gravity dominated. While Wecrit depends linearly on A Bo sinα in both forcing regimes, the slopes of the the limit lines depend on the forcing regime. The difference is attributed to different drop shapes and contact angle distributions that arise depending on whether wind or gravity dominates the depinning behavior. Supported by the National Science Foundation through Grant CBET-1605947.

Anomalous contact angle hysteresis of a captive bubble: advancing contact line pinning.

PubMed

Hong, Siang-Jie; Chang, Feng-Ming; Chou, Tung-He; Chan, Seong Heng; Sheng, Yu-Jane; Tsao, Heng-Kwong

2011-06-07

Contact angle hysteresis of a sessile drop on a substrate consists of continuous invasion of liquid phase with the advancing angle (θ(a)) and contact line pinning of liquid phase retreat until the receding angle (θ(r)) is reached. Receding pinning is generally attributed to localized defects that are more wettable than the rest of the surface. However, the defect model cannot explain advancing pinning of liquid phase invasion driven by a deflating bubble and continuous retreat of liquid phase driven by the inflating bubble. A simple thermodynamic model based on adhesion hysteresis is proposed to explain anomalous contact angle hysteresis of a captive bubble quantitatively. The adhesion model involves two solid–liquid interfacial tensions (γ(sl) > γ(sl)′). Young’s equation with γ(sl) gives the advancing angle θ(a) while that with γ(sl)′ due to surface rearrangement yields the receding angle θ(r). Our analytical analysis indicates that contact line pinning represents frustration in surface free energy, and the equilibrium shape corresponds to a nondifferential minimum instead of a local minimum. On the basis of our thermodynamic model, Surface Evolver simulations are performed to reproduce both advancing and receding behavior associated with a captive bubble on the acrylic glass.

Wettability of MnxSiyOz by Liquid Zn-Al Alloys

NASA Astrophysics Data System (ADS)

Kim, Yunkyum; Shin, Minsoo; Tang, Chengying; Lee, Joonho

2010-08-01

The wettability of MnxSiyOz by liquid Zn-Al alloys was investigated to obtain basic information on the coating properties of high-strength steels with surface oxides in the hot-dip galvanizing process. In this study, the contact angles of liquid Zn-Al alloys (Al concentrations were 0.12 and 0.23 wt pct) on four different MnxSiyOz oxides, namely MnO, MnSiO3, Mn2SiO4, and SiO2, were measured with the dispensed drop method. The contact angle did not change across time. With an increasing Al concentration, the contact angle was slightly decreased for MnO and Mn2SiO4, but there was no change for MnSiO3 and SiO2. With an increasing SiO2 content, the contact angle gradually increased by 54 wt pct to form MnSiO3, and for pure SiO2 substrate, the contact angle decreased again. Consequently, the MnSiO3 substrate showed the worst wettability among the four tested oxide substrates.

Development of graphite/copper composites utilizing engineered interfaces. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Devincent, Sandra M.

1991-01-01

In situ measurements of graphite/copper alloy contact angles were made using the sessile drop method. The interfacial energy values obtained from these measurements were then applied to a model for the fiber matrix interfacial debonding phenomenon found in graphite/copper composites. The formation obtained from the sessile drop tests led to the development of a copper alloy that suitably wets graphite. Characterization of graphite/copper alloy interfaces subjected to elevated temperatures was conducted using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Auger Electron Spectroscopy, and X Ray Diffraction analyses. These analyses indicated that during sessile drop tests conducted at 1130 C for 1 hour, copper alloys containing greater than 0.98 at pct chromium form continuous reaction layers of approx. 10 microns in thickness. The reaction layers are adherent to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 deg or less. X ray diffraction results indicate that the reaction layer is Cr3C2.

Enhanced water repellency of surfaces coated with multiscale carbon structures

NASA Astrophysics Data System (ADS)

Marchalot, Julien; Ramos, Stella. M. M.; Pirat, Christophe; Journet, Catherine

2018-01-01

Low cost and well characterized superhydrophobic surfaces are frequently required for industrial applications. Materials are commonly structured at the micro or nano scale. Surfaces decorated with nanotube derivatives synthesized by plasma enhanced chemical vapor deposition (PECVD) are of particular interest, since suitable modifications in the growth parameters can lead to numerous designs. In this article, we present surfaces that are selected for their specific wetting features with patterns ranging from dense forests to jungles with concave (re-entrant) surface such as flake-like multiscale roughness. Once these surfaces are functionalized adequately, their wetting properties are investigated. Their ability to sustain a superhydrophobic state for sessile water drops is examined. Finally, we propose a design to achieve a robust so-called ;Fakir; state, even for micrometer-sized drops, whereas with classic nanotubes forests it is not achievable. Thus, the drop remains on the apex of the protrusions with a high contact angle and a low contact angle hysteresis, while the surface features demonstrate good mechanical resistance against capillary forces.

Three-gradient regular solution model for simple liquids wetting complex surface topologies

PubMed Central

Akerboom, Sabine; Kamperman, Marleen

2016-01-01

Summary We use regular solution theory and implement a three-gradient model for a liquid/vapour system in contact with a complex surface topology to study the shape of a liquid drop in advancing and receding wetting scenarios. More specifically, we study droplets on an inverse opal: spherical cavities in a hexagonal pattern. In line with experimental data, we find that the surface may switch from hydrophilic (contact angle on a smooth surface θY < 90°) to hydrophobic (effective advancing contact angle θ > 90°). Both the Wenzel wetting state, that is cavities under the liquid are filled, as well as the Cassie–Baxter wetting state, that is air entrapment in the cavities under the liquid, were observed using our approach, without a discontinuity in the water front shape or in the water advancing contact angle θ. Therefore, air entrapment cannot be the main reason why the contact angle θ for an advancing water front varies. Rather, the contact line is pinned and curved due to the surface structures, inducing curvature perpendicular to the plane in which the contact angle θ is observed, and the contact line does not move in a continuous way, but via depinning transitions. The pinning is not limited to kinks in the surface with angles θkink smaller than the angle θY. Even for θkink > θY, contact line pinning is found. Therefore, the full 3D-structure of the inverse opal, rather than a simple parameter such as the wetting state or θkink, determines the final observed contact angle. PMID:27826512

Exploration of the Fundamental Properties and Consequences of Fluorinated Polyhedral Oligomeric Silsequioxanes (FluoroPOSS)

DTIC Science & Technology

2011-07-02

on a lotus leaf and it beads up (as shown in Fig. 1A), then rolls off; this is a familiar demonstration of a ‘ superhydrophobic ’ self-cleaning surface...of biomimetic superhydrophobic surfaces. However, try the same thing with an oily liquid (for example octane or gasoline) and the drop immediately...biomimetic superhydrophobic surfaces (i.e. apparent contact angles (θ*) with water greater than 150° and low contact angle hysteresis). However, prior to

Pinning-Depinning Mechanisms of the Contact Line during Evaporation of Microdroplets on Rough Surfaces: A Lattice Boltzmann Simulation.

PubMed

Yuan, Wu-Zhi; Zhang, Li-Zhi

2018-06-22

In this study, pinning and depinning of the contact line during droplet evaporation on the rough surfaces with randomly distributed structures is theoretically analyzed and numerically investigated. A fast Fourier transformation (FFT) method is used to generate the rough surfaces, whose skewness ( Sk), kurtosis ( K), and root-mean-square ( Rq) are obtained from real surfaces. A thermal multiphase LB model is proposed to simulate the isothermal pinning and depinning processes. The evaporation processes are recorded with the variations in contact angle, contact radius, and drop shape. It is found that the drops sitting on rough surfaces show different behavior from those on smoother surfaces. The former shows a pinned contact line during almost the whole lifetime. By contrast, the latter experiences a stick-slip-jump behavior until the drop disappears. At mesoscopic scale, the pinning of the contact line is actually a slow motion rather than a complete immobilization at the sharp edges. The dynamic equilibrium is achieved by the self-adjustment of the contact line according to each edge.

Cleanability evaluation of ceramic glazes with nanometer far-infrared materials using contact angle measurement.

PubMed

Wang, Lijuan; Liang, Jinsheng; Di, Xingfu; Tang, Qingguo

2014-05-01

The cleanability of easy-to-clean ceramic glazes doped with nanometer far-infrared materials was compared with that of some high-quality household ceramic glazes from the market. The cleanability was evaluated by the contact angle measurement using a sessile drop method with a Dataphysics OCA-30 contact angle analyzer. The results showed that the difference of contact angles of water on the glazes before soiling and after cleaning could be used as a parameter for evaluating the cleanability of the glazes. The relationship between cleanability and surface properties, such as surface free energy and surface topography, was investigated. The surface free energy of the samples and their components were calculated using van Oss acid-base approach. By measuring advancing and receding contact angles, the contact angle hysteresis of the ceramic glazes due to the surface topography was investigated. It was shown that the cleanability of ceramic glazes containing nanometer far-infrared materials (NFIM) is better than that of household ceramic glazes from market, due to a higher ratio of electron-acceptor parameter to electron-donor parameter, which led to the effect of water hydration as well as better hydrophilic property and increased smoothness. The contact angle measurement not only accurately evaluates the cleanability of the ceramic glazes, but also has a contribution to the study of cleanability theory. Moreover, this method is simple, convenient and less sample-consumption.

Contact angles of wetting and water stability of soil structure

NASA Astrophysics Data System (ADS)

Kholodov, V. A.; Yaroslavtseva, N. V.; Yashin, M. A.; Frid, A. S.; Lazarev, V. I.; Tyugai, Z. N.; Milanovskiy, E. Yu.

2015-06-01

From the soddy-podzolic soils and typical chernozems of different texture and land use, dry 3-1 mm aggregates were isolated and sieved in water. As a result, water-stable aggregates and water-unstable particles composing dry 3-1 mm aggregates were obtained. These preparations were ground, and contact angles of wetting were determined by the static sessile drop method. The angles varied from 11° to 85°. In most cases, the values of the angles for the water-stable aggregates significantly exceeded those for the water-unstable components. In terms of carbon content in structural units, there was no correlation between these parameters. When analyzing the soil varieties separately, the significant positive correlation between the carbon content and contact angle of aggregates was revealed only for the loamy-clayey typical chernozem. Based on the multivariate analysis of variance, the value of contact wetting angle was shown to be determined by the structural units belonging to water-stable or water-unstable components of macroaggregates and by the land use type. In addition, along with these parameters, the texture has an indirect effect.

Measurements of advancing and receding contact angles of water on PMMA and CR-39 at various g-levels

NASA Astrophysics Data System (ADS)

Mireault, Nicolas; Abel, Gilles; Andrzejewski, Lukasz; Ross, Guy

2005-03-01

The main purpose of this work is to clarify the controversy that has been widely discussed after the publication of Ward et al. [1, 2, 3] about whether varying g-levels should have an influence on contact angles of liquids on solid surfaces. Surface modification using PBII has been used to vary the contact angles of water on PMMA and CR-39 samples by implantation of O2 and Ar ions. Advancing and receding contact angles (θa and θr) have been measured using the injection and the withdrawn of a 3 μL water drop at a 2 μL/min rate on these PMMA and CR-39 samples, implanted or not. Analysis of the recorded frames of the whole parabola yielded the θa and θr vs g plots that are shown and discussed, while g-level vary from g˜0.03 up to g˜2.5. Comparison of the variable g hystereses with those measured in constant 1 g using the same samples is also made. Angle variations being lower than the measurement precision, the results indicate that the contact angles do not vary with g-level.

Role of Viscous Dissipative Processes on the Wetting of Textured Surfaces

PubMed Central

Grewal, H. S.; Nam Kim, Hong; Cho, Il-Joo; Yoon, Eui-Sung

2015-01-01

We investigate the role of viscous forces on the wetting of hydrophobic, semi-hydrophobic, and hydrophilic textured surfaces as second-order effects. We show that during the initial contact, the transition from inertia- to viscous-dominant regime occurs regardless of their surface topography and chemistry. Furthermore, we demonstrate the effect of viscosity on the apparent contact angle under quasi-static conditions by modulating the ratio of a water/glycerol mixture and show the effect of viscosity, especially on the semi-hydrophobic and hydrophobic textured substrates. The reason why the viscous force does not affect the apparent contact angle of the hydrophilic surface is explained based on the relationship between the disjoining pressure and surface chemistry. We further propose a wetting model that can predict the apparent contact angle of a liquid drop on a textured substrate by incorporating a viscous force component in the force balance equation. This model can predict apparent contact angles on semi-hydrophobic and hydrophobic textured surfaces exhibiting Wenzel state more accurately than the Wenzel model, indicating the importance of viscous forces in determining the apparent contact angle. The modified model can be applied for estimating the wetting properties of arbitrary engineered surfaces. PMID:26390958

Combined Effects of Fatigue and Surface Instability on Jump Biomechanics in Elite Athletes.

PubMed

Prieske, Olaf; Demps, Marie; Lesinski, Melanie; Granacher, Urs

2017-09-01

The present study aimed to examine the effects of fatigue and surface instability on kinetic and kinematic jump performance measures. Ten female and 10 male elite volleyball players (18±2 years) performed repetitive vertical double-leg box jumps until failure. Pre and post fatigue, jump height/performance index, ground reaction force and knee flexion/valgus angles were assessed during drop and countermovement jumps on stable and unstable surfaces. Fatigue, surface condition, and sex resulted in significantly lower drop jump performance and ground reaction force (p≤0.031, 1.1≤d≤3.5). Additionally, drop jump knee flexion angles were significantly lower following fatigue (p=0.006, d=1.5). A significant fatigue×surface×sex interaction (p=0.020, d=1.2) revealed fatigue-related decrements in drop jump peak knee flexion angles under unstable conditions and in men only. Knee valgus angles were higher on unstable compared to stable surfaces during drop jumps and in females compared to males during drop and countermovement jumps (p≤0.054, 1.0≤d≤1.1). Significant surface×sex interactions during countermovement jumps (p=0.002, d=1.9) indicated that knee valgus angles at onset of ground contact were significantly lower on unstable compared to stable surfaces in males but higher in females. Our findings revealed that fatigue and surface instability resulted in sex-specific knee motion strategies during jumping in elite volleyball players. © Georg Thieme Verlag KG Stuttgart · New York.

Contact angle and surface tension measurements of a five-ring polyphenyl ether

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1986-01-01

Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220 C in room air. The critical surface energy of spreading (gamma /sub c/) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma /sub LV/). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma /sub c/). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Contact angle and surface tension measurements of a five-ring polyphenyl ether

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.

1985-01-01

Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220C in room air. The critical surface energy of spreading (gamma (sub c)) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma (sub LV)). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma (sub c). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

Pharmaceutical-grade oral films as substrates for printed medicine.

PubMed

Wimmer-Teubenbacher, M; Planchette, C; Pichler, H; Markl, D; Hsiao, W K; Paudel, A; Stegemann, S

2018-05-18

In contact-less printing, such as piezo-electric drop on demand printing used in the study, the drop formation process is independent of the substrate. This means that having developed a printable formulation, printed pharmaceutical dosage forms can be obtained on any pharmaceutical grade substrate, such as polymer-based films. In this work we evaluated eight different oral films based on their suitability as printing substrates for sodium picosulfate. The different polymer films were compared regarding printed spot morphology, chemical stability and dissolution profile. The morphology of printed sodium picosulfate was investigated with scanning electron microscopy and optical coherence tomography. The spreading of the deposited drops was found to be governed by the contact angle of the ink with the substrate. The form of the sodium picosulfate drops changed on microcrystalline cellulose films at ambient conditions over 8 weeks and stayed unchanged on other tested substrates. Sodium picosulfate remained amorphous on all substrates according to small and wide angle X-ray scattering, differential scanning calorimetry and polarized light microscopy measurements. The absence of chemical interactions between the drug and substrates, as indicated by infrared spectroscopy, makes all tested substrates suitable for printing sodium picosulfate onto them. Copyright © 2018 Elsevier B.V. All rights reserved.

Vibration-Induced Climbing of Drops

NASA Astrophysics Data System (ADS)

Brunet, P.; Eggers, J.; Deegan, R. D.

2007-10-01

We report an experimental study of liquid drops moving against gravity, when placed on a vertically vibrating inclined plate, which is partially wetted by the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a threshold in vibration acceleration, drops experience an upward motion. We attribute this surprising motion to the deformations of the drop, as a consequence of an up or down symmetry breaking induced by the presence of the substrate. We relate the direction of motion to contact angle measurements. This phenomenon can be used to move a drop along an arbitrary path in a plane, without special surface treatments or localized forcing.

The Measurement of Wettability

ERIC Educational Resources Information Center

Pirie, Brian J. S.; Gregory, David W.

1973-01-01

Discusses the use of a simple apparatus to measure contact angles between a liquid drop and a solid surface which are determining factors of wettability. Included are examples of applying this technique to various experimental situations. (CC)

Surface settling in partially filled containers upon step reduction in gravity

NASA Technical Reports Server (NTRS)

Weislogel, Marl M.; Ross, Howard D.

1990-01-01

A large literature exists concerning the equilibrium configurations of free liquid/gas surfaces in reduced gravity environments. Such conditions generally yield surfaces of constant curvature meeting the container wall at a particular (contact) angle. The time required to reach and stabilize about this configuration is less studied for the case of sudden changes in gravity level, e.g. from normal- to low-gravity, as can occur in many drop tower experiments. The particular interest here was to determine the total reorientation time for such surfaces in cylinders (mainly), as a function primarily of contact angle and kinematic viscosity, in order to aid in the development of drop tower experiment design. A large parametric range of tests were performed and, based on an accompanying scale analysis, the complete data set was correlated. The results of other investigations are included for comparison.

Evaporation of inclined water droplets.

PubMed

Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

2017-02-16

When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets.

Evaporation of inclined water droplets

PubMed Central

Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook

2017-01-01

When a drop is placed on a flat substrate tilted at an inclined angle, it can be deformed by gravity and its initial contact angle divides into front and rear contact angles by inclination. Here we study on evaporation dynamics of a pure water droplet on a flat solid substrate by controlling substrate inclination and measuring mass and volume changes of an evaporating droplet with time. We find that complete evaporation time of an inclined droplet becomes longer as gravitational influence by inclination becomes stronger. The gravity itself does not change the evaporation dynamics directly, whereas the gravity-induced droplet deformation increases the difference between front and rear angles, which quickens the onset of depinning and consequently reduces the contact radius. This result makes the evaporation rate of an inclined droplet to be slow. This finding would be important to improve understanding on evaporation dynamics of inclined droplets. PMID:28205642

Development of a highly transparent superamphiphobic plastic sheet by nanoparticle and chemical coating.

PubMed

Wong, Ten It; Wang, Hao; Wang, Fuke; Sin, Sau Leng; Quan, Cheng Gen; Wang, Shi Jie; Zhou, Xiaodong

2016-04-01

A highly transparent superamphiphobic plastic sheet was developed. The plastic sheet polymethyl methacrylate (PMMA) was spin-coated on a glass substrate. Synthesized silica nanoparticles were sprayed on PMMA, followed by fluorosilane drop-coating. The results of contact angle measurements show that the developed PMMA sheet has superamphiphobic properties with high advancing contact angles for water (154°), toluene (139°), and silicone oil (132.9°). The amphiphobicity of the plastic sheet can be tuned by the surface coverage of the silica nanoparticles distributed on the PMMA surface. The surface coverage of the nanoparticles on our PMMA sheet is about 20%, and it agrees with our contact angle calculations for the sheet with and without nanoparticles. Copyright © 2016 Elsevier Inc. All rights reserved.

Theoretical model of droplet wettability on a low-surface-energy solid under the influence of gravity.

PubMed

Yonemoto, Yukihiro; Kunugi, Tomoaki

2014-01-01

The wettability of droplets on a low surface energy solid is evaluated experimentally and theoretically. Water-ethanol binary mixture drops of several volumes are used. In the experiment, the droplet radius, height, and contact angle are measured. Analytical equations are derived that incorporate the effect of gravity for the relationships between the droplet radius and height, radius and contact angle, and radius and liquid surface energy. All the analytical equations display good agreement with the experimental data. It is found that the fundamental wetting behavior of the droplet on the low surface energy solid can be predicted by our model which gives geometrical information of the droplet such as the contact angle, droplet radius, and height from physical values of liquid and solid.

How pinning and contact angle hysteresis govern quasi-static liquid drop transfer.

PubMed

Chen, H; Tang, T; Zhao, H; Law, K-Y; Amirfazli, A

2016-02-21

This paper presents both experimental and numerical simulations of liquid transfer between two solid surfaces with contact angle hysteresis (CAH). Systematic studies on the role of the advancing contact angle (θa), receding contact angle (θr) and CAH in determining the transfer ratio (volume of the liquid transferred onto the acceptor surface over the total liquid volume) and the maximum adhesion force (Fmax) were performed. The transfer ratio was found to be governed by contact line pinning at the end of the transfer process caused by CAH of surfaces. A map based on θr of the two surfaces was generated to identify the three regimes for liquid transfer: (I) contact line pinning occurs only on the donor surface, (II) contact line pinning occurs on both surfaces, and (III) contact line pinning occurs only on the acceptor surface. With this map, an empirical equation is provided which is able to estimate the transfer ratio by only knowing θr of the two surfaces. The value of Fmax is found to be strongly influenced by the contact line pinning in the early stretching stage. For symmetric liquid bridges between two identical surfaces, Fmax may be determined only by θa, only by θr, or by both θa and θr, depending on the magnitude of the contact angles. For asymmetric bridges, Fmax is found to be affected by the period when contact lines are pinned on both surfaces.

Mathematical modeling of two phase stratified flow in a microchannel with curved interface

NASA Astrophysics Data System (ADS)

Dandekar, Rajat; Picardo, Jason R.; Pushpavanam, S.

2017-11-01

Stratified or layered two-phase flows are encountered in several applications of microchannels, such as solvent extraction. Assuming steady, unidirectional creeping flow, it is possible to solve the Stokes equations by the method of eigenfunctions, provided the interface is flat and meets the wall with a 90 degree contact angle. However, in reality the contact angle depends on the pair of liquids and the material of the channel, and differs significantly from 90 degrees in many practical cases. For unidirectional flow, this implies that the interface is a circular arc (of constant curvature). We solve this problem within the framework of eigenfunctions, using the procedure developed by Shankar. We consider two distinct cases: (a) the interface meets the wall with the equilibrium contact angle; (b) the interface is pinned by surface treatment of the walls, so that the flow rates determine the apparent contact angle. We show that the contact angle appreciably affects the velocity profile and the volume fractions of the liquids, while limiting the range of flow rates that can be sustained without the interface touching the top/bottom walls. Non-intuitively, we find that the pressure drop is reduced when the more viscous liquid wets the wall.

Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water

PubMed Central

Roth-Nebelsick, A.; Ebner, M.; Miranda, T.; Gottschalk, V.; Voigt, D.; Gorb, S.; Stegmaier, T.; Sarsour, J.; Linke, M.; Konrad, W.

2012-01-01

The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment. PMID:22356817

Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water.

PubMed

Roth-Nebelsick, A; Ebner, M; Miranda, T; Gottschalk, V; Voigt, D; Gorb, S; Stegmaier, T; Sarsour, J; Linke, M; Konrad, W

2012-08-07

The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment.

Electrowetting on semiconductors

NASA Astrophysics Data System (ADS)

Palma, Cesar; Deegan, Robert

2015-01-01

Applying a voltage difference between a conductor and a sessile droplet sitting on a thin dielectric film separating it from the conductor will cause the drop to spread. When the conductor is a good metal, the change of the drop's contact angle due to the voltage is given by the Young-Lippmann (YL) equation. Here, we report experiments with lightly doped, single crystal silicon as the conductive electrode. We derive a modified YL equation that includes effects due to the semiconductor and contact line pinning. We show that light induces a non-reversible wetting transition, and that our model agrees well with our experimental results.

Electrowetting-driven spreading and jumping of drops in oil

NASA Astrophysics Data System (ADS)

Hong, Jiwoo; Lee, Sang Joon

2013-11-01

Electrowetting-based practical applications include digital microfluidics, liquid lenses, and reflective displays. Most of them are performed in water/oil system, because oil medium reduces the contact-angle hysteresis and prevents drop evaporation. In this study, the effects of drop volume, oil viscosity, and applied voltage on the dynamic behaviors of spreading drops, such as transition of spreading pattern and response time, are investigated. Interestingly, jumping phenomena of drops are observed in oil when the applied voltage is turned off after reaching the electrowetted equilibrium radius of drops. A numerical model to predict the transient behavior of jumping drops is formulated based on the phase-field method. The numerical results for the transient deformation of jumping drops show quantitative agreement with the experimental results.

Joint mobilization acutely improves landing kinematics in chronic ankle instability.

PubMed

Delahunt, Eamonn; Cusack, Kim; Wilson, Laura; Doherty, Cailbhe

2013-03-01

The objective of this study is to examine the acute effect of ankle joint mobilizations akin to those performed in everyday clinical practice on sagittal plane ankle joint kinematics during a single-leg drop landing in participants with chronic ankle instability (CAI). Fifteen participants with self-reported CAI (defined as <24 on the Cumberland Ankle Instability Tool) performed three single-leg drop landings under two different conditions: 1) premobilization and, 2) immediately, postmobilization. The mobilizations performed included Mulligan talocrural joint dorsiflexion mobilization with movement, Mulligan inferior tibiofibular joint mobilization, and Maitland anteroposterior talocrural joint mobilization. Three CODA cx1 units (Charnwood Dynamics Ltd., Leicestershire, UK) were used to provide information on ankle joint sagittal plane angular displacement. The dependent variable under investigation was the angle of ankle joint plantarflexion at the point of initial contact during the drop landing. There was a statistically significant acute decrease in the angle of ankle joint plantarflexion from premobilization (34.89° ± 4.18°) to postmobilization (31.90° ± 5.89°), t(14) = 2.62, P < 0.05 (two-tailed). The mean decrease in the angle of ankle joint plantarflexion as a result of the ankle joint mobilization was 2.98° with a 95% confidence interval ranging from 0.54 to 5.43. The eta squared statistic (0.32) indicated a large effect size. These results indicate that mobilization acted to acutely reduce the angle of ankle joint plantarflexion at initial contact during a single-leg drop landing. Mobilization applied to participants with CAI has a mechanical effect on the ankle joint, thus facilitating a more favorable positioning of the ankle joint when landing from a jump.

The Influence of Dynamic Contact Angle on Wetting Dynamics

NASA Technical Reports Server (NTRS)

Rame, Enrique; Garoff, Steven

2005-01-01

When surface tension forces dominate, and regardless of whether the situation is static or dynamic, the contact angle (the angle the interface between two immiscible fluids makes when it contacts a solid) is the key parameter that determines the shape of a fluid-fluid interface. The static contact angle is easy to measure and implement in models predicting static capillary surface shapes and such associated quantities as pressure drops. By contrast, when the interface moves relative to the solid (as in dynamic wetting processes) the dynamic contact angle is not identified unambiguously because it depends on the geometry of the system Consequently, its determination becomes problematic and measurements in one geometry cannot be applied in another for prediction purposes. However, knowing how to measure and use the dynamic contact angle is crucial to determine such dynamics as a microsystem throughput reliably. In this talk we will present experimental and analytical efforts aimed at resolving modeling issues present in dynamic wetting. We will review experiments that show the inadequacy of the usual hydrodynamic model when a fluid-fluid meniscus moves over a solid surface such as the wall of a small tube or duct. We will then present analytical results that show how to parametrize these problems in a predictive manner. We will illustrate these ideas by showing how to implement the method in numerical fluid mechanical calculations.

Investigation of surface porosity measurements and compaction pressure as means to ensure consistent contact angle determinations.

PubMed

Holm, René; Borkenfelt, Simon; Allesø, Morten; Andersen, Jens Enevold Thaulov; Beato, Stefania; Holm, Per

2016-02-10

Compounds wettability is critical for a number of central processes including disintegration, dispersion, solubilisation and dissolution. It is therefore an important optimisation parameter both in drug discovery but also as guidance for formulation selection and optimisation. Wettability for a compound is determined by its contact angle to a liquid, which in the present study was measured using the sessile drop method applied to a disc compact of the compound. Precise determination of the contact angle is important should it be used to either rank compounds or selected excipients to e.g. increase the wetting from a solid dosage form. Since surface roughness of the compact has been suggested to influence the measurement this study investigated if the surface quality, in terms of surface porosity, had an influence on the measured contact angle. A correlation to surface porosity was observed, however for six out of seven compounds similar results were obtained by applying a standard pressure (866 MPa) to the discs in their preparation. The data presented in the present work therefore suggest that a constant high pressure should be sufficient for most compounds when determining the contact angle. Only for special cases where compounds have poor compressibility would there be a need for a surface-quality-control step before the contact angle determination. Copyright © 2015 Elsevier B.V. All rights reserved.

Extended release of hyaluronic acid from hydrogel contact lenses for dry eye syndrome.

PubMed

Maulvi, Furqan A; Soni, Tejal G; Shah, Dinesh O

2015-01-01

Current dry eye treatment includes delivering comfort enhancing agents to the eye via eye drops, but low residence time of eye drops leads to low bioavailability. Frequent administration leads to incompliance in patients, so there is a great need for medical device such as contact lenses to treat dry eye. Studies in the past have demonstrated the efficacy of hyaluronic acid (HA) in the treatment of dry eyes using eye drops. In this paper, we present two methods to load HA in hydrogel contact lenses, soaking method and direct entrapment. The contact lenses were characterized by studying their optical and physical properties to determine their suitability as extended wear contact lenses. HA-laden hydrogel contact lenses prepared by soaking method showed release up to 48 h with acceptable physical and optical properties. Hydrogel contact lenses prepared by direct entrapment method showed significant sustained release in comparison to soaking method. HA entrapped in hydrogels resulted in reduction in % transmittance, sodium ion permeability and surface contact angle, while increase in % swelling. The impact on each of these properties was proportional to HA loading. The batch with 200-μg HA loading showed all acceptable values (parameters) for contact lens use. Results of cytotoxicity study indicated the safety of hydrogel contact lenses. In vivo pharmacokinetics studies in rabbit tear fluid showed dramatic increase in HA mean residence time and area under the curve with lenses in comparison to eye drop treatment. The study demonstrates the promising potential of delivering HA through contact lenses for the treatment of dry eye syndrome.

Fabrication of micro/nano hierarchical structures with analysis on the surface mechanics

NASA Astrophysics Data System (ADS)

Jheng, Yu-Sheng; Lee, Yeeu-Chang

2016-10-01

Biomimicry refers to the imitation of mechanisms and features found in living creatures using artificial methods. This study used optical lithography, colloidal lithography, and dry etching to mimic the micro/nano hierarchical structures covering the soles of gecko feet. We measured the static contact angle and contact angle hysteresis to reveal the behavior of liquid drops on the hierarchical structures. Pulling tests were also performed to measure the resistance of movement between the hierarchical structures and a testing plate. Our results reveal that hierarchical structures at the micro-/nano-scale are considerably hydrophobic, they provide good flow characteristics, and they generate more contact force than do surfaces with micro-scale cylindrical structures.

Adsorption energy as a metric for wettability at the nanoscale

PubMed Central

Giro, Ronaldo; Bryant, Peter W.; Engel, Michael; Neumann, Rodrigo F.; Steiner, Mathias B.

2017-01-01

Wettability is the affinity of a liquid for a solid surface. For energetic reasons, macroscopic drops of liquid form nearly spherical caps. The degree of wettability is then captured by the contact angle where the liquid-vapor interface meets the solid-liquid interface. As droplet volumes shrink to the scale of attoliters, however, surface interactions become significant, and droplets assume distorted shapes. In this regime, the contact angle becomes ambiguous, and a scalable metric for quantifying wettability is needed, especially given the emergence of technologies exploiting liquid-solid interactions at the nanoscale. Here we combine nanoscale experiments with molecular-level simulation to study the breakdown of spherical droplet shapes at small length scales. We demonstrate how measured droplet topographies increasingly reveal non-spherical features as volumes shrink. Ultimately, the nanoscale droplets flatten out to form layer-like molecular assemblies at the solid surface. For the lack of an identifiable contact angle at small scales, we introduce a droplet’s adsorption energy density as a new metric for a liquid’s affinity for a surface. We discover that extrapolating the macroscopic idealization of a drop to the nanoscale, though it does not geometrically resemble a realistic droplet, can nonetheless recover its adsorption energy if line tension is included. PMID:28397869

Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops.

PubMed

Chen, Longquan; Bonaccurso, Elmar

2014-08-01

In this paper, we experimentally investigated the dynamic spreading of liquid drops on solid surfaces. Drop of glycerol water mixtures and pure water that have comparable surface tensions (62.3-72.8 mN/m) but different viscosities (1.0-60.1 cP) were used. The size of the drops was 0.5-1.2 mm. Solid surfaces with different lyophilic and lyophobic coatings (equilibrium contact angle θ(eq) of 0°-112°) were used to study the effect of surface wettability. We show that surface wettability and liquid viscosity influence wetting dynamics and affect either the coefficient or the exponent of the power law that describes the growth of the wetting radius. In the early inertial wetting regime, the coefficient of the wetting power law increases with surface wettability but decreases with liquid viscosity. In contrast, the exponent of the power law does only depend on surface wettability as also reported in literature. It was further found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does. For low viscosity liquids, the duration of inertial wetting corresponds to the time of capillary wave propagation, which can be determined by Lamb's drop oscillation model for inviscid liquids. For relatively high viscosity liquids, the inertial wetting time increases with liquid viscosity, which may due to the viscous damping of the surface capillary waves. Furthermore, we observed a viscous wetting regime only on surfaces with an equilibrium contact angle θ(eq) smaller than a critical angle θ(c) depending on viscosity. A scaling analysis based on Navier-Stokes equations is presented at the end, and the predicted θ(c) matches with experimental observations without any additional fitting parameters.

Organization of microbeads in Leidenfrost drops.

PubMed

Maquet, Laurent; Colinet, Pierre; Dorbolo, Stéphane

2014-06-21

We investigated the organization of micrometric hydrophilic beads (glass or basalt) immersed in Leidenfrost drops. Starting from a large volume of water compared to the volume of the beads, while the liquid evaporates, we observed that the grains are eventually trapped at the interface of the droplet and accumulate. At a moment, the grains entirely cover the droplet. We measured the surface area at this moment as a function of the total mass of particles inserted in the droplet. We concluded that the grains form a monolayer around the droplet assuming (i) that the packing of the beads at the surface is a random close packing and (ii) that the initial surface of the drop is larger than the maximum surface that the beads can cover. Regarding the evaporation dynamics, the beads are found to reduce the evaporation rate of the drop. The slowdown of the evaporation is interpreted as being the consequence of the dewetting of the particles located at the droplet interface which makes the effective surface of evaporation smaller. As a matter of fact, contact angles of the beads with the water deduced from the evaporation rates are consistent with contact angles of beads directly measured at a flat air-water interface of water in a container.

A drop penetration method to measure powder blend wettability.

PubMed

Wang, Yifan; Liu, Zhanjie; Muzzio, Fernando; Drazer, German; Callegari, Gerardo

2018-03-01

Water wettability of pharmaceutical blends affects important quality attributes of final products. We investigate the wetting properties of a pharmaceutical blend lubricated with Magnesium Stearate (MgSt) as a function of the mechanical shear strain applied to the blend. We measure the penetration dynamics of sessile drops deposited on slightly compressed powder beds. We consider a blend composed of 9% Acetaminophen 90% Lactose and 1% MgSt by weight. Comparing the penetration time of water and a reference liquid Polydimethylsiloxane (silicon oil) we obtain an effective cosine of the contact angle with water, based on a recently developed drop penetration method. We repeat the experiments for blends exposed to increasing levels of shear strain and demonstrate a significant decrease in water wettability (decrease in the cosine of the contact angle). The results are consistent with the development of a hydrophobic film coating the powder particles as a result of the increased shear strain. Finally, we show that, as expected dissolution times increase with the level of shear strain. Therefore, the proposed drop penetration method could be used to directly assess the state of lubrication of a pharmaceutical blend and act as a quality control on powder blend attributes before the blend is tableted. Copyright © 2017 Elsevier B.V. All rights reserved.

Dancing drops over vibrating substrates

NASA Astrophysics Data System (ADS)

Borcia, Rodica; Borcia, Ion Dan; Helbig, Markus; Meier, Martin; Egbers, Christoph; Bestehorn, Michael

2017-04-01

We study the motion of a liquid drop on a solid plate simultaneously submitted to horizontal and vertical harmonic vibrations. The investigation is done via a phase field model earlier developed for describing static and dynamic contact angles. The density field is nearly constant in every bulk region (ρ = 1 in the liquid phase, ρ ≈ 0 in the vapor phase) and varies continuously from one phase to the other with a rapid but smooth variation across the interfaces. Complicated explicit boundary conditions along the interface are avoided and captured implicitly by gradient terms of ρ in the hydrodynamic basic equations. The contact angle θ is controlled through the density at the solid substrate ρ S , a free parameter varying between 0 and 1 [R. Borcia, I.D. Borcia, M. Bestehorn, Phys. Rev. E 78, 066307 (2008)]. We emphasize the swaying and the spreading modes, earlier theoretically identified by Benilov and Billingham via a shallow-water model for drops climbing uphill along an inclined plane oscillating vertically [E.S. Benilov, J. Billingham, J. Fluid Mech. 674, 93 (2011)]. The numerical phase field simulations will be completed by experiments. Some ways to prevent the release of the dancing drops along a hydrophobic surface into the gas atmosphere are also discussed in this paper.

Drop Impact Dynamics with Sessile Drops and Geometries: Spreading, Jetting, and Fragmentation

NASA Astrophysics Data System (ADS)

Tilger, Christopher F.

The tendency of surface tension to cause small parcels of fluid to form into drops allows convenient packaging, transport, dispersal of liquid phase matter. Liquid drop impacts with solids, liquids, and other drops have realized and additional future applications in biological, manufacturing, heat transfer, and combustion systems. Experiments were conducted to investigate the dynamics of multiple drop collisions, rather than the most-studied phenomenon of single drop impacts. Additional drop impacts were performed on rigid hemispheres representing sessile drops, angled substrates, and into the vertex of two tilted surfaces arranged into a vee shape. A qualitative inspection of drop-sessile drop impacts shows distinct post-impact shapes depending on the offset distance between the drops. At intermediate offset distances, distinct jets issue from the overlap region between the two drops projected areas. These jets are observed to reach their maximum extent at a critical offset distance ratio, epsilon epsilon ˜ 0.75-0.80, with substrate contact angle and W e having a lesser effect. Capillary waves that traverse the sessile drop after collision cause a lower aspect ratio liquid column to emanate from the sessile drop opposite the impact. In order to better understand the jetting phenomenon seen in the offset drop-sessile drop impacts, simpler solid geometries are investigated that elicit a similar behavior. Solid hemispheres do not show the singular jetting observed in the fluidic case, however, a simple vee formed by two intersection planar substrates do jet in a similar fashion to the fluidic case. A geometric model with partnered experiments is developed to describe the bisymmetric spread of an impacting drop on an angled substrate. This geometric model is used to guide a time of arrival based model for various features of the drop impact, which is used to predict jetting in various vee channel experiments.

Unidirectional superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Prakash, Manu; Bush, John

2007-11-01

It has long been known that the hairy, waxy cuticle of water-walking insects renders them water-repellent; they thus exhibit high static contact angles. We have recently demonstrated that by the virtue of the geometry and flexibility of the hair, the integument is also directionally anisotropic and so plays a key propulsive role. We here report our attempts to design and implement an analogous synthetic surface that exhibits unidirectional adhesion. The surface effectively acts like a fluidic-diode; allowing contact lines to advance in only one direction. When vibrated randomly, drops suspended on the surface advance in only one direction. Applications in valve-less pumps and drop transport in microfluidic devices are discussed.

The Amateur Scientist.

ERIC Educational Resources Information Center

Walker, Jearl

1985-01-01

Discusses forces that shape the behavior of water as a drop meanders down a windowpane. A homemade apparatus for studying meanders is described along with several experiments. Contact angles, molecule attraction, surface area, air tension, and gravity drag forces are some of the topics addressed. (DH)

Oscillations of a sessile droplet in open air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korenchenko, A. E., E-mail: korenchenko@physics.susu.ac.ru; Beskachko, V. P.

2013-11-15

The open system consisting of a sessile drop, a neutral gas, and a substrate is analyzed by numerical methods. The mode with constant contact angle is considered. The model takes into account evaporation from drop surface, free and forced convection in gas, buoyancy, and Marangoni effect in the liquid phase. It was established that every considered mechanical and thermodynamical disturbance of the system leads to the drop surface oscillations, and thus a drop in an open air oscillates almost inevitably. The displacement of the liquid-gas interface due to oscillations is analyzed in terms of its impact on the accuracy ofmore » measurement of the surface tension by sessile drop method.« less

Characteristic angles in the wetting of an angular region: deposit growth.

PubMed

Popov, Yuri O; Witten, Thomas A

2003-09-01

Solids dispersed in a drying drop migrate to the (pinned) contact line. This migration is caused by outward flows driven by the loss of the solvent due to evaporation and by geometrical constraint that the drop maintains an equilibrium surface shape with a fixed boundary. Here, in continuation of our earlier paper, we theoretically investigate the evaporation rate, the flow field, and the rate of growth of the deposit patterns in a drop over an angular sector on a plane substrate. Asymptotic power laws near the vertex (as distance to the vertex goes to zero) are obtained. A hydrodynamic model of fluid flow near the singularity of the vertex is developed and the velocity field is obtained. The rate of the deposit growth near the contact line is found in two time regimes. The deposited mass falls off as a weak power gamma of distance close to the vertex and as a stronger power beta of distance further from the vertex. The power gamma depends only slightly on the opening angle alpha and stays roughly between -1/3 and 0. The power beta varies from -1 to 0 as the opening angle increases from 0 degrees to 180 degrees. At a given distance from the vertex, the deposited mass grows faster and faster with time, with the greatest increase in the growth rate occurring at the early stages of the drying process.

Motion of a Drop on a Solid Surface Due to a Wettability Gradient

NASA Technical Reports Server (NTRS)

Subramanian, R.; Moumen, Nadjoua; McLaughlin, John B.

2005-01-01

The hydrodynamic force experienced by a spherical-cap drop moving on a solid surface is obtained from two approximate analytical solutions and used to predict the quasi-steady speed of the drop in a wettability gradient. One solution is based on approximation of the shape of the drop as a collection of wedges, and the other is based on lubrication theory. Also, asymptotic results from both approximations for small contact angles, as well as an asymptotic result from lubrication theory that is good when the length scale of the drop is large compared with the slip length, are given. The results for the hydrodynamic force also can be used to predict the quasi-steady speed of a drop sliding down an incline.

Self-Injurious Behavior: An Animal Model of an Autism Endophenotype

DTIC Science & Technology

2012-01-01

time there was a visible release of the pasta (not a drop) or a reformation of the digits holding the pasta via motor patterns of flexion/extension...review of 18 pasta -trials, nine trials randomly selected from each experimental group. Behaviors included on the code sheet were number of drops...failure to contact reaches, angling with head tilt, abnormal posture, use of a unilateral paw technique, and twirling of the pasta . Specific descriptions

Simple treatment of cotton textile to impart high water repellent properties

NASA Astrophysics Data System (ADS)

Ivanova, N. A.; Zaretskaya, A. K.

2010-12-01

We describe two methods to impart the water repellency for the surface of cotton fabric, using a commercially available and a laboratory synthesized fluoroalkylsiloxanes. To characterize the wettability and the durability of water repellent properties of hydrophobic coating produced, we have studied the advancing water contact angles, rolling angles and the evolution of water contact angle in time during a continuous contact of the surface with the water drop. The quality of the coatings was also assessed after the washing procedure. The analysis of the wettability of hydrophobized fabrics indicated that a better effect, leading to the superhydrophobic state of the surface, was observed when the surface relief of the fabric with the coating is determined by not only the structure and braiding of the fabric, but also the additional elements of texture created by the aggregates of molecules of hydrophobic agent.

Fractal characterization and wettability of ion treated silicon surfaces

NASA Astrophysics Data System (ADS)

Yadav, R. P.; Kumar, Tanuj; Baranwal, V.; Vandana, Kumar, Manvendra; Priya, P. K.; Pandey, S. N.; Mittal, A. K.

2017-02-01

Fractal characterization of surface morphology can be useful as a tool for tailoring the wetting properties of solid surfaces. In this work, rippled surfaces of Si (100) are grown using 200 keV Ar+ ion beam irradiation at different ion doses. Relationship between fractal and wetting properties of these surfaces are explored. The height-height correlation function extracted from atomic force microscopic images, demonstrates an increase in roughness exponent with an increase in ion doses. A steep variation in contact angle values is found for low fractal dimensions. Roughness exponent and fractal dimensions are found correlated with the static water contact angle measurement. It is observed that after a crossover of the roughness exponent, the surface morphology has a rippled structure. Larger values of interface width indicate the larger ripples on the surface. The contact angle of water drops on such surfaces is observed to be lowest. Autocorrelation function is used for the measurement of ripple wavelength.

Dynamics of liquid spreading on solid surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalliadasis, S.; Chang, H.C.

1996-09-01

Using simple scaling arguments and a precursor film model, the authors show that the appropriate macroscopic contact angle {theta} during the slow spreading of a completely or partially wetting liquid under conditions of viscous flow and small slopes should be described by tan {theta} = [tan{sup 3} {theta}{sub e} {minus} 9 log {eta}Ca]{sup 1/3} where {theta}{sub e} is the static contact angle, Ca is the capillary number, and {eta} is a scaled Hamaker constant. Using this simple relation as a boundary condition, the authors are able to quantitatively model, without any empirical parameter, the spreading dynamics of several classical spreadingmore » phenomena (capillary rise, sessile, and pendant drop spreading) by simply equating the slope of the leading order static bulk region to the dynamic contact angle boundary condition without performing a matched asymptotic analysis for each case independently as is usually done in the literature.« less

Wetting properties and critical micellar concentration of benzalkonium chloride mixed in sodium hypochlorite.

PubMed

Bukiet, Frédéric; Couderc, Guillaume; Camps, Jean; Tassery, Hervé; Cuisinier, Frederic; About, Imad; Charrier, Anne; Candoni, Nadine

2012-11-01

The purposes of the present study were to (1) assess the effect of the addition of benzalkonium chloride to sodium hypochlorite on its wetting properties, contact angle, and surface energy; (2) determine the critical micellar concentration of benzalkonium chloride in sodium hypochlorite; and (3) investigate the influence of addition of benzalkonium chloride on the free chlorine level, cytotoxicity, and antiseptic properties of the mixture. Solutions of benzalkonium chloride, with concentrations ranging from 0%-1%, were mixed in 2.4% sodium hypochlorite and tested as follows. The wetting properties were investigated by measuring the contact angle of the solutions on a nondehydrated dentin surface by using the static sessile drop method. The pending drop technique was subsequently used to determine the surface energy of the solutions. The critical micellar concentration of benzalkonium chloride mixed in sodium hypochlorite was calculated from the data. When 2.4% NaOCl was mixed with benzalkonium chloride at the critical micellar concentration, 3 parameters were tested: free chloride content, cytotoxicity, and antibacterial effects against Enterococcus faecalis. The contact angle (P < .001) as well as the surface energy (P < .001) significantly decreased with increasing benzalkonium chloride concentrations. The critical micellar concentration of benzalkonium chloride in sodium hypochlorite was 0.008%. At this concentration, the addition of benzalkonium chloride had no effect on the free chlorine content, cytotoxicity, or antibacterial efficiency of the mixture. The addition of benzalkonium chloride to sodium hypochlorite at the critical micellar concentration reduced the contact angle by 51.2% and the surface energy by 53.4%, without affecting the free chloride content, cytotoxicity, or antibacterial properties of the mixture. Copyright © 2012 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Optical monitoring of proteins at solid interfaces

NASA Astrophysics Data System (ADS)

Dunne, G.; McDonnell, L.; Miller, R.; McMillan, N. D.; O'Rourke, B.; Mitchell, C. I.

2005-06-01

The adsorption properties of polymers are of great importance for implant studies. A better understanding of these properties can lead to improved implant materials. In this study the surface energy of different polymers was derived from contact angle measurements taken using profile analysis tensiometry (PAT) of sessile drops of water. The contact angles were measured for advancing and receding water drops on polished polymer surfaces and also on polymer surfaces modified by adsorbing protein to the surface prior to analysis of the sessile drop. The protein used was bovine serum albumin (BSA) and the surfaces were poly-methylmethacrylate (PMMA), poly-ether-ether-ketone (PEEK) and stainless steel. The polymer surfaces were also studied using atomic force microscopy (AFM). Images of the surfaces were taken in different states: rough, smooth and with albumin adsorbed. As a method to identify the proteins on the surface easier, anti-albumin antibodies with 30nm nano gold particles attached were adsorbed to the albumin on the surfaces. Using nano gold particles made the imaging more straightforward and thus made identification of the protein on the surface easier. The results from this work show the differing hydrophobicities of polymer surfaces under different conditions and a new nanotechnological method of protein identification.

Contact interaction of the Bi12GeO20, Bi12SiO20, and Bi4Ge3O12 melts with noble metals

NASA Astrophysics Data System (ADS)

Denisov, V. M.; Podkopaev, O. I.; Denisova, L. T.; Kuchumova, O. V.; Istomin, S. A.; Pastukhov, E. A.

2014-02-01

The sessile drop method is used to study the contact interaction of Ag, Au, Pd, Pt, and Ir with the Bi2O3-GeO2 and Bi2O3-SiO2 melts. These melts spread over Ag and Pd and, in some cases, over Au and Pt at a rather high speed and form equilibrium contact angles on Ir.

Resolving an ostensible inconsistency in calculating the evaporation rate of sessile drops.

PubMed

Chini, S F; Amirfazli, A

2017-05-01

This paper resolves an ostensible inconsistency in the literature in calculating the evaporation rate for sessile drops in a quiescent environment. The earlier models in the literature have shown that adapting the evaporation flux model for a suspended spherical drop to calculate the evaporation rate of a sessile drop needs a correction factor; the correction factor was shown to be a function of the drop contact angle, i.e. f(θ). However, there seemed to be a problem as none of the earlier models explicitly or implicitly mentioned the evaporation flux variations along the surface of a sessile drop. The more recent evaporation models include this variation using an electrostatic analogy, i.e. the Laplace equation (steady-state continuity) in a domain with a known boundary condition value, or known as the Dirichlet problem for Laplace's equation. The challenge is that the calculated evaporation rates using the earlier models seemed to differ from that of the recent models (note both types of models were validated in the literature by experiments). We have reinvestigated the recent models and found that the mathematical simplifications in solving the Dirichlet problem in toroidal coordinates have created the inconsistency. We also proposed a closed form approximation for f(θ) which is valid in a wide range, i.e. 8°≤θ≤131°. Using the proposed model in this study, theoretically, it was shown that the evaporation rate in the CWA (constant wetted area) mode is faster than the evaporation rate in the CCA (constant contact angle) mode for a sessile drop. Copyright © 2016 Elsevier B.V. All rights reserved.

VOF simulations of the contact angle dynamics during the drop spreading: standard models and a new wetting force model.

PubMed

Malgarinos, Ilias; Nikolopoulos, Nikolaos; Marengo, Marco; Antonini, Carlo; Gavaises, Manolis

2014-10-01

In this study,a novel numerical implementation for the adhesion of liquid droplets impacting normally on solid dry surfaces is presented. The advantage of this new approach, compared to the majority of existing models, is that the dynamic contact angle forming during the surface wetting process is not inserted as a boundary condition, but is derived implicitly by the induced fluid flow characteristics (interface shape) and the adhesion physics of the gas-liquid-surface interface (triple line), starting only from the advancing and receding equilibrium contact angles. These angles are required in order to define the wetting properties of liquid phases when interacting with a solid surface. The physical model is implemented as a source term in the momentum equation of a Navier-Stokes CFD flow solver as an "adhesion-like" force which acts at the triple-phase contact line as a result of capillary interactions between the liquid drop and the solid substrate. The numerical simulations capture the liquid-air interface movement by considering the volume of fluid (VOF) method and utilizing an automatic local grid refinement technique in order to increase the accuracy of the predictions at the area of interest, and simultaneously minimize numerical diffusion of the interface. The proposed model is validated against previously reported experimental data of normal impingement of water droplets on dry surfaces at room temperature. A wide range of impact velocities, i.e. Weber numbers from as low as 0.2 up to 117, both for hydrophilic (θadv=10°-70°) and hydrophobic (θadv=105°-120°) surfaces, has been examined. Predictions include in addition to droplet spreading dynamics, the estimation of the dynamic contact angle; the latter is found in reasonable agreement against available experimental measurements. It is thus concluded that theimplementation of this model is an effective approach for overcoming the need of a pre-defined dynamic contact angle law, frequently adopted as an approximate boundary condition for such simulations. Clearly, this model is mostly influential during the spreading phase for the cases of low We number impacts (We<˜80) since for high impact velocities, inertia dominates significantly over capillary forces in the initial phase of spreading. Copyright © 2014 Elsevier B.V. All rights reserved.

Diagenetic and compositional controls of wettability in siliceous sedimentary rocks, Monterey Formation, California

NASA Astrophysics Data System (ADS)

Hill, Kristina M.

Modified imbibition tests were performed on 69 subsurface samples from Monterey Formation reservoirs in the San Joaquin Valley to measure wettability variation as a result of composition and silica phase change. Contact angle tests were also performed on 6 chert samples from outcrop and 3 nearly pure mineral samples. Understanding wettability is important because it is a key factor in reservoir fluid distribution and movement, and its significance rises as porosity and permeability decrease and fluid interactions with reservoir grain surface area increase. Although the low permeability siliceous reservoirs of the Monterey Formation are economically important and prolific, a greater understanding of factors that alter their wettability will help better develop them. Imbibition results revealed a strong trend of decreased wettability to oil with increased detrital content in opal-CT phase samples. Opal-A phase samples exhibited less wettability to oil than both opal-CT and quartz phase samples of similar detrital content. Subsurface reservoir samples from 3 oil fields were crushed to eliminate the effect of capillary pressure and cleansed of hydrocarbons to eliminate wettability alterations by asphaltene, then pressed into discs of controlled density. Powder discs were tested for wettability by dispensing a controlled volume of water and motor oil onto the surface and measuring the time required for each fluid to imbibe into the sample. The syringe and software of a CAM101 tensiometer were used to control the amount of fluid dispensed onto each sample, and imbibition completion times were determined by high-speed photography for water drops; oil drop imbibition was significantly slower and imbibition was timed and determined visually. Contact angle of water and oil drops on polished chert and mineral sample surfaces was determined by image analysis and the Young-Laplace equation. Oil imbibition was significantly slower with increased detrital composition and faster with increased silica content in opal-CT and quartz phase samples, implying decreased wettability to oil with increased detrital (clay) content. However, contact angle tests showed that opal-CT is more wetting to oil with increased detritus and results for oil on quartz-phase samples were inconsistent between different proxies for detritus over their very small compositional range. Water contact angle trends also showed inconsistent wetting trends compared to imbibition tests. We believe this is because the small range in bulk detrital composition between the "pure" samples used in contact angle tests was close to analytical error and because small-scale spatial compositional variability may be significant enough to effect wettability. These experiments show that compositional variables significantly affect wettability, outweighing the effect of silica phase.

Interaction Between Graphene-Coated SiC Single Crystal and Liquid Copper

NASA Astrophysics Data System (ADS)

Homa, M.; Sobczak, N.; Sobczak, J. J.; Kudyba, A.; Bruzda, G.; Nowak, R.; Pietrzak, K.; Chmielewski, M.; Strupiński, W.

2018-04-01

The wettability of graphene-coated SiC single crystal (CGn/SiCsc) by liquid Cu (99.99%) was investigated by a sessile drop method in vacuum conditions at temperature of 1100 °C. The graphene layer was produced via a chemical vapor deposition routine using 4H-SiC single crystal cut out from 6″ wafer. A dispensed drop technique combined with a non-contact heating of a couple of materials was applied. The Cu drop was squeezed from a graphite capillary and deposited on the substrate directly in a vacuum chamber. The first Cu drop did not wet the CGn/SiCsc substrate and showed a lack of adhesion to the substrate: the falling Cu drop only touched the substrate forming a contact angle of θ 0 = 121° and then immediately rolled like a ball along the substrate surface. After settling near the edge of the substrate in about 0.15 s, the Cu drop formed an asymmetric shape with the right and left contact angles of different values (θ R = 86° and θ L = 70°, respectively), while in the next 30 min, θ R and θ L achieved the same final value of 52°. The second Cu drop was put down on the displacement path of the first drop, and immediately after the deposition, it also did not wet the substrate (θ = 123°). This drop kept symmetry and the primary position, but its wetting behavior was unusual: both θ R and θ L decreased in 17 min to the value of 23° and next, they increased to a final value of 65°. Visual observations revealed a presence of 2.5-mm-thick interfacial phase layer reactively formed under the second drop. Scanning electron microscopy (SEM) investigations revealed the presence of carbon-enriched precipitates on the top surface of the first Cu drop. These precipitates were identified by the Raman spectroscopy as double-layer graphene. The Raman spectrum taken from the substrate far from the drop revealed the presence of graphene, while that obtained from the first drop displacement path exhibited a decreased intensity of 2D peak. The results of SEM investigations and Raman spectroscopy studies suggest that the presence of graphene layer on the SiC substrate suppresses but does not completely prevent chemical interaction between liquid Cu drop and SiC. Both chemical degradation (etching) and mechanical degradation of the graphene layer during drop rolling due to high adhesion of the Cu drop to the SiC substrate are responsible for mass transfer through the 2nd drop/substrate interface that in turn results in significant changes of structure and chemistry of the drop and the interface.

Interaction Between Graphene-Coated SiC Single Crystal and Liquid Copper

NASA Astrophysics Data System (ADS)

Homa, M.; Sobczak, N.; Sobczak, J. J.; Kudyba, A.; Bruzda, G.; Nowak, R.; Pietrzak, K.; Chmielewski, M.; Strupiński, W.

2018-05-01

The wettability of graphene-coated SiC single crystal (CGn/SiCsc) by liquid Cu (99.99%) was investigated by a sessile drop method in vacuum conditions at temperature of 1100 °C. The graphene layer was produced via a chemical vapor deposition routine using 4H-SiC single crystal cut out from 6″ wafer. A dispensed drop technique combined with a non-contact heating of a couple of materials was applied. The Cu drop was squeezed from a graphite capillary and deposited on the substrate directly in a vacuum chamber. The first Cu drop did not wet the CGn/SiCsc substrate and showed a lack of adhesion to the substrate: the falling Cu drop only touched the substrate forming a contact angle of θ 0 = 121° and then immediately rolled like a ball along the substrate surface. After settling near the edge of the substrate in about 0.15 s, the Cu drop formed an asymmetric shape with the right and left contact angles of different values ( θ R = 86° and θ L = 70°, respectively), while in the next 30 min, θ R and θ L achieved the same final value of 52°. The second Cu drop was put down on the displacement path of the first drop, and immediately after the deposition, it also did not wet the substrate ( θ = 123°). This drop kept symmetry and the primary position, but its wetting behavior was unusual: both θ R and θ L decreased in 17 min to the value of 23° and next, they increased to a final value of 65°. Visual observations revealed a presence of 2.5-mm-thick interfacial phase layer reactively formed under the second drop. Scanning electron microscopy (SEM) investigations revealed the presence of carbon-enriched precipitates on the top surface of the first Cu drop. These precipitates were identified by the Raman spectroscopy as double-layer graphene. The Raman spectrum taken from the substrate far from the drop revealed the presence of graphene, while that obtained from the first drop displacement path exhibited a decreased intensity of 2D peak. The results of SEM investigations and Raman spectroscopy studies suggest that the presence of graphene layer on the SiC substrate suppresses but does not completely prevent chemical interaction between liquid Cu drop and SiC. Both chemical degradation (etching) and mechanical degradation of the graphene layer during drop rolling due to high adhesion of the Cu drop to the SiC substrate are responsible for mass transfer through the 2nd drop/substrate interface that in turn results in significant changes of structure and chemistry of the drop and the interface.

Linkage between canopy water storage and drop size distributions of leaf drips

NASA Astrophysics Data System (ADS)

Nanko, Kazuki; Watanabe, Ai; Hotta, Norifumi; Suzuki, Masakazu

2013-04-01

Differences in drop size distribution (DSD) of leaf drips among tree species have been estimated and physically interpreted to clarify the leaf drip generation process. Leaf drip generation experiments for nine species were conducted in an indoor location without foliage vibration using an automatic mist spray. Broad-leaved species produced a similar DSD among species whose leaves had a matte surface and a second similar DSD among species whose leaves had a coated surface. The matte broad leaves produced a larger and wider range of DSDs than the coated broad leaves. Coated coniferous needles had a wider range of DSDs than the coated broad leaves and different DSDs were observed for different species. The species with shorter dense needles generated a larger DSD. The leaf drip diameter was calculated through the estimation of a state of equilibrium of a hanging drop on the leaves based on physical theory. The calculations indicated that the maximum diameter of leaf drips was determined by the contact angle, and the range of DSDs was determined by the variation in contact length and the contact diameter at the hanging points. The results revealed that leaf drip DSD changed due to variations in leaf hydrophobicity, leaf roughness, leaf geometry and leaf inclination among the different tree species. This study allows the modelization of throughfall DSD. Furthermore, it indicates the possibility of interpreting canopy water processes from canopy water storage to drainage through the contact angle and leaf drip DSD. The part of this study is published in Nanko et al. (2013, Agric. Forest. Meteorol. 169, 74-84).

Factors Contributing to Pelvis Instability in Female Adolescent Athletes During Unilateral Repeated Partial Squat Activity

PubMed Central

Scarborough, Donna Moxley; Linderman, Shannon; Berkson, Eric M.; Oh, Luke S.

2017-01-01

Objectives: Unilateral partial squat tasks are often used to assess athletes’ lower extremity (LE) neuromuscular control. Single squat biomechanics such as lateral drop of the non-stance limb’s pelvis have been linked to knee injury risk. Yet, there are limited studies on the factors contributing to pelvic instability during the unilateral partial squat such as anatomical alignment of the knee and hip strength. The purpose of this study was 1) to assess the influence of leg dominance on pelvic drop among female athletes during the repeated unilateral partial squat activity and 2) to investigate the contributions that lower limb kinematics and hip strength have on pelvis drop. Methods: 42 female athletes (27= softball pitchers, 15=gymnasts, avg age=16.48 ± 2.54 years) underwent lower limb assessment. The quadriceps angle (Q angle) and the average of 3 trials for hip abduction and extension strength (handheld dynamometer measurements) were used for analyses. 3D biomechanical analysis of the repeated unilateral partial squat activity followed using a 20 motion capture camera system which created a 15 segment model of each subject. The subject stood on one leg at the lateral edge of a 17.78 cm box with hands placed on the hips and squatted so that the free hanging contralateral limb came as close to the ground without contact for 5 continuous repetitions. One trial for each limb was performed. Peak pelvic drop and ankle, knee and hip angles and torques (normalized by weight) at this time point were calculated using Visual 3D (C-Motion) biomechanical software. Paired T-test, Spearman correlations and multiple regression model statistical analyses were performed. Results: Peak pelvic drop during the unilateral partial squat did not differ significantly on the basis of limb dominance (p=0.831, Dom: -3.40 ± 5.10° , ND: -3.46 ± 4.44°). Peak pelvic drop displayed a Spearman correlation with the functional measure of hip abduction/adduction (ABD/ADD) angle (rs= 0.627, p< 0.001) (Figure 1). No association was noted between peak pelvic drop and anatomical measures of Q angle or isometric hip extension strength. A multiple regression was performed to predict pelvis drop angle from the following 6 variables: isometric hip ABD strength, hip ABD/ADD angle, hip internal/external rotation angle, ankle supination/pronation (S/P) angle, height and weight. These variables statistically predicted pelvis drop, F(6,73) = 17.848, p < .0005, R2 = 0.595. The strongest combined predictor variables for pelvic drop in the female athletes were hip abduction/ adduction angle and strength followed by subject’s weight and ankle S/P angle (Table 1). Conclusion: Peak pelvic drop during the repeated unilateral partial squat activity did not correlate significantly with Q angle and hip extension strength. Instead, peak pelvic drop appears more related to a combination of biomechanical limb positioning, hip ABD strength and subject demographics. The regression model run on the repeated unilateral partial squat demonstrates predictive power of this dynamic assessment tool based on kinematic measures across multiple joints. Results could guide clinician screening for excessive pelvic drop in female athletes and based on the predictive model make recommendations for corrective conditioning to help prevent knee injury and guide return to sport following LE surgery. Table 1: Multivariate linear regression model for pelvic drop, Isometric hip strength and lower extremity kinematics during repeated partial squat activity among female athletes. Variable P Isometric hip abduction strength 0.034* Hip Abduction/Adduction Angle <0.001* Hip Internal/External Rotation Angle 0.936 Ankle Internal/External Rotation Angle 0.072 Height 0.398 Weight 0.011* * Level of significance established at p<0.05

Optically transparent, superhydrophobic, biocompatible thin film coatings and methods for producing same

DOEpatents

Armstrong, Beth L.; Aytug, Tolga; Paranthaman, Mariappan Parans; Simpson, John T.; Hillesheim, Daniel A.; Trammell, Neil E.

2017-09-05

An optically transparent, hydrophobic coating, exhibiting an average contact angle of at least 100 degrees with a drop of water. The coating can be produced using low-cost, environmentally friendly components. Methods of preparing and using the optically transparent, hydrophobic coating.

Flower-like Rh/Cu superhydrophobic coating via electrodeposition and its self-cleaning property

NASA Astrophysics Data System (ADS)

Zhao, N.; Lu, S. X.; Xu, W. G.; Cheng, X. L.

2017-01-01

Rh/Cu superhydrophobic coatings with textured flower-like dual micro-nano structures were fabricated on copper substrates via electrodesposition of Rh followed by annealing treatment. The scanning electron microscopy and X-ray diffraction pattern were conducted to analyse the morphology and chemical composition of the coating surfaces, respectively. The water drops exhibited a water contact angle of 168±1° and a sliding angle of 0±1° on the coating surfaces which were obtained by etching in concentrated hydrochloric acid and nitric acid, electrodeposited at -1.0 V for 30 min and annealing in an oven at 180°C for 60 min. The prepared superhydrophobic coatings showed excellent water repellence and self-cleaning property due to its extremely high water contact angle.

Numerical investigation of sliding drops on an inclined surface

NASA Astrophysics Data System (ADS)

Legendre, Dominique; Pedrono, Annaig; Interface Group Team

2017-11-01

Despite it apparent simplicity, the behavior of a drop on an inclined solid surface is far to be properly reproduced by numerical simulation. It involves static, hysteresis and dynamic contact line behaviors. Depending on the fluid properties, the hysteresis and the wall inclination, different drop shapes (rounded, corner or pearling drop) can be observed. The 3D numerical simulations of sliding droplets presented in this work are based on a Volume of Fluid (VoF) solver without any interface reconstruction developed in the JADIM code. The surface tension is solved using the classical CSF (Continuum Surface Force) model and a sub grid model is used to describe under hysteresis conditions both the shape, the dissipation of the non resolved scales of a moving contact line. Numerical simulations are compared with the experiments of. The agreement with experiments is found to be very good for both he critical angle of inclination for siding as well as for the specific shapes: rounded, corner and pearling drops. The simulations have been used to extend the range of hysteresis covered by the experiments.

Surface Properties of PEMFC Gas Diffusion Layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

WoodIII, David L; Rulison, Christopher; Borup, Rodney

2010-01-01

The wetting properties of PEMFC Gas Diffusion Layers (GDLs) were quantified by surface characterization measurements and modeling of material properties. Single-fiber contact-angle and surface energy (both Zisman and Owens-Wendt) data of a wide spectrum of GDL types is presented to delineate the effects of hydrophobic post-processing treatments. Modeling of the basic sessile-drop contact angle demonstrates that this value only gives a fraction of the total picture of interfacial wetting physics. Polar forces are shown to contribute 10-20 less than dispersive forces to the composite wetting of GDLs. Internal water contact angles obtained from Owens-Wendt analysis were measured at 13-19 highermore » than their single-fiber counterparts. An inverse relationship was found between internal contact angle and both Owens-Wendt surface energy and % polarity of the GDL. The most sophisticated PEMFC mathematical models use either experimentally measured capillary pressures or the standard Young-Laplace capillary-pressure equation. Based on the results of the Owens-Wendt analysis, an advancement to the Young-Laplace equation is proposed for use in these mathematical models, which utilizes only solid surface energies and fractional surface coverage of fluoropolymer. Capillary constants for the spectrum of analyzed GDLs are presented for the same purpose.« less

Surface tension and contact angles: Molecular origins and associated microstructure

NASA Technical Reports Server (NTRS)

Davis, H. T.

1982-01-01

Gradient theory converts the molecular theory of inhomogeneous fluid into nonlinear boundary value problems for density and stress distributions in fluid interfaces, contact line regions, nuclei and microdroplets, and other fluid microstructures. The relationship between the basic patterns of fluid phase behavior and the occurrence and stability of fluid microstructures was clearly established by the theory. All the inputs of the theory have molecular expressions which are computable from simple models. On another level, the theory becomes a phenomenological framework in which the equation of state of homogeneous fluid and sets of influence parameters of inhomogeneous fluids are the inputs and the structures, stress tensions and contact angles of menisci are the outputs. These outputs, which find applications in the science and technology of drops and bubbles, are discussed.

Fast Transport of Water Droplets over a Thermo-Switchable Surface Using Rewritable Wettability Gradient.

PubMed

Banuprasad, Theneyur Narayanaswamy; Vinay, Thamarasseril Vijayan; Subash, Cherumannil Karumuthil; Varghese, Soney; George, Sajan D; Varanakkottu, Subramanyan Namboodiri

2017-08-23

In spite of the reported temperature dependent tunability in wettability of poly(N-isopropylacrylamide) (PNIPAAm) surfaces for below and above lower critical solution temperature (32 °C), the transport of water droplets is inhibited by the large contact angle hysteresis. Herein, for the first time, we report on-demand, fast, and reconfigurable droplet manipulation over a PNIPAAm grafted structured polymer surface using temperature-induced wettability gradient. Our study reveals that the PNIPAAm grafted on intrinsically superhydrophobic surfaces exhibit hydrophilic nature with high contact angle hysteresis below 30 °C and superhydrophobic nature with ultralow contact angle hysteresis above 36 °C. The transition region between 30 and 36 °C is characterized by a large change in water contact angle (∼100°) with a concomitant change in contact angle hysteresis. By utilizing this "transport zone" wherein driving forces overcome the frictional forces, we demonstrate macroscopic transport of water drops with a maximum transport velocity of approximately 40 cm/s. The theoretical calculations on the force measurements concur with dominating behavior of driving forces across the transport zone. The tunability in transport velocity by varying the temperature gradient along the surface or the inclination angle of the surface (maximum angle of 15° with a reduced velocity 0.4 mm/s) is also elucidated. In addition, as a practical application, coalescence of water droplets is demonstrated by using the temperature controlled wettability gradient. The presented results are expected to provide new insights on the design and fabrication of smart multifunctional surfaces for applications such as biochemical analysis, self-cleaning, and microfluidics.

Mixing in Sessile Drops Merging on a Surface

NASA Astrophysics Data System (ADS)

Anna, Shelley; Zhang, Ying; Oberdick, Samuel; Garoff, Stephen

2011-11-01

We investigate the mixing of two sessile drops that merge on a surface. The drops consist of low viscosity glycerol-water mixtures deposited on a silicone elastomer surface with contact angle near 90°. We observe the shape of the drops and the location of their intersection by placing a fluorescent dye in one drop and using a laser light sheet to image a plane perpendicular to the surface. The initial healing of the meniscus bridge between the merging drops, and the damping of capillary waves appearing on their surfaces occur on timescales comparable to the inertio-capillary relaxation time. However, the interface between the two fluids remains sharp, broadening diffusively over several minutes. The shape of the merged drops and the boundary between them also continues to evolve on a timescale of minutes. This later motion is controlled by gravity, capillary pressure, and viscous stresses. Images of the 3D drop shape indicate that small contact line motions are correlated to the slow relaxation. Although the two drops contain identical liquids except for the presence of the dye, the shape of the interface consistently evolves asymmetrically, assuming a characteristic crescent shape. We note that very tiny surface tension gradients can produce an asymmetric flow like the one observed here. We characterize the long timescale flow as a function of the drop sizes, and we use numerical simulations to aid in elucidating the essential physics.

When a water drop freezes before it solidifies

NASA Astrophysics Data System (ADS)

Kavehpour, Pirouz; Davis, Stephen; Tavakoli, Faryar

2012-11-01

When a drop of liquid is placed on a substrate which temperature is below the melting point of the liquid, one would expect the drop to solidify instantaneously. However, many liquids, such as water, must be subcooled to solidify below its melting temperature due to homogeneous nucleation's high activation energy. Most of the drop solidification research, particularly for water, phase change is assumed to occur at equilibrium freezing temperature; however, this is not the case. We found that after a certain degree of supercooling, a kinetic based nucleation begins and latent heat of fusion is suddenly liberated, causing an increase in liquid temperature. At the end of this stage, approximately 20% of the drop is crystallized. This phenomenon is known among metallurgists as recalescence. This is followed by a slow solidification process at the melting point. As a water droplet spreads on a cold substrate, its contact line stops just prior to freezing inception from the liquid-solid interface. In this study, we assert that recalescence prior to solidification may be the cause of water's sudden immobility, which results in a fixed contact angle and droplet diameter. In our experiments, the nucleation front initiates from the trijunction point and propagates to the drop volume.

The Effect of Arch Drop on Tibial Rotation and Tibiofemoral Contact Stress in Postpartum Women.

PubMed

Rabe, Kaitlin; Segal, Neil A; Waheed, Saphia; Anderson, Donald D

2018-04-26

Women are at greater risk for knee osteoarthritis and numerous other lower limb musculoskeletal disorders. Arch drop during pregnancy and the resultant excessive pronation of the feet may alter loading patterns and contribute to the greater prevalence of knee osteoarthritis in women. To determine the effect of arch drop on tibial rotation and tibiofemoral contact stress. Interventional study with internal control. Biomechanics laboratory. Eleven postpartum women (age 33.4 ± 5.3 years, body mass 76.1 ± 13.5 kg) who had lost arch height with pregnancy in a previous study. Subjects underwent standing computed tomography (SCT) with their knees in a 20° fixed-flexed position with and without semirigid arch supports to reconstitute prepregnancy arch height. Magnetic resonance imaging of the knee was acquired at a flexion angle equivalent to that of SCT. Bone and cartilage were manually segmented on the magnetic resonance images and segmented surfaces were registered to the 3-dimensional SCT image sets for the arch-supported and -unsupported conditions. These models were used to measure changes in tibial rotation, as well as to estimate contact stress in the medial and lateral tibiofemoral compartments, using computational methods. Change in tibial rotation and tibiofemoral contact stress with arch drop. Arch drop resulted in a mean tibial internal rotation of 0.75 ± 1.33° (P < .05). Changes in mean or peak contact stress were not detected. Arch drop causes internal tibial rotation, resulting in a shift in the tibiofemoral articulation. An associated increase in contact stress was not detected. Internal rotation of the tibia increases stress on the anterior cruciate ligament and menisci, potentially explaining the greater prevalence of knee disorders in postpartum women. Copyright © 2018 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.

Captive bubble and sessile drop surface characterization of a submerged aquatic plant, Hydrilla verticillata

USDA-ARS?s Scientific Manuscript database

The surface energy parameters of the invasive aquatic weed, Hydrilla verticillata, were determined using contact angle measurements using two different methods. The abaxial and adaxial surfaces of the leaves and stem were characterized for the weed while submerged in water using captive air and octa...

Superhydrophobic surface prepared by micro-milling and WEDM on aluminum alloy

NASA Astrophysics Data System (ADS)

Yanling, Wan; Jian, Yang; Huadong, Yu

2018-06-01

To simulate the hydrophobic microstructure of rice leaf surface, high-speed precision micro-milling machine was used to fabricate micro groove array structure on the surface of aluminum alloy. The micro-and nanostructure was constructed on the surface of the grooved convex platform by Wire Cut Electrical Discharge Machining (WEDM). The surface morphology and hydrophobic properties of the aluminum alloy microstructures fabricated by two processing methods were observed respectively, and the hydrophobic mechanism was analyzed. The results show that the contact angle was effectively improved from 49° up to 158.4° in the vertical direction, and 146.7° in the parallel direction. The change of surface wettability from hydrophilic to hydrophobic was realized. By comparison, the micro-and nanostructure fabricated by WEDM had improved the hydrophobic stability of the aluminum alloy surface while enlarging the contact Angle, and the micro-milling groove structure further amplified the contact angle and greatly reduced the contact area of the water droplet, it was also observed that the drop took longer to completely spread on the sample after WEDM.

Dynamics of Contact Line Pinning and Depinning of Droplets Evaporating on Microribs.

PubMed

Mazloomi Moqaddam, Ali; Derome, Dominique; Carmeliet, Jan

2018-05-15

The contact line dynamics of evaporating droplets deposited on a set of parallel microribs is analyzed with the use of a recently developed entropic lattice Boltzmann model for two-phase flow. Upon deposition, part of the droplet penetrates into the space between ribs because of capillary action, whereas the remaining liquid of the droplet remains pinned on top of the microribs. In the first stage, evaporation continues until the droplet undergoes a series of pinning-depinning events, showing alternatively the constant contact radius and constant contact angle modes. While the droplet is pinned, evaporation results in a contact angle reduction, whereas the contact radius remains constant. At a critical contact angle, the contact line depins, the contact radius reduces, and the droplet rearranges to a larger apparent contact angle. This pinning-depinning behavior goes on until the liquid above the microribs is evaporated. By computing the Gibbs free energy taking into account the interfacial energy, pressure terms, and viscous dissipation due to drop internal flow, we found that the mechanism that causes the unpinning of the contact line results from an excess in Gibbs free energy. The spacing distance and the rib height play an important role in controlling the pinning-depinning cycling, the critical contact angle, and the excess Gibbs free energy. However, we found that neither the critical contact angle nor the maximum excess Gibbs free energy depends on the rib width. We show that the different terms, that is, pressure term, viscous dissipation, and interfacial energy, contributing to the excess Gibbs free energy, can be varied differently by varying different geometrical properties of the microribs. It is demonstrated that, by varying the spacing distance between the ribs, the energy barrier is controlled by the interfacial energy while the contribution of the viscous dissipation is dominant if either rib height or width is changed. Main finding of this is study is that, for microrib patterned surfaces, the energy barrier required for the contact line to depin can be enlarged by increasing the spacing or the rib height, which can be important for practical applications.

A semi-analytical method to estimate the effective slip length of spreading spherical-cap shaped droplets using Cox theory

NASA Astrophysics Data System (ADS)

Wörner, M.; Cai, X.; Alla, H.; Yue, P.

2018-03-01

The Cox–Voinov law on dynamic spreading relates the difference between the cubic values of the apparent contact angle (θ) and the equilibrium contact angle to the instantaneous contact line speed (U). Comparing spreading results with this hydrodynamic wetting theory requires accurate data of θ and U during the entire process. We consider the case when gravitational forces are negligible, so that the shape of the spreading drop can be closely approximated by a spherical cap. Using geometrical dependencies, we transform the general Cox law in a semi-analytical relation for the temporal evolution of the spreading radius. Evaluating this relation numerically shows that the spreading curve becomes independent from the gas viscosity when the latter is less than about 1% of the drop viscosity. Since inertia may invalidate the made assumptions in the initial stage of spreading, a quantitative criterion for the time when the spherical-cap assumption is reasonable is derived utilizing phase-field simulations on the spreading of partially wetting droplets. The developed theory allows us to compare experimental/computational spreading curves for spherical-cap shaped droplets with Cox theory without the need for instantaneous data of θ and U. Furthermore, the fitting of Cox theory enables us to estimate the effective slip length. This is potentially useful for establishing relationships between slip length and parameters in numerical methods for moving contact lines.

Wettability of supercritical carbon dioxide/water/quartz systems: simultaneous measurement of contact angle and interfacial tension at reservoir conditions.

PubMed

Saraji, Soheil; Goual, Lamia; Piri, Mohammad; Plancher, Henry

2013-06-11

Injection of carbon dioxide in deep saline aquifers is considered as a method of carbon sequestration. The efficiency of this process is dependent on the fluid-fluid and rock-fluid interactions inside the porous media. For instance, the final storage capacity and total amount of capillary-trapped CO2 inside an aquifer are affected by the interfacial tension between the fluids and the contact angle between the fluids and the rock mineral surface. A thorough study of these parameters and their variations with temperature and pressure will provide a better understanding of the carbon sequestration process and thus improve predictions of the sequestration efficiency. In this study, the controversial concept of wettability alteration of quartz surfaces in the presence of supercritical carbon dioxide (sc-CO2) was investigated. A novel apparatus for measuring interfacial tension and contact angle at high temperatures and pressures based on Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method was developed and validated with a simple system. Densities, interfacial tensions, and dynamic contact angles of CO2/water/quartz systems were determined for a wide range of pressures and temperatures relevant to geological sequestration of CO2 in the subcritical and supercritical states. Image analysis was performed with ADSA-NA method that allows the determination of both interfacial tensions and contact angles with high accuracy. The results show that supercritical CO2 alters the wettability of quartz surface toward less water-wet conditions compared to subcritical CO2. Also we observed an increase in the water advancing contact angles with increasing temperature indicating less water-wet quartz surfaces at higher temperatures.

Numerical study of the effects of contact angle and viscosity ratio on the dynamics of snap-off through porous media

NASA Astrophysics Data System (ADS)

Starnoni, Michele; Pokrajac, Dubravka

2018-01-01

Snap-off is a pore-scale mechanism occurring in porous media in which a bubble of non-wetting phase displacing a wetting phase, and vice-versa, can break-up into ganglia when passing through a constriction. This mechanism is very important in foam generation processes, enhanced oil recovery techniques and capillary trapping of CO2 during its geological storage. In the present study, the effects of contact angle and viscosity ratio on the dynamics of snap-off are examined by simulating drainage in a single pore-throat constriction of variable cross-section, and for different pore-throat geometries. To model the flow, we developed a CFD code based on the Finite Volume method. The Volume-of-fluid method is used to track the interfaces. Results show that the threshold contact angle for snap-off, i.e. snap-off occurs only for contact angles smaller than the threshold, increases from a value of 28° for a circular cross-section to 30-34° for a square cross-section and up to 40° for a triangular one. For a throat of square cross-section, increasing the viscosity of the injected phase results in a drop in the threshold contact angle from a value of 30° when the viscosity ratio μ bar is equal to 1 to 26° when μ bar = 20 and down to 24° when μ bar = 20 .

Drops spreading on flexible fibers

NASA Astrophysics Data System (ADS)

Somszor, Katarzyna; Boulogne, François; Sauret, Alban; Dressaire, Emilie; Stone, Howard

2015-11-01

Fibrous media are encountered in many engineered systems such as textile, paper and insulating materials. In most of these materials, fibers are randomly oriented and form a complex network in which drops of wetting liquid tend to accumulate at the nodes of the network. Here we investigate the role of the fiber flexibility on the spreading of a small volume of liquid on a pair of crossed flexible fibers. A drop of silicone oil is dispensed at the point of contact of the fibers and we characterize the liquid morphologies as we vary the volume of liquid, the angle between the fibers, and the length and bending modulus of the fibers. Drop morphologies previously reported for rigid fibers, i.e. a drop, a column and a mixed morphology, are also observed on flexible fibers with modified domains of existence. Moreover, at small inclination angles of the fibers, a new behavior is observed: the fibers bend and collapse. Depending on the volume, the liquid can adopt a column or a mixed morphology on the collapsed fibers. We rationalize our observations with a model based on energetic considerations. Our study suggests that the fiber flexibility adds a rich variety of behaviors that can be crucial for industrial applications.

Surface Energy of C60 and the Interfacial Interactions in Aqueous Systems

EPA Science Inventory

The surface free energy components of C60 powder in the form of compressed pellets were determined by sessile drop contact angle measurements. Based on van Oss-Chaudhury-Good model to Young-Dupre equation, the surface energy of C60 and the contributions of the apolar (Lifshitz-v...

Influence of Whey Peptides on the Surface Activity of k-casein and ß-lactoglobulin

USDA-ARS?s Scientific Manuscript database

Whey protein hydrolysate (WPH) was fractionated by reverse-phase chromatography to obtain fractions of varying surface-hydrophobicities. A model oil–water interface (MI) was pre-coated with the WPH or fractions thereof. Contact angle (') of sessile drops of '-casein ('-CN) or ß-lactoglobulin A (ß-LG...

Hydrophobic properties of a wavy rough substrate.

PubMed

Carbone, G; Mangialardi, L

2005-01-01

The wetting/non-wetting properties of a liquid drop in contact with a chemically hydrophobic rough surface (thermodynamic contact angle theta(e)>pi/2) are studied for the case of an extremely idealized rough profile: the liquid drop is considered to lie on a simple sinusoidal profile. Depending on surface geometry and pressure values, it is found that the Cassie and Wenzel states can coexist. But if the amplitude h of the substrate is sufficiently large the only possible stable state is the Cassie one, whereas if h is below a certain critical value hcr a transition to the Wenzel state occurs. Since in many potential applications of such super-hydrophobic surfaces, liquid drops often collide with the substrate (e.g. vehicle windscreens), in the paper the critical drop pressure pW is calculated at which the Cassie state is no longer stable and the liquid jumps into full contact with the substrate (Wenzel state). By analyzing the asymptotic behavior of the systems in the limiting case of a large substrate corrugation, a simple criterion is also proposed to calculate the minimum height asperity h necessary to prevent the Wenzel state from being formed, to preserve the super-hydrophobic properties of the substrate, and, hence, to design a robust super-hydrophobic surface.

Feasibility study of a take-home array-based functional electrical stimulation system with automated setup for current functional electrical stimulation users with foot-drop.

PubMed

Prenton, Sarah; Kenney, Laurence P; Stapleton, Claire; Cooper, Glen; Reeves, Mark L; Heller, Ben W; Sobuh, Mohammad; Barker, Anthony T; Healey, Jamie; Good, Timothy R; Thies, Sibylle B; Howard, David; Williamson, Tracey

2014-10-01

To investigate the feasibility of unsupervised community use of an array-based automated setup functional electrical stimulator for current foot-drop functional electrical stimulation (FES) users. Feasibility study. Gait laboratory and community use. Participants (N=7) with diagnosis of unilateral foot-drop of central neurologic origin (>6mo) who were regular users of a foot-drop FES system (>3mo). Array-based automated setup FES system for foot-drop (ShefStim). Logged usage, logged automated setup times for the array-based automated setup FES system and diary recording of problems experienced, all collected in the community environment. Walking speed, ankle angles at initial contact, foot clearance during swing, and the Quebec User Evaluation of Satisfaction with Assistive Technology version 2.0 (QUEST version 2.0) questionnaire, all collected in the gait laboratory. All participants were able to use the array-based automated setup FES system. Total setup time took longer than participants' own FES systems, and automated setup time was longer than in a previous study of a similar system. Some problems were experienced, but overall, participants were as satisfied with this system as their own FES system. The increase in walking speed (N=7) relative to no stimulation was comparable between both systems, and appropriate ankle angles at initial contact (N=7) and foot clearance during swing (n=5) were greater with the array-based automated setup FES system. This study demonstrates that an array-based automated setup FES system for foot-drop can be successfully used unsupervised. Despite setup's taking longer and some problems, users are satisfied with the system and it would appear as effective, if not better, at addressing the foot-drop impairment. Further product development of this unique system, followed by a larger-scale and longer-term study, is required before firm conclusions about its efficacy can be reached. Copyright © 2014 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Water evaporation on highly viscoelastic polymer surfaces.

PubMed

Pu, Gang; Severtson, Steven J

2012-07-03

Results are reported for a study on the evaporation of water droplets from a highly viscoelastic acrylic polymer surface. These are contrasted with those collected for the same measurements carried out on polydimethylsiloxane (PDMS). For PDMS, the evaporation process involves the expected multistep process including constant drop area, constant contact angle, and finally a combination of these steps until the liquid is gone. In contrast, water evaporation from the acrylic polymer shows a constant drop area mode throughout. Furthermore, during the evaporation process, the drop area actually expands on the acrylic polymer. The single mode evaporation process is consistent with formation of wetting structures, which cannot be propagated by the capillary forces. Expansion of the drop area is attributed to the influence of the drop capillary pressure. Furthermore, the rate of drop area expansion is shown to be dependent on the thickness of the polymer film.

Determination of the Wetting Angle of Germanium and Germanium-Silicon Melts on Different Substrate Materials

NASA Technical Reports Server (NTRS)

Kaiser, Natalie; Croell, Arne; Szofran, F. R.; Cobb. S. D.; Dold, P.; Benz, K. W.

1999-01-01

During Bridgman growth of semiconductors detachment of the crystal and the melt meniscus has occasionally been observed, mainly under microgravity (microg) conditions. An important factor for detached growth is the wetting angle of the melt with the crucible material. High contact angles are more likely to result in detachment of the growing crystal from the ampoule wall. In order to achieve detached growth of germanium (Ge) and germanium-silicon (GeSi) crystals under 1g and microg conditions, sessile drop measurements were performed to determine the most suitable ampoule material as well as temperature dependence of the surface tension for GeSi. Sapphire, fused quartz, glassy carbon, graphite, SiC, pyrolytic Boron Nitride (pBN), AIN, and diamond were used as substrates. Furthermore, different cleaning procedures and surface treatments (etching, sandblasting, etc.) of the same substrate material and their effect on the wetting behavior were studied during these experiments. pBN and AIN substrates exhibited the highest contact angles with values around 170 deg.

Super-hydrophobic, highly adhesive, polydimethylsiloxane (PDMS) surfaces.

PubMed

Stanton, Morgan M; Ducker, Robert E; MacDonald, John C; Lambert, Christopher R; McGimpsey, W Grant

2012-02-01

Super-hydrophobic surfaces have been fabricated by casting polydimethylsiloxane (PDMS) on a textured substrate of known surface topography, and were characterized using contact angle, atomic force microscopy, surface free energy calculations, and adhesion measurements. The resulting PDMS has a micro-textured surface with a static contact angle of 153.5° and a hysteresis of 27° when using de-ionized water. Unlike many super-hydrophobic materials, the textured PDMS is highly adhesive, allowing water drops as large as 25.0 μL to be inverted. This high adhesion, super-hydrophobic behavior is an illustration of the "petal effect". This rapid, reproducible technique has promising applications in transport and analysis of microvolume samples. Copyright © 2011 Elsevier Inc. All rights reserved.

Evaluation of the Microsoft Kinect for screening ACL injury.

PubMed

Stone, Erik E; Butler, Michael; McRuer, Aaron; Gray, Aaron; Marks, Jeffrey; Skubic, Marjorie

2013-01-01

A study was conducted to evaluate the use of the skeletal model generated by the Microsoft Kinect SDK in capturing four biomechanical measures during the Drop Vertical Jump test. These measures, which include: knee valgus motion from initial contact to peak flexion, frontal plane knee angle at initial contact, frontal plane knee angle at peak flexion, and knee-to-ankle separation ratio at peak flexion, have proven to be useful in screening for future knee anterior cruciate ligament (ACL) injuries among female athletes. A marker-based Vicon motion capture system was used for ground truth. Results indicate that the Kinect skeletal model likely has acceptable accuracy for use as part of a screening tool to identify elevated risk for ACL injury.

Parametric Investigation of Liquid Jets in Low Gravity

NASA Technical Reports Server (NTRS)

Chato, David J.

2005-01-01

An axisymmetric phase field model is developed and used to model surface tension forces on liquid jets in microgravity. The previous work in this area is reviewed and a baseline drop tower experiment selected for model comparison. This paper uses the model to parametrically investigate the influence of key parameters on the geysers formed by jets in microgravity. Investigation of the contact angle showed the expected trend of increasing contact angle increasing geyser height. Investigation of the tank radius showed some interesting effects and demonstrated the zone of free surface deformation is quite large. Variation of the surface tension with a laminar jet showed clearly the evolution of free surface shape with Weber number. It predicted a breakthrough Weber number of 1.

Knee and Hip Joint Kinematics Predict Quadriceps and Hamstrings Neuromuscular Activation Patterns in Drop Jump Landings.

PubMed

Malfait, Bart; Dingenen, Bart; Smeets, Annemie; Staes, Filip; Pataky, Todd; Robinson, Mark A; Vanrenterghem, Jos; Verschueren, Sabine

2016-01-01

The purpose was to assess if variation in sagittal plane landing kinematics is associated with variation in neuromuscular activation patterns of the quadriceps-hamstrings muscle groups during drop vertical jumps (DVJ). Fifty female athletes performed three DVJ. The relationship between peak knee and hip flexion angles and the amplitude of four EMG vectors was investigated with trajectory-level canonical correlation analyses over the entire time period of the landing phase. EMG vectors consisted of the {vastus medialis(VM),vastus lateralis(VL)}, {vastus medialis(VM),hamstring medialis(HM)}, {hamstring medialis(HM),hamstring lateralis(HL)} and the {vastus lateralis(VL),hamstring lateralis(HL)}. To estimate the contribution of each individual muscle, linear regressions were also conducted using one-dimensional statistical parametric mapping. The peak knee flexion angle was significantly positively associated with the amplitudes of the {VM,HM} and {HM,HL} during the preparatory and initial contact phase and with the {VL,HL} vector during the peak loading phase (p<0.05). Small peak knee flexion angles were significantly associated with higher HM amplitudes during the preparatory and initial contact phase (p<0.001). The amplitudes of the {VM,VL} and {VL,HL} were significantly positively associated with the peak hip flexion angle during the peak loading phase (p<0.05). Small peak hip flexion angles were significantly associated with higher VL amplitudes during the peak loading phase (p = 0.001). Higher external knee abduction and flexion moments were found in participants landing with less flexed knee and hip joints (p<0.001). This study demonstrated clear associations between neuromuscular activation patterns and landing kinematics in the sagittal plane during specific parts of the landing. These findings have indicated that an erect landing pattern, characterized by less hip and knee flexion, was significantly associated with an increased medial and posterior neuromuscular activation (dominant hamstrings medialis activity) during the preparatory and initial contact phase and an increased lateral neuromuscular activation (dominant vastus lateralis activity) during the peak loading phase.

Infiltration of Liquid Droplets Into Porous Media: Effects of Dynamic Contact Angle and Contact Angle Hysteresis

NASA Astrophysics Data System (ADS)

Hilpert, M.

2008-12-01

Infiltration of liquid droplets into dry porous media occurs when rain drops fall onto soil, when accidentally spilling organic liquid (e.g., gasoline and chlorinated solvents) onto ground, or when aerosol pesticides are not intercepted by the vegetation and then released to soils. If harmful chemicals are released from the droplet into the atmosphere through evaporation, it is important to know the time of infiltration. We developed a theory for infiltration, which accounts for a general model for the dynamic contact angle between the droplet and the porous medium as well as contact angle hysteresis. Our theory assumes the droplet to have the shape of a spherical cap and the pressure within the droplet to be uniform. The theory shows that droplet infiltration involves three phases due to contact angle hysteresis: (1) an increasing drawing area (IDA) phase during which the interface between the droplet and the porous medium increases, (2) a constant drawing area (CDA) phase during which the contact line of the droplet remains pinned, and (3) a decreasing drawing area (DDA) phase. We find that infiltration always consists of a cascade process formed by the IDA, CDA, and DDA phases, where the entire process may begin or end in any of the three phases. The entire process is formulated with four nondimensional parameters: three contact angles (initial, advancing, and receding) and a porous permeability parameter that depends on porous medium geometry. The total time of infiltration and the time dependence of drawing area are critically affected by the occurrence of the IDA, CDA, and DDA phases as well as by the permeability. In general, the IDA and DDA phases are described by integro-differential equations. With ordinary differential equations (ODEs), we are able to approximate the IDA phase and to describe exactly infiltration processes that starts out with the CDA or DDA phase.

Evaporation of sessile drops containing colloidal rods: coffee-ring and order-disorder transition.

PubMed

Dugyala, Venkateshwar Rao; Basavaraj, Madivala G

2015-03-05

Liquid drops containing insoluble solutes when dried on solid substrates leave distinct ring-like deposits at the periphery or along the three-phase contact line-a phenomena popularly known as the coffee-ring or the coffee stain effect. The formation of such rings as well as their suppression is shown to have applications in particle separation and disease diagnostics. We present an experimental study of the evaporation of sessile drops containing silica rods to elucidate the structural arrangement of particles in the ring, an effect of the addition of surfactant and salt. To this end, the evaporation of aqueous sessile drops containing model rod-like silica particles of aspect ratio ranging from ∼4 to 15 on a glass slide is studied. We first show that when the conditions such as (1) solvent evaporation, (2) nonzero contact angle, (3) contact line pinning, (4) no surface tension gradient driven flow, and (5) repulsive particle-particle/particle-substrate interactions, that are necessary for the formation of the coffee-ring are met, the suspension drops containing silica rods upon evaporation leave a ring-like deposit. A closer examination of the ring deposits reveals that several layers of silica rods close to the edge of the drop are ordered such that the major axis of the rods are oriented parallel to the contact line. After the first few layers of ordered arrangement of particles, a random arrangement of particles in the drop interior is observed indicating an order-disorder transition in the ring. We monitor the evolution of the ring width and particle velocity during evaporation to elucidate the mechanism of the order-disorder transition. Moreover, when the evaporation rate is lowered, the ordering of silica rods is observed to extend over large areas. We demonstrate that the nature of the deposit can be tuned by the addition of a small quantity of surfactant or salt.

Surfactant Facilitated Spreading of Aqueous Drops on Hydrophobic Surfaces

NASA Technical Reports Server (NTRS)

Kumar, Nitin; Couzis, Alex; Maldarelli, Charles; Singh, Bhim S. (Technical Monitor)

2000-01-01

Microgravity technologies often require aqueous phases to spread over nonwetting hydrophobic solid/surfaces. At a hydrophobic surface, the air/hydrophobic solid tension is low, and the solid/aqueous tension is high. A large contact angle forms as the aqueous/air tension acts together with the solid/air tension to balance the large solid/aqueous tension. The aqueous phase, instead of spreading, is held in a meniscus by the large angle. Surfactants facilitate the wetting of water on hydrophobic surfaces by adsorbing on the water/air and hydrophobic solid/water interfaces and lowering the surface tensions of these interfaces. The tension reductions decrease the contact angle, which increases the equilibrium wetted area. Hydrocarbon surfactants (i.e. amphiphiles with a hydrophobic chain of methylene groups attached to a large polar group to give aqueous solubility) do not reduce significantly the contact angles of the very hydrophobic surfaces such as parafilm or polyethylene. Trisiloxane surfactants (amphiphiles with a hydrophobe consisting of methyl groups linked to a trisiloxane backbone in the form of a disk ((CH3)3-Si-O-Si-O-Si(CH3)3)) and an extended ethoxylate (-(OCH2CH2)n-) polar group in the form of a chain with seven or eight units) can significantly reduce the contact angle of water on a very hydrophobic surface and cause rapid and complete (or nearly complete) spreading (lermed superspreading). The overall goal of the research described in this proposal is to establish and verify a theory for how trisiloxanes cause superspreading, and then use this knowledge as a guide to developing more general hydrocarbon based surfactant systems which superspread and can be used in microgravity. We propose that the trisiloxane surfactants superspread when the siloxane adsorbs, the hydrophobic disk parts of the molecule adsorb onto the surface removing the surface water. Since the cross sectional area of the disk is larger than that of the extended ethoxylate chain, the disks can form a space filling mat on the surface which removes a significant amount of the surface water. The water adjacent to the hydrophobic solid surface is of high energy due to incomplete hydrogen bonding; its removal significantly lowers the tension and reduces the contact angle. Hydrocarbon surfactants cannot remove as much surface water because their large polar groups prevent the chains from cohering lengthwise. In our report last year we presented a poster describing the preparation of model very hydrophobic surfaces which are homogeneous and atomically smooth using self assembled monolayers of octadecyl trichlorosilane (OTS). In this poster we will use these surfaces as test substrates in developing hydrocarbon based surfactant systems which superspread. We studied a binary hydrocarbon surfactant systems consisting of a very soluble large polar group polyethylene oxide surfactant (C12E6 (CH3(CH2)11(OCH2CH2)6OH) and a long chain alcohol dodecanol. By mixing the alcohol with this soluble surfactant we have found that the contact angle of the mixed system on our test hydrophobic surfaces is very low. We hypothesize that the alcohol fills in the gaps between adjacent adsorbed chains of the large polar group surfactant. This filling in removes the surface water and effects the decrease in contact angle. We confirm this hypothesis by demonstrating that at the air/water interface the mixed layer forms condensed phases while the soluble large polar group surfactant by itself does not. We present drop impact experiments which demonstrate that the dodecanol/C12E6 mixture is effective in causing impacting drops to spread on the very hydrophobic model OTS surfaces.

In vitro and in vivo evaluation of ketotifen fumarate-loaded silicone hydrogel contact lenses for ocular drug delivery.

PubMed

Xu, Jinku; Li, Xinsong; Sun, Fuqian

2011-02-01

The purpose of this work was to evaluate the usefulness of silicone hydrogel contact lenses loaded with ketotifen fumarate for ocular drug delivery. First, silicone contact lenses were prepared by photopolymerization of bitelechelic methacrylated polydimethylsiloxanes macromonomer, 3-methacryloxypropyltris(trimethylsiloxy)silane, and N,N-dimethylacrylamide using ethylene glycol dimethacrylate as a cross-linker and Darocur 1173 as an initiator followed by surface plasma treatment. Then, the silicone hydrogel matrices of the contact lenses were characterized by equilibrium swelling ratio (ESR), tensile tests, ion permeability, and surface contact angle. Finally, the contact lenses were loaded with ketotifen fumarate by pre-soaking in drug solution to evaluate drug loading capacity, in vitro and in vivo release behavior of the silicone contact lenses. The results showed that ESR and ion permeability increase, and the surface contact angle and tensile strength decreased with the increase of DMA component in the silicone hydrogel. The drug loading and in vitro releases were dependent on the hydrogel composition of hydrophilic/hydrophobic phase of the contact lenses. In rabbit eyes, the pre-soaked contact lenses sustained ketotifen fumarate release for more than 24 h, which leads to a more stable drug concentration and a longer mean retention time in tear fluid than that of eye drops of 0.05%.

Capillary Driven Flows Along Differentially Wetted Interior Corners

NASA Technical Reports Server (NTRS)

Golliher, Eric L. (Technical Monitor); Nardin, C. L.; Weislogel, M. M.

2005-01-01

Closed-form analytic solutions useful for the design of capillary flows in a variety of containers possessing interior corners were recently collected and reviewed. Low-g drop tower and aircraft experiments performed at NASA to date show excellent agreement between theory and experiment for perfectly wetting fluids. The analytical expressions are general in terms of contact angle, but do not account for variations in contact angle between the various surfaces within the system. Such conditions may be desirable for capillary containment or to compute the behavior of capillary corner flows in containers consisting of different materials with widely varying wetting characteristics. A simple coordinate rotation is employed to recast the governing system of equations for flows in containers with interior corners with differing contact angles on the faces of the corner. The result is that a large number of capillary driven corner flows may be predicted with only slightly modified geometric functions dependent on corner angle and the two (or more) contact angles of the system. A numerical solution is employed to verify the new problem formulation. The benchmarked computations support the use of the existing theoretical approach to geometries with variable wettability. Simple experiments to confirm the theoretical findings are recommended. Favorable agreement between such experiments and the present theory may argue well for the extension of the analytic results to predict fluid performance in future large length scale capillary fluid systems for spacecraft as well as for small scale capillary systems on Earth.

Muscle activity response to external moment during single-leg drop landing in young basketball players: the importance of biceps femoris in reducing internal rotation of knee during landing.

PubMed

Fujii, Meguru; Sato, Haruhiko; Takahira, Naonobu

2012-01-01

Internal tibial rotation with the knee close to full extension combined with valgus collapse during drop landing generally results in non-contact anterior cruciate ligament (ACL) injury. The purpose of this study was to investigate the relationship between internal rotation of the knee and muscle activity from internal and external rotator muscles, and between the internal rotation of knee and externally applied loads on the knee during landing in collegiate basketball players. Our hypothesis was that the activity of biceps femoris muscle would be an important factor reducing internal knee rotation during landing. The subjects were 10 collegiate basketball students: 5 females and 5 males. The subjects performed a single-leg drop landing from a 25-cm height. Femoral and tibial kinematics were measured using a 3D optoelectronic tracking system during the drop landings, and then the knee angular motions were determined. Ground reaction forces and muscle activation patterns (lateral hamstring and medial hamstring) were simultaneously measured and computed. Results indicated that lower peak internal tibial rotation angle at the time of landing was associated with greater lateral hamstring activity (r = -0.623, p < 0.001). When gender was considered, the statistically significant correlation remained only in females. There was no association between the peak internal tibial rotation angle and the knee internal rotation moment. Control of muscle activity in the lateral to medial hamstring would be an important factor in generating sufficient force to inhibit excessive internal rotation during landing. Strengthening the biceps femoris might mitigate the higher incidence of non-contact ACL injury in female athletes. Key pointsLower activity of the external rotator muscle of the knee, which inhibits internal rotation of the knee, may be the reason why females tend to show a large internal rotation of the knee during drop landing.Externally applied internal rotation moment of the knee during landing would not be expected to explain why female athletes tend to show excessive internal knee rotation.Biceps femoris strength training might help decrease the incidence of non-contact ACL injury in female athletes.

Solvent composition of one-step self-etch adhesives and dentine wettability.

PubMed

Grégoire, Geneviève; Dabsie, Firas; Dieng-Sarr, Farimata; Akon, Bernadette; Sharrock, Patrick

2011-01-01

Our aim was to determine the wettability of dentine by four commercial self-etch adhesives and evaluate their spreading rate on the dentine surface. Any correlation with chemical composition was sought, particularly with the amount of solvent or HEMA present in the adhesive. The adhesives used were AdheSE One, Optibond All.In.One, Adper Easy Bond and XenoV. Chemical compositions were determined by proton nuclear magnetic resonance (NMR) spectroscopy of the adhesives dissolved in dimethylsulfoxide. Apparent contact angles for sessile drops of adhesives were measured on dentine slices as a function of time for up to 180s. The water contact angles were determined for fully polymerised adhesives. All adhesives were water-based with total solvent contents ranging from 27% to 73% for HEMA-free adhesives, and averaging 45% for HEMA containing adhesives. The contents in hydrophobic groups decreased as water contents increased. No differences were found in the adhesive contact angles after 180s even though the spreading rates were different for the products tested. Water contact angles differed significantly but were not correlated with HEMA or solvent presence. Manufacturers use different approaches to stabilise acid co-monomer ingredients in self-etch adhesives. Co-solvents, HEMA, or acrylamides without co-solvents are used to simultaneously etch and infiltrate dentine. A large proportion of water is necessary for decalcification action. Copyright © 2010 Elsevier Ltd. All rights reserved.

Simultaneous spreading and evaporation: recent developments.

PubMed

Semenov, Sergey; Trybala, Anna; Rubio, Ramon G; Kovalchuk, Nina; Starov, Victor; Velarde, Manuel G

2014-04-01

The recent progress in theoretical and experimental studies of simultaneous spreading and evaporation of liquid droplets on solid substrates is discussed for pure liquids including nanodroplets, nanosuspensions of inorganic particles (nanofluids) and surfactant solutions. Evaporation of both complete wetting and partial wetting liquids into a nonsaturated vapour atmosphere are considered. However, the main attention is paid to the case of partial wetting when the hysteresis of static contact angle takes place. In the case of complete wetting the spreading/evaporation process proceeds in two stages. A theory was suggested for this case and a good agreement with available experimental data was achieved. In the case of partial wetting the spreading/evaporation of a sessile droplet of pure liquid goes through four subsequent stages: (i) the initial stage, spreading, is relatively short (1-2 min) and therefore evaporation can be neglected during this stage; during the initial stage the contact angle reaches the value of advancing contact angle and the radius of the droplet base reaches its maximum value, (ii) the first stage of evaporation is characterised by the constant value of the radius of the droplet base; the value of the contact angle during the first stage decreases from static advancing to static receding contact angle; (iii) during the second stage of evaporation the contact angle remains constant and equal to its receding value, while the radius of the droplet base decreases; and (iv) at the third stage of evaporation both the contact angle and the radius of the droplet base decrease until the drop completely disappears. It has been shown theoretically and confirmed experimentally that during the first and second stages of evaporation the volume of droplet to power 2/3 decreases linearly with time. The universal dependence of the contact angle during the first stage and of the radius of the droplet base during the second stage on the reduced time has been derived theoretically and confirmed experimentally. The theory developed for pure liquids is applicable also to nanofluids, where a good agreement with the available experimental data has been found. However, in the case of evaporation of surfactant solutions the process deviates from the theoretical predictions for pure liquids at concentration below critical wetting concentration and is in agreement with the theoretical predictions at concentrations above it. Crown Copyright © 2013. All rights reserved.

Wetting and adhesion evaluation of cosmetic ingredients and products: correlation of in vitro-in vivo contact angle measurements.

PubMed

Capra, P; Musitelli, G; Perugini, P

2017-08-01

The aim of this work was to use the contact angle measurement in order to predict the behaviour of ingredients and finished cosmetic products on skin to improve skin feel and product texture. Different classes of cosmetic ingredients and formulations were evaluated. The contact angle measurements were carried out by the sessile drop method using an apparatus, designed and set up in laboratory. Glass, Teflon and human skin were the reference substrates. In a preliminary phase, TEWL parameter, sebum content and hydration of human skin were measured to set up method. Data demonstrated that glass substrate may be used as replacement of the skin:critical surface tension of skin and glass were about of 27 and 31 dyne cm -1 , respectively. Non-ionic surfactant with increasing HLB was evaluated: a correlation between contact angle measured and HLB was not observed because of different and complex molecular structure. In detail, ethylhexyl hydroxystearate (θ glass = 17.1°) showed lower contact angle value with respect to Polysorbate 20 (θ glass = 28.1°). Sodium laureth sulphate and stearalkonium chloride were also evaluated: anionic molecule showed more affinity for glass with respect to Teflon (θ glass = 21.7° and θ Teflon = 52.3°). Lipids and silicones showed different affinity for substrate according to hydrophilic groups and hydrocarbon chain: contact angles of silicones remained unchanged independently from substrate. Finished cosmetic products (O/W, W/O emulsions, cleansing oil, dry skin oil) showed different profiles according to surfactant and its affinity for continuous phase of the formulation. Comparing the values of the contact angle on skin of non-ionic surfactants, as ethylhexyl hydroxystearate and Polysorbate 20, they showed values lower (near to zero) than ones of sodium laureth sulphate and Stearalkonium Chloride (21.7° and 66.8°, respectively). Finally, finished cosmetic products tested on human skin showed different profile: corresponded contact angle values were less than 20°. The product tended to be quickly adsorbed on human skin. Systematic study carried out by evaluating the wettability of single cosmetic ingredients on different substrates allowed to find correlations between the use of certain ingredients and the final performance of a cosmetic product. © 2017 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Preparation of superhydrophobic copper surface by a novel silk-screen printing aided electrochemical machining method

NASA Astrophysics Data System (ADS)

Yan, X. Y.; Chen, G. X.; Liu, J. W.

2018-03-01

A kind of superhydrophobic copper surface with micro-nanocomposite structure has been successfully fabricated by employing a silk-screen printing aided electrochemical machining method. At first silk-screen printing technology has been used to form a column point array mask, and then the microcolumn array would be fabricated by electrochemical machining (ECM) effect. In this study, the drop contact angles have been studied and scanning electron microscopy (SEM) has been used to study the surface characteristic of the workpiece. The experiment results show that the micro-nanocomposite structure with cylindrical array can be successfully fabricated on the metal surface. And the maximum contact angle is 151° when the fluoroalkylsilane ethanol solution was used to modify the machined surface in this study.

Microscale Mechanism of Age Dependent Wetting Properties of Prickly Pear Cacti (Opuntia).

PubMed

Rykaczewski, Konrad; Jordan, Jacob S; Linder, Rubin; Woods, Erik T; Sun, Xiaoda; Kemme, Nicholas; Manning, Kenneth C; Cherry, Brian R; Yarger, Jeffery L; Majure, Lucas C

2016-09-13

Cacti thrive in xeric environments through specialized water storage and collection tactics such as a shallow, widespread root system that maximizes rainwater absorption and spines adapted for fog droplet collection. However, in many cacti, the epidermis, not the spines, dominates the exterior surface area. Yet, little attention has been dedicated to studying interactions of the cactus epidermis with water drops. Surprisingly, the epidermis of plants in the genus Opuntia, also known as prickly pear cacti, has water-repelling characteristics. In this work, we report that surface properties of cladodes of 25 taxa of Opuntia grown in an arid Sonoran climate switch from water-repelling to superwetting under water impact over the span of a single season. We show that the old cladode surfaces are not superhydrophilic, but have nearly vanishing receding contact angle. We study water drop interactions with, as well as nano/microscale topology and chemistry of, the new and old cladodes of two Opuntia species and use this information to uncover the microscopic mechanism underlying this phenomenon. We demonstrate that composition of extracted wax and its contact angle do not change significantly with time. Instead, we show that the reported age dependent wetting behavior primarily stems from pinning of the receding contact line along multilayer surface microcracks in the epicuticular wax that expose the underlying highly hydrophilic layers.

Critical point wetting drop tower experiment

NASA Technical Reports Server (NTRS)

Kaukler, William F.

1990-01-01

The 100 m Drop Tower at NASA-Marshall was used to provide the step change in acceleration from 1.0 to 0.0005 g. An inter-fluid meniscus oscillates vertically within a cylindrical container when suddenly released from earth's gravity and taken into a microgravity environment. Oscillations damp out from energy dissipative mechanisms such as viscosity and interfacial friction. Damping of the oscillations by the later mechanism is affected by the nature of the interfacial junction between the fluid-fluid interface and the container wall. In earlier stages of the project, the meniscus shape which developed during microgravity conditions was applied to evaluations of wetting phenomena near the critical temperature. Variations in equilibrium contact angle against the container wall were expected to occur under critical wetting conditions. However, it became apparent that the meaningful phenomenon was the damping of interfacial oscillations. This latter concept makes up the bulk of this report. Perfluoromethyl cyclohexane and isopropanol in glass were the materials used for the experiment. The wetting condition of the fluids against the wall changes at the critical wetting transition temperature. This change in wetting causes a change in the damping characteristics of the interfacial excursions during oscillation and no measurable change in contact angle. The effect of contact line friction measured above and below the wetting transition temperature was to increase the period of vertical oscillation for the vapor-liquid interface when below the wetting transition temperature.

Evaporation Flux Distribution of Drops on a Hydrophilic or Hydrophobic Flat Surface by Molecular Simulations.

PubMed

Xie, Chiyu; Liu, Guangzhi; Wang, Moran

2016-08-16

The evaporation flux distribution of sessile drops is investigated by molecular dynamic simulations. Three evaporating modes are classified, including the diffusion dominant mode, the substrate heating mode, and the environment heating mode. Both hydrophilic and hydrophobic drop-substrate interactions are considered. To count the evaporation flux distribution, which is position dependent, we proposed an azimuthal-angle-based division method under the assumption of spherical crown shape of drops. The modeling results show that the edge evaporation, i.e., near the contact line, is enhanced for hydrophilic drops in all the three modes. The surface diffusion of liquid molecular absorbed on solid substrate for hydrophilic cases plays an important role as well as the space diffusion on the enhanced evaporation rate at the edge. For hydrophobic drops, the edge evaporation flux is higher for the substrate heating mode, but lower than elsewhere of the drop for the diffusion dominant mode; however, a nearly uniform distribution is found for the environment heating mode. The evidence shows that the temperature distribution inside drops plays a key role in the position-dependent evaporation flux.

Contact Angles and Surface Tension of Germanium-Silicon Melts

NASA Technical Reports Server (NTRS)

Croell, A.; Kaiser, N.; Cobb, S.; Szofran, F. R.; Volz, M.; Rose, M. Franklin (Technical Monitor)

2001-01-01

Precise knowledge of material parameters is more and more important for improving crystal growth processes. Two important parameters are the contact (wetting) angle and the surface tension, determining meniscus shapes and surface-tension driven flows in a variety of methods (Czochralski, EFG, floating-zone, detached Bridgman growth). The sessile drop technique allows the measurement of both parameters simultaneously and has been used to measure the contact angles and the surface tension of Ge(1-x)Si(x) (0 less than or equal to x less than or equal to 1.3) alloys on various substrate materials. Fused quartz, Sapphire, glassy carbon, graphite, SiC, carbon-based aerogel, pyrolytic boron nitride (pBN), AIN, Si3N4, and polycrystalline CVD diamond were used as substrate materials. In addition, the effect of different cleaning procedures and surface treatments on the wetting behavior were investigated. Measurements were performed both under dynamic vacuum and gas atmospheres (argon or forming gas), with temperatures up to 1100 C. In some experiments, the sample was processed for longer times, up to a week, to investigate any changes of the contact angle and/or surface tension due to slow reactions with the substrate. For pure Ge, stable contact angles were found for carbon-based substrates and for pBN, for Ge(1-x)Si(x) only for pBN. The highest wetting angles were found for pBN substrates with angles around 170deg. For the surface tension of Ge, the most reliable values resulted in gamma(T) = (591- 0.077 (T-T(sub m)) 10(exp -3)N/m. The temperature dependence of the surface tension showed similar values for Ge(1-x)Si(x), around -0.08 x 10(exp -3)N/m K, and a compositional dependence of 2.2 x 10(exp -3)N/m at%Si.

Uniting Superhydrophobic, Superoleophobic and Lubricant Infused Slippery Behavior on Copper Oxide Nano-structured Substrates

PubMed Central

Ujjain, Sanjeev Kumar; Roy, Pritam Kumar; Kumar, Sumana; Singha, Subhash; Khare, Krishnacharya

2016-01-01

Alloys, specifically steel, are considered as the workhorse of our society and are inimitable engineering materials in the field of infrastructure, industry and possesses significant applications in our daily life. However, creating a robust synthetic metallic surface that repels various liquids has remained extremely challenging. The wettability of a solid surface is known to be governed by its geometric nano-/micro structure and the chemical composition. Here, we are demonstrating a facile and economical way to generate copper oxide micro-nano structures with spherical (0D), needle (1D) and hierarchical cauliflower (3D) morphologies on galvanized steel substrates using a simple chemical bath deposition method. These nano/micro textured steel surfaces, on subsequent coating of a low surface energy material display excellent superhydrophobic, superoleophobic and slippery behavior. Polydimethylsiloxane coated textured surfaces illustrate superhydrophobicity with water contact angle about 160°(2) and critical sliding angle ~2°. When functionalized with low-surface energy perfluoroalkylsilane, these surfaces display high repellency for low surface tension oils as well as hydrocarbons. Among them, the hierarchical cauliflower morphology exhibits re-entrant structure thereby showing the best superoleophobicity with contact angle 149° for dodecane. Once infused with a lubricant like silicone oil, they show excellent slippery behavior with low contact angle hysteresis (~ 2°) for water drops. PMID:27752098

Uniting Superhydrophobic, Superoleophobic and Lubricant Infused Slippery Behavior on Copper Oxide Nano-structured Substrates

NASA Astrophysics Data System (ADS)

Ujjain, Sanjeev Kumar; Roy, Pritam Kumar; Kumar, Sumana; Singha, Subhash; Khare, Krishnacharya

2016-10-01

Alloys, specifically steel, are considered as the workhorse of our society and are inimitable engineering materials in the field of infrastructure, industry and possesses significant applications in our daily life. However, creating a robust synthetic metallic surface that repels various liquids has remained extremely challenging. The wettability of a solid surface is known to be governed by its geometric nano-/micro structure and the chemical composition. Here, we are demonstrating a facile and economical way to generate copper oxide micro-nano structures with spherical (0D), needle (1D) and hierarchical cauliflower (3D) morphologies on galvanized steel substrates using a simple chemical bath deposition method. These nano/micro textured steel surfaces, on subsequent coating of a low surface energy material display excellent superhydrophobic, superoleophobic and slippery behavior. Polydimethylsiloxane coated textured surfaces illustrate superhydrophobicity with water contact angle about 160°(2) and critical sliding angle ~2°. When functionalized with low-surface energy perfluoroalkylsilane, these surfaces display high repellency for low surface tension oils as well as hydrocarbons. Among them, the hierarchical cauliflower morphology exhibits re-entrant structure thereby showing the best superoleophobicity with contact angle 149° for dodecane. Once infused with a lubricant like silicone oil, they show excellent slippery behavior with low contact angle hysteresis (~ 2°) for water drops.

Dynamics of the Molten Contact Line

NASA Technical Reports Server (NTRS)

Sonin, Ain A.; Duthaler, Gregg; Liu, Michael; Torresola, Javier; Qiu, Taiqing

1999-01-01

The purpose of this program is to develop a basic understanding of how a molten material front spreads over a solid that is below its melting point, arrests, and freezes. Our hope is that the work will contribute toward a scientific knowledge base for certain new applications involving molten droplet deposition, including the "printing" of arbitrary three-dimensional objects by precise deposition of individual molten microdrops that solidify after impact. Little information is available at this time on the capillarity-driven motion and arrest of molten contact line regions. Schiaffino and Sonin investigated the arrest of the contact line of a molten microcrystalline wax spreading over a subcooled solid "target" of the same material. They found that contact line arrest takes place at an apparent liquid contact angle that depends primarily on the Stefan number S=c(T(sub f) -T(sub t)/L based on the temperature difference between the fusion point and the target temperature, and proposed that contact line arrest occurs when the liquid's dynamic contact angle approaches the angle of attack of the solidification front just behind the contact line. They also showed, however, that the conventional continuum equations and boundary conditions have no meaningful solution for this angle. The solidification front angle is determined by the heat flux just behind the contact line, and the heat flux is singular at that point. By comparing experiments with numerical computations, Schiaffino and Sonin estimated that the conventional solidification model must break down within a distance of order 0.1 - 1 microns of the contact line. The physical mechanism for this breakdown is as yet undetermined, and no first-principles theory exists for the contact angle at arrest. Schiaffino and Sonin also presented a framework for understanding how to moderate Weber number molten droplet deposition in terms of similarity laws and experimentation. The study is based on experiments with three molten materials- molten wax on solid wax, water on ice, and mercury on frozen mercury- which between them span a considerable range of the deposition/solidification similarity parameters. Correlations are obtained for the spreading velocity, spreading time scales, the spreading factor (i.e. ratio of deposited drop's final footprint radius and the drop's initial radius), post-spreading liquid oscillation amplitudes and time scales, and bulk solidification time scales. Duthaler carried out an experimental and theoretical investigation of the relationship between the liquid's apparent contact angle and the Capillary number Ca=mu U/sigma based on contact line speed, for molten materials spreading over subcooled solids. This relationship is required for modeling of melt spreading. We have adapted Voinov's methodology to the molten contact line and formulated a theoretical model for the Ca vs. contact angle relationship, based Schiaffino and Sonin#s (1997a,b) wedge-like solidification front model. With the solidification front angle taken from Schiaffino and Sonin, the model is in good agreement with the experimental results for Ca vs. contact angle. Duthaler also extended the experimental investigation of droplet deposition and contact line freezing to more materials, including solder on glass, solder on solder, water on ice, and molten microcrystalline wax on wax. The latter also included tests on inclined targets. Deposition tests have also been done with molten octacosane (C28H58) on various targets. An important objective of our program has been the development of micron-scale sensors for measuring the transient temperature at a point on the substrate surface as a molten contact line moves over it. The expectation is that this temperature history will yield a better understanding of the thermal process in the contact line region. The sensors are of the thermistor type, either 2.5 microns or 1.5 microns square, microfabricated with silicon-based technology on either pure silicon or amorphous silicon dioxide chips. Each chip has 32 sensors distributed on its surface in arrays. The time response is better than 10 ms. At the time of writing, sensor calibration is in progress. Results on thermal transients during contact line passage will be discussed at the conference. While we expect that the data will provide information on the near-contact-line heat transfer process, we also foresee possible problems. First, the spatial resolution of the sensors may be insufficient to resolve the near-contact-line region. Second, the sensors protrude about 0.5 microns above the substrate surface, and may affect the contact line motion. Third, a sensor's temperature history depends on both the heat flux distribution into it from the fusion front and the thermal properties of the substrate below it and the solidified melt between it and the fusion front. The heat flux distribution in the contact line region must therefore be unfolded from computations of the overall system's transient thermal response.

Marangoni Effect on the Shape of Freely Receding Evaporating Sessile Droplets of Perfectly Wetting Liquids

NASA Astrophysics Data System (ADS)

Tsoumpas, Yannis; Dehaeck, Sam; Rednikov, Alexey; Colinet, Pierre

2014-11-01

Freely receding evaporating sessile droplets of perfectly wetting liquids (HFE-7100, 7200 and 7500), with small finite contact angles induced by evaporation, are studied with a Mach-Zehnder interferometer. Surprisingly, the experimentally obtained profiles turn out to deviate from the classical macroscopic static shape of a sessile droplet (as determined by gravity and capillarity), often used when modeling evaporating droplets. These deviations can be seen in two ways. Namely, either the droplet appears to be inflated as compared to the classical static shape assuming the same contact angle and contact radius, or the apparent contact angle appears lower than the classical static one assuming the same volume and contact radius. In reality, the experimental profiles exhibit a local decrease of the slope near the contact line, which we attribute to the Marangoni effect in an evaporating sessile droplet. In this case, the radially inward (along the liquid-air interface) direction of the flow delivers more liquid to the center of the droplet making it appear inflated. When the Marangoni effect is weak, as in the case of the poorly volatile HFE-7500, no significant influence is noticed on the drop shape. The experimental results are compared with the predictions of a lubrication-type theoretical model that incorporates the evaporation-induced Marangoni flow. Financial support of FP7 Marie Curie MULTIFLOW Network (PITN-GA-2008-214919), ESA/BELSPO-PRODEX, BELSPO- μMAST (IAP 7/38) & FRS-FNRS is gratefully acknowledged.

Critical conditions for the buoyancy-driven detachment of a wall-bound pendant drop

NASA Astrophysics Data System (ADS)

Lamorgese, A.; Mauri, R.

2016-03-01

We investigate numerically the critical conditions for detachment of an isolated, wall-bound emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. To that end, we present a simple extension of a diffuse-interface model for partially miscible binary mixtures that was previously employed for simulating several two-phase flow phenomena far and near the critical point [A. G. Lamorgese et al. "Phase-field approach to multiphase flow modeling," Milan J. Math. 79(2), 597-642 (2011)] to allow for static contact angles other than 90°. We use the same formulation of the Cahn boundary condition as first proposed by Jacqmin ["Contact-line dynamics of a diffuse fluid interface," J. Fluid Mech. 402, 57-88 (2000)], which accommodates a cubic (Hermite) interpolation of surface tensions between the wall and each phase at equilibrium. We show that this model can be successfully employed for simulating three-phase contact line problems in stable emulsions with nearly immiscible components. We also show a numerical determination of critical Bond numbers as a function of static contact angle by phase-field simulation.

Biomimetic Superhydrophobic Hollowed-Out Pyramid Surface Based on Self-Assembly.

PubMed

Luo, Weipeng; Yu, Bin; Xiao, Dingbang; Zhang, Meng; Wu, Xuezhong; Li, Guoxi

2018-05-16

In this paper, we present a periodic hollowed-out pyramid microstructure with excellent superhydrophobicity. In our approach, T-topping pillars and capillary-induced self-assembly methods were combined with the photolithography process to fabricate a hollowed-out pyramid structure. First, a wideband ultraviolet source without a filter was used to fabricate the T-topping pillars during the exposure process; then, the evaporation-induced assembly collapsed the pillars and formed the hollowed-out pyramid structure. Scanning electron microscopy images showed the microstructures of the prepared surface. The contact angle of the surface was 154°. The surface showed excellent high temperature and ultraviolet irradiation tolerance, and the contact angle of the surface barely changed when the temperature dropped. This excellent environmental durability of our superhydrophobic surface has potential applications for self-cleaning and friction drag reduction under water.

Properties of carbon composite paper derived from coconut coir as a function of polytetrafluoroethylene content

NASA Astrophysics Data System (ADS)

Destyorini, Fredina; Indriyati; Indayaningsih, Nanik; Prihandoko, Bambang; Zulfia Syahrial, Anne

2018-03-01

The carbon composite papers were produced by utilizing carbon materials from coconut coir. In the present work, carbon composite papers (CCP) were prepared by mixing carbon materials in the form of powder and fibre with polymer (ethylene vinyl acetate and polyethylene glycol) in xylene at 100°C. Then, polytetrafluoroethylene (PTFE) with different content was used to treat the surface of CCP. The properties of PTFE-coated CCP were analysed by means of contact angle measurement, tensile testing, porosity, density, and electrical conductivity measurements. As expected, all CCP’s surfaces treated with PTFE were found to be hydrophobic with contact angle >120° and relatively constant during 60 minutes measurement. Furthermore, water contact angle, density, and mechanical properties of CCP generally increase with increasing PTFE content. However, the porosity and electrical conductivity of CCP decrease slightly as the PTFE content increased from 0 wt% to 30 wt%. Based on the observation and analysis, the optimum PTFE content on CCP was 20 %, in which the mechanical properties and hydrophobicity behaviour were improved significantly, but it was only caused a very small drop in porosity and electrical conductivity

Changes in contact angle providing evidence for surface alteration in multi-component solid foods

NASA Astrophysics Data System (ADS)

Reinke, Svenja K.; Hauf, Katharina; Vieira, Josélio; Heinrich, Stefan; Palzer, Stefan

2015-11-01

Chocolate blooming, one of the major problems in the confectionery industry, is the formation of visible white spots or a greyish haze on the surface of chocolate products due to large sugar or fat crystals on the surface. This leads to aesthetic changes and deterioration of taste and thus large sales losses for the confectionery industry due to consumer complaints. Chocolate blooming is often related to migration of lipids or sugar molecules to the chocolate surface, where they recrystallize with an associated polymorphic change of crystal structure on the surface. The wetting behaviour from contact angle measurements gives further insight into surface properties and is needed to determine surface energies and to evaluate possible migration mechanisms and preferred pathways. Therefore, an equilibrium contact angle is needed which is not directly accessible and is influenced by surface texture and interaction between solid and test liquid. In this study, the surface of cocoa butter and conventional chocolates was characterized by measuring the contact angle with the sessile drop protocol. The influence of roughness, test liquid and pre-crystallization of the samples as well as the storage temperature were investigated. In case of no pre-crystallization, a change in surface properties due to storage at 20 °C was detected, whereas samples stored at 30 °C showed the same wetting behaviour as fresh samples. This is associated with polymorphic transformation from thermodynamically less stable crystals to more stable configurations.

Knee and Hip Joint Kinematics Predict Quadriceps and Hamstrings Neuromuscular Activation Patterns in Drop Jump Landings

PubMed Central

Malfait, Bart; Dingenen, Bart; Smeets, Annemie; Staes, Filip; Pataky, Todd; Robinson, Mark A.; Vanrenterghem, Jos; Verschueren, Sabine

2016-01-01

Purpose The purpose was to assess if variation in sagittal plane landing kinematics is associated with variation in neuromuscular activation patterns of the quadriceps-hamstrings muscle groups during drop vertical jumps (DVJ). Methods Fifty female athletes performed three DVJ. The relationship between peak knee and hip flexion angles and the amplitude of four EMG vectors was investigated with trajectory-level canonical correlation analyses over the entire time period of the landing phase. EMG vectors consisted of the {vastus medialis(VM),vastus lateralis(VL)}, {vastus medialis(VM),hamstring medialis(HM)}, {hamstring medialis(HM),hamstring lateralis(HL)} and the {vastus lateralis(VL),hamstring lateralis(HL)}. To estimate the contribution of each individual muscle, linear regressions were also conducted using one-dimensional statistical parametric mapping. Results The peak knee flexion angle was significantly positively associated with the amplitudes of the {VM,HM} and {HM,HL} during the preparatory and initial contact phase and with the {VL,HL} vector during the peak loading phase (p<0.05). Small peak knee flexion angles were significantly associated with higher HM amplitudes during the preparatory and initial contact phase (p<0.001). The amplitudes of the {VM,VL} and {VL,HL} were significantly positively associated with the peak hip flexion angle during the peak loading phase (p<0.05). Small peak hip flexion angles were significantly associated with higher VL amplitudes during the peak loading phase (p = 0.001). Higher external knee abduction and flexion moments were found in participants landing with less flexed knee and hip joints (p<0.001). Conclusion This study demonstrated clear associations between neuromuscular activation patterns and landing kinematics in the sagittal plane during specific parts of the landing. These findings have indicated that an erect landing pattern, characterized by less hip and knee flexion, was significantly associated with an increased medial and posterior neuromuscular activation (dominant hamstrings medialis activity) during the preparatory and initial contact phase and an increased lateral neuromuscular activation (dominant vastus lateralis activity) during the peak loading phase. PMID:27101130

Droplets and the three-phase contact line at the nano-scale. Statics and dynamics

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Sibley, David; Savva, Nikos; Kalliadasis, Serafim

2014-11-01

Understanding the behaviour of the solid-liquid-vapour contact line at the scale of several tens of molecular diameters is important in wetting hydrodynamics with applications in micro- and nano-fluidics, including the design of lab-on-a-chip devices and surfaces with specific wetting properties. Due to the fluid inhomogeneity at the nano-scale, the application of continuum-mechanical approaches is limited, and a natural way to remedy this is to seek descriptions accounting for the non-local molecular-level interactions. Density Functional Theory (DFT) for fluids offers a statistical-mechanical framework based on expressing the free energy of the fluid-solid pair as a functional of the spatially varying fluid density. DFT allows us to investigate small drops deposited on planar substrates whilst keeping track of the microscopic structural details of the fluid. Starting from a model of intermolecular forces, we systematically obtain interfaces, surface tensions, and the microscopic contact angle. Using a dynamic extension of equilibrium DFT, we investigate the diffusion-driven evolution of the three-phase contact line to gain insight into the dynamic behaviour of the microscopic contact angle, which is still under debate.

Predictive models for moving contact line flows

NASA Technical Reports Server (NTRS)

Rame, Enrique; Garoff, Stephen

2003-01-01

Modeling flows with moving contact lines poses the formidable challenge that the usual assumptions of Newtonian fluid and no-slip condition give rise to a well-known singularity. This singularity prevents one from satisfying the contact angle condition to compute the shape of the fluid-fluid interface, a crucial calculation without which design parameters such as the pressure drop needed to move an immiscible 2-fluid system through a solid matrix cannot be evaluated. Some progress has been made for low Capillary number spreading flows. Combining experimental measurements of fluid-fluid interfaces very near the moving contact line with an analytical expression for the interface shape, we can determine a parameter that forms a boundary condition for the macroscopic interface shape when Ca much les than l. This parameter, which plays the role of an "apparent" or macroscopic dynamic contact angle, is shown by the theory to depend on the system geometry through the macroscopic length scale. This theoretically established dependence on geometry allows this parameter to be "transferable" from the geometry of the measurement to any other geometry involving the same material system. Unfortunately this prediction of the theory cannot be tested on Earth.

Capillary rise between planar surfaces

NASA Astrophysics Data System (ADS)

Bullard, Jeffrey W.; Garboczi, Edward J.

2009-01-01

Minimization of free energy is used to calculate the equilibrium vertical rise and meniscus shape of a liquid column between two closely spaced, parallel planar surfaces that are inert and immobile. States of minimum free energy are found using standard variational principles, which lead not only to an Euler-Lagrange differential equation for the meniscus shape and elevation, but also to the boundary conditions at the three-phase junction where the liquid meniscus intersects the solid walls. The analysis shows that the classical Young-Dupré equation for the thermodynamic contact angle is valid at the three-phase junction, as already shown for sessile drops with or without the influence of a gravitational field. Integration of the Euler-Lagrange equation shows that a generalized Laplace-Young (LY) equation first proposed by O’Brien, Craig, and Peyton [J. Colloid Interface Sci. 26, 500 (1968)] gives an exact prediction of the mean elevation of the meniscus at any wall separation, whereas the classical LY equation for the elevation of the midpoint of the meniscus is accurate only when the separation approaches zero or infinity. When both walls are identical, the meniscus is symmetric about the midpoint, and the midpoint elevation is a more traditional and convenient measure of capillary rise than the mean elevation. Therefore, for this symmetric system a different equation is fitted to numerical predictions of the midpoint elevation and is shown to give excellent agreement for contact angles between 15° and 160° and wall separations up to 30mm . When the walls have dissimilar surface properties, the meniscus generally assumes an asymmetric shape, and significant elevation of the liquid column can occur even when one of the walls has a contact angle significantly greater than 90°. The height of the capillary rise depends on the spacing between the walls and also on the difference in contact angles at the two surfaces. When the contact angle at one wall is greater than 90° but the contact angle at the other wall is less than 90°, the meniscus can have an inflection point separating a region of positive curvature from a region of negative curvature, the inflection point being pinned at zero height. However, this condition arises only when the spacing between the walls exceeds a threshold value that depends on the difference in contact angles.

Energetic analysis of drop's maximum spreading on solid surface with low impact speed

NASA Astrophysics Data System (ADS)

Huang, Hai-Meng; Chen, Xiao-Peng

2018-02-01

Drops impacting on a flat solid surface will spread until it reaches maximum contact with the substrate underneath. After that, it recoils. In the present work, the variations of energy components during the spreading are studied carefully, including kinetic, capillary, and dissipated energies. Our experimental and numerical results show that, when the impact speed is low, the fast slipping of the contact line (in inertia-capillary regime) and corresponding "interface relaxation" lead to extra dissipation. An auxiliary dissipation is therefore introduced into the traditional theoretical model. The energy components predicted by the improved model agree with the experimental and numerical results very well. As the impact speed increases (the Weber number, W e =ρ D0V02/γ , becomes larger than 40 in the present work), the dissipation induced by the initial velocity plays more important roles. The analyses also indicate that on the hydrophobic surfaces the auxiliary dissipation is lower than that on hydrophilic ones. In the later circumstances, the contact angle is larger and the spreading is weaker.

Elasticity modulated Electrowetting of a sessile liquid droplet

NASA Astrophysics Data System (ADS)

Kumar, Sumit; Subramanian, Sri Ganesh; Dasgupta, Sunando; Chakraborty, Suman

2017-11-01

The sessile liquid droplets on the elastic and soft deformable surface produce strong deformation near the three-phase contact line (TPCL). The capillary and elastic forces play an important role during this deformation, and deteriorate the wetting behaviour of a sessile drop. The present work combines the effects of liquid viscosity and substrate elasticity on the dynamics of EWOD. The influence of decreasing film elasticity and viscosity on the electrowetting response of a sessile drop is experimentally investigated by delineating the changes in equilibrium apparent contact angles on substrates with varying Young's modulus of elasticity. The increase in viscosity of the liquid leads to greater electrowetting for non-deformable substrates whereas; the dynamics are not greatly affected in case of soft substrates. Although the viscosity appears to be an influential factor, the dynamics are more skewed towards the substrate rigidity. The vertical component of Young's force creates a wetting ridge at the three-phase contact line, the height of which is a direct function of the substrate rigidity. The produced ridges reduce the overall wettability of the droplet.

In situ contact angle measurements of liquid CO 2, brine, and Mount Simon sandstone core using micro X-ray CT imaging, sessile drop, and Lattice Boltzmann modeling

DOE PAGES

Tudek, John; Crandall, Dustin; Fuchs, Samantha; ...

2017-01-30

Three techniques to measure and understand the contact angle, θ, of a CO 2/brine/rock system relevant to geologic carbon storage were performed with Mount Simon sandstone. Traditional sessile drop measurements of CO 2/brine on the sample were conducted and a water-wet system was observed, as is expected. A novel series of measurements inside of a Mount Simon core, using a micro X-ray computed tomography imaging system with the ability to scan samples at elevated pressures, was used to examine the θ of residual bubbles of CO 2. Within the sandstone core the matrix appeared to be neutrally wetting, with anmore » average θ around 90°. A large standard deviation of θ (20.8°) within the core was also observed. To resolve this discrepancy between experimental measurements, a series of Lattice Boltzmann model simulations were performed with differing intrinsic θ values. The model results with a θ = 80° were shown to match the core measurements closely, in both magnitude and variation. The small volume and complex geometry of the pore spaces that CO 2 was trapped in is the most likely explanation of this discrepancy between measured values, though further work is warranted.« less

Fabricating customized hydrogel contact lens

NASA Astrophysics Data System (ADS)

Childs, Andre; Li, Hao; Lewittes, Daniella M.; Dong, Biqin; Liu, Wenzhong; Shu, Xiao; Sun, Cheng; Zhang, Hao F.

2016-10-01

Contact lenses are increasingly used in laboratories for in vivo animal retinal imaging and pre-clinical studies. The lens shapes often need modification to optimally fit corneas of individual test subjects. However, the choices from commercially available contact lenses are rather limited. Here, we report a flexible method to fabricate customized hydrogel contact lenses. We showed that the fabricated hydrogel is highly transparent, with refractive indices ranging from 1.42 to 1.45 in the spectra range from 400 nm to 800 nm. The Young’s modulus (1.47 MPa) and hydrophobicity (with a sessile drop contact angle of 40.5°) have also been characterized experimentally. Retinal imaging using optical coherence tomography in rats wearing our customized contact lenses has the quality comparable to the control case without the contact lens. Our method could significantly reduce the cost and the lead time for fabricating soft contact lenses with customized shapes, and benefit the laboratorial-used contact lenses in pre-clinical studies.

Fabricating customized hydrogel contact lens

PubMed Central

Childs, Andre; Li, Hao; Lewittes, Daniella M.; Dong, Biqin; Liu, Wenzhong; Shu, Xiao; Sun, Cheng; Zhang, Hao F.

2016-01-01

Contact lenses are increasingly used in laboratories for in vivo animal retinal imaging and pre-clinical studies. The lens shapes often need modification to optimally fit corneas of individual test subjects. However, the choices from commercially available contact lenses are rather limited. Here, we report a flexible method to fabricate customized hydrogel contact lenses. We showed that the fabricated hydrogel is highly transparent, with refractive indices ranging from 1.42 to 1.45 in the spectra range from 400 nm to 800 nm. The Young’s modulus (1.47 MPa) and hydrophobicity (with a sessile drop contact angle of 40.5°) have also been characterized experimentally. Retinal imaging using optical coherence tomography in rats wearing our customized contact lenses has the quality comparable to the control case without the contact lens. Our method could significantly reduce the cost and the lead time for fabricating soft contact lenses with customized shapes, and benefit the laboratorial-used contact lenses in pre-clinical studies. PMID:27748361

Pore-scale distribution of mucilage affecting water repellency in the rhizosphere

NASA Astrophysics Data System (ADS)

Benard, Pascal; Zarebanadkouki, Mohsen; Hedwig, Clemens; Holz, Maire; Ahmed, Mutez; Carminati, Andrea

2017-04-01

The hydraulic properties of the rhizosphere are altered by plants, fungi and microorganism. Plant roots release different compounds into the soil. One of these substances is mucilage, a gel which turns water repellent upon drying. We introduce a conceptual model of mucilage deposition during soil drying and its impact on the soil wettability. As the soil dries, water menisci recede and draw mucilage towards the contact region between particles where it is deposited. At high mucilage content, mucilage deposits expand into the open pore space and finally block water infiltration when a critical fraction of the pore space is blocked. To test this hypothesis, we mixed mucilage and particles of different grain size, we let them dry and measured the contact angle using the sessile drop method. Mucilage deposition was visualized by light microscopy imaging. Contact angle measurements showed a distinct threshold-like behavior with a sudden increase in apparent contact angle at high mucilage concentrations. Particle roughness induced a more uniform distribution of mucilage. The observed threshold corresponds to the concentration when mucilage deposition occupies a critical fraction of the pore space, as visualized with the microscope images. In conclusion, water repellency is critically affected by the distribution of mucilage on the pore-scale. This microscopic heterogeneity has to be taken into account in the description of macroscopic processes, like water infiltration or rewetting of water repellent soil.

Effect of droplet shrinking on surface acoustic wave response in microfluidic applications

NASA Astrophysics Data System (ADS)

Bui, ThuHang; Nguyen, Van; Vollebregt, Sten; Morana, Bruno; van Zeijl, Henk; Chu Duc, Trinh; Sarro, Pasqualina M.

2017-12-01

The effect of the contact angle and radius of a microsize droplet on the surface acoustic wave (SAW) response for microfluidic applications is reported. It is studied through the dynamic change of the droplet shape during the evaporation process. An aluminium nitride SAW device, operating at 125.7 MHz, is utilized to investigate the deformation of the droplet shape (contact angle and contact radius) caused by shrinking. The large cavity placed on the propagation path distorts the in-band SAW response one time at the centre frequency. The fractional coefficient of the SAW insertion loss, before and after dropping the liquid on the propagation path, is continuously recorded. The change in the fractional coefficient shows that the radiated acoustic kinetic energy depends on the contact area between the sessile micro-size droplet and the SAW device more than the contact angle of the droplet. Three droplet volumes have been considered, namely 0.05, 0.1 and 0.13 μl, and the electrical results show a better agreement with the theoretical data than the optical image data. The average duration of the fractional coefficient change for these cases is 420, 573 and 760 s, respectively. The effect of the hydrophobicity versus hydrophilicity of the contact surface on the duration of the fractional coefficient change is studied by coating the SAW with a silicon oxide or hexamethyldisilazane (HMDS) thin layer. For the same 0.05 μl sessile droplet on the hydrophobic surface, this duration is on average 110 s longer than that on the hydrophilic surface.

Induced wettability and surface-volume correlation of composition for bovine bone derived hydroxyapatite particles

NASA Astrophysics Data System (ADS)

Maidaniuc, Andreea; Miculescu, Florin; Voicu, Stefan Ioan; Andronescu, Corina; Miculescu, Marian; Matei, Ecaterina; Mocanu, Aura Catalina; Pencea, Ion; Csaki, Ioana; Machedon-Pisu, Teodor; Ciocan, Lucian Toma

2018-04-01

Hydroxyapatite powders characteristics need to be determined both for quality control purposes and for a proper control of microstructural features of bone reconstruction products. This study combines bulk morphological and compositional analysis methods (XRF, SEM-EDS, FT-IR) with surface-related methods (XPS, contact angle measurements) in order to correlate the characteristics of hydroxyapatite powders derived from bovine bone for its use in medical applications. An experimental approach for correlating the surface and volume composition was designed based on the analysis depth of each spectral method involved in the study. Next, the influences of powder particle size and forming method on the contact angle between water drops and ceramic surface were evaluated for identifying suitable strategies of tuning hydroxyapatite's wettability. The results revealed a preferential arrangement of chemical elements at the surface of hydroxyapatite particles which could induce a favourable material behaviour in terms of sinterability and biological performance.

Fabrication of hydrophobic structures on coronary stent surface based on direct three-beam laser interference lithography

NASA Astrophysics Data System (ADS)

Gao, Long-yue; Zhou, Wei-qi; Wang, Yuan-bo; Wang, Si-qi; Bai, Chong; Li, Shi-ming; Liu, Bin; Wang, Jun-nan; Cui, Cheng-kun; Li, Yong-liang

2016-05-01

To solve the problems with coronary stent implantation, coronary artery stent surface was directly modified by three-beam laser interference lithography through imitating the water-repellent surface of lotus leaf, and uniform micro-nano structures with the controllable period were fabricated. The morphological properties and contact angle (CA) of the microstructure were measured by scanning electron microscope (SEM) and CA system. The water repellency of stent was also evaluated by the contact and then separation between the water drop and the stent. The results show that the close-packed concave structure with the period of about 12 μm can be fabricated on the stent surface with special parameters (incident angle of 3°, laser energy density of 2.2 J·cm-2 and exposure time of 80 s) by using the three-beam laser at 1 064 nm, and the structure has good water repellency with CA of 120°.

Superhydrophobic films and methods for making superhydrophobic films

DOEpatents

Aytug, Tolga; Paranthaman, Mariappan Parans; Simpson, John T.; Bogorin, Daniela Florentina

2017-09-26

This disclosure relates to methods that include depositing a first component and a second component to form a film including a plurality of nanostructures, and coating the nanostructures with a hydrophobic layer to render the film superhydrophobic. The first component and the second component can be immiscible and phase-separated during the depositing step. The first component and the second component can be independently selected from the group consisting of a metal oxide, a metal nitride, a metal oxynitride, a metal, and combinations thereof. The films can have a thickness greater than or equal to 5 nm; an average surface roughness (Ra) of from 90 to 120 nm, as measured on a 5 .mu.m.times.5 .mu.m area; a surface area of at least 20 m.sup.2/g; a contact angle with a drop of water of at least 120 degrees; and can maintain the contact angle when exposed to harsh conditions.

Icephobicity of Leaves

NASA Astrophysics Data System (ADS)

Kavehpour, H. Pirouz; Shirazi, Elika T.; Alizadeh-Birjandi, Elaheh

2016-11-01

Ice adhesion and excessive accumulation on exposed structures and equipment are well known to cause serious problems in cold-climate regions; therefore, the development of coatings that can resist icing can solve many challenges in various areas of industry. This work was inspired by nature and ice-resistivity and superhydrophobicity of plants leaves. Kale is an example of a plant that can be harvested in winter. It shows superhydrophobic behavior, which is normally known as an advantage for cleaning the leaves, but we were able to show that its surface structure and high contact angle of water drops on kale leaves could delay the ice formation process making it a good candidate for an ice-repellent coating. We have performed in-depth experimental analyses on how different plants can prevent icing, and contact angle measurements and scanning electron microscopy (SEM) of the leaves were taken to further mimic their surface morphology.

Preparation and characterization of antibacterial electrospun chitosan/poly (vinyl alcohol)/graphene oxide composite nanofibrous membrane

NASA Astrophysics Data System (ADS)

Yang, Shuai; Lei, Peng; Shan, Yujuan; Zhang, Dawei

2018-03-01

In this paper, chitosan (CS)/poly (vinyl alcohol) (PVA)/graphene oxide (GO) composite nanofibrous membranes were prepared via electrospinning. Such nanofibrous membranes have been characterized and investigated for their morphological, structural, thermal stability, hydrophilic and antibacterial properties. SEM images showed that the uniform and defect-free nanofibers were obtained and GO sheets, shaping spindle and spherical, were partially embedded into nanofibers. FTIR, XRD, DSC and TGA indicated the good compatibility between CS and PVA. There were strong intermolecular hydrogen bonds between the chitosan and PVA molecules. Contact angle measurement indicated that while increasing the content of GO, the distance between fibers increased and water drop showed wetting state on the surface of nanofibrous membranes. As a result, the contact angle decreased significantly. Meanwhile, good antibacterial activity of the prepared nanofibrous membranes were exhibited against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus.

The possible equilibrium shapes of static pendant drops

NASA Astrophysics Data System (ADS)

Sumesh, P. T.; Govindarajan, Rama

2010-10-01

Analytical and numerical studies are carried out on the shapes of two-dimensional and axisymmetric pendant drops hanging under gravity from a solid surface. Drop shapes with both pinned and equilibrium contact angles are obtained naturally from a single boundary condition in the analytical energy optimization procedure. The numerical procedure also yields optimum energy shapes, satisfying Young's equation without the explicit imposition of a boundary condition at the plate. It is shown analytically that a static pendant two-dimensional drop can never be longer than 3.42 times the capillary length. A related finding is that a range of existing solutions for long two-dimensional drops correspond to unphysical drop shapes. Therefore, two-dimensional drops of small volume display only one static solution. In contrast, it is known that axisymmetric drops can display multiple solutions for a given volume. We demonstrate numerically that there is no limit to the height of multiple-lobed Kelvin drops, but the total volume is finite, with the volume of successive lobes forming a convergent series. The stability of such drops is in question, though. Drops of small volume can attain large heights. A bifurcation is found within the one-parameter space of Laplacian shapes, with a range of longer drops displaying a minimum in energy in the investigated space. Axisymmetric Kelvin drops exhibit an infinite number of bifurcations.

Water permeability, hybrid layer long-term integrity and reaction mechanism of a two-step adhesive system.

PubMed

Grégoire, Geneviève; Dabsie, Firas; Delannée, Mathieu; Akon, Bernadette; Sharrock, Patrick

2010-07-01

Our aim was to investigate the reaction mechanism of formation of the hybrid layer by a HEMA-containing self-etch adhesive and to study fluid filtration, contact angle and interfacial ultrastructure by SEM following a 1 year ageing period. Acidic behaviour and chemical interactions between Silorane System Adhesive and dentine were studied by potentiometric titrations, atomic absorption spectroscopy and infrared spectroscopy. The hydrophilicity of the adhesive was evaluated using the sessile drop method and dentine permeability by hydraulic conductance. The morphological study of the dentine/adhesive system interface was conducted using SEM. The Silorane System Adhesive behaved as a multi-acid with several different pK(a) values. When the adhesive was in contact with dentine, the acid was progressively consumed and calcium ions were released. The acrylate substituted phosphonate bound strongly to apatite crystals. The polyacrylic acid copolymer reacted with calcium ions and formed an interpenetrating polymer network (IPN). Water contact angle measurements showed rapid spreading on primer (angles reached 15 degrees at 30s) and larger contact angles when the Silorane bonding layer was added (from over 60 degrees to 44 degrees ). A thick, homogeneous hybrid layer was observed both initially and after 1 year of ageing, with a corresponding hydraulic conductance of -48.50% initially and -52.07% at 12 months. The Silorane System Adhesive is capable of both dissolving calcium ions and binding to apatite surfaces. The results showed the hydrophilicity of the adhesive, which formed an IPN-like hybrid layer that conserved adequate impermeability over a 1-year period. Copyright 2010 Elsevier Ltd. All rights reserved.

Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy Crystals

NASA Technical Reports Server (NTRS)

Szofran, F. R.; Volz, M. P.; Schweizer, M.; Cobb, S. D.; Motakef, S.; Croell, A.; Dold, P.; Curreri, Peter A. (Technical Monitor)

2002-01-01

Earth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2 at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS). The purpose of the microgravity experiments includes differentiating among proposed mechanisms contributing to detachment, and confirming or refining our understanding of the detachment mechanism. Because large contact angle are critical to detachment, sessile drop measurements were used to determine the contact angles as a function of temperature and composition for a large number of substrates made of potential ampoule materials. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases from 150 deg to an equilibrium value of 117 deg (Ge) or from 129 deg to an equilibrium value of 100 deg (GeSi) over the duration of the experiment. The nature and extent of detachment is determined by using profilometry in conjunction with optical and electron microscopy. The stability of detachment has been analyzed, and an empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed. Results in this presentation will show that we have established the effects on detachment of ampoule material, pressure difference above and below the melt, and silicon concentration; samples that are nearly completely detached can be grown repeatedly in pBN.

Experiments on the Motion of Drops on a Horizontal Solid Surface due to a Wettability Gradient

NASA Technical Reports Server (NTRS)

Moumen, Nadjoua; Subramanian, R, Shankar; MLaughlin, john B.

2006-01-01

Results from experiments performed on the motion of drops of tetraethylene glycol in a wettability gradient present on a silicon surface are reported and compared with predictions from a recently developed theoretical model. The gradient in wettability was formed by exposing strips cut from a silicon wafer to decyltrichlorosiland vapors. Video images of the drops captured during the experiments were subsequently analyzed for drop size and velocity as functions of position along the gradient. In separate experiments on the same strips, the static contact angle formed by small drops was measured and used to obtain the local wettability gradient to which a drop is subjected. The velocity of the drops was found to be a strong function of position along the gradient. A quasi-steady theoretical model that balances the local hydrodynamic resistance with the local driving force generally describes the observations; possible reasons for the remaining discrepancies are discussed. It is shown that a model in which the driving force is reduced to accomodate the hysteresis effect inferred from the data is able to remove most of the discrepancy between the observed and predicted velocities.

A deformable surface model for real-time water drop animation.

PubMed

Zhang, Yizhong; Wang, Huamin; Wang, Shuai; Tong, Yiying; Zhou, Kun

2012-08-01

A water drop behaves differently from a large water body because of its strong viscosity and surface tension under the small scale. Surface tension causes the motion of a water drop to be largely determined by its boundary surface. Meanwhile, viscosity makes the interior of a water drop less relevant to its motion, as the smooth velocity field can be well approximated by an interpolation of the velocity on the boundary. Consequently, we propose a fast deformable surface model to realistically animate water drops and their flowing behaviors on solid surfaces. Our system efficiently simulates water drop motions in a Lagrangian fashion, by reducing 3D fluid dynamics over the whole liquid volume to a deformable surface model. In each time step, the model uses an implicit mean curvature flow operator to produce surface tension effects, a contact angle operator to change droplet shapes on solid surfaces, and a set of mesh connectivity updates to handle topological changes and improve mesh quality over time. Our numerical experiments demonstrate a variety of physically plausible water drop phenomena at a real-time rate, including capillary waves when water drops collide, pinch-off of water jets, and droplets flowing over solid materials. The whole system performs orders-of-magnitude faster than existing simulation approaches that generate comparable water drop effects.

Preliminary drop-tower experiments on liquid-interface geometry in partially filled containers at zero gravity

NASA Technical Reports Server (NTRS)

Smedley, G.

1990-01-01

Plexiglass containers with rounded trapezoidal cross sections were designed and built to test the validity of Concus and Finn's existence theorem (1974, 1983) for a bounded free liquid surface at zero gravity. Experiments were carried out at the NASA Lewis two-second drop tower. Dyed ethanol-water solutions and three immiscible liquid pairs, with one liquid dyed, were tested. High-speed movies were used to record the liquid motion. Liquid rose to the top of the smaller end of the containers when the contact angle was small enough, in agreement with the theory. Liquid interface motion demonstrated a strong dependence on physical properties, including surface roughness and contamination.

Numerical study of drop spreading on a flat surface

NASA Astrophysics Data System (ADS)

Wang, Sheng; Desjardins, Olivier

2017-11-01

In this talk, we perform a numerical study of a droplet on a flat surface with special emphasis on capturing the spreading dynamics. The computational methodology employed is tailored for simulating large-scale two-phase flows within complex geometries. It combines a conservative level-set method to capture the liquid-gas interface, a conservative immersed boundary method to represent the solid-fluid interface, and a sub-grid curvature model at the triple-point to implicitly impose the contact angle of the liquid-gas interface. The performance of the approach is assessed in the inertial droplet spreading regime, the viscous spreading regime of high viscosity drops, and with the capillary oscillation of low viscosity droplets.

Imaging electron flow from collimating contacts in graphene

NASA Astrophysics Data System (ADS)

Bhandari, S.; Lee, G. H.; Watanabe, K.; Taniguchi, T.; Kim, P.; Westervelt, R. M.

2018-04-01

The ballistic motion of electrons in graphene opens exciting opportunities for electron-optic devices based on collimated electron beams. We form a collimating contact in a hBN-encapsulated graphene hall bar by adding zigzag contacts on either side of an electron emitter that absorb stray electrons; collimation can be turned off by floating the zig-zag contacts. The electron beam is imaged using a liquid-He cooled scanning gate microscope (SGM). The tip deflects electrons as they pass from the collimating contact to a receiving contact on the opposite side of the channel, and an image of electron flow can be made by displaying the change in transmission as the tip is raster scanned across the sample. The angular half width Δθ of the electron beam is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. The images reveal that the electron flow from the collimating contact drops quickly at B  =  0.05 T when the electron orbits miss the receiving contact. The flow for the non-collimating case persists longer, up to B  =  0.19 T, due to the broader range of entry angles. Ray-tracing simulations agree well with the experimental images. By fitting the fields B at which the magnitude of electron flow drops in the experimental SGM images, we find Δθ  =  9° for electron flow from the collimating contact, compared with Δθ  =  54° for the non-collimating case.

Basic surface properties of mononuclear cells from Didelphis marsupialis.

PubMed

Nacife, V P; de Meirelles, M de N; Silva Filho, F C

1998-01-01

The electrostatic surface charge and surface tension of mononuclear cells/monocytes obtained from young and adult marsupials (Didelphis marsupialis) were investigated by using cationized ferritin and colloidal iron hydroxyde, whole cell electrophoresis, and measurements of contact angles. Anionic sites were found distributed throughout the entire investigated cell surfaces. The results revealed that the anionic character of the cells is given by electrostatic charges corresponding to -18.8 mV (cells from young animals) and -29.3 mV (cells from adult animals). The surface electrostatic charge decreased from 10 to 65.2% after treatment of the cells with each one of trypsin, neuraminidase and phospholipase C. The hydrophobic nature of the mononuclear cell surfaces studied by using the contact angle method revealed that both young and adult cells possess cell surfaces of high hidrofilicity since the angles formed with drops of saline water were 42.5 degrees and 40.8 degrees, respectively. Treatment of the cells with trypsin or neuraminidase rendered their surfaces more hydrophobic, suggesting that sialic acid-containing glycoproteins are responsible for most of the hydrophilicity observed in the mononuclear cell surfaces from D. marsupialis.

The Lower Extremity Biomechanics of Single- and Double-Leg Stop-Jump Tasks

PubMed Central

2011-01-01

The anterior cruciate ligament (ACL) injury is a common occurrence in sports requiring stop-jump tasks. Single- and double-leg stop-jump techniques are frequently executed in sports. The higher risk of ACL injury in single-leg drop landing task compared to a double-leg drop landing task has been identified. However the injury bias between single- and double-leg landing techniques has not been investigated for stop-jump tasks. The purpose of this study was to determine the differences between single- and double-leg stop-jump tasks in knee kinetics that were influenced by the lower extremity kinematics during the landing phase. Ground reaction force, lower extremity kinematics, and knee kinetics data during the landing phase were obtained from 10 subjects performing single- and double-leg stop-jump tasks, using motion-capture system and force palates. Greater peak posterior and vertical ground reaction forces, and peak proximal tibia anterior and lateral shear forces (p < 0.05) during landing phase were observed of single-leg stop-jump. Single-leg stop-jump exhibited smaller hip and knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground (p < 0.05). We found smaller peak hip and knee flexion angles (p < 0.05) during the landing phase of single-leg stop-jump. These results indicate that single-leg landing may have higher ACL injury risk than double-leg landing in stop-jump tasks that may be influenced by the lower extremity kinematics during the landing phase. Key points Non-contact ACL injuries are more likely to occur during the single-leg stop-jump task than during the double-leg stop-jump task. Single-leg stop-jump exhibited greater peak proximal tibia anterior and lateral shear forces, and peak posterior and vertical ground reaction forces during the landing phase than the double-leg stop-jump task. Single-leg stop-jump exhibited smaller hip flexion angle, knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground. Single-leg stop-jump exhibited greater peak knee extension and valgus moment during the landing phase than the double-leg stop-jump task. Single-leg stop-jump extended the hip joint at initial foot contact with the ground. PMID:24149308

Links between nanoscale and macroscale surface properties of natural root mucilage studied by atomic force microscopy and contact angle.

PubMed

Kaltenbach, Robin; Diehl, Dörte; Schaumann, Gabriele E

2018-04-15

Soil water repellency originating from organic coatings plays a crucial role for soil hydraulics and plant water uptake. Focussing on hydrophobicity in the rhizosphere induced by root-mucilage, this study aims to explore the link between macroscopic wettability and nano-microscopic surface properties. The existing knowledge of the nanostructures of organic soil compounds and its effect on wettability is limited by the lack of a method capable to assess the natural spatial heterogeneity of physical and chemical properties. In this contribution, this task is tackled by a geostatistical approach via variogram analysis of topography and adhesion force data acquired by atomic force microscopy and macroscopic sessile drop measurements on dried films of mucilage. The results are discussed following the wetting models given by Wenzel and Cassie-Baxter. Undiluted mucilage formed homogeneous films on the substrate with contact angles >90°. For diluted samples contact angles were smaller and incomplete mucilage surface coverage with hole-like structures frequently exhibited increased adhesion forces. Break-free distances of force curves indicated enhanced capillary forces due to adsorbed water films at atmospheric RH (35 ± 2%) that promote wettability. Variogram analysis enabled a description of complex surface structures exceeding the capability of comparative visual inspection. Copyright © 2018 Elsevier Inc. All rights reserved.

Impact of drainage on wettability of fen peat-moorsh soils

NASA Astrophysics Data System (ADS)

Szajdak, L.; Szatyłowicz, J.; Brandyk, T.

2009-04-01

High water retention in peat is attributed to structural voids (macro-pores) due to the partial degradation of the structure of peat-forming plants, and molecular absorption sites (micro-pores) associated with the formation of humic substances. Water retention by the heterogeneously-structured system in peat organic matter depends on the chemical structure of solid surfaces. These naturally wet solids, if dried sufficiently, lose the ability to rewet quickly when immersed in water. The ability of peat surfaces to attract and hold water is attributed to hydrophilic functional groups which characterize the organic substances of peat. The investigations of chemical and physical properties were performed for three different peat-moorsh soils located in the Biebrza River Valley in Poland. All examined soils were used as meadow. Soil samples were taken from two depths: 5-10 cm (moorsh) and 50-80 cm (peat). Total organic carbon (TOC), dissolved organic carbon (DOC) and humic acids (HA) extracted from these samples were analysed. Also basic physical properties such as ash content and bulk density were measured. Wetting behavior of soils was quantified using water drop penetration time test (WDPT) and measured values of the soil-water contact angle using sessile drop method. The measurements were conducted on air-dry soil samples which volumetric moisture content was not exceeding 7%. The significant differences in the concentrations of TOC, DOC and properties of HA between two investigated depth of among peat and moorsh samples were observed. The measured concentrations of total organic carbon in the considered soils ranged from 37.2 to 45.6%. Generally, the decrease of total organic carbon concentration with depth of profiles was observed. The contents of dissolved organic carbon in the soils ranged from 5.3 to 19.4%. The quantities of dissolved organic carbon decreased simultaneously with E4/E6 values and with the depth of the soil profiles. For the investigated peat's, an increase of the depth is accompanied by the decrease in the degree of humification or an increase in chemical maturity of HA. The measured values of the contact angle for investigated soils were in the range from 81.4˚ to 114.3˚ what indicates their high water repellency. The WDPT was positively correlated with total organic carbon, organic matter and humic acids content while ash content, soil bulk density, pH and absorbance were correlated negatively. The highest value of correlation coefficient (statistically significant) was obtained for relation between WDPT and ash content. The soil water contact angle was less correlated with peat-moorsh soil properties in comparison with WDPT with one exception pH. The pH against the contact angle indicates tendency of increasing the contact angle with decreasing pH.

Not spreading in reverse: The dewetting of a liquid film into a single drop

PubMed Central

Edwards, Andrew M. J.; Ledesma-Aguilar, Rodrigo; Newton, Michael I.; Brown, Carl V.; McHale, Glen

2016-01-01

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet—a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction. PMID:27704042

Not spreading in reverse: The dewetting of a liquid film into a single drop.

PubMed

Edwards, Andrew M J; Ledesma-Aguilar, Rodrigo; Newton, Michael I; Brown, Carl V; McHale, Glen

2016-09-01

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting. A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet-a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. We report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes. Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, our results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.

Behavior of fluids in a weightless environment

NASA Technical Reports Server (NTRS)

Fester, D. A.; Eberhardt, R. N.; Tegart, J. R.

1977-01-01

Fluid behavior in a low-g environment is controlled primarily by surface tension forces. Certain fluid and system characteristics determine the magnitude of these forces for both a free liquid surface and liquid in contact with a solid. These characteristics, including surface tension, wettability or contact angle, system geometry, and the relationships governing their interaction, are discussed. Various aspects of fluid behavior in a low-g environment are then presented. This includes the formation of static interface shapes, oscillation and rotation of drops, coalescence, the formation of foams, tendency for cavitation, and diffusion in liquids which were observed during the Skylab fluid mechanics science demonstrations. Liquid reorientation and capillary pumping to establish equilibrium configurations for various system geometries, observed during various free-fall (drop-tower) low-g tests, are also presented. Several passive low-g fluid storage and transfer systems are discussed. These systems use surface tension forces to control the liquid/vapor interface and provide gas-free liquid transfer and liquid-free vapor venting.

THE INFLUENCE OF HIP STRENGTH ON KNEE KINEMATICS DURING A SINGLE-LEGGED MEDIAL DROP LANDING AMONG COMPETITIVE COLLEGIATE BASKETBALL PLAYERS.

PubMed

Suzuki, Hidetomo; Omori, Go; Uematsu, Daisuke; Nishino, Katsutoshi; Endo, Naoto

2015-10-01

A smaller knee flexion angle and larger knee valgus angle during weight-bearing activities have been identified as risk factors for non-contact anterior cruciate ligament (ACL) injuries. To prevent such injuries, attention has been focused on the role of hip strength in knee motion control. However, gender differences in the relationship between hip strength and knee kinematics during weight-bearing activities in the frontal plane have not been evaluated. The purpose of this study was to determine the influence of hip strength on knee kinematics in both genders during a single-legged landing task in the frontal plane. The hypotheses were that 1) subjects with a greater hip strength would demonstrate larger knee flexion and smaller knee valgus and internal rotation angles and 2) no gender differences would exist during the single-legged landing task. Forty-three Japanese collegiate basketball players (20 males, 23 females) participated in this study. Three-dimensional motion analysis was used to evaluate knee kinematics during a single-legged medial drop landing (SML). A hand-held dynamometer was used to assess hip extensor (HEXT), abductor (HAB), and external rotator (in two positions: seated position [SHER] and prone [PHER]) isometric strength. Spearman rank correlation coefficients (ρ) were determined for correlations between hip strength and knee kinematics at initial contact (IC) and peak (PK) during SML (p < 0.05). Negative correlations were observed between the knee valgus angle at IC and HEXT (ρ = -0.48, p = 0.02), HAB (ρ = -0.46, p = 0.03) and PHER (ρ = -0.44, p = 0.04) strength in females. In addition, a significant positive correlation was observed between the knee flexion angle at PK and HEXT strength (ρ = 0.61, p = 0.004) in males. Significant correlations between hip strength and knee kinematics during SML were observed in both genders. Hip strength may, therefore, play an important role in knee motion control during sports activities, suggesting that increased hip strength may help to prevent non-contact ACL injuries in athletes of both genders. Moreover, gender-specific programs may be needed to control abnormal knee motion, as the influence of hip strength on knee kinematics may differ based on gender. 3.

Highly Transparent Water-Repelling Surfaces based on Biomimetic Hierarchical Structure

NASA Astrophysics Data System (ADS)

Wooh, Sanghyuk; Koh, Jai; Yoon, Hyunsik; Char, Kookheon

2013-03-01

Nature is a great source of inspiration for creating unique structures with special functions. The representative examples of water-repelling surfaces in nature, such as lotus leaves, rose petals, and insect wings, consist of an array of bumps (or long hairs) and nanoscale surface features with different dimension scales. Herein, we introduced a method of realizing multi-dimensional hierarchical structures and water-repellancy of the surfaces with different drop impact scenarios. The multi-dimensional hierarchical structures were fabricated by soft imprinting method with TiO2 nanoparticle pastes. In order to achieve the enhanced hydrophobicity, fluorinated moieties were attached to the etched surfaces to lower the surface energy. As a result, super-hydrophobic surfaces with high transparency were realized (over 176° water contact angle), and for further investigation, these hierarchical surfaces with different drop impact scenarios were characterized by varying the impact speed, drop size, and the geometry of the surfaces.

Drop splashing: the role of surface wettability and liquid viscosity

NASA Astrophysics Data System (ADS)

Almohammadi, Hamed; Amirfazli, Alidad; -Team

2017-11-01

There are seemingly contradictory results in the literature about the role of surface wettability and drop viscosity for the splashing behavior of a drop impacting onto a surface. Motivated by such issues, we conducted a systematic experimental study where splashing behavior for a wide range of the liquid viscosity (1-100 cSt) and surface wettability (hydrophilic to hydrophobic) are examined. The experiments were performed for the liquids with both low and high surface tensions ( 20 and 72 mN/m). We found that the wettability affects the splashing threshold at high or low contact angle values. At the same drop velocity, an increase of the viscosity (up to 4 cSt) promotes the splashing; while, beyond such value, any increase in viscosity shows the opposite effect. It is also found that at a particular combination of liquid surface tension and viscosity (e.g. silicone oil, 10 cSt), an increase in the drop velocity changes the splashing to spreading. We relate such behaviors to the thickness, shape, and the velocity of the drop's lamella. Finally, to predict the splashing, we developed an empirical correlation which covers all of the previous reported data, hence clarifying the ostensible existing contradictions.

The impact of uropygial gland secretions on mechanically induced wearing of barn owl and pigeon body feathers

NASA Astrophysics Data System (ADS)

Ott, Benjamin; Müsse, Annika; Wagner, Hermann

2016-04-01

Bird feathers are remarkable structures light but yet durable providing insulation and the ability of flight. Owls are highly specialized birds of prey, widely known for their ability to y silently which is enabled by (micro-) structural specializations of the feathers. The barn owl replaces feathers less frequently in comparison to other same sized birds like pigeons, indicating a much better resistance against material fatigue of these delicate microstructures. We used axisymmetric drop shape analysis (ADSA) of water drop contact angles as a non-destructive method of characterizing wearing processes in feathers. We hypothesized that feathers become more wettable when worn. We also investigated the impact of ethanol treatment in order to remove fatty residues of the uropygial gland secretions, barn owls and pigeons use for preening, on ageing processes. Ethanol treatment resulted in a slight, but significant increase of water repellency in barn owl but not in pigeon flight feathers. Our preliminary data also suggest that the uropygial gland secretions decelerate the wearing process of the feather keratin. We observed this effect in both species, however, it was more distinct for barn owl uropygial gland secretions. The results of this study, obtained by contact angle measurements used as a non-destructive evaluation method of material fatigue, yield insights into the material fatigue of feathers and the decelerating effect of uropygial gland secretions on wear on the other hand.

Dosage variability of topical ocular hypotensive products: a densitometric assessment.

PubMed

Gaynes, Bruce I; Singa, Ramesh M; Cao, Ying

2009-02-01

To ascertain consequence of variability in drop volume obtained from multiuse topical ocular hypotensive products in terms of uniformity of product dosage. Densitometric assessment of drop volume dispensed from 2 alternative bottle positions. All except one product demonstrated a statistically significant difference in drop volume when administered at either a 45-degree or 90-degree bottle angle (Student t test, P<0.001). Product-specific drop volume ranged from a nadir of 22.36 microL to a high of 53.54 microL depending on bottle angle of administration. Deviation in drop dose was directly proportional to variability in drop volume. Variability in per drop dosage was conspicuous among products with a coefficient of variation from 1.49% to 15.91%. In accordance with drop volume, all products demonstrated a statistically significant difference in drop dose at 45-degree versus 90-degree administration angles. Drop volume was found unrelated to drop uniformity (Spearman r=0.01987 and P=0.9463). Variability and lack of uniformity in drop dosage is clearly evident among select ocular hypotensive products and is related to angle of drop administration. Erratic dosage of topical ocular hypotensive therapy may contribute in part to therapeutic failure and/or toxicity.

Wettability of eutectic NaLiCO3 salt on magnesium oxide substrates at 778 K

NASA Astrophysics Data System (ADS)

Li, Chuan; Li, Qi; Cao, Hui; Leng, Guanghui; Li, Yongliang; Wang, Li; Zheng, Lifang; Ding, Yulong

2018-06-01

We investigated the wetting behavior of a eutectic carbonate salt of NaLiCO3 on MgO substrates at an elevated temperature of 778 K by measuring contact angle with a sessile drop method. Both sintered and non-sintered MgO were prepared and used as the substrates. The sintered substrates were obtained by sintering compacted MgO powders at 500-1300 °C. For comparison purposes, a single crystal MgO substrate was also used in the work. The different sintering temperatures provided MgO substrates with different structures, allowing their effects on salt penetration and hence wettability and surface energy to be investigated. A scanning electron microscope equipped with energy dispersive spectrometry and an atomic force microscope were used to observe the morphology and structures of the MgO substrates as well as the salt penetration. The results showed a good wettability of the carbonate salt on both the sintered and non-sintered MgO substrates and the wettability depended strongly on the structure of the substrates. The non-sintered MgO substrate has a loose surface particle packing with large pores and crevices, leading to significant salt infiltration, and the corresponding contact angle was measured to be ∼25°. The contact angle of the salt on the sintered MgO substrates increased with an increase in the sintering temperature of the MgO substrate, and the contact angle of the salt on the single crystal substrate was the highest at ∼40°. The effect of the sintering temperature for making the MgO substrate could be linked to the surface energy, and the linkage is validated by the AFM measurements of the adhesion forces of the MgO substrates.

Marginal adaptation of four inlay casting waxes on stone, titanium, and zirconia dies.

PubMed

Michalakis, Konstantinos X; Kapsampeli, Vassiliki; Kitsou, Aikaterini; Kirmanidou, Yvone; Fotiou, Anna; Pissiotis, Argirios L; Calvani, Pasquale Lino; Hirayama, Hiroshi; Kudara, Yukio

2014-07-01

Different inlay casting waxes do not produce copings with satisfactory marginal accuracy when used on different die materials. The purpose of this study was to evaluate the marginal accuracy of 4 inlay casting waxes on stone dies and titanium and zirconia abutments and to correlate the findings with the degree of wetting between the die specimens and the inlay casting waxes. The inlay casting waxes tested were Starwax (Dentaurum), Unterziehwachs (Bredent), SU Esthetic wax (Schuler), and Sculpturing wax (Renfert). The marginal opening of the waxes was measured with a stereomicroscope on high-strength stone dies and on titanium and zirconia abutments. Photographic images were obtained, and the mean marginal opening for each specimen was calculated. A total of 1440 measurements were made. Wetting between die materials and waxes was determined after fabricating stone, titanium, and zirconia rectangular specimens. A calibrated pipette was used to place a drop of molten wax onto each specimen. The contact angle was calculated with software after an image of each specimen had been made with a digital camera. Collected data were subjected to a 2-way analysis of variance (α=.05). Any association between marginal accuracy and wetting of different materials was found by using the Pearson correlation. The wax factor had a statistically significant effect both on the marginal discrepancy (F=158.31, P<.001) and contact angle values (F=68.09, P<.001). A statistically significant effect of the die material factor both on the marginal adaptation (F=503.47, P<.001) and contact angle values (F=585.02, P<.001) was detected. A significant correlation between the marginal accuracy and the contact angle values (Pearson=0.881, P=.01) was also found. Stone dies provided wax copings with the best marginal integrity, followed by titanium and zirconia abutments. Unterziehwachs (Bredent), wax produced the best marginal adaptation on different die materials. A significant correlation was found between the marginal accuracy and the contact angle values. As the contact angle value became smaller, the marginal accuracy improved. All combinations of waxes and stone and titanium dies presented a high wettability. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Shear shedding of drops and the use of superhydrophobic surfaces in microgravity: PFC and ground based results

NASA Astrophysics Data System (ADS)

Milne, Andrew; Amirfazli, Alidad

In free fall, the absence of gravity poses many challenges for fluid handling systems. One such example of this is condensers. On earth, the condensed liquid is removed from the tilted condenser plate by gravity forced shedding. In microgravity, proposed solutions include the use of surfaces with gradients in wettability [1], the use of electrowetting [2], and shearing airflow [3]. In this talk, shear shedding results for a variety of surface (hydrophilic to superhydrophobic (extremely water repelling)) will be presented. Surface science and aerodynamics are used to reveal fundamental parameters controlling incipient motion for drops exposed to shearing airflow. It is found that wetting parameters such as contact angle and surface tension are very influential in determining the minimum required air velocity for drop shedding. Based on experimental results for drops of water and hexadecane (0.5-100 l) on PMMA, Teflon, and a superhydrophobic aluminum surface, an exponential function is proposed that relates the critical air velocity for shedding to the ratio of drop base length to projected area. The results for the water systems can be collapsed to a self similar curve by normalization, which also explains results from other researchers. Since shedding from superhydrophobic surfaces (SHS) is seen to be easier compared to other surfaces, the behaviour of SHS is also probed in this talk. SHS have space-based applications to shedding, self cleaning, anti-icing (spacecraft launch/re-entry), anti-fouling, fluid actuation, and decreased fluid friction. The mechanism for SHS is understood to be the existence of an air layer between large portions of the drop and solid. The first concrete visual evidence of this was gained performing a parabolic flight experiment with the ESA. Results of this experi-ment will be discussed, showing the extreme water repelling potential of SHS in microgravity, and demonstrating how the wetting behaviours seen (partial penetration, transition of wetting states, unpredicted contact angle behaviour) affect models of superhydrophobicity and the use of SHS to both space and Earth based applications. 1) Darhuber, A. A.; Troian, S. M. Annual Review of Fluid Mechanics 2005, 425-455. 2) Berthier, J.; Dubois, P.; Clementz, P.; Claustre, P.; Peponnet, C.; Fouillet, Y. Sensors and Actuators A: Physical 2007, 134, 471-479. 3) Milne, A. J. B.; Amirfazli, A. Langmuir 2009, 25, 14155-14164.

Hydraulic droplet coarsening in open-channel capillaries

NASA Astrophysics Data System (ADS)

Warren, Patrick B.

2016-11-01

Over a range of liquid-solid contact angles, an open-channel capillary with curved or angled sides can show a maximum in the Laplace pressure as a function of the filling state. Examples include double-angle wedges, grooves scored into flat surfaces, steps on surfaces, and the groove between touching parallel cylinders. The liquid in such a channel exhibits a beading instability if the channel is filled beyond the Laplace pressure maximum. The subsequent droplet coarsening takes place by hydraulic transport through the connecting liquid columns that remain in the groove. A mean-field scaling argument predicts the characteristic droplet radius R ˜t1 /7 , as a function of time t . This is confirmed by one-dimensional simulations of the coarsening kinetics. Some remarks are also made on the spreading kinetics of an isolated drop deposited in such a channel.

Evidence for phase separation of ethanol-water mixtures at the hydrogen terminated nanocrystalline diamond surface.

PubMed

Janssens, Stoffel D; Drijkoningen, Sien; Saitner, Marc; Boyen, Hans-Gerd; Wagner, Patrick; Larsson, Karin; Haenen, Ken

2012-07-28

Interactions between ethanol-water mixtures and a hydrophobic hydrogen terminated nanocrystalline diamond surface, are investigated by sessile drop contact angle measurements. The surface free energy of the hydrophobic surface, obtained with pure liquids, differs strongly from values obtained by ethanol-water mixtures. Here, a model which explains this difference is presented. The model suggests that, due to a higher affinity of ethanol for the hydrophobic surface, when compared to water, a phase separation occurs when a mixture of both liquids is in contact with the H-terminated diamond surface. These results are supported by a computational study giving insight in the affinity and related interaction at the liquid-solid interface.

Marangoni Flow Induced Evaporation Enhancement on Binary Sessile Drops.

PubMed

Chen, Pin; Harmand, Souad; Ouenzerfi, Safouene; Schiffler, Jesse

2017-06-15

The evaporation processes of pure water, pure 1-butanol, and 5% 1-butanol aqueous solution drops on heated hydrophobic substrates are investigated to determine the effect of temperature on the drop evaporation behavior. The evolution of the parameters (contact angle, diameter, and volume) during evaporation measured using a drop shape analyzer and the infrared thermal mapping of the drop surface recorded by an infrared camera were used in investigating the evaporation process. The pure 1-butanol drop does not show any thermal instability at different substrate temperatures, while the convection cells created by the thermal Marangoni effect appear on the surface of the pure water drop from 50 °C. Because 1-butanol and water have different surface tensions, the infrared video of the 5% 1-butanol aqueous solution drop shows that the convection cells are generated by the solutal Marangoni effect at any substrate temperature. Furthermore, when the substrate temperature exceeds 50 °C, coexistence of the thermal and solutal Marangoni flows is observed. By analyzing the relation between the ratio of the evaporation rate of pure water and 1-butanol aqueous solution drops and the Marangoni number, a series of empirical equations for predicting the evaporation rates of pure water and 1-butanol aqueous solution drops at the initial time as well as the equations for the evaporation rate of 1-butanol aqueous solution drop before the depletion of alcohol are derived. The results of these equations correspond fairly well to the experimental data.

A mesoscopic simulation of static and dynamic wetting using many-body dissipative particle dynamics

NASA Astrophysics Data System (ADS)

Ghorbani, Najmeh; Pishevar, Ahmadreza

2018-01-01

A many-body dissipative particle dynamics simulation is applied here to pave the way for investigating the behavior of mesoscale droplets after impact on horizontal solid substrates. First, hydrophobic and hydrophilic substrates are simulated through tuning the solid-liquid interfacial interaction parameters of an innovative conservative force model. The static contact angles are calculated on homogeneous and several patterned surfaces and compared with the predicted values by the Cassie's law in order to verify the model. The results properly evaluate the amount of increase in surface superhydrophobicity as a result of surface patterning. Then drop impact phenomenon is studied by calculating the spreading factor and dimensionless height versus dimensionless time and the comparisons made between the results and the experimental values for three different static contact angles. The results show the capability of the procedure in calculating the amount of maximum spreading factor, which is a significant concept in ink-jet printing and coating process.

Wettability and Flow Rate Impacts on Immiscible Displacement: A Theoretical Model

NASA Astrophysics Data System (ADS)

Hu, Ran; Wan, Jiamin; Yang, Zhibing; Chen, Yi-Feng; Tokunaga, Tetsu

2018-04-01

When a more viscous fluid displaces a less viscous one in porous media, viscous pressure drop stabilizes the displacement front against capillary pressure fluctuation. For this favorable viscous ratio conditions, previous studies focused on the front instability under slow flow conditions but did not address competing effects of wettability and flow rate. Here we study how this competition controls displacement patterns. We propose a theoretical model that describes the crossover from fingering to stable flow as a function of invading fluid contact angle θ and capillary number Ca. The phase diagram predicted by the model shows that decreasing θ stabilizes the displacement for θ≥45° and the critical contact angle θc increases with Ca. The boundary between corner flow and cooperative filling for θ < 45° is also described. This work extends the classic phase diagram and has potential applications in predicting CO2 capillary trapping and manipulating wettability to enhance gas/oil displacement efficiency.

Multifunctional Poro-Vascular Composites for UAV Performance Enhancement

DTIC Science & Technology

2012-07-31

structural “skin” materials with surface pores and internal vascular channels filled with an ionic- liquid whose height and shape at the pore exits is...2 V t e e q q          Intrinsic contact angle (zero voltage) Applied potential Interfacial tension (IFT) of ionic liquid Lippmann...Characterization flat plates  single (capillary) pore  PV pore arrays FTA 1000 Drop-Shape Characterization • Microscope lens : 0.5 to 12x magnification • Side

Ceramic coatings for water-repellent textiles

NASA Astrophysics Data System (ADS)

Colleoni, C.; Esposito, F.; Guido, E.; Migani, V.; Trovato, V.; Rosace, G.

2017-10-01

In recent years, ceramic coatings have been widely studied for their potential performance in many scientific and technological fields. Ceramic coatings are also used as a textile-finishing agent to impart several properties such as anti-bacterial, anti-abrasion, flame retardant. In this study, fluoro free water repellent finishings have been developed to assess the features of the silica films on the textile fabrics. The water repellency of the treated samples has been evaluated by different tests such as water contact angle, water uptake and drop test.

Scleral Buckling Using a Non-contact Wide-Angle Viewing System with a 25-Gauge Chandelier Endoilluminator.

PubMed

Jo, Jaehyuck; Moon, Byung Gil; Lee, Joo Yong

2017-12-01

To report the outcome of scleral buckling using a non-contact wide-angle viewing system with a 25-gauge chandelier endoilluminator. Retrospective analyses of medical records were performed for 17 eyes of 16 patients with primary rhegmatogenous retinal detachment (RRD) without proliferative vitreoretinopathy who had undergone conventional scleral buckling with cryoretinopexy using the combination of a non-contact wide-angle viewing system and chandelier endoillumination. The patients were eight males and five females with a mean age of 26.8 ± 10.2 (range, 11 to 47) years. The mean follow-up period was 7.3 ± 3.1 months. Baseline best-corrected visual acuity was 0.23 ± 0.28 logarithm of the minimum angle of resolution units. Best-corrected visual acuity at the final visit showed improvement (0.20 ± 0.25 logarithm of the minimum angle of resolution units), but the improvement was not statistically significant (p = 0.722). As a surgery-related complication, there was vitreous loss at the end of surgery in one eye. As a postoperative complication, increased intraocular pressure (four cases) and herpes simplex epithelial keratitis (one case) were controlled postoperatively with eye drops. One case of persistent RRD after primary surgery needed additional vitrectomy, and the retina was postoperatively attached. Scleral buckling with chandelier illumination as a surgical technique for RRD has the advantages of relieving the surgeon's neck pain from prolonged use of the indirect ophthalmoscope and sharing the surgical procedure with another surgical team member. In addition, fine retinal breaks that are hard to identify using an indirect ophthalmoscope can be easily found under the microscope by direct endoillumination. © 2017 The Korean Ophthalmological Society

Effect of C-implantation on Nerve-Cell Attachment to Polystyrene Films

NASA Astrophysics Data System (ADS)

Sommani, Piyanuch; Tsuji, Hiroshi; Kitamura, Tsuyoshi; Hattori, Mitsutaka; Yamada, Tetsuya; Sato, Hiroko; Gotoh, Yasuhito; Ishikawa, Junzo

The surfaces of the polystyrene films spin-coated on glass were modified by carbon negative-ion implantation with various ion doses from 1×1014 to 3×1016 ions/cm2 at 5 and 10 keV. The implantation conditions with and without a pattering mask were for investigation of the cell-attachment properties and for evaluation of surface physical properties of contact angle, respectively. The contact angles of modified surface were investigated by pure water drop and air bubble method. The lowest angle value of the implanted films at 5 and 10 keV were approximately 72° at 3×1015 ions/cm2 after dipping in the de-ionized water for 2 hours. The lowering of contact angles on C-implanted surfaces when increase the ion dose is due to formation of the OH and C-O bonds. Nerve-cell-attachment properties of modified surface were investigated by the nerve-like cell of rat adrenal pheochromocytoma (PC12h) in vitro. After 2 days culture of the PC12h cells, no cells attached on the polystyrene films implanted with low ion dose from 1×1014 to 3×1014 ions/cm2. On the polystyrene films implanted with the dose order of 1015 ions/cm2, the cells selectively attached only on the implanted region. Whereas on the surfaces implanted with high dose such as 1×1016 and 3×1016 ions/cm2 mostly cells attached on the implanted region, and some attached on the unimplanted region, as well as cells were abnormal in shape and large size. Therefore, the suitable dose implantation for the selective-attachment of nerve-cells on the polystyrene films implanted at 5 and 10 keV were obtained around the dose order of 1015 ions/cm2, and the best condition for the selective attachment properties was at 3×1015 ions/cm2 corresponding to the lowest contact angle.

Controlling the Transient Interface Shape and Deposition Profile Left by Desiccation of Colloidal Droplets on Multiple Polymer Surfaces

NASA Astrophysics Data System (ADS)

Dunning, Peter David

A colloidal suspension is a small constituent of insoluble solid particles suspended in a liquid medium. Control over the wetting, evaporation, and deposition patterns left by colloidal suspensions is valuable in many biological, medical, industrial, and agricultural applications. Understanding the governing principles of wetting and evaporative phenomena of these colloidal suspensions may lead to greater control over resultant deposition patterns. Perhaps the most familiar pattern forms when an initially heterogeneous colloidal suspension leaves a dark ring pattern at the edge of a drop. This pattern is referred to as a coffee-stain and it can be seen from dried droplets of spilled coffee. This coffee-stain effect was first investigated by Deegan et. al. who discovered that these patterns occur when outward radial flows driven by evaporation at the triple contact line dominate over other effects. While the presence of coffee-stain patterns is undesirable in many printing and medical diagnostic processes, it can also be advantageous in the production of low cost transparent conductive films, the deposition of metal vapor, and the manipulation of biological structures. Controlling the interactions between the substrate, liquid, vapor, and particles can lead to control over the size and morphology of evaporative deposition patterns left by aqueous colloidal suspensions. Several methods have been developed to control the evaporation of colloidal suspensions to either suppress or enhance the coffee stain effect. Electrowetting on Dielectric (EWOD) is one promising method that has been used to control colloidal depositions by applying either an AC or DC electric field. EWOD actuation has the potential to dynamically control colloidal deposition left by desiccated droplets to either suppress or enhance the coffee stain effect. It may also allow for independent control of the fluidic interface and deposition of particles via electrowetting and electrokinetic forces. Implementation of this technique requires that the colloidal droplet be separated from the active electrode by a dielectric layer to prevent electrolysis. A variety of polymer layers have been used in EWOD devices for a variety of applications. In applications that involve desiccation of colloidal suspensions, the material for this layer should be chosen carefully as it can play an important role in the resulting deposition pattern. An experimental method to monitor the transient evolution of the shape of an evaporating colloidal droplet and optically quantify the resultant deposition pattern is presented. Unactuated colloidal suspensions will be desiccated on a variety of substrates commonly used in EWOD applications. Transient image profiles and particle deposition patterns are examined for droplets containing fluorescent micro-particles. Qualitative and quantitative comparisons of these results will be used to compare multiple different cases in an effort to provide insight into the effects of polymer selection on the drying dynamics and resultant deposition patterns of desiccated colloidal materials. It was found that the equilibrium and receding contact angles between the surface and the droplet play a key role in the evaporation dynamics and the resulting deposition patterns left by a desiccated colloidal suspension. The equilibrium contact angle controls the initial contact diameter for a droplet of a given volume. As a droplet on a surface evaporates, the evolution of the interface shape and the contact diameter can generally be described by three different regimes. The Constant Contact Radius (CCR) regime occurs when the contact line is pinned while the contact angle decreases. The Constant Contact Angle (CCA) regime occurs when the contact line recedes while the contact angle remains constant. The Mixed regime occurs when the contact radius and angle both reduce over time. The presence of the CCA regime allows the contact line to recede creating a more uniform deposition. However, not all droplets move into the CCA regime. Some remain in the CCR regime creating a coffee-stain pattern. In order to transition into the CCA regime, the dynamic contact angle of the droplet must be reduced to an angle close to the receding contact angle. Transient interface shapes and deposition patterns were examined on four surfaces: (i) Glass, (ii) Kapton HN polyimide tape, (iii) SU-8 3005, and (iv) Teflon AF. Glass has a low equilibrium contact angle and a very low receding contact angle resulting in a large uniform coffee-stain deposition. Kapton HN and SU-8 3005 have similar equilibrium contact angles that result in similar initial contact diameters. However, Kapton HN pins at that initial diameter due to a low receding contact angle producing a smaller more intense coffee-stain. SU-8 3005 has a large receding contact angle that allows for the transition into the CCA regime which results in a smaller, more uniform, and more intense spot. Teflon AF has the largest equilibrium and receding contact angle producing the smallest, most uniform, and most intense spot. Results presented here suggest that a lower receding contact angle is beneficial in areas where the coffee-stain effect needs to be enhanced while a larger receding contact angle is beneficial in areas where the coffee-stain needs to be suppressed. Preliminary results are also presented examining droplets actuated via AC electrowetting to examine the effect of electrode geometry and applied voltage on electrowetting behavior and colloidal depositions in these cases. It was found that the Young-Lippmann equation needs to be modified to satisfy the modified capacitance per unit area of a system with different electrode geometries.

An optimized microstructure to minimizing in-plane and through-plane pressure drops of fibrous materials: Counter-intuitive reduction of gas diffusion layer permeability with porosity

NASA Astrophysics Data System (ADS)

Sadeghifar, Hamidreza

2018-05-01

The present study experimentally investigates the realistic functionality of in-plane and through-plane pressure drops of layered fibrous media with porosity, fiber diameter, fiber spacing, fiber-fiber angles and fiber-flow angles. The study also reveals that pressure drop may increase with porosity and fiber diameter under specific circumstances. This counter-intuitive point narrows down the validity range of widely-used permeability-porosity-diameter models or correlations. It is found that, for fibrous materials, the most important parameter that impacts the in-plane pressure drop is not their porosities but the number of fibers extended in the flow direction. It is also concluded that in-plane pressure drop is highly dependent upon the flow direction (fiber-flow angles), especially at lower porosities. Contrary to in-plane pressure drop, through-plane pressure drop is a weak function of fiber-fiber angles but is strongly impacted by fiber spacing, especially at lower porosities. At a given porosity, low through-plane pressure drops occur if fiber spacing does not change practically from one layer to another. Through-plane pressure drop also, insignificantly, increases with the intersecting angles between fibers. An optimized microstructure of fibrous media resulting in minimal in-plane and through-plane pressure drops is also offered for the first time in this work.

Spreading of an inkjet droplet on a solid surface with a controlled contact angle at low Weber and Reynolds numbers.

PubMed

Son, Yangsoo; Kim, Chongyoup; Yang, Doo Ho; Ahn, Dong June

2008-03-18

Even though the inkjet technology has been recognized as one of the most promising technologies for electronic and bio industries, the full understanding of the dynamics of an inkjet droplet at its operating conditions is still lacking. In this study, the normal impact of water droplets on solid substrates was investigated experimentally. The size of water droplets studied here was 46 microm and was much smaller than the most of the previous studies on drop impact. The Weber number (We) and Reynolds number (Re) were 0.05-2 and 10-100, respectively, and the Ohnesorge number was fixed at 0.017. The wettability of the solid substrate was varied by adsorbing a self-assembled monolayer of octadecyltrichlorosilane followed by the exposure to UV-ozone plasma. The impact scenarios for low We impacts were found to be qualitatively different from the high to moderate We impacts. Neither the development of a thin film and lamella under the traveling sphere nor the entrapment of small bubbles was observed. The dynamics of droplet impact at the conditions studied here is found to proceed under the combined influences of inertia, surface tension, and viscosity without being dominated by one specific mechanism. The maximum spreading factor (beta), the ratio of the diameter of the wetted surface and the drop diameter before impact, was correlated well with the relationship ln beta=0.090 ln We/(fs-cos theta)+0.151 for three decades of We/(fs-cos theta), where theta is the equilibrium contact angle, and fs is the ratio between the surface areas contacting the air and the solid substrate. The result implies that the final shape of the droplet is determined by the surface phenomenon rather than fluid mechanical effects.

Impact of pressure and temperature on CO2-brine-mica contact angles and CO2-brine interfacial tension: Implications for carbon geo-sequestration.

PubMed

Arif, Muhammad; Al-Yaseri, Ahmed Z; Barifcani, Ahmed; Lebedev, Maxim; Iglauer, Stefan

2016-01-15

Precise characterization of wettability of CO2-brine-rock system and CO2-brine interfacial tension at reservoir conditions is essential as they influence capillary sealing efficiency of caprocks, which in turn, impacts the structural and residual trapping during CO2 geo-sequestration. In this context, we have experimentally measured advancing and receding contact angles for brine-CO2-mica system (surface roughness ∼12nm) at different pressures (0.1MPa, 5MPa, 7MPa, 10MPa, 15MPa, 20MPa), temperatures (308K, 323K, and 343K), and salinities (0wt%, 5wt%, 10wt%, 20wt% and 30wt% NaCl). For the same experimental matrix, CO2-brine interfacial tensions have also been measured using the pendant drop technique. The results indicate that both advancing and receding contact angles increase with pressure and salinity, but decrease with temperature. On the contrary, CO2-brine interfacial tension decrease with pressure and increase with temperature. At 20MPa and 308K, the advancing angle is measured to be ∼110°, indicating CO2-wetting. The results have been compared with various published literature data and probable factors responsible for deviations have been highlighted. Finally we demonstrate the implications of measured data by evaluating CO2 storage heights under various operating conditions. We conclude that for a given storage depth, reservoirs with lower pressures and high temperatures can store larger volumes and thus exhibit better sealing efficiency. Copyright © 2015 Elsevier Inc. All rights reserved.

Testing the performance of superhydrophobic aluminum surfaces.

PubMed

Ruiz-Cabello, F Javier Montes; Ibáñez-Ibáñez, Pablo F; Gómez-Lopera, J Francisco; Martínez-Aroza, José; Cabrerizo-Vílchez, Miguel; Rodríguez-Valverde, Miguel A

2017-12-15

The analysis of wetting properties of superhydrophobic surfaces may be a difficult task due to the restless behavior of drops on this type of surfaces and the limitations of goniometry for high contact angles. A method to validate the performance of superhydrophobic surfaces, rather than standard goniometry, is required. In this work, we used bouncing drop dynamics as a useful tool to predict the water repellency of different superhydrophobic surfaces. From bouncing drop experiments conducted over a wide range of superhydrophobic surfaces, we found that those surfaces with a proper roughness degree and homogeneous chemical composition showed higher water-repellency. We also conducted a drop condensation study at saturating conditions aimed to determine whether there is direct correlation between water repellency and condensation delay. We found that the drop condensation process is strongly related to the surface topography, as well as the intrinsic wettability. The condensation is promoted on rough surfaces but it is delayed on intrinsically hydrophobic surfaces. However, the differences found in condensation delay between the superhydrophobic surfaces explored in this study cannot be justified by their chemical homogeneity nor their efficiency as water repellent surfaces, separately. Copyright © 2017 Elsevier Inc. All rights reserved.

Viscoelastic drops moving on hydrophilic and superhydrophobic surfaces.

PubMed

Xu, H; Clarke, A; Rothstein, J P; Poole, R J

2018-03-01

So-called "superhydrophobic" surfaces are strongly non-wetting such that fluid droplets very easily roll off when the surface is tilted. Our interest here is in understanding if this is also true, all else held equal, for viscoelastic fluid drops. We study the movement of Newtonian and well-characterised constant-viscosity elastic liquids when various surfaces, including hydrophilic (smooth glass), weakly hydrophobic (embossed polycarbonate) and superhydrophobic surfaces (embossed PTFE), are impulsively tilted. Digital imaging is used to record the motion and extract drop velocity. Optical and SEM imaging is used to probe the surfaces. In comparison with "equivalent" Newtonian fluids (same viscosity, density surface tension and contact angles), profound differences for the elastic fluids are only observed on the superhydrophobic surfaces: the elastic drops slide at a significantly reduced rate and complex branch-like patterns are left on the surface by the drop's wake including, on various scales, beads-on-a-string-like phenomena. The strong viscoelastic effect is caused by stretching filaments of fluid from isolated islands, residing at pinning sites on the surface pillars, of order ∼30 µm in size. On this scale, the local strain rates are sufficient to extend the polymer chains, locally increasing the extensional viscosity of the solution, retarding the drop. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Viscous drop collisions on surfaces of varying wettability

NASA Astrophysics Data System (ADS)

Bolleddula, Daniel; Berchielli, Al; Aliseda, Alberto

2010-11-01

We present an experimental study of increasingly viscous acetone rich and Newtonian equivalent liquid drops colliding on surfaces of varying wettability. This class of liquids applies directly to spray coating processes in pharmaceutical industries. The results from this study will elucidate the physics in a regime where resisting viscous forces and the restoring forces of capillarity are balanced, Oh˜ 1. Early spreading dynamics τ=Ut/D 1 indicate negligible dependence on contact angles while longer times demonstrate deviations from Tanner's law, D˜t^1/10. We will compare our results with recent theory to demonstrate the feasibility of modelling complex rheology spreading characteristics over short and long time scales. Preliminary results indicate an intermediate spreading regime following the inertial phase where the diameter, D˜t^n with 1/7 < n < 1/5.

Fabrication of Super-Hydrophobic Microchannels via Strain-Recovery Deformations of Polystyrene and Oxygen Reactive Ion Etch.

PubMed

Chakraborty, Anirban; Xiang, Mingming; Luo, Cheng

2013-08-19

In this article, we report a simple approach to generate micropillars (whose top portions are covered by sub-micron wrinkles) on the inner surfaces of polystyrene (PS) microchannels, as well as on the top surface of the PS substrate, based on strain-recovery deformations of the PS and oxygen reactive ion etch (ORIE). Using this approach, two types of micropillar-covered microchannels are fabricated. Their widths range from 118 μm to 132 μm, depths vary from 40 μm to 44 μm, and the inclined angles of their sidewalls are from 53° to 64°. The micropillars enable these microchannels to have super-hydrophobic properties. The contact angles observed on the channel-structured surfaces are above 162°, and the tilt angles to make water drops roll off from these channel-structured substrates can be as small as 1°.

Wetting of TiC by Al-Cu alloys and interfacial characterization.

PubMed

Contreras, A

2007-07-01

The wetting behavior and the interfacial reactions that occurred between molten Al-Cu alloys (1, 4, 8, 20, 33, and 100 wt% Cu) and solid TiC substrates were studied by the sessile drop technique in the temperature range of 800-1130 degrees C. The effect of wetting behavior on the interfacial reaction layer was studied. All the Al-Cu alloys react with TiC at the interface forming an extensive reaction layer. The interface thickness varied with the samples, and depends on the temperature, chemical composition of the alloy and the time of the test. Wetting increases with increasing concentration of copper in the Al-Cu alloy at 800 and 900 degrees C. In contrast, at higher temperature such as 1000 degrees C wetting decreases with increasing copper content. The spreading kinetics and the work of adhesion were evaluated. The high values of activation energies indicated that spreading is not a simple viscosity controlled phenomenon but is a chemical reaction process. The spreading of the aluminum drop is observed to occur according to the formation of Al4C3, CuAl2O4, CuAl2, TiCux mainly, leading to a decreases in the contact angle. As the contact angle decreases the work of adhesion increases with increasing temperature. Al-Cu/TiC assemblies showed cohesive fracture corresponding to a strong interface. However, using pure Cu the adhesion work is poor, and the percentage of cohesion work is also too low (27-34%).

Thermal stability of Ag, Al, Sn, Pb, and Hg films reinforced by 2D (C, Si) crystals and the formation of interfacial fluid states in them upon heating. MD experiment

NASA Astrophysics Data System (ADS)

Polukhin, V. A.; Kurbanova, E. D.

2016-02-01

Molecular dynamics simulation is used to study the thermal stability of the interfacial states of metallic Al, Ag, Sn, Pb, and Hg films (i.e., the structural elements of superconductor composites and conducting electrodes) reinforced by 2D graphene and silicene crystals upon heating up to disordering and to analyze the formation of nonautonomous fluid pseudophases in interfaces. The effect of perforation defects in reinforcing 2D-C and 2D-Si planes with passivated edge covalent bonds on the atomic dynamics is investigated. As compared to Al and Ag, the diffusion coefficients in Pd and Hg films increase monotonically with temperature during thermally activated disordering processes, the interatomic distances decrease, the sizes decrease, drops form, and their density profile grows along the normal. The coagulation of Pb and Hg drops is accompanied by a decrease in the contact angle, the reduction of the interface contact with graphene, and the enhancement of its corrugation (waviness).

Microscopic treatment of a barrel drop on fibers and nanofibers.

PubMed

Berim, Gersh O; Ruckenstein, Eli

2005-06-15

The microscopic approach of Berim and Ruckenstein (J. Phys. Chem. B 108 (2004) 19330, 19339) regarding the shape and stability of a liquid drop on a planar bare solid surface is extended to a liquid barrel drop on the bare surface of a solid cylinder (fiber) of arbitrary radius. Assuming the interaction potentials of the liquid molecules between themselves and with the molecules of the solid of the London-van der Waals form, the potential energy of a liquid molecule with an infinitely long fiber was calculated analytically. A differential equation for the drop profile was derived by the variational minimization of the total potential energy of the drop by taking into account the structuring of the liquid near the fiber. This equation was solved in quadrature and the shape and stability of the barrel drop were analyzed as functions of the radius of the fiber and the microscopic contact angle theta(0) which the drop profile makes with the surface of the fiber. The latter angle is dependent on the fiber radius and on the microscopic parameters of the model (strength of the intermolecular interactions, densities of the liquid and solid phases, hard core radii, etc.). Expressions for the evaluation of the microcontact angle from experimentally measurable characteristics of the drop profile (height, length, volume, location of inflection point) are obtained. All drop characteristics, such as stability, shape, are functions of theta(0) and a certain parameter a which depends on the model parameters. In particular, the range of drop stability consists of three domains in the plane theta(0)-a, separated by two critical curves a=a(c)(theta(0)) and a=a(c1)(theta(0)) [a(c)(theta(0))h(m1) cannot exist, whereas in the third domain (between those curves) the drop can have values of h(m) either smaller than h(m1) or larger than h(m2), where h(m2)>h(m1) is a second critical height. For sufficiently large fiber radii, R(f)1 >/= microm, the critical curves almost coincide and only two domains, the first and the second, remain. The smaller the radius, the larger is the difference between the critical curves and the larger is the second domain of drop stability. The shape of the drop depends on whether the point (theta(0),a) on the theta(0)-a plane is far from the critical curve or near it. In the first case the drop profile has generally a large circular part, while in the second case the shape is either almost planar or contains a long manchon that is similar to a film on the fiber.

Unstable bidimensional grids of liquid filaments: Drop pattern after breakups

NASA Astrophysics Data System (ADS)

Diez, Javier; Cuellar, Ingrith; Ravazzoli, Pablo; Gonzalez, Alejandro

2017-11-01

A rectangular grid formed by liquid filaments on a partially wetting substrate evolves in a series of breakups leading to arrays of drops with different shapes distributed in a rather regular bidimensional pattern. Our study is focused on the configuration produced when two long parallel filaments of silicone oil, which are placed upon a glass substrate previously coated with a fluorinated solution, are crossed perpendicularly by another pair of long parallel filaments. A remarkable feature of this kind of grids is that there are two qualitatively different types of drops. While one set is formed at the crossing points, the rest are consequence of the breakup of shorter filaments formed between the crossings. Here, we analyze the main geometric features of all types of drops, such as shape of the footprint and contact angle distribution along the drop periphery. The formation of a series of short filaments with similar geometric and physical properties allows us to have simultaneously quasi identical experiments to study the subsequent breakups. We develop a simple hydrodynamic model to predict the number of drops that results from a filament of given initial length and width. This model is able to yield the length intervals corresponding to a small number of drops. We acknowledge support from CONICET-Argentina (Grant PIP 844/2012) and ANPCyT-Argentina (Grant PICT 931/2012).

Phase-field simulation of counter-current spontaneous imbibition in a fractured heterogeneous porous medium

NASA Astrophysics Data System (ADS)

Rokhforouz, M. R.; Akhlaghi Amiri, H. A.

2017-06-01

Spontaneous imbibition is well-known to be one of the most effective processes of oil recovery in fractured reservoirs. However, the detailed pore-scale mechanisms of the counter-current imbibition process and the effects of different fluid/rock parameters on this phenomenon have not yet been deeply addressed. This work presents the results of a new pore-level numerical study of counter-current spontaneous imbibition, using coupled Cahn-Hilliard phase field and Navier-Stokes equations, solved by a finite element method. A 2D fractured medium was constructed consisting of a nonhomogeneous porous matrix, in which the grains were represented by an equilateral triangular array of circles with different sizes and initially saturated with oil, and a fracture, adjacent to the matrix, initially saturated with water and supported by low rate water inflow. Through invasion of water into the matrix, oil drops were expelled one by one from the matrix to the fracture, and in the matrix, water progressed by forming capillary fingerings, with characteristics corresponding to the experimental observations. The effects of wettability, viscosity ratio, and interfacial tension were investigated. In strongly water-wet matrix, with grain contact angles of θ < π/8, different micro-scale mechanisms were successfully captured, including oil film thinning and rupture, fluids' contact line movement, water bridging, and oil drop detachment. It was notified that there was a specific grain contact angle for this simulated model, θ = π/4, above it, matrix oil recovery was negligible by imbibition, while below it, the imbibition rate and oil recovery were significantly increased by decreasing the contact angle. In simulated mixed wet models, water, coming from the fracture, just invaded the neighboring water-wet grains; the water front was stopped moving as it met the oil-wet grains or wide pores/throats. Increasing water-oil interfacial tension, in the range of 0.005-0.05 N/m, resulted in both higher rate of imbibition and higher ultimate oil recovery. Changing the water-oil viscosity ratio (M), in the range of 0.1-10, had a negligible effect on the imbibition rate, while due to co-effects of capillary fingering and viscous mobility ratio, the model with M = 1 had relatively higher ultimate oil recovery.

Frontal plane landing mechanics in high-arched compared with low-arched female athletes.

PubMed

Powell, Douglas W; Hanson, Nicholas J; Long, Benjamin; Williams, D S Blaise

2012-09-01

To examine ground reaction forces (GRFs); frontal plane hip, knee, and ankle joint angles; and moments in high-arched (HA) and low-arched (LA) athletes during landing. Experimental study. Controlled research laboratory. Twenty healthy female recreational athletes (10 HA and 10 LA). Athletes performed 5 barefoot drop landings from a height of 30 cm. Frontal plane ankle, knee, and hip joint angles (in degrees) at initial contact, peak vertical GRF, and peak knee flexion; peak ankle, knee, and hip joint moments in the frontal plane. Vertical GRF profiles were similar between HA and LA athletes (P = 0.78). The HA athletes exhibited significantly smaller peak ankle inversion angles than the LA athletes (P = 0.01) at initial contact. At peak vertical GRF, HA athletes had significantly greater peak knee (P = 0.01) and hip abduction angles than LA athletes (P = 0.02). There were no significant differences between HA and LA athletes in peak joint moments (hip: P = 0.68; knee: P = 0.71; ankle: P = 0.15). These findings demonstrate that foot type is associated with altered landing mechanics, which may underlie lower extremity injuries. The ankle-driven strategy previously reported in female athletes suggests that foot function may have a greater relationship with lower extremity injury than that in male athletes. Future research should address the interaction of foot type and gender during landing tasks.

The effect of videotape augmented feedback on drop jump landing strategy: Implications for anterior cruciate ligament and patellofemoral joint injury prevention.

PubMed

Munro, Allan; Herrington, Lee

2014-10-01

Modification of high-risk movement strategies such as dynamic knee valgus is key to the reduction of anterior cruciate ligament (ACL) and patellofemoral joint (PFJ) injuries. Augmented feedback, which includes video and verbal feedback, could offer a quick, simple and effective alternative to training programs for altering high-risk movement patterns. It is not clear whether feedback can reduce dynamic knee valgus measured using frontal plane projection angle (FPPA). Vertical ground reaction force (vGRF), two-dimensional FPPA of the knee, contact time and jump height of 20 recreationally active university students were measured during a drop jump task pre- and post- an augmented feedback intervention. A control group of eight recreationally active university students were also studied at baseline and repeat test. There was a significant reduction in vGRF (p=0.033), FPPA (p<0.001) and jump height (p<0.001) and an increase in contact time (p<0.001) post feedback in the intervention group. No changes were evident in the control group. Augmented feedback leads to significant decreases in vGRF, FPPA and contact time which may help to reduce ACL and PFJ injury risk. However, these changes may result in decreased performance. Augmented feedback reduces dynamic knee valgus, as measured via FPPA, and forces experienced during the drop jump task and therefore could be used as a tool for helping decrease ACL and PFJ injury risk prior to, or as part of, the implementation of injury prevention training programs. Copyright © 2014 Elsevier B.V. All rights reserved.

Wetting failure of hydrophilic surfaces promoted by surface roughness

PubMed Central

Zhao, Meng-Hua; Chen, Xiao-Peng; Wang, Qing

2014-01-01

Wetting failure is of vital importance to many physical phenomena, such as industrial coating and drop emission. Here we show when and how the surface roughness promotes the destabilization of a moving contact line on a hydrophilic surface. Beyond the balance of the driving force and viscous resistance where a stable wetting interface is sustained, wetting failure occurs and is modified by the roughness of the surface. The promoting effect arises only when the wetting velocity is high enough to create a gas-liquid-solid composite interface in the vicinity of the moving contact line, and it is a function of the intrinsic contact angle and proportion of solid tops. We propose a model to explain splashes of rough solid spheres impacting into liquids. It reveals a novel concept that dynamic wetting on hydrophilic rough surfaces can be similar to that on hydrophobic surfaces, and brings a new way to design surfaces with specific wetting properties. PMID:24948390

Liquid crystalline pattern formation in drying droplets of biopolymers

NASA Astrophysics Data System (ADS)

Smalyukh, Ivan; Zribi, Olena; Butler, John; Lavrentovich, Oleg; Wong, Gerard

2006-03-01

When a droplet of DNA in water dries out, a ring-like deposit is observed along the perimeter, similar to the stains in spilled drops of coffee. However, the dried ring of DNA is a self-similar birefringent pattern composed of extended molecules. We examine dynamics of the pattern formation at the droplet's rim. This gives us an insight into the underlining physics. During the major part of drying process the contact line is pinned so that DNA molecules are brought to the perimeter and extended by the radial capillary flow. Lyotropic nematic phase is formed in which highly concentrated DNA aligns along the triple line to minimize elastic energy. When the contact angle becomes small, the contact line starts to retract and the radial dilative stress causes buckling distortions at the rim which then propagate deep into the elastic liquid- crystalline medium and give rise to the pattern.

Separation of polycarbonate and acrylonitrile–butadiene–styrene waste plastics by froth flotation combined with ammonia pretreatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chong-qing; Wang, Hui, E-mail: huiwang1968@163.com; Liu, Qun

Highlights: • Ammonia treatment changes selectively floatability of PC. • The effects of ammonia on PC were investigated through contact angle and XPS. • Reactions between ammonia and PC surface make PC more hydrophilic. • PC and ABS mixtures with different particle sizes were separated effectively. - Abstract: The objective of this research is flotation separation of polycarbonate (PC) and acrylonitrile–butadiene–styrene (ABS) waste plastics combined with ammonia pretreatment. The PC and ABS plastics show similar hydrophobicity, and ammonia treatment changes selectively floatability of PC plastic while ABS is insensitive to ammonia treatment. The contact angle measurement indicates the dropping ofmore » flotation recovery of PC is ascribed to a decline of contact angle. X-ray photoelectron spectroscopy demonstrates reactions occur on PC surface, which makes PC surface more hydrophilic. Separation of PC and ABS waste plastics was conducted based on the flotation behavior of single plastic. At different temperatures, PC and ABS mixtures were separated efficiently through froth flotation with ammonia pretreatment for different time (13 min at 23 °C, 18 min at 18 °C and 30 min at 23 °C). For both PC and ABS, the purity and recovery is more than 95.31% and 95.35%, respectively; the purity of PC and ABS is up to 99.72% and 99.23%, respectively. PC and ABS mixtures with different particle sizes were separated effectively, implying that ammonia treatment possesses superior applicability.« less

Adaptation of running pattern to the drop of standard cushioned shoes: A randomised controlled trial with a 6-month follow-up.

PubMed

Malisoux, Laurent; Gette, Paul; Chambon, Nicolas; Urhausen, Axel; Theisen, Daniel

2017-08-01

While several cross-sectional studies have investigated the acute effects of shoe drop on running biomechanics, the long-term consequences are currently unknown. This study aimed to investigate if the drop of standard cushioned shoes induces specific adaptations in running technique over a six-month period in leisure-time runners. Double-blinded randomised controlled trial. The participants (n=59) received a pair of shoes with a heel-to-toe drop of 10mm (D10), 6mm (D6) or 0mm (D0) and were followed-up regarding running training over 6 months or 500km, whichever came first. Spatio-temporal variables and kinematics (foot/ground, ankle and knee joint angles) were investigated while running at preferred speed on a treadmill before and after the follow-up. The participants ran 332±178km in the study shoes between pre- and post-tests. There was no shoe version by time interaction for any of the spatio-temporal variables nor for lower limb angles at initial ground contact. A small but significant shoe drop effect was found for knee abduction at mid-stance (p=0.032), as it decreased for the D0 version (-0.3±3.1 vs. -1.3±2.6°) while it increased for the D6 (0.3±2.7 vs. 1.3±3.1°) and D10 version (-0.2±3.2 vs. 0.5±3.1°). However, none of the pairwise comparisons was significant in the post-hoc analysis. Apart from knee abduction at mid-stance, no specific adaptation in spatio-temporal variables and kinematics was found between the three shoe versions during this 6-month follow-up. Thus, shoe drop of standard cushioned shoes does not seem to influence running biomechanics in the long term. Copyright © 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Rocking and rolling: A can that appears to rock might actually roll

NASA Astrophysics Data System (ADS)

Srinivasan, Manoj; Ruina, Andy

2008-12-01

A beer bottle or soda can on a table, when slightly tipped and released, falls to an upright position and then rocks up to a somewhat opposite tilt. Superficially this rocking motion involves a collision when the flat circular base of the container slaps the table before rocking up to the opposite tilt. A keen eye notices that the after-slap rising tilt is not generally just diametrically opposite the initial tilt but is veered to one side or the other. Cushman and Duistermaat [Regular Chaotic Dyn. 11, 31 (2006)] recently noticed such veering when a flat disk with rolling boundary conditions is dropped nearly flat. Here, we generalize these rolling disk results to arbitrary axi-symmetric bodies and to frictionless sliding. More specifically, we study motions that almost but do not quite involve a face-down collision of the round container’s bottom with the tabletop. These motions involve a sudden rapid motion of the contact point around the circular base. Surprisingly, similar to the rolling disk, the net angle of motion of this contact point is nearly independent of initial conditions. This angle of turn depends simply on the geometry and mass distribution but not on the moment of inertia about the symmetry axis. We derive simple asymptotic formulas for this “angle of turn” of the contact point and check the result with numerics and with simple experiments. For tall containers (height much bigger than radius) the angle of turn is just over π and the sudden rolling motion superficially appears as a nearly symmetric collision leading to leaning on an almost diametrically opposite point on the bottom rim.

Three-dimensional trajectory analyses of two drop sizing instruments: PMS OAP and PMS FSSP

NASA Technical Reports Server (NTRS)

Norment, Hillyer G.

1988-01-01

Flow induced distortions of water drop fluxes and speeds seen by the instruments were predicted by use of three dimensional flow and trajectory calculation methods. Sensitivities were determined for the instruments, in isolation and mounted under the wing of an airplane, to: water drop diameter (2 to 1000 microns), angle of attack and free stream air speed. For the optical array probe in isolation and on the airplane at 0 deg angle of attack, flux distortions of practical consequence are not found. At 4 deg airplane angle of attack, partial flow stagnation under the uptilted wing causes significant decreases in both flux and speed for cloud size droplets. For the forward scattering spectrometer probe in isolation, only marginally significant sensitivities to free stream air speed are found, and no sensitivity is found to angle of attack. Both speed and flux of cloud size droplets are predicted to be undermeasured by from 12 to 24 percent depending on airplane angle of attack. For the wing-mounted instruments, effects of flow about the instruments themselves are found to be equal in importance to effects of flow about the airplane. Preferred orientation (canting) angles of distorted water drops are found to be functions of drop size, angle of attack and air speed.

Pinus sylvestris L. needle surface wettability parameters as indicators of atmospheric environment pollution impacts: Novel contact angle hysteresis methodology

NASA Astrophysics Data System (ADS)

Pogorzelski, Stanisław J.; Rochowski, Pawel; Szurkowski, Janusz

2014-02-01

An investigation of water contact angles (CAs), contact angle hysteresis (CAH) was carried out for 1-year to 4-year old needles (Pinus sylvestris) collected in urban (Gdansk) and rural (Karsin) locations using an original measuring technique based on the geometry of the drop on a vertical filament. Concentrations of air pollutants (SO2, NOx, C6H6, and suspended particular matter - SPM) currently considered to be most important in causing direct damage to vegetation were simultaneously monitored. A set of the surface wettability parameters: the apparent surface free energy γSV, adhesive film tension Π, work of adhesion WA, and spreading WS, were determined from CAH data using the approach developed by Chibowski (2003) to quantify the surface energetics of the needle substrata affected by aging and pollution impacts. This formalism relates the total apparent surface free energy of the solid γSV with only three measurable quantities: the surface tension of the probe liquid γLV and its advancing θA and receding θR contact angle hysteresis. Since CAH depends on the outermost wax layer surface roughness and spatial physicochemical heterogeneity of a solid surface, CA data were corrected using surface architecture profiles registered with confocal scanning laser microscopy. It was found that the roughness parameter r is significantly negatively correlated (R = -0.74) with the needle age (collected at Karsin). The needle surface aging process resulted in its surface hydrophilization (CA↓ and CAH↓ with γSV↑ and WA↑). A temporal evolution of the needles wettability was traced with the data point distribution in the 2D space of CAH plotted versus WS. The wettability parameters were closely correlated to pollutant concentrations as evidenced from Spearman's rank correlation procedure (R = 0.63-0.91; p < 0.05). The aim of the study was to validate the established CA methodology to create a new non-invasive, low-cost technique suitable for monitoring of structural changes at interfaces of biological systems.

Residual Gas Effects on Detached Solidification in Microgravity

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.; Ramakrishnan; Kota, Arun; Anand, Gaurav

2004-01-01

Our long term goal has been to make detached solidification reproducible, which requires a full understanding of the mechanisms underlying it. Our Moving Meniscus Model of steady-state detachment predicts that it depends strongly on the surface tension of the melt and the advancing contact angle with the ampoule wall. Thus, the objective of the current project was to determine the influence of residual gases on the surface tension and contact angle of molten semiconductors on typical ampoule materials. Our focus was on the influence of oxygen on indium antimonide on clean silica ("quartz"). The research was performed by three chemical engineering graduate students, the third of whom will complete his research in the summer of 2005. Originally, we had planned to use a sealed silica cell containing a zirconia electrochemical element to control the oxygen partial pressure. However, zirconia requires an operating temperature above the 530 C melting point of InSb and is difficult to form a gas-tight seal with silica. Thus, we decided instead to flow an oxygen-containing gas through the cell. A special apparatus was designed, built and perfected. A piece of InSb was placed on a horizontal silica plate in a quartz cell. High purity argon, helium or hydrogen-containing gas is passed continuously through the cell while the oxygen concentration in the effluent gas is measured. The shape of the resulting drop was used to determine contact angle and surface tension of Ga-doped and high purity InSb. Oxygen appeared to decrease the contact angle, and definitely did not increase it. The following section gives the background for the research. Section 2 summarizes the results obtained on Ga-doped InSb with relatively high oxygen concentrations. Section 3 describes recent improvements made to the apparatus and methods of analysis. Section 4 gives recent results for high-purity InSb at low oxygen concentrations. Final results will be obtained only this summer (2005). Each section has its own references.

A personal airbag system for the Orion Crew Exploration Vehicle

NASA Astrophysics Data System (ADS)

Do, Sydney; de Weck, Olivier

2012-12-01

Airbag-based methods for crew impact attenuation have been highlighted as a potential simple, lightweight means of enabling safe land-landings for the Orion Crew Exploration Vehicle, and the next generation of ballistic shaped spacecraft. To investigate the feasibility of this concept during a nominal 7.62 m/s Orion landing, a full-scale personal airbag system 24% lighter than the Orion baseline has been developed, and subjected to 38 drop tests on land. Through this effort, the system has demonstrated the ability to maintain the risk of injury to an occupant during a 7.85 m/s, 0° impact angle land-landing to within the NASA specified limit of 0.5%. In accomplishing this, the personal airbag system concept has been proven to be feasible. Moreover, the obtained test results suggest that by implementing anti-bottoming airbags to prevent direct contact between the system and the landing surface, the system performance during landings with 0° impact angles can be further improved, by at least a factor of two. Additionally, a series of drop tests from the nominal Orion impact angle of 30° indicated that severe injury risk levels would be sustained beyond impact velocities of 5 m/s. This is a result of the differential stroking of the airbags within the system causing a shearing effect between the occupant seat structure and the spacecraft floor, removing significant stroke from the airbags.

Modeling the Restraint of Liquid Jets by Surface Tension in Microgravity

NASA Technical Reports Server (NTRS)

Chato, David J.; Jacqmim, David A.

2001-01-01

An axisymmetric phase field model is developed and used to model surface tension forces on liquid jets in microgravity. The previous work in this area is reviewed and a baseline drop tower experiment selected 'for model comparison. A mathematical model is developed which includes a free surface. a symmetric centerline and wall boundaries with given contact angles. The model is solved numerically with a compact fourth order stencil on a equally spaced axisymmetric grid. After grid convergence studies, a grid is selected and all drop tower tests modeled. Agreement was assessed by comparing predicted and measured free surface rise. Trend wise agreement is good but agreement in magnitude is only fair. Suspected sources of disagreement are suspected to be lack of a turbulence model and the existence of slosh baffles in the experiment which were not included in the model.

Determining efficacy of monitoring devices on ceramic bond to resin composite

PubMed Central

Osorio, Estrella; Aguilera, Fátima S.; Osorio, Raquel; García-Godoy, Franklin; Cabrerizo-Vilchez, Miguel A.; Toledano, Manuel

2012-01-01

Objectives: This paper aims to assess the effectiveness of 3D nanoroughness and 2D microroughness evaluations, by their correlation with contact angle measurements and shear bond strength test, in order to evaluate the effect of two different acids conditioning on the bonding efficacy of a leucite-based glass-ceramic to a composite resin. Study Design: Ceramic (IPS Empress) blocks were treated as follows: 1) no treatment, 2) 37% phosphoric acid (H3PO4), 15 s, 3) 9% hydrofluoric acid (HF), 5 min. Micro- and nano-roughness were assessed with a profilometer and by means of an atomic force microscopy (AFM). Water contact angle (CA) measurements were determined to assess wettability of the ceramic surfaces with the asixymetric drop shape analysis contact diameter technique. Shear bond strength (SBS) was tested to a resin composite (Z100) with three different adhesive systems (Scotchbond Multipurpose Plus, Clearfil New Bond, ProBOND). Scanning electron microscopy (SEM) images were performed. Results: Nanoroughness values assessed in 50x50 μm areas were higher for the HF group, these differences were not detected by profilometric analysis. HF treatment created the nano- roughest surfaces and the smallest CA (p<0.05), producing the highest SBS to the composite resin with all tested adhesive systems (p<0.05). No differences existed between the SBS produced by the adhesive systems evaluated with any of the surface treatments tested. Conclusions: Nano-roughness obtained in a 50x50 µm scan size areas was the most reliable data to evaluate the topographical changes produced by the different acid treatments on ceramic surfaces. Key words:Dental ceramic, acid etching, bonding efficacy, resin composite, adhesive systems, contact angle, roughness. PMID:22549693

Kinetic and kinematic adjustments during perturbed walking across visible and camouflaged drops in ground level.

PubMed

Müller, Roy; Tschiesche, Kevin; Blickhan, Reinhard

2014-07-18

Walking in even the most familiar environment posesses a challenge to humans due to continuously changing surface conditions such as compliance, slip, or level. These changes can be visible or invisible due to camouflage. In order to prevent falling, camouflaged changes in the ground level in particular require a quick response of the locomotor system. For ten subjects we investigated kinematics and ground reaction forces of two consecutive contacts while they were walking across visible (drops of 0, -5 and -10 cm at second contact) and camouflaged (drops of 0 or -5 cm, and drops of 0 or -10 cm at second contact) changes in the ground level. For both situations we found significant kinetic and kinematic adjustments during the perturbed second contact but also one step earlier, in the preparatory first contact. During walking across visible changes in the ground level, second peak ground reaction force at first contact decreased whereas the drop height increased at the second contact. In addition, at the end of this first contact the ankle and knee were more flexed and the trunk was more erect compared to level walking. During the perturbed second contact, first peak ground reaction force increased with drop height, whereas kinematic adjustments at touchdown were less. The visual perception of the perturbation facilitated prior adaptations. During walking across camouflaged changes in ground level such a visually guided preadaptation was not possible and the adaptations prior to the perturbation were less than those observed during walking across visible changes in the ground. However, when stepping into a camouflaged drop, the kinetic and kinematic adjustments became more obvious and they increased with increasing camouflaged drop height. Copyright © 2014 Elsevier Ltd. All rights reserved.

Axisymmetric Lattice Boltzmann Model of Droplet Impact on Solid Surfaces

NASA Astrophysics Data System (ADS)

Dalgamoni, Hussein; Yong, Xin

2017-11-01

Droplet impact is a ubiquitous fluid phenomena encountered in scientific and engineering applications such as ink-jet printing, coating, electronics manufacturing, and many others. It is of great technological importance to understand the detailed dynamics of drop impact on various surfaces. The lattice Boltzmann method (LBM) emerges as an efficient method for modeling complex fluid systems involving rapidly evolving fluid-fluid and fluid-solid interfaces with complex geometries. In this work, we model droplet impact on flat solid substrates with well-defined wetting behavior using a two-phase axisymmetric LBM with high density and viscosity contrasts. We extend the two-dimensional Lee and Liu model to capture axisymmetric effect in the normal impact. First we compare the 2D axisymmetric results with the 2D and 3D results reported by Lee and Liu to probe the effect of axisymmetric terms. Then, we explore the effects of Weber number, Ohnesorge number, and droplet-surface equilibrium contact angle on the impact. The dynamic contact angle and spreading factor of the droplet during impact are investigated to qualitatively characterize the impact dynamics.

Application of fluorinated nanofluid for production enhancement of a carbonate gas-condensate reservoir through wettability alteration

NASA Astrophysics Data System (ADS)

Sakhaei, Zahra; Azin, Reza; Naghizadeh, Arefeh; Osfouri, Shahriar; Saboori, Rahmatollah; Vahdani, Hosein

2018-03-01

Condensate blockage phenomenon in near-wellbore region decreases gas production rate remarkably. Wettability alteration using fluorinated chemicals is an efficacious way to vanquish this problem. In this study, new synthesized fluorinated silica nanoparticles with an optimized condition and mean diameter of 50 nm is employed to modify carbonate rock surface wettability. Rock characterization tests consisting Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive x-ray Spectroscopy (EDX) were utilized to assess the nanofluid adsorption on rock surface after treatment. Contact angle, spontaneous imbibition and core flooding experiments were performed to investigate the effect of synthesized nanofluid adsorption on wettability of rock surface and liquid mobility. Results of contact angle experiments revealed that wettability of rock could alter from strongly oil-wetting to the intermediate gas-wetting even at elevated temperature. Imbibition rates of oil and brine were diminished noticeably after treatment. 60% and 30% enhancement in pressure drop of condensate and brine floods after wettability alteration with modified nanofluid were observed which confirm successful field applicability of this chemical.

Hydrophilic group formation and cell culturing on polystyrene Petri-dish modified by ion-assisted reaction

NASA Astrophysics Data System (ADS)

Kim, Ki-Hwan; Cho, Jun-Sik; Choi, Doo-Jin; Koh, Seok-Keun

2001-04-01

Polystyrene (PS) Petri-dishes were modified by an ion-assisted reaction (IAR) to improve wettability and to supply a suitable surface for cell culturing. Low energy Ar + ions with 1000 eV were irradiated on the surface of PS in oxygen gas environment. Water contact angles of PS were not reduced much by ion irradiation without oxygen gas and had a value of 40°. In the case of ion irradiation with flowing oxygen gas, however, the water contact angles were dropped significantly from 73° to 19°. X-ray photoelectron spectroscopy analysis showed that the hydrophilic groups were formed on the surface of PS by a chemical reaction between unstable chains induced by ion irradiation and the oxygen gas. Newly formed hydrophilic groups were identified as -(C-O)-, -(CO)- and -(CO)-O- bonds. The influence of the surface modification on growth of the rat pheochromocytoma (PC12) cells was investigated. The IAR-treated PS surfaces showed enhanced attachment and growth in PC12 cell culture test.

Waterborne Superhydrophobic and Superoleophobic Coatings for the Protection of Marble and Sandstone

PubMed Central

Aslanidou, Dimitra; Lampakis, Dimitrios

2018-01-01

Silica nanoparticles were dispersed in an aqueous emulsion of alkoxy silanes and organic fluoropolymer. The dispersion was sprayed onto white marble and sandstone. The deposited composite coatings exhibited (i) superhydrophobicity and superoleophobicity, as evidenced by the high (>150°) static contact angles of water and oil drops as well as (ii) water and oil repellency according to the low (<7°) corresponding tilt contact angles. Apart from marble and sandstone, the coatings with extreme wetting properties were deposited onto concrete, silk, and paper, thus demonstrating the versatility of the method. The siloxane/fluoropolymer product was characterized using Fourier Transform Infrared Spectroscopy (FT-IR), Raman spectroscopy and Scanning Electron Microscopy equipped with an Energy Dispersive X-ray Spectrometer (SEM-EDX). Moreover, SEM and FT-IR were used to reveal the surface structures of the composite coatings and their transition from superhydrophobicity to superhydrophilicity which occurred after severe thermal treatment. The composite coatings slightly reduced the breathability of marble and sandstone and had practically no optical effect on the colour of the two stones. Moreover, the coatings offered good protection against water penetration by capillarity. PMID:29642652

Surface treatment of polypropylene (PP) film by 50 Hz dielectric barrier discharge produced in air and argon/air mixture at atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Ujjwal Man, E-mail: umjoshi@gmail.com; Subedi, Deepak Prasad, E-mail: deepaksubedi2001@yahoo.com

Thin films of polypropylene (PP) are treated for improving hydrophilicity using non-thermal plasma generated by 50 Hz line frequency dielectric barrier discharge produced in air and argon/air mixture at atmospheric pressure. PP samples before and after the treatments are studied using contact angle measurements, surface free energy calculations and scanning electron microscopy (SEM). Distilled water (H{sub 2}O), glycerol (C{sub 3}H{sub 8}O{sub 3}) and diiodomethane (CH{sub 2}I{sub 2}) are used as test liquids. The contact angle measurements between test liquids and PP samples are used to determine total surface free energy using sessile drop technique. PP films show a remarkable increase inmore » surface free energy after plasma treatment. SEM analysis of the plasma-treated PP films shows that plasma treatment introduces greater roughness on the surface leading to the increased surface free energy. Furthermore, it is found that introducing a small quantity of argon can enhance the surface treatment remarkably.« less

Superhydrophobicity of biological and technical surfaces under moisture condensation: stability in relation to surface structure.

PubMed

Mockenhaupt, Bernd; Ensikat, Hans-Jürgen; Spaeth, Manuel; Barthlott, Wilhelm

2008-12-02

The stability of superhydrophobic properties of eight plants and four technical surfaces in respect to water condensation has been compared. Contact and sliding angles were measured after application of water drops of ambient temperature (20 degrees C) onto cooled surfaces. Water evaporating from the drops condensed, due to the temperature difference between the drops and the surface, on the cooled samples, forming "satellite droplets" in the vicinity of the drops. Surface cooling to 15, 10, and 5 degrees C showed a gradual decrease of superhydrophobicity. The decrease was dependent on the specific surface architecture of the sample. The least decrease was found on hierarchically structured surfaces with a combination of a coarse microstructure and submicrometer-sized structures, similar to that of the Lotus leaf. Control experiments with glycerol droplets, which show no evaporation, and thus no condensation, were carried out to verify that the effects with water were caused by condensation from the drop (secondary condensation). Furthermore, the superhydrophobic properties after condensation on cooled surfaces from a humid environment for 10 min were examined. After this period, the surfaces were covered with spherical water droplets, but most samples retained their superhydrophobicity. Again, the best stability of the water-repellent properties was found on hierarchically structured surfaces similar to that of the Lotus leaf.

Effects of varying oxygen partial pressure on molten silicon-ceramic substrate interactions

NASA Technical Reports Server (NTRS)

Ownby, D. P.; Barsoum, M. W.

1980-01-01

The silicon sessile drop contact angle was measured on hot pressed silicon nitride, silicon nitride coated on hot pressed silicon nitride, silicon carbon coated on graphite, and on Sialon to determine the degree to which silicon wets these substances. The post-sessile drop experiment samples were sectioned and photomicrographs were taken of the silicon-substrate interface to observe the degree of surface dissolution and degradation. Of these materials, silicon did not form a true sessile drop on the SiC on graphite due to infiltration of the silicon through the SiC coating, nor on the Sialon due to the formation of a more-or-less rigid coating on the liquid silicon. The most wetting was obtained on the coated Si3N4 with a value of 42 deg. The oxygen concentrations in a silicon ribbon furnace and in a sessile drop furnace were measured using the protable thoria-yttria solid solution electrolyte oxygen sensor. Oxygen partial pressures of 10 to the minus 7 power atm and 10 to the minus 8 power atm were obtained at the two facilities. These measurements are believed to represent nonequilibrium conditions.

Experimental and theoretical analysis of the rate of solvent equilibration in the hanging drop method of protein crystal growth

NASA Technical Reports Server (NTRS)

Fowlis, William W.; Delucas, Lawrence J.; Twigg, Pamela J.; Howard, Sandra B.; Meehan, Edward J.

1988-01-01

The principles of the hanging-drop method of crystal growth are discussed, and the rate of water evaporation in a water droplet (containing protein, buffer, and a precipitating agent) suspended above a well containing a double concentration of precipitating agent is investigated theoretically. It is shown that, on earth, the rate of evaporation may be determined from diffusion theory and the colligative properties of solutions. The parameters affecting the rate of evaporation include the temperature, the vapor pressure of water, the ionization constant of the salt, the volume of the drop, the contact angle between the droplet and the coverslip, the number of moles of salt in the droplet, the number of moles of water and salt in the well, the molar volumes of water and salt, the distance from the droplet to the well, and the coefficient of diffusion of water vapor through air. To test the theoretical equations, hanging-drop experiments were conducted using various reagent concentrations in 25-microliter droplets and measuring the evaporation times at 4 C and 25 C. The results showed good agreement with the theory.

Development of a Direct Contact Heat Exchanger, Phase 1 Study Report

NASA Technical Reports Server (NTRS)

Manvi, R.

1978-01-01

Electric power generation from geothermal brine requires, first, bringing the hot brine to the surface and then converting the heat to electric power. Binary conversion schemes were proposed, with the heat transfer between the brine and the working organic fluid taking place in a conventional tube and shell heat exchanger. If the brine is heavily laden with dissolved solids, however, solids buildup on the heat exchanger surfaces leads to a considerable degree of fouling and an accompanying drop in performance is experienced. A possible solution to this problem is the use of a direct contact exchanger with the secondary fluid power cycle. The proposed concept involves the formation of fluid sheets and bells as heat angles. Results of a study concerning the fluid mechanics of such surfaces are given.

Electrohydrodynamics of drops in strong uniform dc electric fields

NASA Astrophysics Data System (ADS)

Salipante, Paul F.; Vlahovska, Petia M.

2010-11-01

Drop deformation in an uniform dc electric field is a classic problem. The pioneering work of Taylor demonstrated that for weakly conducting media, the drop fluid undergoes a toroidal flow and the drop adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. However, recent studies have revealed a nonaxisymmetric rotational flow in strong fields, similar to the rotation of solid dielectric particles observed by Quincke in the 19th century. We present a systematic experimental study of this phenomenon, which highlights the importance of charge convection along the drop surface. The critical electric field, drop inclination angle, and rate of rotation are measured. We find that for small, high viscosity drops, the threshold field strength is well approximated by the Quincke rotation criterion. Reducing the viscosity ratio shifts the onset for rotation to stronger fields. The drop inclination angle increases with field strength. The rotation rate is approximately given by the inverse Maxwell-Wagner polarization time. Novel features are also observed such as a hysteresis in the tilt angle for large low-viscosity drops.

Deformation and Rotation of a Drop in a Uniform Electric Field

NASA Astrophysics Data System (ADS)

Salipante, Paul; Hanna, James; Vlahovska, Petia

2009-11-01

Drop deformation in uniform electric fields is a classic problem. The pioneering work of G.I.Taylor demonstrated that for weakly conducting media, the drop fluid undergoes a toroidal flow and the drop adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. However, recent studies have revealed a nonaxisymmetric rotational mode for drops of lower conductivity than the surrounding medium, similar to the rotation of solid dielectric particles observed by Quincke in the 19th century. We will present an experimental and theoretical study of this phenomenon in DC fields. The critical electric field, drop inclination angle, and rate of rotation are measured. For small, high viscosity drops, the threshold field strength is well approximated by the Quincke rotation criterion. Reducing the viscosity ratio shifts the onset for rotation to stronger fields. The drop inclination angle increases with field strength. The rotation rate is approximately given by the inverse Maxwell-Wagner polarization time. We also observe a hysteresis in the tilt angle for low-viscosity drops. The effects of AC fields and surfactants are also explored.

Apparent contact angle and contact angle hysteresis on liquid infused surfaces.

PubMed

Semprebon, Ciro; McHale, Glen; Kusumaatmaja, Halim

2016-12-21

We theoretically investigate the apparent contact angle and contact angle hysteresis of a droplet placed on a liquid infused surface. We show that the apparent contact angle is not uniquely defined by material parameters, but also has a dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the contact angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict contact angle hysteresis on liquid infused surfaces generated by the pinning of the contact lines by the surface corrugations. Our analytical expressions for both the apparent contact angle and contact angle hysteresis can be interpreted as 'weighted sums' between the contact angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.

Influence of pH on wetting kinetics of a pine forest soil

NASA Astrophysics Data System (ADS)

Amer, Ahmad; Schaumann, Gabriele; Diehl, Dörte

2014-05-01

Water repellent properties of organic matter significantly alter soil water dynamics. Various environmental factors control appearance and breakup of repellency in soil. Beside water content and temperature also pH exerts an influence on soil water repellency although investigations achieved partly ambiguous results; some found increasing repellency with increasing pH (Terashima et al. 2004; Duval et al. 2005), other with decreasing pH (Karnok et al. 1993; Roper 2005) and some found repellency maxima at intermediate pH and an increase with decreasing and with increasing pH (Bayer and Schaumann 2007; Diehl et al. 2010). The breakup of repellency may be observed via the time dependent sessile drop contact angle (TISED). With water contact time, soil-water contact angle decreases until complete wetting is reached. Diehl and Schaumann (2007) calculated the activation energy of the wetting process from the rate of sessile drop wetting obtained at different temperatures and draw conclusions on chemical or physical nature of repellency. The present study aims at the influence of pH on the wetting kinetics of soil. Therefore, TISED of soil was determined as a function of pH and temperature. We used upper soil samples (0 - 10 cm) from a pine forest in the southwest of Germany (Rheinland-Pfalz). Samples were air-dried, sieved < 1.0 mm and pH was modified by NH3 and HCl gas (Diehl et al. 2010) and measured electrometrically in 0.01 M CaCl2 solution. TISED measurements (2007)were conducted at 10, 20 and 30 oC using OCA 15 Contact Angle Meter (Dataphysics, Germany) on three replications for each soil sample. Apparent work of adhesion was calculated, plotted vs. time and mathematically fitted using double exponential function. Rate constants of wetting were used to determine the activation energy by Arrhenius equation. First results indicated that despite comparable initial contact angles, pH alteration strongly changed the wetting rate suggesting maximum wetting resistance at the natural pH of 4.3 and decreasing wetting resistance at lower and at higher pH. The poster will present further current results of the ongoing study and discuss the activation energy of the wetting process in dependence of artificially altered soil pH. References: Bayer, J. V. and G. E. Schaumann (2007). Hydrol. Processes 21(17): 2266 - 2275. Diehl, D., J. V. Bayer, et al. (2010). Geoderma 158(3-4): 375-384. Diehl, D. and G. E. Schaumann (2007). Hydrol. Processes 21(17): 2255 - 2265. Duval, J. F. L., K. J. Wilkinson, et al. (2005). Environ Sci Technol 39(17): 6435-6445. Karnok, K. A., E. J. Rowland, et al. (1993). Agron J 85(5): 983-986. Roper, M. M. (2005). Aust J Soil Res 43: 803-810. Terashima, M., M. Fukushima, et al. (2004). Colloids and Surfaces, A: Physicochemical and Engineering Aspects 247(1-3): 77-83.

The wettability of selected organic soils in Poland

NASA Astrophysics Data System (ADS)

Całka, A.; Hajnos, M.

2009-04-01

The wettability was measured in the laboratory by means of two methods: Water Drop Penetration Time (WDPT) test and Thin Column Wicking (TCW) method. WDPT is fast and simple method and was used to investigate potential water repellency of analyzed samples. TCW is an indirect method and was used to determine contact angles and surface free energy components. The measurement was performed in horizontal teflon chambers for thin-layer chromatography, adapted for tubes 10 cm long. The experiment was carried out on muck soils (samples were taken from two levels of soil profile: 0-20 cm and 20-40 cm) and peat soils. There were two types of peats: low-moor peats and high moor peats. Samples of low-moor peats were taken from level 25-75 cm (alder peat) and 75-125cm (sedge peat) and 25-75 cm (peloid peat). Samples of high moor peats from level 25-175 cm (sphagnum peat) and 175-225 cm (sphagnum peat with Eriophorum). There was found no variability in persistence of potential water repellency but there were differences in values of contact angles of individual soil samples. Both muck and peat samples are extremely water repellent soils. Water droplets persisted on the surface of soils for more than 24 hours. Contact angles and surface free energy components for all samples were differentiated. Ranges of water contact angles for organic soils are from 27,54o to 96,50o. The highest values of contact angles were for sphagnum peats, and the lowest for muck soil from 20-40 cm level. It means, that there are differences in wettability between these samples. Muck soil is the best wettable and sphagnum peats is the worst wettable soil. If the content of organic compounds in the soil exceeds 40% (like in peats), the tested material displays only dispersion-type interactions. Therefore for peat soils, the technique of thin column wicking could only be used to determine the dispersive component γiLW. For muck soils it was also determined electron-acceptor (Lewis acid) γ+ and electron-donor (Lewis base) γ- surface free energy components. The authors gratefully acknowledge the Ministry of Science and Higher Education for financial support of this work (grant No. N N310 149335).

Contact angle distribution of particles at fluid interfaces.

PubMed

Snoeyink, Craig; Barman, Sourav; Christopher, Gordon F

2015-01-27

Recent measurements have implied a distribution of interfacially adsorbed particles' contact angles; however, it has been impossible to measure statistically significant numbers for these contact angles noninvasively in situ. Using a new microscopy method that allows nanometer-scale resolution of particle's 3D positions on an interface, we have measured the contact angles for thousands of latex particles at an oil/water interface. Furthermore, these measurements are dynamic, allowing the observation of the particle contact angle with high temporal resolution, resulting in hundreds of thousands of individual contact angle measurements. The contact angle has been found to fit a normal distribution with a standard deviation of 19.3°, which is much larger than previously recorded. Furthermore, the technique used allows the effect of measurement error, constrained interfacial diffusion, and particle property variation on the contact angle distribution to be individually evaluated. Because of the ability to measure the contact angle noninvasively, the results provide previously unobtainable, unique data on the dynamics and distribution of the adsorbed particles' contact angle.

Ring formation on an inclined surface

NASA Astrophysics Data System (ADS)

Deegan, Robert; Du, Xiyu

2015-11-01

A drop dried on a solid surface will typically leave a narrow band of solute deposited along the contact line. We examined variations of this deposit due to the inclination of the substrate using numerical simulations of a two-dimensional drop, equivalent to a strip-like drop. An asymptotic analysis of the contact line region predicts that the upslope deposit will grow faster at early times, but the growth of this deposit ends sooner because the upper contact line depins first. From our simulations we find that the deposit can be larger at either the upper or lower contact line depending on the initial drop volume and substrate inclination. For larger drops and steeper inclinations, the early lead in deposited mass at the upper contact line is wiped out by the earlier depinning of the upper contact line and subsequent continued growth at the lower contact line. Conversely, for smaller drops and shallower inclinations, the early lead of the upper contact line is insurmountable despite its earlier termination in growth. Our results show that it is difficult to reconstruct a postiorithe inclination of the substrate based solely on the shape of the deposit. The authors thank the James S. McDonnell Foundation for support through a 21st Century Science Initiative in Studying Complex Systems Research Award, and the National Science Foundation for support under Grant No. 0932600.

Drop test analysis of fuselage section of R80 commuter aircraft by using finite element method

NASA Astrophysics Data System (ADS)

Anggono, Agus Dwi; Ardianto, Adik Nofa Rochma Wahyu

2017-04-01

In commercial aerospace development, feasibility accidents design or crashworthiness is a major concern in aviation safety. Fuselage structure plays an important role in absorbing energy during an accident. The research aims are to determine drop test phenomenon on the fuselage, to investigate deformation occurred in the structure of the fuselage, and to know the influence of the airframe falls position to the stress strain which occurred in the structure of the fuselage. This research was conducted by varying the fall angle of the fuselage in a vertical position or 0° and 15°. Fuselage design was modeled by using SolidWorks. Then the model is imported to the Abaqus for drop test simulation. From the simulation results, it can be obtained the phenomenon of deformation on the structure of the fuselage when it comes in contact with the rigid ground. The high deformation occurs shows the structure capabilities in order to absorb the impact. It could be happened because the deformation is influenced by internal energy and strain energy. The various positions shows the structure capability in order to withstand impact loads during periods of 4-8 seconds and the maximum deformation was reached in 12 seconds. The experiment on the vertical position and the position falls of 15° angle was delivered the highest stress strain. The stress was 483 MPa in struts section, 400.78 MPa in skin section, 358.28 MPa in the floor and 483 MPa in the cargo frame section.

Drop pattern resulting from the breakup of a bidimensional grid of liquid filaments

NASA Astrophysics Data System (ADS)

Cuellar, Ingrith; Ravazzoli, Pablo D.; Diez, Javier A.; González, Alejandro G.

2017-10-01

A rectangular grid formed by liquid filaments on a partially wetting substrate evolves in a series of breakups leading to arrays of drops with different shapes distributed in a rather regular bidimensional pattern. Our study is focused on the configuration produced when two long parallel filaments of silicone oil, which are placed upon a glass substrate previously coated with a fluorinated solution, are crossed perpendicularly by another pair of long parallel filaments. A remarkable feature of this kind of grids is that there are two qualitatively different types of drops. While one set is formed at the crossing points, the rest are consequence of the breakup of shorter filaments formed between the crossings. Here, we analyze the main geometric features of all types of drops, such as shape of the footprint and contact angle distribution along the drop periphery. The formation of a series of short filaments with similar geometric and physical properties allows us to have simultaneously quasi identical experiments to study the subsequent breakups. We develop a simple hydrodynamic model to predict the number of drops that results from a filament of given initial length and width. This model is able to yield the length intervals corresponding to a small number of drops, and its predictions are successfully compared with the experimental data as well as with numerical simulations of the full Navier-Stokes equation that provide a detailed time evolution of the dewetting motion of the filament till the breakup into drops. Finally, the prediction for finite filaments is contrasted with the existing theories for infinite ones.

Collective Cell Migration in Embryogenesis Follows the Laws of Wetting.

PubMed

Wallmeyer, Bernhard; Trinschek, Sarah; Yigit, Sargon; Thiele, Uwe; Betz, Timo

2018-01-09

Collective cell migration is a fundamental process during embryogenesis and its initial occurrence, called epiboly, is an excellent in vivo model to study the physical processes involved in collective cell movements that are key to understanding organ formation, cancer invasion, and wound healing. In zebrafish, epiboly starts with a cluster of cells at one pole of the spherical embryo. These cells are actively spreading in a continuous movement toward its other pole until they fully cover the yolk. Inspired by the physics of wetting, we determine the contact angle between the cells and the yolk during epiboly. By choosing a wetting approach, the relevant scale for this investigation is the tissue level, which is in contrast to other recent work. Similar to the case of a liquid drop on a surface, one observes three interfaces that carry mechanical tension. Assuming that interfacial force balance holds during the quasi-static spreading process, we employ the physics of wetting to predict the temporal change of the contact angle. Although the experimental values vary dramatically, the model allows us to rescale all measured contact-angle dynamics onto a single master curve explaining the collective cell movement. Thus, we describe the fundamental and complex developmental mechanism at the onset of embryogenesis by only three main parameters: the offset tension strength, α, that gives the strength of interfacial tension compared to other force-generating mechanisms; the tension ratio, δ, between the different interfaces; and the rate of tension variation, λ, which determines the timescale of the whole process. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Bepotastine Ophthalmic

MedlinePlus

... that you think may be caused by contact lenses. Bepotastine eye drops contain benzalkonium chloride, which can be absorbed ... you are wearing contact lenses. Remove your contact lenses before you use bepotastine eye drops and do not replace them for at ...

Formation of curved micrometer-sized single crystals.

PubMed

Koifman Khristosov, Maria; Kabalah-Amitai, Lee; Burghammer, Manfred; Katsman, Alex; Pokroy, Boaz

2014-05-27

Crystals in nature often demonstrate curved morphologies rather than classical faceted surfaces. Inspired by biogenic curved single crystals, we demonstrate that gold single crystals exhibiting curved surfaces can be grown with no need of any fabrication steps. These single crystals grow from the confined volume of a droplet of a eutectic composition melt that forms via the dewetting of nanometric thin films. We can control their curvature by controlling the environment in which the process is carried out, including several parameters, such as the contact angle and the curvature of the drops, by changing the surface tension of the liquid drop during crystal growth. Here we present an energetic model that explains this phenomenon and predicts why and under what conditions crystals will be forced to grow with the curvature of the microdroplet even though the energetic state of a curved single crystal is very high.

Reaction layer formation at the graphite/copper-chromium alloy interface

NASA Technical Reports Server (NTRS)

Devincent, Sandra M.; Michal, Gary M.

1992-01-01

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Reaction layer formation at the graphite/copper-chromium alloy interface

NASA Technical Reports Server (NTRS)

Devincent, Sandra M.; Michal, Gary M.

1993-01-01

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Drop Impingement on Highly Wetting Micro/Nano Porous Surfaces

NASA Astrophysics Data System (ADS)

Buie, Cullen; Joung, Youngsoo

2011-11-01

Recently, we developed a novel fabrication method using a combination of electrophoretic deposition (EPD) and break down anodization (BDA) to achieve highly wetting nanoporous surfaces with microscale features. In this study we investigate droplet impingement behavior on these surfaces as a function of impact velocity, droplet size, and liquid properties. We observe impingement modes we denote as ``necking'' (droplet breaks before full penetration in the porous surface), ``spreading'' (continuous wicking into the porous surface), and ``jetting'' (jets of liquid emanate from the edges of the wicking liquid). To predict the droplet impingement modes, we've developed a non-dimensional parameter that is a function of droplet velocity, dynamic viscosity, effective pore radius and contact angle. The novel dimensionless parameter successfully predicts drop impingement modes across multiple fluids. Results of this study will inform the design of spray impingement cooling systems for electronics applications where the ``spreading'' mode is preferred.

Microgravity experiment study on the vane type surface tension tank

NASA Astrophysics Data System (ADS)

Kang, Qi; Duan, Li; Rui, Wei

Having advantages of low cost, convenience and high level of microgravity, the drop tower has become a significant microgravity experiment facility. National Microgravity Laboratory/CAS(NMLC) drop tower has 3.5s effective microgravity time, meanwhile the level of microgravity can reach 10 (-5) g. And the impact acceleration is less than 15g in the recovery period. The microgravity experiments have been conducted on the scaling model of vane type surface tension tank in NMLC’s drop tower. The efficiency of Propellant Management Devices (PMDs) was studied, which focus on the effects of Propellant Management Devices (PMDs), numbers of PMDs, contact angle, and liquid viscosity on the flow rate. The experimental results shown that the numbers of PMDs have little or no effect on the flow rate while the liquid is sufficient. The experiments about the influence of different charging ratio have been carried out while tank is placed positively and reversely, and we find the charging ratio has less effect on the capillary flow rate when the charging ratio is greater than 2%.

Squeezing and de-wetting of a shear thinning fluid drop between plane parallel surfaces: capillary adhesion phenomenon

NASA Astrophysics Data System (ADS)

Ward, Thomas

2017-11-01

The radial squeezing and de-wetting of a thin film of viscous shear thinning fluid filling the gap between parallel plane walls is examined both experimentally and theoretically for gap spacing much smaller than the capillary length. The interaction between motion of fluid in the gap driven by squeezing or de-wetting and surface tension is parameterized by a dimensionless variable, F, that is the ratio of the constant force supplied by the top plate (either positive or negative) to surface tension at the drop's circumference. Furthermore, the dimensionless form of the rate equation for the gap's motion reveals a time scale that is dependent on the drop volume when analyzed for a power law shear thinning fluid. In the de-wetting problem the analytical solution reveals the formation of a singularity, leading to capillary adhesion, as the gap spacing approaches a critical value that depends on F and the contact angle. Experiments are performed to test the analytical predictions for both squeezing, and de-wetting in the vicinity of the singularity.

The effects of flexion-distraction and drop techniques on disorders and Ferguson’s angle in female patients with lumbar intervertebral disc herniation

PubMed Central

Oh, Hyunju; Lee, Sangyong; Lee, Kwansub; Jeong, Mugeun

2018-01-01

[Purpose] This study examines the effects of the flexion-distraction technique and the drop technique on disorders and on Ferguson’s angle in female patients with lumbar intervertebral disc herniation. [Subjects and Methods] Thirty female patients with lumbar intervertebral disc herniation were divided into an experimental group (n=15) treated with flexion-distraction and drop techniques and a control group (n=15) treated with spinal decompression therapy. Both groups were treated three times a week over an eight-week period. [Results] In the comparison of changes within each group after treatment, both groups showed statistically significant decreases in disorders and in Ferguson’s angle. [Conclusion] Flexion-distraction and drop techniques may be an effective intervention to improve disorders and Ferguson’s angle in female patients with lumbar intervertebral disc herniation. PMID:29706701

Control of stain geometry by drop evaporation of surfactant containing dispersions.

PubMed

Erbil, H Yildirim

2015-08-01

Control of stain geometry by drop evaporation of surfactant containing dispersions is an important topic of interest because it plays a crucial role in many applications such as forming templates on solid surfaces, in ink-jet printing, spraying of pesticides, micro/nano material fabrication, thin film coatings, biochemical assays, deposition of DNA/RNA micro-arrays, and manufacture of novel optical and electronic materials. This paper presents a review of the published articles on the diffusive drop evaporation of pure liquids (water), the surfactant stains obtained from evaporating drops that do not contain dispersed particles and deposits obtained from drops containing polymer colloids and carbon based particles such as carbon nanotubes, graphite and fullerenes. Experimental results of specific systems and modeling attempts are discussed. This review also has some special subtopics such as suppression of coffee-rings by surfactant addition and "stick-slip" behavior of evaporating nanosuspension drops. In general, the drop evaporation process of a surfactant/particle/substrate system is very complex since dissolved surfactants adsorb on both the insoluble organic/inorganic micro/nanoparticles in the drop, on the air/solution interface and on the substrate surface in different extends. Meanwhile, surfactant adsorbed particles interact with the substrate giving a specific contact angle, and free surfactants create a solutal Marangoni flow in the drop which controls the location of the particle deposition together with the rate of evaporation. In some cases, the presence of a surfactant monolayer at the air/solution interface alters the rate of evaporation. At present, the magnitude of each effect cannot be predicted adequately in advance and consequently they should be carefully studied for any system in order to control the shape and size of the final deposit. Copyright © 2014 Elsevier B.V. All rights reserved.

Feasibility Study of an Airbag-Based Crew Impact Attenuation System for the Orion MPCV

NASA Technical Reports Server (NTRS)

Do, Sydney; deWeck, Olivier

2011-01-01

Airbag-based methods for crew impact attenuation have been highlighted as a potential lightweight means of enabling safe land-landings for the Orion Multi-Purpose Crew Vehicle, and the next generation of ballistic shaped spacecraft. To investigate the performance feasibility of this concept during a nominal 7.62m/s Orion landing, a full-scale personal airbag system 24% lighter than the Orion baseline has been developed, and subjected to 38 drop tests on land. Through this effort, the system has demonstrated the ability to maintain the risk of injury to an occupant during a 7.85m/s, 0 deg. impact angle land-landing to within the NASA specified limit of 0.5%. In accomplishing this, the airbag-based crew impact attenuation concept has been proven to be feasible. Moreover, the obtained test results suggest that by implementing anti-bottoming airbags to prevent direct contact between the system and the landing surface, the system performance during landings with 0 deg impact angles can be further improved, by at least a factor of two. Additionally, a series of drop tests from the nominal Orion impact angle of 30 deg indicated that severe injury risk levels would be sustained beyond impact velocities of 5m/s. This is a result of the differential stroking of the airbags within the system causing a shearing effect between the occupant seat structure and the spacecraft floor, removing significant stroke from the airbags.

A variational approach to the study of capillary phenomena

NASA Technical Reports Server (NTRS)

Emmer, M.; Gonzalez, E.; Tamanini, I.

1982-01-01

The problem of determining the free surface of a liquid in a capillary tube, and of a liquid drop, sitting first on a horizontal plane and then on more general surfaces is considered. With some modifications, the method applies to the study of pendent drops and of rotating drops as well. The standard capillary problem, i.e. the determination of the free surface of a liquid in a thin tube of general cross section, which resuls from the simultaneous action of surface tension, boundary adhesion and gravity is discussed. It turns out that in this case the existence of the solution surface depends heavily on the validity of a simple geometric condition about the mean curvature of the boundary curve of the cross section of the capillary tube. Some particular examples of physical interest are also be discussed. Liquid drops sitting on or hanging from a fixed horizontal plane are discussed. The symmetry of the solutions (which can actually be proved, as consequence of a general symmetrization argument) now plays the chief role in deriving both the existence and the regularity of energy-minimizing configurations. When symmetry fails (this is the case, for example, when the contact angle between the drop and the plate is not constant, or when the supporting surface is not itself symmetric), then more sophisticated methods must be used. Extensions in this direction are outlined.

Oblique drop impact onto a deep liquid pool

NASA Astrophysics Data System (ADS)

Gielen, Marise V.; Sleutel, Pascal; Benschop, Jos; Riepen, Michel; Voronina, Victoria; Visser, Claas Willem; Lohse, Detlef; Snoeijer, Jacco H.; Versluis, Michel; Gelderblom, Hanneke

2017-08-01

Oblique impact of drops onto a solid or liquid surface is frequently observed in nature. Most studies on drop impact and splashing, however, focus on perpendicular impact. Here we study oblique impact of 100 μ m drops onto a deep liquid pool, where we quantify the splashing threshold, maximum cavity dimensions and cavity collapse by high-speed imaging above and below the water surface. Gravity can be neglected in these experiments. Three different impact regimes are identified: smooth deposition onto the pool, splashing in the direction of impact only, and splashing in all directions. We provide scaling arguments that delineate these regimes by accounting for the drop impact angle and Weber number. The angle of the axis of the cavity created below the water surface follows the impact angle of the drop irrespectively of the Weber number, while the cavity depth and its displacement with respect to the impact position do depend on the Weber number. Weber number dependency of both the cavity depth and displacement is modeled using an energy argument.

Wettability, soil organic matter and structure-properties of typical chernozems under the forest and under the arable land

NASA Astrophysics Data System (ADS)

Bykova, Galina; Umarova, Aminat; Tyugai, Zemfira; Milanovskiy, Evgeny; Shein, Evgeny

2017-04-01

Intensive tillage affects the properties of soil: decrease in content of soil organic matter and in hydrophobicity of the soil's solid phase, the reduction of amount of water stable aggregates - all this leads to deterioration of the structure of the soil and affects the process of movement of moisture in the soil profile. One of the hypotheses of soil's structure formation ascribes the formation of water stable aggregates with the presence of hydrophobic organic substances on the surface of the soil's solid phase. The aim of this work is to study the effect of tillage on properties of typical chernozems (pachic Voronic Chernozems, Haplic Chernozems) (Russia, Kursk region), located under the forest and under the arable land. The determination of soil-water contact angle was performed by a Drop Shape Analyzer DSA100 (Krüss GmbH, Germany) by the static sessile drop method. For all samples the content of total and organic carbon by dry combustion in oxygen flow and the particle size distribution by the laser diffraction method on the device Analysette 22 comfort, FRITCH, Germany were determined. The estimation of aggregate composition was performed by dry sieving (AS 200, Retsch, Germany), the content of water stable aggregates was estimated by the Savvinov method. There was a positive correlation between the content of organic matter and soil's wettability in studied soils, a growth of contact angle with the increasing the content of organic matter. Under the forest the content of soil organic matter was changed from 6,41% on the surface up to 1,9% at the depth of 100 cm. In the Chernozem under the arable land the organic carbon content in arable horizon is almost two times less. The maximum of hydrophobicity (78.1o) was observed at the depth of 5 cm under the forest. In the profile under the arable land the contact angle value at the same depth was 50o. The results of the structure analysis has shown a decrease in the content of agronomically valuable and water stable aggregates in the profile under arable land. These data indicate the correlation between the wettability of soils with the content of organic matter and their influence on the formation of water stable structure, as well as the negative impact of tillage on the analyzed characteristics.

Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Jian; Graber, Christof; Liburdy, James

This study examines the hydrodynamics and temperature characteristics of distilled deionized water droplets impinging on smooth and nano-structured surfaces using high speed (HS) and infrared (IR) imaging at We = 23.6 and Re = 1593, both based on initial drop impingement parameters. Results for a smooth and nano-structured surface for a range of surface temperatures are compared. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. The near surface average droplet fluid temperatures are evaluated for conditions of evaporative cooling and boiling. Also included are surface temperature results using a gold layered IR opaque surface on silicon.more » Four stages of the impingement process are identified: impact, boiling, near constant surface diameter evaporation, and final dry-out. For the boiling conditions there is initial nucleation followed by severe boiling, then near constant diameter evaporation resulting in shrinking of the droplet height. When a critical contact angle is reached during evaporation the droplet rapidly retracts to a smaller diameter reducing the contact area with the surface. This continues as a sequence of retractions until final dry out. The basic trends are the same for all surfaces, but the nano-structured surface has a lower dissipated energy during impact and enhances the heat transfer for evaporative cooling with a 20% shorter time to achieve final dry out. (author)« less

Direct determination of three-phase contact line properties on nearly molecular scale

DOE PAGES

Winkler, P. M.; McGraw, R. L.; Bauer, P. S.; ...

2016-05-17

Wetting phenomena in multi-phase systems govern the shape of the contact line which separates the different phases. For liquids in contact with solid surfaces wetting is typically described in terms of contact angle. While in macroscopic systems the contact angle can be determined experimentally, on the molecular scale contact angles are hardly accessible. Here we report the first direct experimental determination of contact angles as well as contact line curvature on a scale of the order of 1nm. For water nucleating heterogeneously on Ag nanoparticles we find contact angles around 15 degrees compared to 90 degrees for the corresponding macroscopicallymore » measured equilibrium angle. The obtained microscopic contact angles can be attributed to negative line tension in the order of –10 –10 J/m that becomes increasingly dominant with increasing curvature of the contact line. Furthermore, these results enable a consistent theoretical description of heterogeneous nucleation and provide firm insight to the wetting of nanosized objects.« less

Does wastewater from olive mills induce toxicity and water repellency in soil?

NASA Astrophysics Data System (ADS)

Peikert, B.; Bandow, N.; Schaumann, G. E.

2012-04-01

Olive oil mill wastewater is the effluent generated by the olive oil extraction process. It is the main waste product of this industry mainly being produced in the Mediterranean Basin. Because proper treatment options are rare it is often disposed into the environment, e.g. fields or wadies. Due to its high concentration of fatty acids and phytotoxic phenolic compounds and its high chemical and biological oxygen demand, olive oil mill wastewater becomes a serious environmental problem. In this screening study we investigated long-term effects of olive oil mill wastewater application on soil properties in several locations in the West Bank and Israel. We determined wettability via water drop penetration time and the contact angle as well as general soil properties including pH, EC, carbon content, and we conducted thermogravimetrical analyses in order to characterize the impact of the waste water on the quality of soil organic matter. Our results show that application of olive oil mill wastewater has various effects. We determined contact angles between 110 and 120° and water drop penetration times up to 1367 s indicating significant reduction in wettability. Furthermore, soil carbon and nitrogen content and water extractable organic matter increased as well as electric conductivity, which could be pointed out as a fertilizing effect. In contrast soil pH was significantly reduced. Conducting thermal analyses we observed an increase in the labile and refractory carbon fraction. Probably first one is responsible for induced water repellency. As a consequence the reduced wettability negatively affects soil quality. It would therefore be promising to minimize the hydrophobizing impacts without losing fertilizing effects of the olive oil mill wastewater.

Experimental Investigation of Two-Phase Oil (D130)-Water Flow in 4″ Pipe for Different Inclination Angles

NASA Astrophysics Data System (ADS)

Shaahid, S. M.; Basha, Mehaboob; Al-Hems, Luai M.

2018-03-01

Oil and water are often produced and transported together in pipelines that have various degrees of inclination from the horizontal. The flow of two immiscible liquids oil and water in pipes has been a research topic since several decades. In oil and chemical industries, knowledge of the frictional pressure loss in oil-water flows in pipes is necessary to specify the size of the pump required to pump the emulsions. An experimental investigation has been carried out for measurement of pressure drop of oil (D130)-water two-phase flows in 4 inch diameter inclined stainless steel pipe at different flow conditions. Experiments were conducted for different inclination angles including; 0°, 15°, 30° (for water cuts “WC” 0 - 100%). The flow rates at the inlet were varied from 4000 to 8000 barrels-per-day (BPD). For a given flow rate the frictional pressure drop has been found to increase (for all angles) from WC = 0 - 60%, and thereafter friction pressure drop decreases, this could be due phase inversion. For a given WC 40%, the frictional pressure drop has been found to increase with angle and flow rate. It has been noticed that inclination angle has appreciable effect on frictional pressure drop.

The wettability and swelling of selected mucoadhesive polymers in simulated saliva and vaginal fluids.

PubMed

Rojewska, M; Olejniczak-Rabinek, M; Bartkowiak, A; Snela, A; Prochaska, K; Lulek, J

2017-08-01

The surface properties play a particularly important role in the mucoadhesive drug delivery systems. In these formulations, the adsorption of polymer matrix to mucous membrane is limited by the wetting and swelling process of the polymer structure. Hence, the performance of mucoadhesive drug delivery systems made of polymeric materials depends on multiple factors, such as contact angle, surface free energy and water absorption rate. The aim of our study was to analyze the effect of model saliva and vaginal fluids on the wetting properties of selected mucoadhesive (Carbopol 974P NF, Noveon AA-1, HEC) and film-forming (Kollidon VA 64) polymers as well as their blends at the weight ratio 1:1 and 1:1:1, prepared in the form of discs. Surface properties of the discs were determined by measurements of advancing contact angle on the surface of polymers and their blends using the sessile drop method. The surface energy was determined by the OWRK method. Additionally, the mass swelling factor and hydration percentage of examined polymers and their blends in simulated biological fluids were evaluated. Copyright © 2017 Elsevier B.V. All rights reserved.

Interaction between Air Bubbles and Superhydrophobic Surfaces in Aqueous Solutions.

PubMed

Shi, Chen; Cui, Xin; Zhang, Xurui; Tchoukov, Plamen; Liu, Qingxia; Encinas, Noemi; Paven, Maxime; Geyer, Florian; Vollmer, Doris; Xu, Zhenghe; Butt, Hans-Jürgen; Zeng, Hongbo

2015-07-07

Superhydrophobic surfaces are usually characterized by a high apparent contact angle of water drops in air. Here we analyze the inverse situation: Rather than focusing on water repellency in air, we measure the attractive interaction of air bubbles and superhydrophobic surfaces in water. Forces were measured between microbubbles with radii R of 40-90 μm attached to an atomic force microscope cantilever and submerged superhydrophobic surfaces. In addition, forces between macroscopic bubbles (R = 1.2 mm) at the end of capillaries and superhydrophobic surfaces were measured. As superhydrophobic surfaces we applied soot-templated surfaces, nanofilament surfaces, micropillar arrays with flat top faces, and decorated micropillars. Depending on the specific structure of the superhydrophobic surfaces and the presence and amount of entrapped air, different interactions were observed. Soot-templated surfaces in the Cassie state showed superaerophilic behavior: Once the electrostatic double-layer force and a hydrodynamic repulsion were overcome, bubbles jumped onto the surface and fully merged with the entrapped air. On nanofilaments and micropillar arrays we observed in addition the formation of sessile bubbles with finite contact angles below 90° or the attachment of bubbles, which retained their spherical shape.

Separation of polycarbonate and acrylonitrile-butadiene-styrene waste plastics by froth flotation combined with ammonia pretreatment.

PubMed

Wang, Chong-Qing; Wang, Hui; Liu, Qun; Fu, Jian-Gang; Liu, You-Nian

2014-12-01

The objective of this research is flotation separation of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) waste plastics combined with ammonia pretreatment. The PC and ABS plastics show similar hydrophobicity, and ammonia treatment changes selectively floatability of PC plastic while ABS is insensitive to ammonia treatment. The contact angle measurement indicates the dropping of flotation recovery of PC is ascribed to a decline of contact angle. X-ray photoelectron spectroscopy demonstrates reactions occur on PC surface, which makes PC surface more hydrophilic. Separation of PC and ABS waste plastics was conducted based on the flotation behavior of single plastic. At different temperatures, PC and ABS mixtures were separated efficiently through froth flotation with ammonia pretreatment for different time (13 min at 23 °C, 18 min at 18 °C and 30 min at 23 °C). For both PC and ABS, the purity and recovery is more than 95.31% and 95.35%, respectively; the purity of PC and ABS is up to 99.72% and 99.23%, respectively. PC and ABS mixtures with different particle sizes were separated effectively, implying that ammonia treatment possesses superior applicability. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effect of crystal habits on the surface energy and cohesion of crystalline powders.

PubMed

Shah, Umang V; Olusanmi, Dolapo; Narang, Ajit S; Hussain, Munir A; Gamble, John F; Tobyn, Michael J; Heng, Jerry Y Y

2014-09-10

The role of surface properties, influenced by particle processing, in particle-particle interactions (powder cohesion) is investigated in this study. Wetting behaviour of mefenamic acid was found to be anisotropic by sessile drop contact angle measurements on macroscopic (>1cm) single crystals, with variations in contact angle of water from 56.3° to 92.0°. This is attributed to variations in surface chemical functionality at specific facets, and confirmed using X-ray photoelectron spectroscopy (XPS). Using a finite dilution inverse gas chromatography (FD-IGC) approach, the surface energy heterogeneity of powders was determined. The surface energy profile of different mefenamic acid crystal habits was directly related to the relative exposure of different crystal facets. Cohesion, determined by a uniaxial compression test, was also found to relate to surface energy of the powders. By employing a surface modification (silanisation) approach, the contribution from crystal shape from surface area and surface energy was decoupled. By "normalising" contribution from surface energy and surface area, needle shaped crystals were found to be ∼2.5× more cohesive compared to elongated plates or hexagonal cuboid shapes crystals. Copyright © 2014. Published by Elsevier B.V.

Sodium hydrogen carbonate as an alternative blowing agent in the preparation of palm-based polyurethane foam

NASA Astrophysics Data System (ADS)

Shakir, Amira Shakim Abdul; Badri, Khairiah Haji; Hua, Chia Chin

2016-11-01

An environmental-friendly blowing agent has been used to fabricate flexible polyurethane (PU) foam. Polyurethane foam was prepared from palm kernel oil-based monoester polyol (PKO-p) via prepolymerization method. Acetone has been used as solvent in this study. The developed polyurethane foam was characterized using tensile, differential scanning calorimetry analysis (DSC), thermogravimetric analysis (TGA), optical microscope and drop shape analyzer. The mechanical properties of the PU-reference (PU-R) and PU-NaHCO3 foam was analyzed by tensile using ASTM D 3574-01. From the results, the elongation of PU- NaHCO3 shows reduction to 26.3 % compared to PU-R. The DSC showed two glass transition temperatures in all samples that belonged to the PU-R and PU-NaHCO3. TGA revealed that the incorporation of sodium hydrogen carbonate into the PU system did not show significant difference as compared to the control PU. The morphology of both PU was investigated using optical microscope. Contact angle has been measured to determine the hydrophobicity of the PU. The PU- NaHCO3 exhibited an increase in contact angle (93.1°).

Repeatability of a dynamic rollover test system.

PubMed

Seppi, Jeremy; Toczyski, Jacek; Crandall, Jeff R; Kerrigan, Jason

2016-08-17

The goal of this study was to characterize the rollover crash and to evaluate the repeatability of the Dynamic Rollover Test System (DRoTS) in terms of initial roof-to-ground contact conditions, vehicle kinematics, road reaction forces, and vehicle deformation. Four rollover crash tests were performed on 2 pairs of replicate vehicles (2 sedan tests and 2 compact multipurpose van [MPV] tests), instrumented with a custom inertial measurement unit to measure vehicle and global kinematics and string potentiometers to measure pillar deformation time histories. The road was instrumented with load cells to measure reaction loads and an optical encoder to measure road velocity. Laser scans of pre- and posttest vehicles were taken to provide detailed deformation maps. Initial conditions were found to be repeatable, with the largest difference seen in drop height of 20 mm; roll rate, roll angle, pitch angle, road velocity, drop velocity, mass, and moment of inertia were all 7% different or less. Vehicle kinematics (roll rate, road speed, roll and pitch angle, global Z' acceleration, and global Z' velocity) were similar throughout the impact; however, differences were seen in the sedan tests because of a vehicle fixation problem and differences were seen in the MPV tests due to an increase in reaction forces during leading side impact likely caused by disparities in roll angle (3° difference) and mass properties (2.2% in moment of inertia [MOI], 53.5 mm difference in center of gravity [CG] location). Despite those issues, kinetic and deformation measures showed a high degree of repeatability, which is necessary for assessing injury risk in rollover because roof strength positively correlates with injury risk (Brumbelow 2009). Improvements of the test equipment and matching mass properties will ensure highly repeatable initial conditions, vehicle kinematics, kinetics, and deformations.

A contact angle hysteresis model based on the fractal structure of contact line.

PubMed

Wu, Shuai; Ma, Ming

2017-11-01

Contact angle is one of the most popular concept used in fields such as wetting, transport and microfludics. In practice, different contact angles such as equilibrium, receding and advancing contact angles are observed due to hysteresis. The connection among these contact angles is important in revealing the chemical and physical properties of surfaces related to wetting. Inspired by the fractal structure of contact line, we propose a single parameter model depicting the connection of the three angles. This parameter is decided by the fractal structure of the contact line. The results of this model agree with experimental observations. In certain cases, it can be reduced to other existing models. It also provides a new point of view in understanding the physical nature of the contact angle hysteresis. Interestingly, some counter-intuitive phenomena, such as the binary receding angles, are indicated in this model, which are waited to be validated by experiments. Copyright © 2017 Elsevier Inc. All rights reserved.

Sex Differences in Drop Landing: More Apparent in Recreational Surfers Than in Competitive Surfers or Nonsurfers.

PubMed

Bruton, Michaela R; Adams, Roger D; O'Dwyer, Nicholas J

2017-10-01

We suspected that the observed inconsistency of sex differences in drop-landing motor skills might be due to the confounding factor of prior experience. Thus, in this study, we explored the role of experience in shaping male and female surfboard riders' motor skill kinematics during drop landings while surfboard riding. We recruited 42 participants (21 females and 21 males) from three groups of surfing experience levels (competitive surfers, recreational surfers, and nonsurfers), each equally comprising seven males and seven females. Sagittal plane kinematics and vertical ground reaction force data were collected from all participants during a laboratory-based 60-cm drop-landing task. Knee flexion and ankle dorsiflexion at initial ground contact were greater among male participants, independent of experience level. In both sexes, greater range of motion at these joints was related to greater experience. Recreational female surfers landed in a more upright posture with more extended ankle and knee angles and less ankle dorsiflexion at the end of landing than participants in all other groups. We discuss our results in the context of possible remaining experience differences between male and female participants despite being grouped in the same experience levels in our study, individualized motor patterns that may still achieve similar success, and a need for continued research.

Contact angle hysteresis on doubly periodic smooth rough surfaces in Wenzel's regime: The role of the contact line depinning mechanism

NASA Astrophysics Data System (ADS)

Iliev, Stanimir; Pesheva, Nina; Iliev, Pavel

2018-04-01

We report here on the contact angle hysteresis, appearing when a liquid meniscus is in contact with doubly sinusoidal wavelike patterned surfaces in Wenzel's wetting regime. Using the full capillary model we obtain numerically the contact angle hysteresis as a function of the surface roughness factor and the equilibrium contact angle for a block case and a kink case contact line depinning mechanism. We find that the dependencies of the contact angle hysteresis on the surface roughness factor are different for the different contact line depinning mechanisms. These dependencies are different also for the two types of rough surfaces we studied. The relations between advancing, receding, and equilibrium contact angles are investigated. A comparison with the existing asymptotical, numerical, and experimental results is carried out.

Contact angle hysteresis on doubly periodic smooth rough surfaces in Wenzel's regime: The role of the contact line depinning mechanism.

PubMed

Iliev, Stanimir; Pesheva, Nina; Iliev, Pavel

2018-04-01

We report here on the contact angle hysteresis, appearing when a liquid meniscus is in contact with doubly sinusoidal wavelike patterned surfaces in Wenzel's wetting regime. Using the full capillary model we obtain numerically the contact angle hysteresis as a function of the surface roughness factor and the equilibrium contact angle for a block case and a kink case contact line depinning mechanism. We find that the dependencies of the contact angle hysteresis on the surface roughness factor are different for the different contact line depinning mechanisms. These dependencies are different also for the two types of rough surfaces we studied. The relations between advancing, receding, and equilibrium contact angles are investigated. A comparison with the existing asymptotical, numerical, and experimental results is carried out.

Apparent and microscopic dynamic contact angles in confined flows

NASA Astrophysics Data System (ADS)

Omori, Takeshi; Kajishima, Takeo

2017-11-01

An abundance of empirical correlations between a dynamic contact angle and a capillary number representing a translational velocity of a contact line have been provided for the last decades. The experimentally obtained dynamic contact angles are inevitably apparent contact angles but often undistinguished from microscopic contact angles formed right on the wall. As Bonn et al. ["Wetting and spreading," Rev. Mod. Phys. 81, 739-805 (2009)] pointed out, however, most of the experimental studies simply report values of angles recorded at some length scale which is quantitatively unknown. It is therefore hard to evaluate or judge the physical validity and the generality of the empirical correlations. The present study is an attempt to clear this clutter regarding the dynamic contact angle by measuring both the apparent and the microscopic dynamic contact angles from the identical data sets in a well-controlled manner, by means of numerical simulation. The numerical method was constructed so that it reproduced the fine details of the flow with a moving contact line predicted by molecular dynamics simulations [T. Qian, X. Wang, and P. Sheng, "Molecular hydrodynamics of the moving contact line in two-phase immiscible flows," Commun. Comput. Phys. 1, 1-52 (2006)]. We show that the microscopic contact angle as a function of the capillary number has the same form as Blake's molecular-kinetic model [T. Blake and J. Haynes, "Kinetics of liquid/liquid displacement," J. Colloid Interface Sci. 30, 421-423 (1969)], regardless of the way the flow is driven, the channel width, the mechanical properties of the receding fluid, and the value of the equilibrium contact angle under the conditions where the Reynolds and capillary numbers are small. We have also found that the apparent contact angle obtained by the arc-fitting of the interface behaves surprisingly universally as claimed in experimental studies in the literature [e.g., X. Li et al., "An experimental study on dynamic pore wettability," Chem. Eng. Sci. 104, 988-997 (2013)], although the angle deviates significantly from the microscopic contact angle. It leads to a practically important point that it suffices to measure arc-fitted contact angles to make formulae to predict flow rates in capillary tubes.

Differences in Neuromuscular Strategies Between Landing and Cutting Tasks in Female Basketball and Soccer Athletes

PubMed Central

Cowley, Hanni R; Ford, Kevin R; Myer, Gregory D; Kernozek, Thomas W; Hewett, Timothy E

2006-01-01

Context: High school female athletes are most likely to sustain a serious knee injury during soccer or basketball, 2 sports that often involve a rapid deceleration before a change of direction or while landing from a jump. Objective: To determine if female high school basketball and soccer players show neuromuscular differences during landing and cutting tasks and to examine neuromuscular differences between tasks and between dominant and nondominant sides. Design: A 3-way mixed factorial design investigating the effects of sport (basketball, soccer), task (jumping, cutting), and side (dominant, nondominant). Setting: Laboratory. Patients or Other Participants: Thirty high school female athletes who listed either basketball or soccer as their only sport of participation (basketball: n = 15, age = 15.1 ± 1.7 years, experience = 6.9 ± 2.2 years, height = 165.3 ± 7.9 cm, mass = 61.8 ± 9.3 kg; soccer: n = 15, age = 14.8 ± 0.8 years, experience = 8.8 ± 2.5 years, height = 161.8 ± 4.1 cm, mass = 54.6 ± 7.6 kg). Main Outcome Measure(s): Ground reaction forces, stance time, valgus angles, and valgus moments were assessed during (1) a drop vertical jump with an immediate maximal vertical jump and (2) an immediate side-step cut at a 45° angle. Results: Basketball athletes had greater ground reaction forces (P < .001) and decreased stance time (P < .001) during the drop vertical jump, whereas soccer players had greater ground reaction forces (P <.001) and decreased stance time (P < .001) during the cut. Subjects in both sports had greater valgus angles (initial contact and maximum, P = .02 and P = .012, respectively) during cutting than during the drop vertical jump. Greater valgus moments (P = .006) were noted on the dominant side during cutting. Conclusions: Our subjects demonstrated differences in ground reaction forces and stance times during 2 movements associated with noncontact anterior cruciate ligament injuries. Knee valgus moment and angle were significantly influenced by the type of movement performed. Sport-specific neuromuscular training may be warranted, with basketball players focusing on jumping and landing and soccer players focusing on unanticipated cutting maneuvers. PMID:16619097

Capillary Phenomena: Investigations in Compressed Bubble Migration, Geometric Wetting, and Blade-Bound Droplet Stability

NASA Astrophysics Data System (ADS)

Blackmore, William Henry

Capillary flows continue to be important in numerous spacecraft systems where the effective magnitude of the gravity vector is approximately one millionth that of normal Earth gravity. Due to the free fall state of orbiting spacecraft, the effects of capillarity on the fluid systems onboard can dominate the fluid behavior over large length scales. In this research three investigations are pursued where the unique interplay between surface tension forces, wetting characteristics, and system geometry control the fluid behavior, whether in large systems aboard spacecraft, or micro-scale systems on Earth. First, efforts in support of two International Space Station (ISS) experiments are reported. A description of the development of a new NASA ground station at Portland State University is provided along with descriptions of astronaut training activities for the proper operation of four handheld experiments currently in orbit as part of the second iteration of the Capillary Flow Experiments (CFE-2). Concerning the latter, seven more vessels are expected to be launched to the ISS shortly. Analysis of the data alongside numerical simulations shows excellent agreement with theory, and a new intuitive method of viewing critical wetting angles and fluid bulk shift phenomena is offered. Secondly, during the CFE-2 space experiments, unplanned peripheral observations revealed that, on occasion, rapidly compressed air bubbles migrate along paths with vector components common to the residual acceleration onboard the ISS. Unexpectedly however, the migration velocities could be shown to be up to three orders of magnitude greater than the appropriate Stokes flow limit! Likely mechanisms are explored analytically and experimentally while citing prior theoretical works that may have anticipated such phenomena. Once properly understood, compressed bubble migration may be used as an elegant method for phase separation in spacecraft systems or microgravity-based materials manufacturing. Lastly, the stability of drops on surfaces is important in a variety of natural and industrial processes. So called 'wall-edge-vertex bound drops' (a.k.a. drops on blade tips or drops on leaf tips which they resemble) are explored using a numerical approach which applies the Surface Evolver algorithm through implementation of a new file layer and a multi-parameter sweep function. As part of a recently open sourced SE-FIT software, thousands of critical drop configurations are efficiently computed as functions of contact angle, blade edge vertex half-angle, and g-orientation. With the support of other graduate students, simple experiments are performed to benchmark the computations which are then correlated for ease of application. It is shown that sessile, pendant, and wall-edge bound drops are only limiting cases of the more generalized blade-bound drops, and that a ubiquitous 'dry leaf tip' is observed for a range of the critical geometric and wetting parameters.

Condensing Heat Exchanger with Hydrophilic Antimicrobial Coating

NASA Technical Reports Server (NTRS)

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor)

2014-01-01

A multi-layer antimicrobial hydrophilic coating is applied to a substrate of anodized aluminum, although other materials may form the substrate. A silver layer is sputtered onto a thoroughly clean anodized surface of the aluminum to about 400 nm thickness. A layer of crosslinked, silicon-based macromolecular structure about 10 nm thickness overlies the silver layer, and the outermost surface of the layer of crosslinked, silicon-based macromolecular structure is hydroxide terminated to produce a hydrophilic surface with a water drop contact angle of less than 10.degree.. The coated substrate may be one of multiple fins in a condensing heat exchanger for use in the microgravity of space, which has narrow channels defined between angled fins such that the surface tension of condensed water moves water by capillary flow to a central location where it is pumped to storage. The antimicrobial coating prevents obstruction of the capillary passages.

Three-tier rough superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Cao, Yuanzhi; Yuan, Longyan; Hu, Bin; Zhou, Jun

2015-08-01

A three-tier rough superhydrophobic surface was fabricated by growing hydrophobic modified (fluorinated silane) zinc oxide (ZnO)/copper oxide (CuO) hetero-hierarchical structures on silicon (Si) micro-pillar arrays. Compared with the other three control samples with a less rough tier, the three-tier surface exhibits the best water repellency with the largest contact angle 161° and the lowest sliding angle 0.5°. It also shows a robust Cassie state which enables the water to flow with a speed over 2 m s-1. In addition, it could prevent itself from being wetted by the droplet with low surface tension (mixed water and ethanol 1:1 in volume) which reveals a flow speed of 0.6 m s-1 (dropped from the height of 2 cm). All these features prove that adding another rough tier on a two-tier rough surface could futher improve its water-repellent properties.

Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Raza, Muhammad; Kooij, Stefan; van Silfhout, Arend; Zandvliet, Harold; Poelsema, Bene

2011-11-01

The importance of superhydrophobic substrates (contact angle >150° with sliding angle <10°) in modern technology is undeniable. We present a simple colloidal route to manufacture superstructured arrays with single- and multi-length-scaled roughness to obtain sticky and non-sticky superhydrophobic surfaces. The largest length scale is provided by (multi-)layers of silica spheres (1 μm, 500nm and 150nm diameter). Decoration with gold nanoparticles (14nm, 26nm and 47nm) gives rise to a second length scale. To lower the surface energy, gold nanoparticles are functionalized with dodecanethiol and the silica spheres by perfluorooctyltriethoxysilane. The morphology was examined by helium ion microscopy (HIM), while wettability measurements were performed by using the sessile drop method. We conclude that wettability can be controlled by changing the surface chemistry and/or length scales of the structures. To achieve truly non-sticky superhydrophobic surfaces, hierarchical roughness plays a vital role.

Wettability and friction coefficient of micro-magnet arrayed surface

NASA Astrophysics Data System (ADS)

Huang, Wei; Liao, Sijie; Wang, Xiaolei

2012-01-01

Surface coating is an important part of surface engineering and it has been successfully used in many applications to improve the performance of surfaces. In this paper, magnetic arrayed films with different thicknesses were fabricated on the surface of 316 stainless steel disks. Controllable colloid - ferrofluids (FF) was chosen as lubricant, which can be adsorbed on the magnetic surface. The wettability of the micro-magnet arrayed surface was evaluated by measuring the contract angle of FF drops on surface. Tribological experiments were carried out to investigate the effects of magnetic film thickness on frictional properties when lubricated by FF under plane contact condition. It was found that the magnetic arrayed surface with thicker magnetic films presented larger contract angle. The frictional test results showed that samples with thicker magnetic films could reduce friction and wear more efficiently at higher sliding velocity under the lubrication of FF.

Three-tier rough superhydrophobic surfaces.

PubMed

Cao, Yuanzhi; Yuan, Longyan; Hu, Bin; Zhou, Jun

2015-08-07

A three-tier rough superhydrophobic surface was fabricated by growing hydrophobic modified (fluorinated silane) zinc oxide (ZnO)/copper oxide (CuO) hetero-hierarchical structures on silicon (Si) micro-pillar arrays. Compared with the other three control samples with a less rough tier, the three-tier surface exhibits the best water repellency with the largest contact angle 161° and the lowest sliding angle 0.5°. It also shows a robust Cassie state which enables the water to flow with a speed over 2 m s(-1). In addition, it could prevent itself from being wetted by the droplet with low surface tension (mixed water and ethanol 1:1 in volume) which reveals a flow speed of 0.6 m s(-1) (dropped from the height of 2 cm). All these features prove that adding another rough tier on a two-tier rough surface could futher improve its water-repellent properties.

Molecular Simulations of Carbon Dioxide and Water: Cation Solvation and Wettability

NASA Astrophysics Data System (ADS)

Criscenti, L. J.; Bracco, J.; Cygan, R. T.

2010-12-01

Proposed carbon dioxide sequestration scenarios in sedimentary basins require investigation into the interaction between supercritical carbon dioxide, brines, and the mineral phases found in the basin and overlying caprock. Classical molecular dynamics (MD) simulations can be used to investigate some of these interactions such as the partitioning of metal cations between aqueous solutions and supercritical carbon dioxide, and the relative wettability of basin and caprock minerals with different fluid phases including water, carbon dioxide, and oil. Initial research has lead to the development of a new flexible carbon dioxide force field that successfully reproduces the vibrational properties of carbon dioxide, and a methodology for extracting contact angle information from large-scale MD simulations. Molecular simulations were performed to compare the solvation of alkali and alkaline metal cations in water and liquid carbon dioxide at 300K, using a flexible simple point charge (SPC) model for water and the new carbon dioxide force field. Solvation energies for Na+, Cs+, Mg2+, and Ba2+ are larger in water than in carbon dioxide, suggesting that these cations will partition preferentially into water. In both solutions, the solvation energy for the cations decreases with ion size and increases with ion charge. However, changes in solvation energy with increasing ionic radii are smaller in carbon dioxide than in water. Therefore, the overall partitioning of cations into carbon dioxide is predicted to increase with ion size. Molecular dynamics simulations are also useful to examine the relative wettability of minerals with different fluid phases. Large-scale MD simulations involving between 100,000 and 200,000 atoms have been conducted to establish a dynamic equilibrium between a drop of liquid water, water vapor, and kaolinite surfaces. The water drops consisted of at least 1700 molecules. Simulations were performed for five nanoseconds. The contact angle calculated for the siloxane surface of kaolinite is approximately 110°, and compares well with calculated contact angles for silica reported in the literature. The contact angle determined for the gibbsite surface of kaolinite is approximately 13° and compares favorably to reported experimental results. As expected, the siloxane surface is calculated to be hydrophobic and the gibbsite surface hydrophilic. This technique should prove useful to investigate the relative wettability of different minerals with subsurface fluids including supercritical CO2. This material is based upon work partially supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Effect of dimethyl sulfoxide on dentin collagen.

PubMed

Mehtälä, P; Pashley, D H; Tjäderhane, L

2017-08-01

Infiltration of adhesive on dentin matrix depends on interaction of surface and adhesive. Interaction depends on dentin wettability, which can be enhanced either by increasing dentin surface energy or lowering the surface energy of adhesive. The objective was to examine the effect of dimethyl sulfoxide (DMSO) on demineralized dentin wettability and dentin organic matrix expansion. Acid-etched human dentin was used for sessile drop contact angle measurement to test surface wetting on 1-5% DMSO-treated demineralized dentin surface, and linear variable differential transformer (LVDT) to measure expansion/shrinkage of dentinal matrix. DMSO-water binary liquids were examined for surface tension changes through concentrations from 0 to 100% DMSO. Kruskal-Wallis and Mann-Whitney tests were used to test the differences in dentin wettability, expansion and shrinkage, and Spearman test to test the correlation between DMSO concentration and water surface tension. The level of significance was p<0.05. Pretreatment with 1-5% DMSO caused statistically significant concentration-dependent increase in wetting: the immediate contact angles decreased by 11.8% and 46.6% and 60s contact angles by 9.5% and 47.4% with 1% and 5% DMSO, respectively. DMSO-water mixtures concentration-dependently expanded demineralized dentin samples less than pure water, except with high (≥80%) DMSO concentrations which expanded demineralized dentin more than water. Drying times of LVDT samples increased significantly with the use of DMSO. Increased dentin wettability may explain the previously demonstrated increase in adhesive penetration with DMSO-treated dentin, and together with the expansion of collagen matrix after drying may also explain previously observed increase in dentin adhesive bonding. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of Electric Field on the Wetting Behavior of Eutectic Gallium-Indium Alloys in Aqueous Environment

NASA Astrophysics Data System (ADS)

Yuan, Bo; He, Zhi-Zhu; Liu, Jing

2018-02-01

Room-temperature liquid metals have many intriguing properties that have not previously been fully understood. Among them, surface tension behaviors of such metals are especially critical in a group of newly emerging areas such as printed electronics, functional materials and soft machines, etc. This study is dedicated to clarifying the wettability of liquid metals on various substrate surfaces with varied roughness immersed in solutions when subject to an electric field. The contact angles of Ga75.5In24.5 in several typical liquids were comprehensively measured and interpreted, and were revealed to be affected by the components and concentration of the environmental solution. Meanwhile, the roughness of the substrates is also revealed to be an important parameter dominating the process. The dynamic wetting behaviors of liquid metal in aqueous environment under an electric field were quantified. The contact angle values of eutectic gallium-indium alloys (eGaIn) on titanium substrates with different roughness would lead to better electrowetting performances on rougher surfaces. In particular, using an electrical field to control the wetting status of liquid metal with the matching substrate have been illustrated, which would offer a practical way to flexibly control liquid metal-based functional devices working in an aqueous environment. Furthermore, Lippmann-Young's equation reveals the relationship between contact angle and applied voltage, explaining the excellent electrowetting property of eGaIn. The power law, R = αt β , was adopted to characterize the two-stage wetting process of eGaIn under different voltages. In the initial process, β ≈ 1/2 represents the complete wetting law, while the later one, β ≈ 1/10, meets with Tanner's law of a drop spontaneously spreading on a smooth surface.

Apparent-contact-angle model at partial wetting and evaporation: impact of surface forces.

PubMed

Janeček, V; Nikolayev, V S

2013-01-01

This theoretical and numerical study deals with evaporation of a fluid wedge in contact with its pure vapor. The model describes a regime where the continuous wetting film is absent and the actual line of the triple gas-liquid-solid contact appears. A constant temperature higher than the saturation temperature is imposed at the solid substrate. The fluid flow is solved in the lubrication approximation. The introduction of the surface forces in the case of the partial wetting is discussed. The apparent contact angle (the gas-liquid interface slope far from the contact line) is studied numerically as a function of the substrate superheating, contact line velocity, and parameters related to the solid-fluid interaction (Young and microscopic contact angles, Hamaker constant, etc.). The dependence of the apparent contact angle on the substrate temperature is in agreement with existing approaches. For water, the apparent contact angle may be 20° larger than the Young contact angle for 1 K superheating. The effect of the surface forces on the apparent contact angle is found to be weak.

Apparent-contact-angle model at partial wetting and evaporation: Impact of surface forces

NASA Astrophysics Data System (ADS)

Janeček, V.; Nikolayev, V. S.

2013-01-01

This theoretical and numerical study deals with evaporation of a fluid wedge in contact with its pure vapor. The model describes a regime where the continuous wetting film is absent and the actual line of the triple gas-liquid-solid contact appears. A constant temperature higher than the saturation temperature is imposed at the solid substrate. The fluid flow is solved in the lubrication approximation. The introduction of the surface forces in the case of the partial wetting is discussed. The apparent contact angle (the gas-liquid interface slope far from the contact line) is studied numerically as a function of the substrate superheating, contact line velocity, and parameters related to the solid-fluid interaction (Young and microscopic contact angles, Hamaker constant, etc.). The dependence of the apparent contact angle on the substrate temperature is in agreement with existing approaches. For water, the apparent contact angle may be 20∘ larger than the Young contact angle for 1 K superheating. The effect of the surface forces on the apparent contact angle is found to be weak.

Influence of spin creepage and contact angle on curve squeal: A numerical approach

NASA Astrophysics Data System (ADS)

Zenzerovic, I.; Kropp, W.; Pieringer, A.

2018-04-01

Curve squeal is a loud tonal sound that may arise when a railway vehicle negotiates a tight curve. Due to the nonlinear nature of squeal, time-domain models provide a higher degree of accuracy in comparison to frequency-domain models and also enable the determination of squeal amplitudes. In the present paper, a previously developed engineering time-domain model for curve squeal is extended to include the effects of the contact angle and spin creepage. The extensions enable the evaluation of more realistic squeal cases with the computationally efficient model. The model validation against Kalker's variational contact model shows good agreement between the models. Results of studies on the influence of spin creepage and contact angle show that the contact angle has a significant influence on the vertical-lateral dynamics coupling and, therefore, influences both squeal amplitude and frequency. Spin creepage mainly influences processes in the contact, therefore influencing the tangential contact force amplitude. In the combined spin-contact angle study the spin creepage value is kinematically related to the contact angle value. Results indicate that the influence of the contact angle is dominant over the influence of spin creepage. In general, results indicate that the most crucial factors in squeal are those that influence the dynamics coupling: the contact angle, wheel/rail contact positions and friction.

Fabrication of surfaces with extremely high contact angle hysteresis from polyelectrolyte multilayer.

PubMed

Wang, Liming; Wei, Jingjing; Su, Zhaohui

2011-12-20

High contact angle hysteresis on polyelectrolyte multilayers (PEMs) ion-paired with hydrophobic perfluorooctanoate anions is reported. Both the bilayer number of PEMs and the ionic strength of deposition solutions have significant influence on contact angle hysteresis: higher ionic strength and greater bilayer number cause increased contact angle hysteresis values. The hysteresis values of ~100° were observed on smooth PEMs and pinning of the receding contact line on hydrophilic defects is implicated as the cause of hysteresis. Surface roughness can be used to further tune the contact angle hysteresis on the PEMs. A surface with extremely high contact angle hysteresis of 156° was fabricated when a PEM was deposited on a rough substrate coated with submicrometer scale silica spheres. It was demonstrated that this extremely high value of contact angle hysteresis resulted from the penetration of water into the rough asperities on the substrate. The same substrate hydrophobized by chemical vapor deposition of 1H,1H,2H,2H-perfluorooctyltriethoxysilane exhibits high advancing contact angle and low hysteresis. © 2011 American Chemical Society

[Bloodstain pattern analysis on examples from practice: Are calculations with application parabolic trajectory usable?].

PubMed

Makovický, Peter; Matlach, Radek; Pokorná, Olga; Mošna, František; Makovický, Pavol

2015-01-01

The bloodstain pattern analysis (BPA) is useful in the forensic medicine. In Czechoslovakian criminology is this method not commonly used. The objective of this work is to calculate the impact length, height and distance splashing of blood drops. The results are compared with the real values for specific cases. It is also compared to calculate the angle of incidence of blood drops, using sinα with a form using tgα. For this purposes we used two different character cases from practice with well-preserved condition and readable blood stains. Selected blood stains were documented in order to calculate the angle of incidence of blood drops and to calculateorigin splashes. For this drop of blood, the distance of impact of the drops of blood (x), the height of the sprayed blood drops (y) and the length of the flight path the drop of blood (l). The obtained data was retrospectively analysed for the two models. The first straight line is represented by the triangle (M1) and the other is the parabolic model (M2). The formulae were derived using the Euler substitution. The results show that the angle of incidence of the drop of blood can be calculated as sinα and the tgα. When applying, the triangle is appropriate to consider the application and sinα parabolic requires the calculation of the angle of incidence drops of blood tgα. Parabola is useful for the BPA. In Czechoslovakian should be providing workplace training seminars BPA primarily intended for forensic investigators.We recommend the use of this method during investigations, verification of acts in forensic practice.

Ketorolac Ophthalmic

MedlinePlus

... soft contact lenses. You should not use ketorolac eye drops while wearing your soft contact lenses.use caution when driving or operating machinery because your vision may be blurred after you instill the drops.

[Determination of contact angle of pharmaceutical excipients and regulating effect of surfactants on their wettability].

PubMed

Hua, Dong-dong; Li, He-ran; Yang, Bai-xue; Song, Li-na; Liu, Tiao-tiao; Cong, Yu-tang; Li, San-ming

2015-10-01

To study the effects of surfactants on wettability of excipients, the contact angles of six types of surfactants on the surface of two common excipients and mixture of three surfactants with excipients were measured using hypsometry method. The results demonstrated that contact angle of water on the surface of excipients was associated with hydrophilcity of excipients. Contact angle was lowered with increase in hydrophilic groups of excipient molecules. The sequence of contact angle from small to large was starch < sodium benzoate < polyvinylpyrrolidone < sodium carboxymethylcellulose < sodium alginate < chitosan < hydroxypropyl methyl cellulose

Grafted self-assembled monolayers derived from naturally occurring phenolic lipids.

PubMed

Pillot, J-P; Birot, M; Tran, T T T; Dao, T M; Belin, C; Desbat, B; Lazare, S

2005-04-12

Self-assembled monolayers grafted onto silicon surfaces were obtained from the hydrosilylation products by trialcoxysilanes of naturally occurring phenolic lipid allyl ethers. The as-obtained materials were characterized by various physical and physicochemical methods. Thus, contact angles of water drops showed that they possess very high hydrophobicity. Their excellent regularity was corroborated by AFM microscopy. The frequencies of the stretching CH2 infrared modes indicate the presence of alkyl chains mainly in the trans/trans conformation. Additionally, optical ellipsometry and quartz microbalance measurements enabled us to estimate the thickness of the films. The results, as a whole, are in good agreement with the formation of densely packed monolayers.

Contact angle and local wetting at contact line.

PubMed

Li, Ri; Shan, Yanguang

2012-11-06

This theoretical study was motivated by recent experiments and theoretical work that had suggested the dependence of the static contact angle on the local wetting at the triple-phase contact line. We revisit this topic because the static contact angle as a local wetting parameter is still not widely understood and clearly known. To further clarify the relationship of the static contact angle with wetting, two approaches are applied to derive a general equation for the static contact angle of a droplet on a composite surface composed of heterogeneous components. A global approach based on the free surface energy of a thermodynamic system containing the droplet and solid surface shows the static contact angle as a function of local surface chemistry and local wetting state at the contact line. A local approach, in which only local forces acting on the contact line are considered, results in the same equation. The fact that the local approach agrees with the global approach further demonstrates the static contact angle as a local wetting parameter. Additionally, the study also suggests that the wetting described by the Wenzel and Cassie equations is also the local wetting of the contact line rather than the global wetting of the droplet.

Light transfer through windows with external condensation

NASA Astrophysics Data System (ADS)

Zhu, Keyong; Li, Shaoling; Pilon, Laurent

2018-03-01

This study investigates systematically light transfer through windows supporting cap-shaped droplets on their external face. The presence of such droplets may have negative effects on the conversion efficiency of solar cells, distorts image quality of lenses, or hinders visibility through windows and windshields. Here, the directional-hemispherical transmittance was predicted by the Monte Carlo ray-tracing method. The droplets were monodisperse or polydisperse randomly distributed on the outside face of optically smooth windows. For nonabsorbing droplets, the diameter and size distribution did not have a significant effect on the window directional-hemispherical transmittance. The latter was nearly independent of contact angle for incident angle θi ≤ 30°. However, the directional-hemispherical transmittance decreased monotonously with increasing incident angle and droplet contact angle for contact angle θc ≤ 70° to reach a minimum at a contact angle θc,min beyond which it increased with increasing contact angle before reaching a plateau at large contact angles. This was attributed to total internal reflection at the back window/air and droplet/air interfaces. For absorbing droplets, the normal-hemispherical transmittance decreased significantly with increasing droplet contact angle, mean diameter, polydispersity, and projected surface area coverage due to strong absorption within the droplets. Moreover, the normal-hemispherical transmittance decreased with increasing contact angle for θc< 90° and remained constant and independent of the droplets' absorption index, mean diameter, and contact angle for θc ≥ 90°. Finally, Analytical expressions for the upper and lower bounds of the normal-hemispherical transmittance as a function of droplet contact angle, optical properties, and projected surface area coverage were derived.

Beyond Cassie equation: Local structure of heterogeneous surfaces determines the contact angles of microdroplets

PubMed Central

Zhang, Bo; Wang, Jianjun; Liu, Zhiping; Zhang, Xianren

2014-01-01

The application of Cassie equation to microscopic droplets is recently under intense debate because the microdroplet dimension is often of the same order of magnitude as the characteristic size of substrate heterogeneities, and the mechanism to describe the contact angle of microdroplets is not clear. By representing real surfaces statistically as an ensemble of patterned surfaces with randomly or regularly distributed heterogeneities (patches), lattice Boltzmann simulations here show that the contact angle of microdroplets has a wide distribution, either continuous or discrete, depending on the patch size. The origin of multiple contact angles observed is ascribed to the contact line pinning effect induced by substrate heterogeneities. We demonstrate that the local feature of substrate structure near the contact line determines the range of contact angles that can be stabilized, while the certain contact angle observed is closely related to the contact line width. PMID:25059292

Actuation of digital micro drops by electrowetting on open microfluidic chips fabricated in photolithography.

PubMed

Ko, Hyojin; Lee, Jeong Soo; Jung, Chan-Hee; Choi, Jae-Hak; Kwon, Oh-Sun; Shin, Kwanwoo

2014-08-01

Basic manipulations of discrete liquid drops on opened microfluidic chips based on electrowetting on dielectrics were described. While most developed microfluidic chips are closed systems equipped with a top plate to cover mechanically and to contact electrically to drop samples, our chips are opened systems with a single plate without any electric contact to drops directly. The chips consist of a linear array of patterned electrodes at 1.8 mm pitch was fabricated on a glass plate coated with thin hydrophobic and dielectric layers by using various methods including photolithography, spin coating and ion sputtering. Several actuations such as lateral oscillation, colliding mergence and translational motion for 3-10 μL water drops have been demonstrated satisfactory. All these kinetic performances of opened chips were similar to those of closed chip systems, indicating superiority of a none-contact method for the transport of drops on opened microfluidic chips actuated by using electrowetting technique.

Effective Wettability Measurements of CO2-Brine-Sandstone System at Different Reservoir Conditions

NASA Astrophysics Data System (ADS)

Al-Menhali, Ali; Krevor, Samuel

2014-05-01

The wetting properties of CO2-brine-rock systems will have a major impact on the management of CO2 injection processes. The wettability of a system controls the flow and trapping efficiency during the storage of CO2 in geological formations as well as the efficiency of enhanced oil recovery operations. Despite its utility in EOR and the continued development of CCS, little is currently known about the wetting properties of the CO2-brine system on reservoir rocks, and no investigations have been performed assessing the impact of these properties on CO2 flooding for CO2 storage or EOR. The wetting properties of multiphase fluid systems in porous media have major impacts on the multiphase flow properties such as the capillary pressure and relative permeability. While recent studies have shown CO2 to generally act as a non-wetting phase in siliciclastic rocks, some observations report that the contact angle varies with pressure, temperature and water salinity. Additionally, there is a wide range of reported contact angles for this system, from strongly to weakly water-wet. In the case of some minerals, intermediate wet contact angles have been observed. Uncertainty with regard to the wetting properties of CO2-brine systems is currently one of the remaining major unresolved issues with regards to reservoir management of CO2 storage. In this study, we make semi-dynamic capillary pressure measurements of supercritical CO2 and brine at reservoir conditions to observe shifts in the wetting properties. We utilize a novel core analysis technique recently developed by Pini et al in 2012 to evaluate a core-scale effective contact angle. Carbon dioxide is injected at constant flow rate into a core that is initially fully saturated with water, while maintaining a constant outlet pressure. In this scenario, the pressure drop across the core corresponds to the capillary pressure at the inlet face of the core. When compared with mercury intrusion capillary pressure measurements, core-scale effective contact angle can be determined. In addition to providing a quantitative measure of the core-averaged wetting properties, the technique allows for the observation of shifts in contact angle with changing conditions. We examine the wettability changes of the CO2-brine system in Berea sandstone with variations in reservoir conditions including supercritical, gaseous and liquid CO2injection. We evaluate wettability variation within a single rock with temperature, pressure, and salinity across a range of conditions relevant to subsurface CO2 storage. This study will include results of measurements in a Berea sandstone sample across a wide range of conditions representative of subsurface reservoirs suitable for CO2 storage (5-20 MPa, 25-90 oC, 0-5 mol kg-1). The measurement uses X-ray CT imaging in a state of the art core flooding laboratory designed to operate at high temperature, pressure, and concentrated brines.

Effects of foot rotation positions on knee valgus during single-leg drop landing: Implications for ACL injury risk reduction.

PubMed

Teng, P S P; Kong, P W; Leong, K F

2017-06-01

Non-contact anterior cruciate ligament (ACL) injuries commonly occur when athletes land in high risk positions such as knee valgus. The position of the foot at landing may influence the transmission of forces from the ankle to the knee. Using an experimental approach to manipulate foot rotation positions, this study aimed to provide new insights on how knee valgus during single-leg landing may be influenced by foot positions. Eleven male recreational basketball players performed single-leg drop landings from a 30-cm high platform in three foot rotation positions (toe-in, toe-forward and toe-out) at initial contact. A motion capture system and a force plate were used to measure lower extremity kinematics and kinetics. Knee valgus angles at initial contact (KVA) and maximum knee valgus moments (KVM), which were known risk factors associated with ACL injury, were measured. A one-way repeated measures Analysis of Variance was conducted (α=0.05) to compare among the three foot positions. Foot rotation positions were found to have a significant effect on KVA (p<0.001, η 2 =0.66) but the difference between conditions (about 1°) was small and not clinically meaningful. There was a significant effect of foot position on KVM (p<0.001, η 2 =0.55), with increased moment observed in the toe-out position as compared to toe-forward (p=0.012) or toe-in positions (p=0.002). When landing with one leg, athletes should avoid extreme toe-out foot rotation positions to minimise undesirable knee valgus loading associated with non-contact ACL injury risks. Copyright © 2017 Elsevier B.V. All rights reserved.

Forefoot angle at initial contact determines the amplitude of forefoot and rearfoot eversion during running.

PubMed

Monaghan, Gail M; Hsu, Wen-Hao; Lewis, Cara L; Saltzman, Elliot; Hamill, Joseph; Holt, Kenneth G

2014-09-01

Clinically, foot structures are assessed intrinsically - relation of forefoot to rearfoot and rearfoot to leg. We have argued that, from a biomechanical perspective, the interaction of the foot with the ground may influence forces and torques that are propagated through the lower extremity. We proposed that a more appropriate measure is an extrinsic one that may predict the angle the foot makes with ground at contact. The purposes of this study were to determine if the proposed measure predicts contact angles of the forefoot and rearfoot and assess if the magnitude of those angles influences amplitude and duration of foot eversion during running. With the individual in prone, extrinsic clinical forefoot and rearfoot angles were measured relative to the caudal edge of the examination table. Participants ran over ground while frontal plane forefoot and rearfoot contact angles, forefoot and rearfoot eversion amplitude and duration were measured. Participants were grouped twice, once based on forefoot contact inversion angle (moderatemedian) and once based on rearfoot contact inversion angle (moderatemedian). The forefoot and rearfoot extrinsic clinical angles predicted, respectively, the forefoot and rearfoot angles at ground contact. Large forefoot contact angles were associated with greater amplitudes (but not durations) of forefoot and rearfoot eversion during stance. Rearfoot contact angles, however, were associated with neither amplitudes nor durations of forefoot and rearfoot eversion. Possible mechanisms for the increased risk of running injuries associated with large forefoot angles are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-12-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed Central

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-01-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations. PMID:29643592

A method to measure internal contact angle in opaque systems by magnetic resonance imaging.

PubMed

Zhu, Weiqin; Tian, Ye; Gao, Xuefeng; Jiang, Lei

2013-07-23

Internal contact angle is an important parameter for internal wettability characterization. However, due to the limitation of optical imaging, methods available for contact angle measurement are only suitable for transparent or open systems. For most of the practical situations that require contact angle measurement in opaque or enclosed systems, the traditional methods are not effective. Based upon the requirement, a method suitable for contact angle measurement in nontransparent systems is developed by employing MRI technology. In the Article, the method is demonstrated by measuring internal contact angles in opaque cylindrical tubes. It proves that the method also shows great feasibility in transparent situations and opaque capillary systems. By using the method, contact angle in opaque systems could be measured successfully, which is significant in understanding the wetting behaviors in nontransparent systems and calculating interfacial parameters in enclosed systems.

Contact angle adjustment in equation-of-state-based pseudopotential model.

PubMed

Hu, Anjie; Li, Longjian; Uddin, Rizwan; Liu, Dong

2016-05-01

The single component pseudopotential lattice Boltzmann model has been widely applied in multiphase simulation due to its simplicity and stability. In many studies, it has been claimed that this model can be stable for density ratios larger than 1000. However, the application of the model is still limited to small density ratios when the contact angle is considered. The reason is that the original contact angle adjustment method influences the stability of the model. Moreover, simulation results in the present work show that, by applying the original contact angle adjustment method, the density distribution near the wall is artificially changed, and the contact angle is dependent on the surface tension. Hence, it is very inconvenient to apply this method with a fixed contact angle, and the accuracy of the model cannot be guaranteed. To solve these problems, a contact angle adjustment method based on the geometry analysis is proposed and numerically compared with the original method. Simulation results show that, with our contact angle adjustment method, the stability of the model is highly improved when the density ratio is relatively large, and it is independent of the surface tension.

Contact angle adjustment in equation-of-state-based pseudopotential model

NASA Astrophysics Data System (ADS)

Hu, Anjie; Li, Longjian; Uddin, Rizwan; Liu, Dong

2016-05-01

The single component pseudopotential lattice Boltzmann model has been widely applied in multiphase simulation due to its simplicity and stability. In many studies, it has been claimed that this model can be stable for density ratios larger than 1000. However, the application of the model is still limited to small density ratios when the contact angle is considered. The reason is that the original contact angle adjustment method influences the stability of the model. Moreover, simulation results in the present work show that, by applying the original contact angle adjustment method, the density distribution near the wall is artificially changed, and the contact angle is dependent on the surface tension. Hence, it is very inconvenient to apply this method with a fixed contact angle, and the accuracy of the model cannot be guaranteed. To solve these problems, a contact angle adjustment method based on the geometry analysis is proposed and numerically compared with the original method. Simulation results show that, with our contact angle adjustment method, the stability of the model is highly improved when the density ratio is relatively large, and it is independent of the surface tension.

Desiccation of a pool of blood: from fluid mechanics to forensic investigations

NASA Astrophysics Data System (ADS)

Nicloux, Celine; Brutin, David

2012-11-01

The evaporation of biological fluids (with droplet configuration) has been studied since a few years due to several applications in medical fields such as medical tests, drug screening, biostabilization... The evaporation of a drop of whole blood leads to the formation of final typical pattern of cracks. Flow motion, adhesion, gelation and fracturation all occur during the evaporation of this complex matter. During the drying, a sol-gel transition develops. The evaporation of a pool of blood is studied in order to link the pattern formation and the evaporation dynamics. We intend to transfer the knowledge acquired for drops on pool to improve the forensic investigations. In this study, we focus on both pool of blood and pure water to determine the transition region from drop to pool and then to characterize the evaporation rate in the pool configuration. The spreading of blood which can be seen as a complex fluid is strongly influenced the substrate nature. The initial contact angle of blood on different substrate nature will influence the maximum thickness of the layer and then will influence the evaporation mass flux. The authors gratefully acknowledge the help and the fruitful discussions raised with A. Boccoz.

Effect of nanoparticle size on sessile droplet contact angle

NASA Astrophysics Data System (ADS)

Munshi, A. M.; Singh, V. N.; Kumar, Mukesh; Singh, J. P.

2008-04-01

We report a significant variation in the static contact angle measured on indium oxide (IO) nanoparticle coated Si substrates that have different nanoparticle sizes. These IO nanoparticles, which have well defined shape and sizes, were synthesized by chemical vapor deposition in a horizontal alumina tube furnace. The size of the IO nanoparticles was varied by changing the source material, substrate temperature, and the deposition time. A sessile droplet method was used to determine the macroscopic contact angle on these IO nanoparticle covered Si substrate using two different liquids: de-ionized water and diethylene glycol (DEG). It was observed that contact angle depends strongly on the nanoparticle size. The contact angle was found to vary from 24° to 67° for de-ionized water droplet and from 15° to 60° for DEG droplet, for the nanoparticle sizes varying from 14 to 620 nm. The contact angle decreases with a decrease in the particles size. We have performed a theoretical analysis to determine the dependence of contact angle on the nanoparticle size. This formulation qualitatively shows a similar trend of decrease in the contact angle with a decrease in nanoparticle size. Providing a rough estimate of nanoparticle size by sessile droplet contact angle measurement is the novelty in this work.

Asymmetric or symmetric bilayer formation during oblique drop impact depends on rheological properties of saturated and unsaturated lipid monolayers.

PubMed

Vranceanu, Marcel; Terinte, Nicoleta; Nirschl, Hermann; Leneweit, Gero

2011-02-01

Bilayer structures are formed by approaching two liquid surfaces with phospholipid monolayers, which are brought into contact by oblique drop impact on a liquid surface. Asymmetric bilayers can be produced by the coupling of drop and target monolayers. In contrast, symmetric bilayers or multilayers are formed by collapse of the compressed target monolayer. We show that under all studied conditions bilayer/multilayer synthesis takes place. The experimental conditions for the synthesis of asymmetric or symmetric bilayers are described quantitatively in terms of the surface rheological (surface elasticity and dilational viscosity) and the hydrodynamical parameters (Weber number and impact angle). The composition and mechanical properties of the phospholipid monolayers strongly influences the patterns of drop impact and the bilayer/multilayer formation. Cholesterol stiffens unsaturated phospholipid monolayers and fluidifies saturated monolayers. All monolayers form asymmetric vesicle-like structures, which are stable in the aqueous medium. Additionally, unsaturated phospholipid monolayers without cholesterol form symmetric vesicles by folding parts of the target monolayer. Sufficient presence of cholesterol in unsaturated phospholipid monolayers inhibits the folding of the target monolayer and the subsequent formation of symmetric bilayers. The rheological properties of saturated and unsaturated phospholipid monolayers and their mixtures with cholesterol are discussed. Based on drop impact results it is shown that the state of a so far undefined region in the DPPC/cholesterol phase diagram is a fluid phase. Copyright © 2010 Elsevier Inc. All rights reserved.

Measuring contact angle and meniscus shape with a reflected laser beam.

PubMed

Eibach, T F; Fell, D; Nguyen, H; Butt, H J; Auernhammer, G K

2014-01-01

Side-view imaging of the contact angle between an extended planar solid surface and a liquid is problematic. Even when aligning the view perfectly parallel to the contact line, focusing one point of the contact line is not possible. We describe a new measurement technique for determining contact angles with the reflection of a widened laser sheet on a moving contact line. We verified this new technique measuring the contact angle on a cylinder, rotating partially immersed in a liquid. A laser sheet is inclined under an angle φ to the unperturbed liquid surface and is reflected off the meniscus. Collected on a screen, the reflection image contains information to determine the contact angle. When dividing the laser sheet into an array of laser rays by placing a mesh into the beam path, the shape of the meniscus can be reconstructed from the reflection image. We verified the method by measuring the receding contact angle versus speed for aqueous cetyltrimethyl ammonium bromide solutions on a smooth hydrophobized as well as on a rough polystyrene surface.

Measuring contact angle and meniscus shape with a reflected laser beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eibach, T. F.; Nguyen, H.; Butt, H. J.

2014-01-15

Side-view imaging of the contact angle between an extended planar solid surface and a liquid is problematic. Even when aligning the view perfectly parallel to the contact line, focusing one point of the contact line is not possible. We describe a new measurement technique for determining contact angles with the reflection of a widened laser sheet on a moving contact line. We verified this new technique measuring the contact angle on a cylinder, rotating partially immersed in a liquid. A laser sheet is inclined under an angle φ to the unperturbed liquid surface and is reflected off the meniscus. Collectedmore » on a screen, the reflection image contains information to determine the contact angle. When dividing the laser sheet into an array of laser rays by placing a mesh into the beam path, the shape of the meniscus can be reconstructed from the reflection image. We verified the method by measuring the receding contact angle versus speed for aqueous cetyltrimethyl ammonium bromide solutions on a smooth hydrophobized as well as on a rough polystyrene surface.« less

Drop impact upon micro- and nanostructured superhydrophobic surfaces.

PubMed

Tsai, Peichun; Pacheco, Sergio; Pirat, Christophe; Lefferts, Leon; Lohse, Detlef

2009-10-20

We experimentally investigate drop impact dynamics onto different superhydrophobic surfaces, consisting of regular polymeric micropatterns and rough carbon nanofibers, with similar static contact angles. The main control parameters are the Weber number We and the roughness of the surface. At small We, i.e., small impact velocity, the impact evolutions are similar for both types of substrates, exhibiting Fakir state, complete bouncing, partial rebouncing, trapping of an air bubble, jetting, and sticky vibrating water balls. At large We, splashing impacts emerge forming several satellite droplets, which are more pronounced for the multiscale rough carbon nanofiber jungles. The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small We less than or approximately equal 120 but an important one for large We greater than or approximately equal 120. Finally, we find the effect of ambient air pressure to be negligible in the explored parameter regime We less than or approximately equal 150.

Drop-Off Detection with the Long Cane: Effects of Different Cane Techniques on Performance

ERIC Educational Resources Information Center

Kim, Dae Shik; Emerson, Robert Wall; Curtis, Amy

2009-01-01

This study compared the drop-off detection performance with the two-point touch and constant contact cane techniques using a repeated-measures design with a convenience sample of 15 cane users with visual impairments. The constant contact technique was superior to the two-point touch technique in the drop-off detection rate and the 50% detection…

A fiber-optic technique for the measurement of contact angle in a clearance-fit pin-loaded hole

NASA Technical Reports Server (NTRS)

Prabhakaran, R.; Naik, R. A.

1987-01-01

A fiber-optic technique for measuring contact angle during pin loading of a specimen is proposed. The experimental design and procedures for loading a 49.8-mm-diameter instrumented pin into an quasi-isotropic graphite-epoxy specimen are described. The optical fiber was located just above the surface of the pin outer diameter in order to obtain accurate pin-hole contact-angle measurements at increasing load levels. The movement of the optical fiber through the no-contact, contact, and no-contact regions is discussed; the photodiode output decreased monotonically as the fiber moved from the no-contact to the contact region and then decreased monotonically as the fiber moved from the contact region to the no-contact region. Variations in the contact angle measurements are examined as function of applied load level. The measurements are compared to contact angle values obtained using a finite element analysis and an electrical technique; it is determined that the data correlate well.

Drop-off detection with the long cane: effect of cane shaft weight and rigidity on performance

PubMed Central

Kim, Dae Shik; Emerson, Robert Wall; Naghshineh, Koorosh; Auer, Alexander

2016-01-01

Most travellers who are blind rely on a long cane to detect drop-offs on their walking paths. We examined how different cane shaft materials affect drop-off detection performance through providing different vibrotactile and proprioceptive feedbacks to the cane user. Results of the study showed a significant interaction between cane shaft weight and how the cane is used. A heavier cane was advantageous for detecting drop-offs when the individual used the ‘constant contact technique’ – cane tip stays in contact with the walking surface at all times – but not when he used the ‘two-point touch technique’ – cane tip is rhythmically tapped on the surface. In addition, a more flexible cane was advantageous for detecting drop-offs when the two-point touch technique was used but not when the constant contact technique was used. It is recommended that, when blind individuals select a cane shaft material, they consider which long cane technique they use more often. Practitioner Summary: Long cane shaft material affects how well a blind individual can detect drop-offs. A heavier shaft was advantageous when using the constant contact technique (cane tip stays in continuous contact with the surface), while a more flexible shaft was better when using the two-point touch technique (cane tip rhythmically taps the surface). PMID:27065052

Investigation of the Dynamic Contact Angle Using a Direct Numerical Simulation Method.

PubMed

Zhu, Guangpu; Yao, Jun; Zhang, Lei; Sun, Hai; Li, Aifen; Shams, Bilal

2016-11-15

A large amount of residual oil, which exists as isolated oil slugs, remains trapped in reservoirs after water flooding. Numerous numerical studies are performed to investigate the fundamental flow mechanism of oil slugs to improve flooding efficiency. Dynamic contact angle models are usually introduced to simulate an accurate contact angle and meniscus displacement of oil slugs under a high capillary number. Nevertheless, in the oil slug flow simulation process, it is unnecessary to introduce the dynamic contact angle model because of a negligible change in the meniscus displacement after using the dynamic contact angle model when the capillary number is small. Therefore, a critical capillary number should be introduced to judge whether the dynamic contact model should be incorporated into simulations. In this study, a direct numerical simulation method is employed to simulate the oil slug flow in a capillary tube at the pore scale. The position of the interface between water and the oil slug is determined using the phase-field method. The capacity and accuracy of the model are validated using a classical benchmark: a dynamic capillary filling process. Then, different dynamic contact angle models and the factors that affect the dynamic contact angle are analyzed. The meniscus displacements of oil slugs with a dynamic contact angle and a static contact angle (SCA) are obtained during simulations, and the relative error between them is calculated automatically. The relative error limit has been defined to be 5%, beyond which the dynamic contact angle model needs to be incorporated into the simulation to approach the realistic displacement. Thus, the desired critical capillary number can be determined. A three-dimensional universal chart of critical capillary number, which functions as static contact angle and viscosity ratio, is given to provide a guideline for oil slug simulation. Also, a fitting formula is presented for ease of use.

In Situ Local Contact Angle Measurement in a CO2-Brine-Sand System Using Microfocused X-ray CT.

PubMed

Lv, Pengfei; Liu, Yu; Wang, Zhe; Liu, Shuyang; Jiang, Lanlan; Chen, Junlin; Song, Yongchen

2017-04-11

The wettability of porous media is of major interest in a broad range of natural and engineering applications. The wettability of a fluid on a solid surface is usually evaluated by the contact angle between them. While in situ local contact angle measurements are complicated by the topology of porous media, which can make it difficult to use traditional methods, recent advances in microfocused X-ray computed tomography (micro-CT) and image processing techniques have made it possible to measure contact angles on the scale of the pore sizes in such media. However, the effects of ionic strength, CO 2 phase, and flow pattern (drainage or imbibition) on pore-scale contact angle distribution are still not clear and have not been reported in detail in previous studies. In this study, we employed a micro-CT scanner for in situ investigation of local contact angles in a CO 2 -brine-sand system under various conditions. The effects of ionic strength, CO 2 phase, and flow pattern on the local contact-angle distribution were examined in detail. The results showed that the local contact angles vary over a wide range as a result of the interaction of surface contaminants, roughness, pore topology, and capillarity. The wettability of a porous surface could thus slowly weaken with increasing ionic strength, and the average contact angle could significantly increase when gaseous CO 2 (gCO 2 ) turns into supercritical CO 2 (scCO 2 ). Contact angle hysteresis also occurred between drainage and imbibition procedures, and the hysteresis was more significant under gCO 2 condition.

A level-set method for two-phase flows with moving contact line and insoluble surfactant

NASA Astrophysics Data System (ADS)

Xu, Jian-Jun; Ren, Weiqing

2014-04-01

A level-set method for two-phase flows with moving contact line and insoluble surfactant is presented. The mathematical model consists of the Navier-Stokes equation for the flow field, a convection-diffusion equation for the surfactant concentration, together with the Navier boundary condition and a condition for the dynamic contact angle derived by Ren et al. (2010) [37]. The numerical method is based on the level-set continuum surface force method for two-phase flows with surfactant developed by Xu et al. (2012) [54] with some cautious treatment for the boundary conditions. The numerical method consists of three components: a flow solver for the velocity field, a solver for the surfactant concentration, and a solver for the level-set function. In the flow solver, the surface force is dealt with using the continuum surface force model. The unbalanced Young stress at the moving contact line is incorporated into the Navier boundary condition. A convergence study of the numerical method and a parametric study are presented. The influence of surfactant on the dynamics of the moving contact line is illustrated using examples. The capability of the level-set method to handle complex geometries is demonstrated by simulating a pendant drop detaching from a wall under gravity.

Modeling drop impacts on inclined flowing soap films

NASA Astrophysics Data System (ADS)

Basu, Saikat; Yawar, Ali; Concha, Andres; Bandi, Mahesh

2015-11-01

Small drops impinging on soap films flowing at an angle primarily exhibit three fundamental regimes of post-impact dynamics: (a) the drop bounces off the film surface, (b) it coalesces with the downstream flow, and (c) it pierces through the film. During impact, the drop deforms along with a simultaneous, almost elastic deformation of the film transverse to the stream direction. Hence, the governing dynamics for this interaction present the rare opportunity to explore the in-tandem effects of elasticity and hydrodynamics alike. In this talk, we outline the analytical framework to study the drop impact dynamics. The model assumes a deformable drop and a deformable three-dimensional soap film and invokes a parametric study to qualify the three mentioned impact types. The physical parameters include the impact angle, drop impact speed, and the diameters of the drop prior to and during impact when it deforms and spreads out. Our model system offers a path towards optimization of interactions between a spray and a flowing liquid.

Modeling Thermal Contact Resistance

NASA Technical Reports Server (NTRS)

Kittel, Peter; Sperans, Joel (Technical Monitor)

1994-01-01

One difficulty in using cryocoolers is making good thermal contact between the cooler and the instrument being cooled. The connection is often made through a bolted joint. The temperature drop associated with this joint has been the subject of many experimental and theoretical studies. The low temperature behavior of dry joints have shown some anomalous dependence on the surface condition of the mating parts. There is also some doubts on how well one can extrapolate from the test samples to predicting the performance of a real system. Both finite element and analytic models of a simple contact system have been developed. The model assumes (a) the contact is dry (contact limited to a small portion of the total available area and the spaces in-between the actual contact patches are perfect insulators), (b) contacts are clean (conductivity of the actual contact is the same as the bulk), (c) small temperature gradients (the bulk conductance may be assumed to be temperature independent), (d) the absolute temperature is low (thermal radiation effects are ignored), and (e) the dimensions of the nominal contact area are small compared to the thickness of the bulk material (the contact effects are localized near the contact). The models show that in the limit of actual contact area much less than the nominal area (a much less than A), that the excess temperature drop due to a single point of contact scales as a(exp -1/2). This disturbance only extends a distance approx. A(exp 1/2) into the bulk material. A group of identical contacts will result in an excess temperature drop that scales as n(exp -1/2), where n is the number of contacts and n dot a is constant. This implies that flat rough surfaces will have a lower excess temperature drop than flat polished surfaces.

Effect of Oxygen Inhibition Layer of Universal Adhesives on Enamel Bond Fatigue Durability and Interfacial Characteristics With Different Etching Modes.

PubMed

Ouchi, H; Tsujimoto, A; Nojiri, K; Hirai, K; Takamizawa, T; Barkmeier, W W; Latta, M A; Miyazaki, M

The purpose of this study was to evaluate the effect of the oxygen inhibition layer of universal adhesive on enamel bond fatigue durability and interfacial characteristics with different etching modes. The three universal adhesives used were Scotchbond Universal Adhesive (3M ESPE, St Paul, MN, USA), Adhese Universal (Ivoclar Vivadent, Schaan, Lichtenstein), and G-Premio Bond (GC, Tokyo, Japan). The initial shear bond strength and shear fatigue strength to enamel was determined in the presence and absence of the oxygen inhibition layer, with and without phosphoric acid pre-etching. The water contact angle was also measured in all groups using the sessile drop method. The enamel bonding specimens with an oxygen inhibition layer showed significantly higher (p<0.05) initial shear bond strengths and shear fatigue strengths than those without, regardless of the adhesive type and etching mode. Moreover, the water contact angles on the specimens with an oxygen inhibition layer were significantly lower (p<0.05) than on those without, regardless of etching mode. The results of this study suggest that the oxygen inhibition layer of universal adhesives significantly increases the enamel bond fatigue durability and greatly changes interfacial characteristics, suggesting that the bond fatigue durability and interfacial characteristics of these adhesives strongly rely on its presence.

Induced superhydrophobic and antimicrobial character of zinc metal modified ceramic wall tile surfaces

NASA Astrophysics Data System (ADS)

Özcan, Selçuk; Açıkbaş, Gökhan; Çalış Açıkbaş, Nurcan

2018-04-01

Hydrophobic surfaces are also known to have antimicrobial effect by restricting the adherence of microorganisms. However, ceramic products are produced by high temperature processes resulting in a hydrophilic surface. In this study, an industrial ceramic wall tile glaze composition was modified by the inclusion of metallic zinc powder in the glaze suspension applied on the pre-sintered wall tile bodies by spraying. The glazed tiles were gloss fired at industrially applicable peak temperatures ranging from 980 °C to 1100 °C. The fired tile surfaces were coated with a commercial fluoropolymer avoiding water absorption. The surfaces were characterized with SEM, EDS, XRD techniques, roughness, sessile water drop contact angle, surface energy measurements, and standard antimicrobial tests. The surface hydrophobicity and the antimicrobial activity results were compared with that of unmodified, uncoated gloss fired wall tiles. A superhydrophobic contact angle of 150° was achieved at 1000 °C peak temperature due to the formation of micro-structured nanocrystalline zinc oxide granules providing a specific surface topography. At higher peak temperatures the hydrophobicity was lost as the specific granular surface topography deteriorated with the conversion of zinc oxide granules to the ubiquitous willemite crystals embedded in the glassy matrix. The antimicrobial efficacy also correlated with the hydrophobic character.

Effect of MnO content on the interfacial property of mold flux and steel

NASA Astrophysics Data System (ADS)

Wang, Wanlin; Li, Jingwen; Zhou, Lejun; Yang, Jian

2016-07-01

The interfacial property between liquid mold flux and steel has significant impact on the quality of casting slab, and this property is mainly determined by the chemical composition of mold flux and the reaction between the flux and steel. The effect of MnO content on the contact angle and interfacial tension between liquid mold flux and ultra-low carbon steel was investigated by sessile drop method in this article, and the results suggested that both the contact angle and interfacial tension decreased with the increase of MnO content in the mold flux. The increase of Si and Mn and the reduction of Al and Ti in the interaction layer were caused by the chemical reactions occurred in the vicinity of interface between mold flux and steel substrate. Besides, the thickness of the interaction layer increased from 4 μm to 7 μm, then to 9 μm, 11 μm and 15 μm when the MnO content was added from 1 wt% to 3 wt%, then to 5 wt%, 7 wt%, and 9 wt% due to the fact that MnO can simplify the polymerized structure of the melt and improve the penetrability of molten mold flux to make the interfacial reaction easier.

Impregnation transition in a powder

NASA Astrophysics Data System (ADS)

Raux, Pascal; Cockenpot, Heloise; Quere, David; Clanet, Christophe

2011-11-01

When an initially dry pile of micrometrical grains comes into contact with a liquid, one can observe different behaviors, function of the wetting properties. If the contact angle with the solid is low, the liquid will invade the pile (impregnation), while for higher contact angles, the grains will stay dry. We present an experimental study of this phenomenon: a dry pile of glass beads is deposed on the liquid surface, and we vary the contact angle of the liquid on the grains. We report a critical contact angle below which impregnation always occurs, and develop a model to explain its value. Different parameters modifying this critical contact angle are also investigated. Collaboration with Marco Ramaioli, Nestle Research Center, Lausanne, Switzerland.

Bilateral contact ground reaction forces and contact times during plyometric drop jumping.

PubMed

Ball, Nick B; Stock, Christopher G; Scurr, Joanna C

2010-10-01

Drop jumping (DJ) is used in training programs aimed to improve lower extremity explosive power. When performing double-leg drop jumps, it is important to provide an equal stimulus to both legs to ensure balanced development of the lower legs. The aim of this study was to bilaterally analyze the ground reactions forces and temporal components of drop jumping from 3 heights. Ten recreationally active male subjects completed 3 bounce-drop jumps from 3 starting heights (0.2, 0.4, and 0.6 m). Two linked force platforms were used to record left- and right-leg peak vertical force, time to peak force, average force, ground contact time, impulse and time differential. Between-height and between-leg comparisons for each variable were made using a multivariate analysis of variance with post hoc Wilcoxon tests (p < 0.05). Results indicated that force and time variables increased as drop jump height increased (p < 0.0001). Post hoc analyses showed that at 0.2- and 0.4-m bilateral differences were present in the time to peak force, average force, and impulse. No bilateral differences for any variables were shown at 0.6-m starting height. The contact time for all jumps was <0.26 seconds. At 0.2 m, only 63% of the subjects had a starting time differential of <0.01 seconds, rising to 96.3% at 0.6 m. The results indicated that 0.6 m is the suggested drop jump height to ensure that no bilateral differences in vertical forces and temporal components occur; however, shorter contact times were found at the lower heights.

Estimation of dynamic stability parameters from drop model flight tests

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Iliff, K. W.

1981-01-01

A recent NASA application of a remotely-piloted drop model to studies of the high angle-of-attack and spinning characteristics of a fighter configuration has provided an opportunity to evaluate and develop parameter estimation methods for the complex aerodynamic environment associated with high angles of attack. The paper discusses the overall drop model operation including descriptions of the model, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods used. Static and dynamic stability derivatives were obtained for an angle-of-attack range from -20 deg to 53 deg. The results of the study indicated that the variations of the estimates with angle of attack were consistent for most of the static derivatives, and the effects of configuration modifications to the model (such as nose strakes) were apparent in the static derivative estimates. The dynamic derivatives exhibited greater uncertainty levels than the static derivatives, possibly due to nonlinear aerodynamics, model response characteristics, or additional derivatives.

Molecular Modeling of Three Phase Contact for Static and Dynamic Contact Angle Phenomena

NASA Astrophysics Data System (ADS)

Malani, Ateeque; Amat, Miguel; Raghavanpillai, Anilkumar; Wysong, Ernest; Rutledge, Gregory

2012-02-01

Interfacial phenomena arise in a number of industrially important situations, such as repellency of liquids on surfaces, condensation, etc. In designing materials for such applications, the key component is their wetting behavior, which is characterized by three-phase static and dynamic contact angle phenomena. Molecular modeling has the potential to provide basic insight into the detailed picture of the three-phase contact line resolved on the sub-nanometer scale which is essential for the success of these materials. We have proposed a computational strategy to study three-phase contact phenomena, where buoyancy of a solid rod or particle is studied in a planar liquid film. The contact angle is readily evaluated by measuring the position of solid and liquid interfaces. As proof of concept, the methodology has been validated extensively using a simple Lennard-Jones (LJ) fluid in contact with an LJ surface. In the dynamic contact angle analysis, the evolution of contact angle as a function of force applied to the rod or particle is characterized by the pinning and slipping of the three phase contact line. Ultimately, complete wetting or de-wetting is observed, allowing molecular level characterization of the contact angle hysteresis.

Calculation of contact angles at triple phase boundary in solid oxide fuel cell anode using the level set method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xiaojun; Hasegawa, Yosuke; CREST, JST

2014-10-15

A level set method is applied to characterize the three dimensional structures of nickel, yttria stabilized zirconia and pore phases in solid oxide fuel cell anode reconstructed by focused ion beam-scanning electron microscope. A numerical algorithm is developed to evaluate the contact angles at the triple phase boundary based on interfacial normal vectors which can be calculated from the signed distance functions defined for each of the three phases. Furthermore, surface tension force is estimated from the contact angles by assuming the interfacial force balance at the triple phase boundary. The average contact angle values of nickel, yttria stabilized zirconiamore » and pore are found to be 143°–156°, 83°–138° and 82°–123°, respectively. The mean contact angles remained nearly unchanged after 100 hour operation. However, the contact angles just after reduction are different for the cells with different sintering temperatures. In addition, standard deviations of the contact angles are very large especially for yttria stabilized zirconia and pore phases. The calculated surface tension forces from mean contact angles were close to the experimental values found in the literature. Slight increase of surface tensions of nickel/pore and nickel/yttria stabilized zirconia were observed after operation. Present data are expected to be used not only for the understanding of the degradation mechanism, but also for the quantitative prediction of the microstructural temporal evolution of solid oxide fuel cell anode. - Highlights: • A level set method is applied to characterize the 3D structures of SOFC anode. • A numerical algorithm is developed to evaluate the contact angles at the TPB. • Surface tension force is estimated from the contact angles. • The average contact angle values are found to be 143o-156o, 83o-138o and 82o-123o. • Present data are expected to understand degradation and predict evolution of SOFC.« less

Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Raza, Muhammad Akram; Kooij, Stefan; van Silfhout, Arend; Zandvliet, Harold; Poelsema, Bene; Physics Of Interfaces; Nanomaterials Team

2011-03-01

The importance of superhydrophobic substrates (contact angle > 150 r withslidingangle 10 r) inmoderntechnologyisundeniable . Wepresentasimplecolloidalroutetomanufacturesuperstructuredarrayswithsingle - andmulti - length - scaledroughnesstoobtainstickyandnon - stickysuperhydrophobicsurfaces . Thelargestlengthscaleisprovidedby (multi -) layersofsilicaspheres (1 μ m, 500nm and 150nm diameter). Decoration with gold nanoparticles (14nm, 26nm and 47nm) gives rise to a second length scale. To lower the surface energy, gold nanoparticles are functionalized with dodecanethiol and the silica spheres by perfluorooctyltriethoxysilane. The morphology was examined by helium ion microscopy (HIM), while wettability measurements were performed by using the sessile drop method. We conclude that wettability can be controlled by changing the surface chemistry and/or length scales of the structures. To achieve truly non-sticky superhydrophobic surfaces, hierarchical roughness plays a vital role.

Wettability dynamics of liquid filaments on horizontal substrates

NASA Astrophysics Data System (ADS)

Diez, Javier; Ravazzoli, Pablo; Cuellar, Ingrith; Gonzalez, Alejandro

2017-11-01

We study the hydrodynamic mechanisms involved in the motion of the contact line formed at the end region of a liquid filament laying on a planar and horizontal substrate. Since the flow develops under partially wetting conditions, the tip of the filament recedes and forms a bulged region (head) that subsequently develops a neck region behind it. Later the neck breaks up leading to a separated drop, while the rest of the filament restarts the sequence. One main feature of this flow is that the whole dynamics and final drop shapes are strongly influenced by the hysteresis of the contact angle typical in most of the liquid-substrate systems. The time evolution till breakup is studied experimentally and pictured in terms of a hybrid wettability theory which involves the Cox-Voinov hydrodynamic approach combined with the molecular kinetic theory developed by Blake. The parameters of this theory are determined for our liquid-substrate system (silicone oil ``coated glass). The experimental results of the retracting filament are described in terms of a simple heuristic model and compared with numerical simulations of the full Navier-Stokes equations. This study is of special interest in the context of pulsed laser-induced dewetting. The authors acknowledge support from Consejo Nacional de Investigaciones Cientficas y Tcnicas (CONICET, Argentina) with Grant PIP 844/2012 and Agencia Nacional de Promocin Cientfica y Tecnolgica (ANPCyT, Argentina) with Grant PICT 931/2012.

Bilateral neuromuscular and force differences during a plyometric task.

PubMed

Ball, Nick B; Scurr, Joanna C

2009-08-01

The purpose of this article is to compare the bilateral neuromuscular and force contribution during a plyometric bounce drop jump task and to assess the affects of nonsimultaneous foot placement. Sixteen male participants performed bounce drop jumps from a height of 0.4 m. Mean peak electromyography activity of the soleus, medial, and lateral gastrocnemius of both legs was recorded from each phase of the drop jump and normalized to a reference dynamic muscle action. Resultant ground reaction force, ground contact time, and duration of the drop jumps were recorded from each leg. Multivariate analysis of variance was used to compare bilateral electromyographic activity, resultant peak ground reaction force, and contact duration. Pearson's correlations (r) ascertained relationships between normalized electromyographic activity and contact time. Significant differences were shown between left and right triceps surae normalized electromyography during precontact and contact40ms (p < 0.01). No significant differences were present in the contactpost40ms phase (p > 0.01). Significant differences were found between normalized soleus electromyography and both gastrocnemii for both legs during precontact (p < 0.01). No significant differences were found for within-leg normalized electromyography for the contact40ms phases and contactpost40ms phase (p > 0.01). Weak relationships were found between normalized electromyographic activity and nonsimultaneous foot contact (r < 0.2). This study showed differences between left and right triceps surae in neuromuscular strategies engaged in the early stages of a drop jump task. Differences in contact time initiation were present; however, they are not significant enough to cause neuromuscular differences in the plantar flexor muscles.

Travoprost Ophthalmic

MedlinePlus

... by soft contact lenses. If you wear contact lenses, remove them before instilling travoprost and put them back in 15 minutes later.if you have an eye injury, infection, or surgery while using travoprost eye drops, ask your doctor if you should continue using the same eye drops container.

ODS - modified TiO2 nanoparticles for the preparation of self-cleaning superhydrophobic coating

NASA Astrophysics Data System (ADS)

Kokare, Ashvini M.; Sutar, Rajaram S.; Deshmukh, S. G.; Xing, Ruimin; Liu, Shanhu; Latthe, Sanjay S.

2018-05-01

Rolling water drops takes off dust particles from lotus leaf showing self-cleaning performance. Self-cleaning effect has great importance in industry as well as in daily life. The present paper describes the preparation of self-cleaning superhydrophobic coating through simple and low cost dip coating technique. The prepared superhydrophobic surface enact as lotus leaf. Firstly TiO2 nanoparticles were dispersed in ethanol and different concentration of octadecyltrichlorosilane (ODS) was added in TiO2 dispersion. The effect of number of deposition layer on the wettability of the coating was studied. The coating prepared from five deposition layers showed contact angle higher than 150° and sliding angle less than 10°. The superhydrophobicity increases with increasing concentration of ODS. The hierarchical rough morphology which is preferable for superhydrophobicity was obtained. The prepared coatings were stable against water jet impact and showed repellent towards colored and muddy water. Such superhydrophobic coating can find enormous scope in self-cleaning application.

Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution

NASA Astrophysics Data System (ADS)

Derby, Brian

2010-08-01

Inkjet printing is viewed as a versatile manufacturing tool for applications in materials fabrication in addition to its traditional role in graphics output and marking. The unifying feature in all these applications is the dispensing and precise positioning of very small volumes of fluid (1-100 picoliters) on a substrate before transformation to a solid. The application of inkjet printing to the fabrication of structures for structural or functional materials applications requires an understanding as to how the physical processes that operate during inkjet printing interact with the properties of the fluid precursors used. Here we review the current state of understanding of the mechanisms of drop formation and how this defines the fluid properties that are required for a given liquid to be printable. The interactions between individual drops and the substrate as well as between adjacent drops are important in defining the resolution and accuracy of printed objects. Pattern resolution is limited by the extent to which a liquid drop spreads on a substrate and how spreading changes with the overlap of adjacent drops to form continuous features. There are clearly defined upper and lower bounds to the width of a printed continuous line, which can be defined in terms of materials and process variables. Finer-resolution features can be achieved through appropriate patterning and structuring of the substrate prior to printing, which is essential if polymeric semiconducting devices are to be fabricated. Low advancing and receding contact angles promote printed line stability but are also more prone to solute segregation or “coffee staining” on drying.

Optical profiling of anticoagulation status (Conference Presentation)

NASA Astrophysics Data System (ADS)

Tshikudi, Diane M.; Tripathi, Markandey M.; Hajjarian, Zeinab; Nadkarni, Seemantini K.

2016-02-01

Defective blood coagulation resulting from excessive procoagulant activity often leads to thrombotic disorders such as stroke and myocardial infarction. A variety of oral and injectable anticoagulant drugs are prescribed to prevent or treat life-threatening thrombosis. However, due to bleeding complications often associated with anticoagulant treatment, routine monitoring and accurate dosing of anticoagulant therapy is imperative. We have developed Optical thromboelastography (OTEG), a non-contact approach that utilizes a drop of whole blood to measure blood coagulation status in patients. Here, we demonstrate the capability of OTEG for rapidly monitoring anticoagulation in whole blood samples. OTEG monitors coagulation status by assessing changes in blood viscosity from temporal intensity fluctuations of laser speckle patterns during clotting. In OTEG a blood drop is illuminated with coherent light and the blood viscosity is measured from the speckle intensity autocorrelation curve, g2 (t). The metrics, clotting time (R+k), clot progression (angle) and maximum clot stiffness (MA) are then extracted. The aim of the current study was to evaluate the accuracy of OTEG in assessing anticoagulation status of common anticoagulants including heparin, argatroban and rivaroxaban status. A dose-dependent prolongation of R+k was observed in anticoagulated blood, which closely corresponded with standard-reference Thromboelastography (TEG) (r 0.87-0.99, P>0.01 for all cases). OTEG angle was unaltered by anticoagulation whereas TEG angle presented a dose-dependent diminution probably linked to clot rupture. In both OTEG and TEG, MA was unaffected by heparin, argatroban or rivaroxaban. We conclude that OTEG can accurately monitor anticoagulation status following treatment, potentially providing a powerful tool for routine monitoring of patients in the doctor's office or in the home setting.

Anti-icing properties of superhydrophobic ZnO/PDMS composite coating

NASA Astrophysics Data System (ADS)

Yang, Chao; Wang, Fajun; Li, Wen; Ou, Junfei; Li, Changquan; Amirfazli, Alidad

2016-01-01

We present the excellent anti-icing performance for a superhydrophobic coating surface based on ZnO/polydimethylsiloxane (ZnO/PDMS) composite. The superhydrophobic ZnO/PDMS coating surface was prepared by a facile solution mixing, drop coating, room-temperature curing and surface abrading procedure. The superhydrophobic ZnO/PDMS composite coating possesses a water contact angle of 159.5° and a water sliding angle of 8.3° at room temperature (5 °C). The anti-icing properties of the superhydrophobic coating were investigated by continuously dropping cold-water droplets (about 0 °C) onto the pre-cooled surface using a home-made apparatus. The sample was placed at different tilting angle (0° and 10°) and pre-cooled to various temperatures (-5, -10 and -15 °C) prior to measure. The pure Al surface was also studied for comparison. It was found that icing accretion on the surface could be reduced apparently because the water droplets merged together and slid away from the superhydrophobic surface at all of the measuring temperatures when the surface is horizontally placed. In addition, water droplet slid away completely from the superhydrophobic surface at -5 and -10 °C when the surface is tilted at 10°, which demonstrates its excellent anti-icing properties at these temperatures. When the temperature decreased to -15 °C, though ice accretion on the tilted superhydrophobic coating surface could not be avoided absolutely, the amount of ice formed on the surface is very small, which indicated that the coating surface with superhydrophobicity could significantly reduce ice accumulation on the surface at very low temperature (-15 °C). Importantly, the sample is also stable against repeated icing/deicing cycles. More meaningfully, once the superhydrophobic surface is damaged, it can be repaired easily and rapidly.

Contact Angle Measurements: an Alternative Approach Towards Understanding the Mechanism of Increased Drug Dissolution from Ethylcellulose Tablets Containing Surfactant and Exploring the Relationship Between Their Contact Angles and Dissolution Behaviors.

PubMed

Liu, Tiaotiao; Hao, Jingqiang; Yang, Baixue; Hu, Beibei; Cui, Zhixiang; Li, Sanming

2018-05-01

The addition of surfactant in tablet was a well-defined approach to improve drug dissolution rate. While the selected surfactant played a vital role in improving the wettability of tablet by medium, it was equally important to improve the dissolution rate by permeation effect due to production of pores or the reduced inter-particle adhesion. Furthermore, understanding the mechanism of dissolution rate increased was significant. In this work, contact angle measurement was taken up as an alternative approach for understanding the dissolution rate enhancement for tablet containing surfactant. Ethylcellulose, as a substrate, was used to prepare tablet. Four surfactants, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), and sodium lauryl sulfonate (SLS), were used. Berberine hydrochloride, metformin hydrochloride, and rutin were selected as model drugs. The contact angle of tablet in the absence and presence of surfactant was measured to explore the mechanism. The dissolution test was investigated to verify the mechanism and to establish a correlation with the contact angle. The result showed that the mechanism was the penetration effect rather than the wetting effect. The dissolution increased with a reduction in the contact angle. DTAB was found to obtain the highest level of dissolution enhancement and the lowest contact angle, while SDS, SDBS, and SLS were found to be the less effective in both dissolution enhancement and contact angle decrease. Therefore, contact angle was a good indicator for dissolution behavior besides exploring the mechanism of increased dissolution, which shows great potential in formula screening.

Spontaneous formation of nanostructures inside inkjet-printed colloidal drops

NASA Astrophysics Data System (ADS)

Yang, Xin; Thorne, Nathaniel; Sun, Ying

2013-11-01

Nanostructures formed in inkjet-printed colloidal drops are systematically examined with different substrates and ink formulations. Various deposition patterns from multi-ring, radial spoke, firework to spider web, foam and island structures are observed. With a high particle loading, deposition transitions from multi-ring near the drop edge to spider web and finally to foam and islands in the center of the drop with 20 nm sulfate-modified polystyrene particles. At the same particle loading, 200 nm particles self-assemble into radial spokes at the drop edge and islands in the center, due to reduced contact line pinning resulted from less particles. In drops with a low particle concentration, due to fingering instability of the contact line, 20 nm particles form radial spokes enclosed by a ring, while 200 nm particles assemble into firework-like structures without a ring. Moreover, at a high particle loading, ruptures are observed on the multi-ring structure formed by 20 nm carboxylic-modified particles, due to stronger capillary forces from the contact line. Furthermore, for a drop printed on a less hydrophilic substrate, the interparticle interactions enable a more uniform deposition rather than complex nanostructures.

Treatment of contact lens related dry eye with antibacterial honey.

PubMed

Wong, Daniel; Albietz, Julie M; Tran, Huan; Du Toit, Cimonette; Li, Anita Hui; Yun, Tina; Han, Jee; Schmid, Katrina L

2017-12-01

Contact lens induced dry eye affects approximately 50% of contact lens wearers. The aim was to assess the effects of Manuka (Leptospermum sp.) honey eye drops (Optimel, Melcare, Australia) on dry eye in contact lens wearers. The safety of the honey eye drops in contact lens wear and contact lens wearers' compliance were also evaluated. Prospective, randomised, cross over study, examiner masked, pilot treatment trial. Twenty-four participants aged 20 to 55 years with contact lens related dry eye were recruited and randomised to two treatment groups; 20 completed the study. One group used Optimel eye drops twice a day for two weeks followed by conventional lubricant (Systane Ultra, Alcon) therapy for two weeks; the other group completed the treatments in the reverse order. Before and after each treatment dry eye symptomology, ocular surface inflammation, and tear quantity and quality were assessed. Participants completed a daily log detailing their usage of treatments and any issues. Dry eye symptoms improved significantly after Optimel treatment. Patients with more severe symptoms at baseline showed a greater improvement in symptoms. No significant differences were observed in the objective signs of dry eye; presumably because of the short treatment duration. Seventy-five% of contact lens wearers reported good adherence to Optimel treatment and 95% reported no issues using this product. Optimel Eye Drops reduce the symptoms of dry eye in contact lens wearers and are safe to use. A longer treatment period to assess the effect on clinical signs of dry eye is required. Copyright © 2017 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Brinzolamide Ophthalmic

MedlinePlus

... see if you should still use the same eye drop bottle.tell your doctor if you wear soft contact lenses. Wait at least 15 minutes after using the medicine to put in soft contact lenses.use caution when driving or operating machinery because vision may be blurred after inserting the drops.

Dynamic Measurement of Low Contact Angles by Optical Microscopy.

PubMed

Campbell, James M; Christenson, Hugo K

2018-05-16

Precise measurement of contact angles is an important challenge in surface science, in the design and characterization of materials and in many crystallization experiments. Here we present a novel technique for measuring the contact angles of droplets between about 2° and 30°, with the lowest experimental uncertainty at the lower end of this range, typically ±0.1°. The lensing effect of a droplet interface produces the appearance of bright circles in low-aperture light, whose diameter is related to the contact angle. The technique requires no specialized equipment beyond an ordinary optical microscope, and may be used to study the dynamic evolution of the contact angle in situ during an experiment.

Spontaneous jumping, bouncing and trampolining of hydrogel drops on a heated plate.

PubMed

Pham, Jonathan T; Paven, Maxime; Wooh, Sanghyuk; Kajiya, Tadashi; Butt, Hans-Jürgen; Vollmer, Doris

2017-10-13

The contact between liquid drops and hot solid surfaces is of practical importance for industrial processes, such as thermal spraying and spray cooling. The contact and bouncing of solid spheres is also an important event encountered in ball milling, powder processing, and everyday activities, such as ball sports. Using high speed video microscopy, we demonstrate that hydrogel drops, initially at rest on a surface, spontaneously jump upon rapid heating and continue to bounce with increasing amplitudes. Jumping is governed by the surface wettability, surface temperature, hydrogel elasticity, and adhesion. A combination of low-adhesion impact behavior and fast water vapor formation supports continuous bouncing and trampolining. Our results illustrate how the interplay between solid and liquid characteristics of hydrogels results in intriguing dynamics, as reflected by spontaneous jumping, bouncing, trampolining, and extremely short contact times.Drops of liquid on a hot surface can exhibit fascinating behaviour such as the Leidenfrost effect in which drops hover on a vapour layer. Here Pham et al. show that when hydrogel drops are placed on a rapidly heated plate they bounce to increasing heights even if they were initially at rest.

Riding position and lumbar spine angle in recreational cyclists: A pilot study

PubMed Central

SCHULZ, SAMANTHA J.; GORDON, SUSAN J.

2010-01-01

This pilot study investigated the reliability of an inclinometer to assess lumbar spine angle in three different cycling positions, and explored the relationship between lumbar spine angle and riding position, anthropometry, bike measures and low back pain (LBP). Cyclists were recruited from two cycle clubs. Anthropometric variables and bike setup were measured before participants’ bikes were secured in a wind trainer. Cyclists then adopted three positions for riding, upright on the handlebars, on the brake levers and on the drops, according to a random allocation. The angle of the lumbar spine was measured; using an inclinometer, at zero minutes and after cyclists had completed 10 minutes of cycling. Intra-measurer reliability for inclinometer use to measure lumbar spine angle in each position was excellent (ICC=0.97). The angle of the lumbar spine changed significantly over 10 minutes in the brake position (p=0.004). Lumbar spine angle at 10 minutes was significantly different between the brake and drop positions (p=0.018, p<0.05), and between upright and drop positions (p=0.012, p<0.05). Lumbar spine angle was not related to anthropometric measures. The change in lumbar spine angle varied from one degree of extension to 12 degrees of flexion, with increased flexion occurring in 95% of trials. An inclinometer has excellent intra-measurer reliability to measure lumbar spine angle in cycling positions. Future research with a sample of 72 or more participants is required to determine if there is a significant relationship between LBP and lumbar spine angle in different cycling positions. PMID:27182345

Evaporation of Nanosuspensions on Substrates with Different Hydrophobicity.

PubMed

Perrin, Lionel; Pajor-Swierzy, Anna; Magdassi, Shlomo; Kamyshny, Alexander; Ortega, Francisco; Rubio, Ramón G

2018-01-24

Liquid drop evaporation on surfaces is present in many industrial and medical applications, e.g., printed electronics, spraying of pesticides, DNA mapping, etc. Despite this strong interest, a theoretical description of the dynamic of the evaporation of complex liquid mixtures and nanosuspensions is still lacking. Indeed, one of the aspects that have not been included in the current theoretical descriptions is the competition between the kinetics of evaporation and the adsorption of surfactants and/or particles at the liquid/vapor and liquid/solid interfaces. Materials formed by an electrically isolating solid on which a patterned conducting layer was formed by the deposits left after drop evaporation have been considered as very promising for building electrical circuits on flexible plastic substrates. In this work, we have done an exhaustive study of the evaporation of nanosuspensions of latex and hydrophobized silver nanoparticles on four substrates of different hydrophobicity. The advancing and receding contact angles as well as the time dependence of the volume of the droplets have been measured over a broad range of particle concentrations. Also, mixtures of silver particles and a surfactant, commonly used in industrial printing, have been examined. Furthermore, the adsorption kinetics at both the air/liquid and solid/liquid interfaces have been measured. Whereas the latex particles do not adsorb at the solid/liquid and only slightly reduce the surface tension, the silver particles strongly adsorb at both interfaces. The experimental results of the evaporation process were compared with the predictions of the theory of Semenov et al. (Evaporation of Sessile Water Droplets: Universal Behavior in the Presence of Contact Angle Hysteresis. Colloids Surf. Physicochem. Eng. Asp. 2011, 391 (1-3), 135-144) and showed surprisingly good agreement despite that the theory was developed for pure liquids. The morphology of the deposits left by the droplets after total evaporation was studied by scanning electronic microscopy, and the effects of the substrate, the particle nature, and their concentrations on these patterns are discussed.

Detached Bridgman Growth of Germanium and Germanium-Silicon Alloy Crystals

NASA Technical Reports Server (NTRS)

Szofran, F. R.; Volz, M. P.; Schweizer, M.; Kaiser, N.; Cobb, S. D.; Motakef, S.; Vujisic, L. J.; Croell, A.; Dold, P.; Rose, M. Franklin (Technical Monitor)

2001-01-01

Earth based experiments on the science of detached crystal growth are being conducted on germanium and germanium-silicon alloys (2at% Si average composition) in preparation for a series of experiments aboard the International Space Station (ISS) to differentiate among proposed mechanisms contributing to detachment. Sessile drop measurements were first carried out for a large number of substrates made of potential ampoule materials to determine the contact angles and the surface tension as a function of temperature and composition. The process atmosphere and duration of the experiment (for some cases) were also found to have significant influence on the wetting angle. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. The contact angles were 173 deg (Ge) and 165 deg (GeSi) for pBN. For fused silica, the contact angle decreases to an equilibrium value with duration of measurement ranging from 150 to 117 deg (Ge), 129 to 100 deg (GeSi). Forming gas (Ar + 2% H2) and vacuum have been used in the growth ampoules. With gas in the ampoule, a variation of the temperature profile during growth has been used to control the pressure difference between the top of the melt and the volume below the melt caused by detachment of the growing crystal. The stability of detachment has been modeled and substantial insight has been gained into the reasons that detachment has most often been observed in reduced gravity but nonetheless has occurred randomly even there. An empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed and will be presented. Methods for determining the nature and extent of detachment include profilometry and optical and electron microscopy. This surface study is the subject of another presentation at this Congress. Results in this presentation will show that we have established the effects of different ampoule materials, temperature profiles, pressure differences, and silicon concentrations and that samples that are nearly completely detached can be grown repeatedly.

Pore-scale water dynamics during drying and the impacts of structure and surface wettability

NASA Astrophysics Data System (ADS)

Cruz, Brian C.; Furrer, Jessica M.; Guo, Yi-Syuan; Dougherty, Daniel; Hinestroza, Hector F.; Hernandez, Jhoan S.; Gage, Daniel J.; Cho, Yong Ku; Shor, Leslie M.

2017-07-01

Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loam soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. Lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.

In situ assessment of the contact angles of nanoparticles adsorbed at fluid interfaces by multiple angle of incidence ellipsometry.

PubMed

Stocco, Antonio; Su, Ge; Nobili, Maurizio; In, Martin; Wang, Dayang

2014-09-28

Here multiple angle of incidence ellipsometry was successfully applied to in situ assess the contact angle and surface coverage of gold nanoparticles as small as 18 nm, coated with stimuli-responsive polymers, at water-oil and water-air interfaces in the presence of NaCl and NaOH, respectively. The interfacial adsorption of the nanoparticles was found to be very slow and took days to reach a fairly low surface coverage. For water-oil interfaces, in situ nanoparticle contact angles agree with the macroscopic equilibrium contact angles of planar gold surfaces with the same polymer coatings, whilst for water-air interfaces, significant differences have been observed.

Boiling regimes of impacting drops on a heated substrate under reduced pressure

NASA Astrophysics Data System (ADS)

van Limbeek, Michiel A. J.; Hoefnagels, Paul B. J.; Shirota, Minori; Sun, Chao; Lohse, Detlef

2018-05-01

We experimentally investigate the boiling behavior of impacting ethanol drops on a heated smooth sapphire substrate at pressures ranging from P =0.13 bar to atmospheric pressure. We employ frustrated total internal reflection imaging to study the wetting dynamics of the contact between the drop and the substrate. The spreading drop can be in full contact (contact boiling), it can partially touch (transition boiling), or the drop can be fully levitated (Leidenfrost boiling). We show that the temperature of the boundary between contact and transition boiling shows at most a weak dependence on the impact velocity, but a significant decrease with decreasing ambient gas pressure. A striking correspondence is found between the temperature of this boundary and the static Leidenfrost temperature for all pressures. We therefore conclude that both phenomena share the same mechanism and are dominated by the dynamics taking place at the contact line. On the other hand, the boundary between transition boiling and Leidenfrost boiling, i.e., the dynamic Leidenfrost temperature, increases for increasing impact velocity for all ambient gas pressures. Moreover, the dynamic Leidenfrost temperature coincides for pressures between P =0.13 and 0.54 bar, whereas for atmospheric pressure the dynamic Leidenfrost temperature is slightly elevated. This indicates that the dynamic Leidenfrost temperature is at most weakly dependent on the enhanced evaporation by the lower saturation temperature of the liquid.

The influence of a foot orthotic on lower extremity transverse plane kinematics in collegiate female athletes with pes planus.

PubMed

Christopher, R Carcia; Drouin, Joshua M; Houglum, Peggy A

2006-01-01

Non-contact anterior cruciate ligament (ACL) injuries in female athletes remain prevalent. Athletes with excessive foot pronation have been identified to be at greater risk for non-contact ACL injury. Excessive foot pronation has been linked to increased medial tibial rotation. Increased medial tibial rotation heightens ACL strain and has been observed at or near the time of ACL injury. Foot orthotics have been shown to decrease medial tibial rotation during walking and running tasks. The effect of a foot orthotic on activities that simulate a non-contact ACL injury mechanism (i.e. landing) however is unknown. Therefore, the objective of this study was to determine whether a foot orthotic was capable of altering transverse plane lower extremity kinematics in female athletes during landing. Twenty uninjured collegiate female athletes participating in the sports of basketball, soccer or volleyball with pes planus volunteered. Utilizing a repeated measures counterbalanced design, subjects completed two landing tasks with and without a foot orthotic using standardized footwear. The prefabricated orthotic had a rigid shell and a 6 extrinsic rear-foot varus post. Dependent measures included initial contact angle, peak angle, excursion and time to peak angle for both the tibia and femur. Statistical analysis suggested that the selected foot orthosis had little influence over lower extremity transverse plane kinematics. Several factors including: the limitation of a static measure to predict dynamic movement, inter-subject variability and the physical characteristics of the orthotic device likely account for the results. Future research should examine the influence of different types of foot orthotics not only on lower extremity kinematics but also tibiofemoral kinetics. Key PointsLower extremity transverse plane kinematics in female athletes during a landing task exhibit substantial variability.A rigid prefabricated foot orthotic does not significantly alter transverse plane lower extremity kinematics in female athletes with a navicular drop of at least 8mm.Additional study is necessary before firm conclusions regarding the influence of an orthotic device on lower extremity kinematics, kinetics, neuromuscular control and ultimately injury rates can be made.

Simultaneous Soft Sensing of Tissue Contact Angle and Force for Millimeter-scale Medical Robots

PubMed Central

Arabagi, Veaceslav; Gosline, Andrew; Wood, Robert J.; Dupont, Pierre E.

2013-01-01

A novel robotic sensor is proposed to measure both the contact angle and the force acting between the tip of a surgical robot and soft tissue. The sensor is manufactured using a planar lithography process that generates microchannels that are subsequently filled with a conductive liquid. The planar geometry is then molded onto a hemispherical plastic scaffolding in a geometric configuration enabling estimation of the contact angle (angle between robot tip tangent and tissue surface normal) by the rotation of the sensor around its roll axis. Contact force can also be estimated by monitoring the changes in resistance in each microchannel. Bench top experimental results indicate that, on average, the sensor can estimate the angle of contact to within ±2° and the contact force to within ±5.3 g. PMID:24241496

A Contact Pressure Analysis Comparing an All-Inside and Inside-Out Surgical Repair Technique for Bucket-Handle Medial Meniscus Tears.

PubMed

Marchetti, Daniel Cole; Phelps, Brian M; Dahl, Kimi D; Slette, Erik L; Mikula, Jacob D; Dornan, Grant J; Bucci, Gabriella; Turnbull, Travis Lee; Singleton, Steven B

2017-10-01

To directly compare effectiveness of the inside-out and all-inside medial meniscal repair techniques in restoring native contact area and contact pressure across the medial tibial plateau at multiple knee flexion angles. Twelve male, nonpaired (n = 12), fresh-frozen human cadaveric knees underwent a series of 5 consecutive states: (1) intact medial meniscus, (2) MCL tear and repair, (3) simulated bucket-handle longitudinal tear of the medial meniscus, (4) inside-out meniscal repair, and (5) all-inside meniscal repair. Knees were loaded with a 1,000-N axial compressive force at 5 knee flexion angles (0°, 30°, 45°, 60°, 90°), and contact area, mean contact pressure, and peak contact pressure were calculated using thin film pressure sensors. No significant differences were observed between the inside-out and all-inside repair techniques at any flexion angle for contact area, mean contact pressure, and peak contact pressure (all P > .791). Compared with the torn meniscus state, inside-out and all-inside repair techniques resulted in increased contact area at all flexion angles (all P < .005 and all P < .037, respectively), decreased mean contact pressure at all flexion angles (all P < .007 and all P < .001, respectively) except for 0° (P = .097 and P = .39, respectively), and decreased peak contact pressure at all flexion angles (all P < .001, all P < .001, respectively) except for 0° (P = .080 and P = .544, respectively). However, there were significant differences in contact area and peak contact pressure between the intact state and inside-out technique at angles ≥45° (all P < .014 and all P < .032, respectively). Additionally, there were significant differences between the intact state and all-inside technique in contact area at 60° and 90° and peak contact pressure at 90° (both P < .005 and P = .004, respectively). Median values of intact contact area, mean contact pressure, and peak contact pressure over the tested flexion angles ranged from 498 to 561 mm 2 , 786 to 997 N/mm 2 , and 1,990 to 2,215 N/mm 2 , respectively. Contact area, mean contact pressure, and peak contact pressure were not significantly different between the all-inside and inside-out repair techniques at any tested flexion angle. Both techniques adequately restored native meniscus biomechanics near an intact level. An all-inside repair technique provided similar, native-state-restoring contact mechanics compared with an inside-out repair technique for the treatment of displaced bucket-handle tears of the medial meniscus. Thus, both techniques may adequately decrease the likelihood of cartilage degeneration. Copyright © 2017 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Parametric effects on pinch-off modes in liquid/liquid jet systems

NASA Astrophysics Data System (ADS)

Milosevic, Ilija N.

Many industries rely on liquid/liquid extraction systems, where jet pinch off occurs on a regular basis. Inherent short time and length scales make analytical and numerical simulation of the process very challenging. A main objective of this work was to document the details of various pinch-off modes at different length scales using Laser Induced Fluorescence and Particle Image Velocimetry. A water glycerine mixture was injected into ambient either silicone oil or 1-octanol. The resultant viscosity ratios, inner to outer fluid, were 1.6 and 2.8, respectively. Ohnesorge numbers were 0.013 for ambient silicone oil and 0.08 for ambient 1-octanol. Reynolds and Strouhal numbers ranged from 30 to 100 and 0.5 to 3.5, respectively. Decreasing the Strouhal number increased the number of drops formed per forcing. Increasing the Reynolds number suppressed satellite formation, and in some cases the number of drops decreased from two to one per cycle. Increasing the Ohnesorge number to 0.08 suppressed the pinch off yielding a longer jet with three-dimensional threads. At Ohnesorge number 0.013, increasing the forcing amplitude shortened the jet, and eventually led to a dripping mode. High-resolution measurements of pinch-off angles were compared to results from similarity theory. Two modes were investigated: drops breaking from the jet (jet/drop) and, one drop splitting into two (splitting drop). The jet/drop mode angle measurements agreed with similarity predictions. The splitting drop mode converged towards smaller angles. Scaling analysis showed that a Stokesian similarity regime applied for a neck radius of 6 microns or less. The smallest radius observed in experiments was 15 microns. Therefore, it is not known whether splitting drop mode might still converge to same behavior.

Unusual Contact-Line Dynamics of Thick Films and Drops

NASA Technical Reports Server (NTRS)

Veretennikov, Igor; Agarwal, Abhishek; Indeikina, Alexandra; Chang, Hsueh-Chia

1999-01-01

We report several novel phenomena In contact-line and fingering dynamics of macroscopic spinning drops and gravity-driven films with dimensions larger than the capillary length. It is shown through experimental and theoretical analysis that such macroscopic films can exhibit various interfacial shapes, including multi valued ones, near the contact line due to a balance between the external body forces with capillarity. This rich variety of front shapes couples with the usual capillary, viscous, and intermolecular forces at the contact line to produce a rich and unexpected spectrum of contact-line dynamics. A single finger develops when part of the front becomes multivalued on a partially wetting macroscopic spinning drop in contrast to a different mechanism for microscopic drops of completely wetting fluids. Contrary to general expectation, we observe that, at high viscosity and low frequencies of rotation, the speed of a glycerine finger increases with increasing viscosity. Completely wetting Dow Corning 200 Fluid spreads faster over a dry inclined plane than a prewetted one. The presence of a thin prewetted film suppresses fingering both for gravity-driven flow and for spin coating. We analyze some of these unique phenomena in detail and offer qualitative physical explanations for the others.

Evaluation of wetting ability of five new saliva substitutes on heat-polymerized acrylic resin for retention of complete dentures in dry mouth patients: a comparative study

PubMed Central

Mohsin, Abdul Habeeb Bin; Reddy, Varalakshmi; Kumar, Praveen; Raj, Jeevan; Babu, Siva Santosh

2017-01-01

Introduction The aim of this study was to evaluate & compare the wetting ability of five saliva substitutes & distilled water on heat-polymerized acrylic resin. Contact angle of the saliva substitute on denture base can be taken as an indicator of wettability. Good wetting of heat-polymerized acrylic resin is critical for optimum retention of complete dentures. Methods Two hundred & forty samples of heat-polymerized acrylic resin were fabricated using conventional method. 240 samples divided into 6 groups with 40 samples in each group. Advancing & Receding contact angles were measured using Contact Angle Goniometer & DSA4 software analysis. Results Anova test was carried out to test the significance in difference of contact angle values in the six groups. The mean of advancing angle values & mean of receding angle values of all the six groups has shown statistically significant difference between the groups. The mean of angle of hysteresis values of all the six groups are statistically not significant between the groups. A multiple comparison using Bonferroni’s test was carried out to verify the significance of difference between the contact angles in a pair of groups. Statistically significant difference was seen when Aqwet (Group II) was compared to Distilled water (Group I), Wet Mouth (Group III), E-Saliva (Group IV), Biotene (Group V), and Moi-Stir (Group VI). Conclusion The contact angles of five saliva substitutes and distilled water were measured and compared. Group II (AQWET) has the lowest advancing and receding contact angle values and the highest angle of hysteresis on heat-polymerized acrylic resin. Based on contact angle values, Group II (AQWET) has the best wetting ability on heat-cured acrylic resins. The ability of saliva to wet the denture surface is one of the most important properties for complete denture retention in dry mouth cases. PMID:29187918

Design and fabrication of highly hydrophobic Mn nano-sculptured thin films and evaluation of surface properties on hydrophobicity

NASA Astrophysics Data System (ADS)

Hosseini, Somaye; Savaloni, Hadi; Gholipour-Shahraki, Mehran

2017-03-01

The wettability of solid surfaces is important from the aspects of both science and technology. The Mn nano-sculptured thin films were designed and fabricated by oblique angle deposition of Mn on glass substrates at room temperature. The obtained structure was characterized by field emission scanning electron microscopy and atomic force microscopy. The wettability of thin films samples was investigated by water contact angle (WCA). The 4-pointed helical star-shaped structure exhibits hydrophobicity with static WCAs of more than 133° for a 10-mg distilled water droplet. This sample also shows the rose petal effect with the additional property of high adhesion. The Mn nano-sculptured thin films also act as a sticky surface which is confirmed by hysteresis of the contact angle obtained from advancing and receding contact angles measurements. Physicochemical property of liquid phase could effectively change the contact angle, and polar solvents in contact with hydrophobic solid surfaces do not necessarily show high contact angle value.

Hysteresis of the Contact Angle of a Meniscus Inside a Capillary with Smooth, Homogeneous Solid Walls.

PubMed

Kuchin, Igor V; Starov, Victor M

2016-05-31

A theory of contact angle hysteresis of a meniscus inside thin capillaries with smooth, homogeneous solid walls is developed in terms of surface forces (disjoining/conjoining pressure isotherm) using a quasi-equilibrium approach. The disjoining/conjoining pressure isotherm includes electrostatic, intermolecular, and structural components. The values of the static receding θr, advancing θa, and equilibrium θe contact angles in thin capillaries were calculated on the basis of the shape of the disjoining/conjoining pressure isotherm. It was shown that both advancing and receding contact angles depend on the capillary radius. The suggested mechanism of the contact angle hysteresis has a direct experimental confirmation: the process of receding is accompanied by the formation of thick β-films on the capillary walls. The effect of the transition from partial to complete wetting in thin capillaries is predicted and analyzed. This effect takes place in very thin capillaries, when the receding contact angle decreases to zero.

Thermodynamic analysis of effects of contact angle on interfacial interactions and its implications for membrane fouling control.

PubMed

Chen, Jianrong; Shen, Liguo; Zhang, Meijia; Hong, Huachang; He, Yiming; Liao, Bao-Qiang; Lin, Hongjun

2016-02-01

Concept of hydrophobicity always fails to accurately assess the interfacial interaction and membrane fouling, which calls for reliable parameters for this purpose. In this study, effects of contact angle on interfacial interactions related to membrane fouling were investigated based on thermodynamic analysis. It was found that, total interaction energy between sludge foulants and membrane monotonically decreases and increases with water and glycerol contact angle, respectively, indicating that these two parameters can be reliable indicators predicting total interaction energy and membrane fouling. Membrane roughness decreases interaction strength for over 20 times, and effects of membrane roughness on membrane fouling should consider water and glycerol contact angle on membrane. It was revealed existence of a critical water and glycerol contact angle for a given membrane bioreactor. Meanwhile, diiodomethane contact angle has minor effect on the total interaction, and cannot be regarded as an effective indicator assessing interfacial interactions and membrane fouling. Copyright © 2015 Elsevier Ltd. All rights reserved.

Experimental Study of Static Contact-angle on Peak-like Microstructural Surfaces Produced by PIII Technology

NASA Astrophysics Data System (ADS)

Yang, Runhua; Yang, Lixin

2018-06-01

Plasma immersion ion implantation (PIII) was used to fabricate micro/nano structures on monocrystalline Si surfaces with different ratios of mixed gases (SF6/O2). The micro/nano structures on the surfaces of the sample were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that with increasing ratio of mixed gases (SF6/O2), the height of the micro/nano structures first increased and then decreased. Contact-angle measurements indicated that the surfaces' micro/nano structures have an obvious effect on the contact-angle, and could cause a change in surface wettability. The theoretical analysis of contact-angle showed that the Wenzel and Cassie theories cannot predict the contact-angle of a roughened surface accurately, and should be corrected for practical applications using an actual model. Moreover, the contact-angle first increased and then decreased with increasing ratio of mixed gases (SF6/O2), which is in accordance with the change of the height of micro/nano structures.

A comparison of men's and women's strength to body mass ratio and varus/valgus knee angle during jump landings.

PubMed

Haines, Tracie L; McBride, Jeffrey M; Triplett, N Travis; Skinner, Jared W; Fairbrother, Kimberly R; Kirby, Tyler J

2011-10-01

The purpose of this investigation was to compare valgus/varus knee angles during various jumps and lower body strength between males and females relative to body mass. Seventeen recreationally active females (age: 21.94 ± 2.59 years; height: 1.67 ± 0.05 m; mass: 64.42 ± 8.39 kg; percent body fat: 26.89 ± 6.26%; squat one-repetition maximum: 66.18 ± 19.47 kg; squat to body mass ratio: 1.03 ± 0.28) and 13 recreationally active males (age: 21.69 ± 1.65 years; height: 1.77 ± 0.07 m; mass: 72.39 ± 9.23 kg; percent body fat: 13.15 ± 5.18%; squat one-repetition maximum: 115.77 ± 30.40 kg; squat to body mass ratio: 1.59 ± 0.31) performed a one-repetition maximum in the squat and three of each of the following jumps: countermovement jump, 30 cm drop jump, 45 cm drop jump, and 60 cm drop jump. Knee angles were analysed using videography and body composition was analysed by dual-energy X-ray absorptiometry to allow for squat to body mass ratio and squat to fat free mass ratio to be calculated. Significant differences (P ≤ 0.05) were found between male and female one-repetition maximum, male and female squat to body mass ratio, and male and female squat to fat free mass ratio. Significant differences were found between male and female varus/valgus knee positions during maximum flexion of the right and left leg in the countermovement jump, drop jump from 30 cm, drop jump from 45 cm, and drop jump from 60 cm. Correlations between varus/valgus knee angles and squat to body mass ratio for all jumps displayed moderate, non-significant relationships (countermovement jump: r = 0.445; drop jump from 30 cm: r = 0.448; drop jump from 45 cm: r = 0.449; drop jump from 60 cm: r = 0.439). In conclusion, males and females have significantly different lower body strength and varus/valgus knee position when landing from jumps.

Evaluation of touch-sensitive screen tablet terminal button size and spacing accounting for effect of fingertip contact angle.

PubMed

Nishimura, T; Doi, K; Fujimoto, H

2015-08-01

Touch-sensitive screen terminals enabling intuitive operation are used as input interfaces in a wide range of fields. Tablet terminals are one of the most common devices with a touch-sensitive screen. They have a feature of good portability, enabling use under various conditions. On the other hand, they require a GUI designed to prevent decrease of usability under various conditions. For example, the angle of fingertip contact with the display changes according to finger posture during operation and how the case is held. When a human fingertip makes contact with an object, the contact area between the fingertip and contact object increases or decreases as the contact angle changes. A touch-sensitive screen detects positions using the change in capacitance of the area touched by the fingertip; hence, differences in contact area between the touch-sensitive screen and fingertip resulting from different forefinger angles during operation could possibly affect operability. However, this effect has never been studied. We therefore conducted an experiment to investigate the relationship between size/spacing and operability, while taking the effect of fingertip contact angle into account. As a result, we have been able to specify the button size and spacing conditions that enable accurate and fast operation regardless of the forefinger contact angle.

Contact mechanics of reverse total shoulder arthroplasty during abduction: the effect of neck-shaft angle, humeral cup depth, and glenosphere diameter.

PubMed

Langohr, G Daniel G; Willing, Ryan; Medley, John B; Athwal, George S; Johnson, James A

2016-04-01

Implant design parameters can be changed during reverse shoulder arthroplasty (RSA) to improve range of motion and stability; however, little is known regarding their impact on articular contact mechanics. The purpose of this finite element study was to investigate RSA contact mechanics during abduction for different neck-shaft angles, glenosphere sizes, and polyethylene cup depths. Finite element RSA models with varying neck-shaft angles (155°, 145°, 135°), sizes (38 mm, 42 mm), and cup depths (deep, normal, shallow) were loaded with 400 N at physiological abduction angles. The contact area and maximum contact stress were computed. The contact patch and the location of maximum contact stress were typically located inferomedially in the polyethylene cup. On average for all abduction angles investigated, reducing the neck-shaft angle reduced the contact area by 29% for 155° to 145° and by 59% for 155° to 135° and increased maximum contact stress by 71% for 155° to 145° and by 286% for 155° to 135°. Increasing the glenosphere size increased the contact area by 12% but only decreased maximum contact stress by 2%. Decreasing the cup depth reduced the contact area by 40% and increased maximum contact stress by 81%, whereas increasing the depth produced the opposite effect (+52% and -36%, respectively). The location of the contact patch and maximum contact stress in this study matches the area of damage seen frequently on clinical retrievals. This finding suggests that damage to the inferior cup due to notching may be potentiated by contact stresses. Increasing the glenosphere diameter improved the joint contact area and did not affect maximum contact stress. However, although reducing the neck-shaft angle and cup depth can improve range of motion, our study shows that this also has some negative effects on RSA contact mechanics, particularly when combined. Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

Effect of inclination and anteversion angles on kinematics and contact mechanics of dual mobility hip implants.

PubMed

Gao, Yongchang; Chen, Zhenxian; Zhang, Zhifeng; Chen, Shibin; Jin, Zhongmin

2018-06-12

Steep inclination and excessive anteversion angles of acetabular cups could result in adverse edge-loading. This, in turn, increases contact pressure and impingement risk for traditional artificial hip joints. However, the influence of high inclination and anteversion angles on both the kinematics and contact mechanics of dual mobility hip implants has rarely been examined. This study focuses on investigating both the kinematics and contact mechanics of a dual mobility hip implant under different inclination and anteversion angles using a dynamic explicit finite element method developed in a previous study. The results showed that an inclination angle of both the back shell and liner ranging from 30° to 70° had little influence on the maximum contact pressure and the accumulated sliding distance of inner and outer surfaces of the liner under normal walking gait. The same results were obtained for an anteversion angle of the liner varying between -20° and +20°. However, when the anteversion angle of the liner was beyond this range, the contact between the femoral neck and the inner rim of the liner occurred. Consequently, this caused a relative rotation at the outer articulation. This suggests that both inclination and modest anteversion angles have little influence on the kinematics and contact mechanics of dual mobility hip implants. However, too excessive anteversion angle could result in a rotation for this kind of hip implant at both articulations. Copyright © 2018 Elsevier Ltd. All rights reserved.

A two-angle model of dynamic wetting in microscale capillaries under low capillary numbers with experiments.

PubMed

Lei, Da; Lin, Mian; Li, Yun; Jiang, Wenbin

2018-06-15

An accurate model of the dynamic contact angle θ d is critical for the calculation of capillary force in applications like enhanced oil recovery, where the capillary number Ca ranges from 10 -10 to 10 -5 and the Bond number Bo is less than 10 -4 . The rate-dependence of the dynamic contact angle under such conditions remains blurred, and is the main target of this study. Featuring with pressure control and interface tracking, the innovative experimental system presented in this work achieves the desired ranges of Ca and Bo, and enables the direct optical measurement of dynamic contact angles in capillaries as tiny as 40 × 20 (width × height) μm and 80 × 20 μm. The advancing and receding processes of wetting and nonwetting liquids were tested. The dynamic contact angle was confirmed velocity-independent with 10 -9  < Ca < 10 -5 (contact line velocity V = 0.135-490 μm/s) and it can be described by a two-angle model with desirable accuracy. A modified two-angle model was developed and an empirical form was obtained from experiments. For different liquids contacting the same surface, the advancing angle θ adv approximately equals the static contact angle θ o . The receding angle θ rec was found to be a linear function of θ adv , in good agreement with our and other experiments from the literature. Copyright © 2018 Elsevier Inc. All rights reserved.

Automated contact angle estimation for three-dimensional X-ray microtomography data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klise, Katherine A.; Moriarty, Dylan; Yoon, Hongkyu

2015-11-10

Multiphase flow in capillary regimes is a fundamental process in a number of geoscience applications. The ability to accurately define wetting characteristics of porous media can have a large impact on numerical models. In this paper, a newly developed automated three-dimensional contact angle algorithm is described and applied to high-resolution X-ray microtomography data from multiphase bead pack experiments with varying wettability characteristics. The algorithm calculates the contact angle by finding the angle between planes fit to each solid/fluid and fluid/fluid interface in the region surrounding each solid/fluid/fluid contact point. Results show that the algorithm is able to reliably compute contactmore » angles using the experimental data. The in situ contact angles are typically larger than flat surface laboratory measurements using the same material. Furthermore, wetting characteristics in mixed-wet systems also change significantly after displacement cycles.« less

AFM Study of Surface Nanobubbles on Binary Self-Assembled Monolayers on Ultraflat Gold with Identical Macroscopic Static Water Contact Angles and Different Terminal Functional Groups.

PubMed

Song, Bo; Chen, Kun; Schmittel, Michael; Schönherr, Holger

2016-11-01

All experimental findings related to surface nanobubbles, such as their pronounced stability and the striking differences of macroscopic and apparent nanoscopic contact angles, need to be addressed in any theory or model of surface nanobubbles. In this work we critically test a recent explanation of surface nanobubble stability and their consequences and contrast this with previously proposed models. In particular, we elucidated the effect of surface chemical composition of well-controlled solid-aqueous interfaces of identical roughness and defect density on the apparent nanoscopic contact angles. Expanding on a previous atomic force microscopy (AFM) study on the systematic variation of the macroscopic wettability using binary self-assembled monolayers (SAMs) on ultraflat template stripped gold (TSG), we assessed here the effect of different surface chemical composition for macroscopically identical static water contact angles. SAMs on TSG with a constant macroscopic water contact angle of 81 ± 2° were obtained by coadsorption of a methyl-terminated thiol and a second thiol with different terminal functional groups, including hydroxy, amino, and carboxylic acid groups. In addition, surface nanobubbles formed by entrainment of air on SAMs of a bromoisobutyrate-terminated thiol were analyzed by AFM. Despite the widely differing surface potentials and different functionality, such as hydrogen bond acceptor or donor, and different dipole moments and polarizability, the nanoscopic contact angles (measured through the condensed phase and corrected for AFM tip broadening effects) were found to be 145 ± 10° for all surfaces. Hence, different chemical functionalities at identical macroscopic static water contact angle do not noticeably influence the apparent nanoscopic contact angle of surface nanobubbles. This universal contact angle is in agreement with recent models that rely on contact line pinning and the equilibrium of gas outflux due to the Laplace pressure and gas influx due to gas oversaturation in the aqueous medium.

Block Copolymer as a Surface Modifier to Monodisperse Patchy Silica Nanoparticles for Superhydrophobic Surfaces.

PubMed

Lou, Shuo; Wang, Junzheng; Yin, Xiaohong; Qu, Wenxiu; Song, Yuexiao; Xin, Feng; Qaraah, Fahim Abdo Ali

2018-06-18

Monodisperse patchy silica nanoparticles (PSNPs) less than 100 nm are prepared based on the seed-regrowth method using a poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO-type block copolymer as a surface modifier. Well-defined patches are controllably synthesized through area-selective deposition of silica onto the surface of seeds. After colloidal PSNPs are further modified with trimethylchlorosilane, the advancing and receding contact angles of water for PSNPs are 168 ± 2° and 167 ± 2°, respectively. The superhydrophobic and transparent coatings on the various types of substrates are obtained by a simple drop-casting procedure. Additionally, almost the same superhydrophobicity can be achieved by using colloidal PSNPs via redispersing the powder of superhydrophobic PSNPs in ethanol.

Chitin based polyurethanes using hydroxyl terminated polybutadiene, part III: surface characteristics.

PubMed

Zia, Khalid Mahmood; Zuber, Mohammad; Saif, Muhammad Jawwad; Jawaid, Mohammad; Mahmood, Kashif; Shahid, Muhammad; Anjum, Muhammad Naveed; Ahmad, Mirza Nadeem

2013-11-01

Hydroxy terminated polybutadiene (HTPB)-chitin based polyurethanes (PUs) with controlled hydrophobicity were synthesized using HTPB and toluene diisocyanate (TDI). The prepolymer was extended with different mass ratios of chitin and 1,4-butane diol (BDO). The effect of chitin contents in chain extender (CE) proportions on surface properties was studied and investigated. Incorporation of chitin contents into the final PU showed decrease in contact angle value of water drop, water absorption (%) and swelling behavior. The antibacterial activity of the prepared samples was affected by varying the chitin contents in the chemical composition of the final PU. The results demonstrated that the use of prepared material can be suggested as non-absorbable suture. Copyright © 2013 Elsevier B.V. All rights reserved.

Taming Self-Organization Dynamics to Dramatically Control Porous Architectures.

PubMed

Daly, Ronan; Sader, John E; Boland, John J

2016-03-22

We demonstrate templating of functional materials with unexpected and intricate micro- and nanostructures by controlling the condensation, packing, and evaporation of water droplets on a polymer solution. Spontaneous evaporation of a polymer solution induces cooling of the liquid surface and water microdroplet condensation from the ambient vapor. These droplets pack together and act as a template to imprint an entangled polymer film. This breath figure (BF) phenomenon is an example of self-organization that involves the long-range ordering of droplets. Equilibrium-based analysis provides many insights into contact angles and drop stability of individual drops, but the BF phenomenon remains poorly understood thus far, preventing translation to real applications. Here we investigate the dynamics of this phenomenon to separate out the competing influences and then introduce a modulation scheme to ultimately manipulate the water vapor-liquid equilibrium independently from the solvent evaporation. This approach to BF control provides insights into the mechanism, a rationale for microstructure design, and evidence for the benefits of dynamical control of self-organization systems. We finally present dramatically different porous architectures from this approach reminiscent of microscale Petri dishes, conical flasks, and test tubes.

Electric generation and ratcheted transport of contact-charged drops

NASA Astrophysics Data System (ADS)

Cartier, Charles A.; Graybill, Jason R.; Bishop, Kyle J. M.

2017-10-01

We describe a simple microfluidic system that enables the steady generation and efficient transport of aqueous drops using only a constant voltage input. Drop generation is achieved through an electrohydrodynamic dripping mechanism by which conductive drops grow and detach from a grounded nozzle in response to an electric field. The now-charged drops are transported down a ratcheted channel by contact charge electrophoresis powered by the same voltage input used for drop generation. We investigate how the drop size, generation frequency, and transport velocity depend on system parameters such as the liquid viscosity, interfacial tension, applied voltage, and channel dimensions. The observed trends are well explained by a series of scaling analyses that provide insight into the dominant physical mechanisms underlying drop generation and ratcheted transport. We identify the conditions necessary for achieving reliable operation and discuss the various modes of failure that can arise when these conditions are violated. Our results demonstrate that simple electric inputs can power increasingly complex droplet operations with potential opportunities for inexpensive and portable microfluidic systems.

Electric generation and ratcheted transport of contact-charged drops.

PubMed

Cartier, Charles A; Graybill, Jason R; Bishop, Kyle J M

2017-10-01

We describe a simple microfluidic system that enables the steady generation and efficient transport of aqueous drops using only a constant voltage input. Drop generation is achieved through an electrohydrodynamic dripping mechanism by which conductive drops grow and detach from a grounded nozzle in response to an electric field. The now-charged drops are transported down a ratcheted channel by contact charge electrophoresis powered by the same voltage input used for drop generation. We investigate how the drop size, generation frequency, and transport velocity depend on system parameters such as the liquid viscosity, interfacial tension, applied voltage, and channel dimensions. The observed trends are well explained by a series of scaling analyses that provide insight into the dominant physical mechanisms underlying drop generation and ratcheted transport. We identify the conditions necessary for achieving reliable operation and discuss the various modes of failure that can arise when these conditions are violated. Our results demonstrate that simple electric inputs can power increasingly complex droplet operations with potential opportunities for inexpensive and portable microfluidic systems.

Applications of asymmetric nanotextured parylene surface using its wetting and transport properties

NASA Astrophysics Data System (ADS)

Sekeroglu, Koray

In this thesis, basic digital fluidics devices were introduced using polymeric nanorods (nano-PPX) inspired from nature. Natural inspiration ignited this research by observing butterfly wings, water strider legs, rye grass leaves, and their asymmetric functions. Nano-PPX rods, manufactured by an oblique angle polymerization (OAP) method, are asymmetrically aligned structures that have unidirectional wetting properties. Nano-PPX demonstrates similar functions to the directional textured surfaces of animals and plants in terms of wetting, adhesion, and transport. The water pin-release mechanism on the asymmetric nano-PPX surface with adhesion function provides a great transport property. How the asymmetry causes transport is discussed in terms of hysteresis and interface contact of water droplets. In this study, the transport property of nano-PPX rods is used to guide droplets as well as transporting cargo such as microgels. With the addition of tracks on the nano-PPX rods, the surfaces were transformed into basic digital fluidics devices. The track-assisted nano-PPX has been employed to applications (i.e. sorting, mixing, and carrying cargo particles). Thus, digital fluidics devices fabricated on nano-PPX surface is a promising pathway to assemble microgels in the field of bioengineering. The characterization of the nano textured surface was completed using methods such as Scanning Electron Microscopy, Atomic Force Microscopy, Contact Angle Goniometry, and Fourier Transform Infra-Red Spectroscopy. These methods helped to understand the physical and chemical properties of nano-PPX. Parameters such as advancing and receding contact angles, nanorod tilt angle, and critical drop volumes were utilized to investigate the anisotropic wetting properties of nano-PPX surface. This investigation explained the directional wetting behavior of the surface as well as approaching new design parameters for adjusting surface properties. The nanorod tilt angle was a key parameter, thus changing the angle provided the surface with essential wetting properties. This adjustment on the nano-PPX surface exhibited excellent control on water droplet transport as well as guided the droplets from desired points to targets. The results demonstrated that it is possible to create railroad-like paths to manipulate the droplet movements by deforming the nano-PPX surface. Controlling physical properties of the surface granted the inspiration for fabricating basic fluidic devices to sort and mix droplets. These devices are promising for assembly purposes in terms of using microgels in engineering applications (i.e. building blocks for bioengineering). The surface has potential for further development to achieve the directed assembly of microgels into close proximity.

Drop-off Detection with the Long Cane: Effects of Different Cane Techniques on Performance

PubMed Central

Kim, Dae Shik; Emerson, Robert Wall; Curtis, Amy

2010-01-01

This study compared the drop-off detection performance with the two-point touch and constant contact cane techniques using a repeated-measures design with a convenience sample of 15 cane users with visual impairments. The constant contact technique was superior to the two-point touch technique in the drop-off detection rate and the 50% detection threshold. The findings may help an orientation and mobility instructor select an appropriate technique for a particular client or training situation. PMID:21209791

High-Temperature Wettability and Interactions between Y-Containing Ni-Based Alloys and Various Oxide Ceramics.

PubMed

Li, Jinpeng; Zhang, Huarui; Gao, Ming; Li, Qingling; Bian, Weidong; Tao, Tongxiang; Zhang, Hu

2018-05-07

To obtain appropriate crucible materials for vacuum induction melting of MCrAlY alloys, four different oxide ceramics, including MgO, Y₂O₃, Al₂O₃, and ZrO₂, with various microstructures were designed and characterized. The high-temperature wettability and interactions between Ni-20Co-20Cr-10Al-1.5Y alloys and oxide ceramics were studied by sessile drop experiments under vacuum. The results showed that all the systems exhibited non-wetting behavior. The contact angles were stable during the melting process of alloys and the equilibrium contact angles were 140° (MgO), 148° (Y₂O₃), 154° (Al₂O₃), and 157° (ZrO₂), respectively. The interfacial reaction between the ceramic substrates and alloys occurred at high temperature. Though the ceramics had different microstructures, similar continuous Y₂O₃ reaction layer with thicknesses of about 25 μm at the alloy-ceramic interface in MgO, Al₂O₃, and ZrO₂ systems formed. The average area percentage of oxides in the alloy matrices were 0.59% (MgO), 0.11% (Al₂O₃), 0.09% (ZrO₂), and 0.02% (Y₂O₃), respectively. The alloys, after reacting with MgO ceramic, had the highest inclusion content, while those with the lowest content were in the Y₂O₃ system. Y₂O₃ ceramic was the most beneficial for vacuum induction melting of high-purity Y-containing Ni-based alloys.

Wetting of single crystal mullite by borosilicate and yttrium-aluminosilicate glasses and wetting phenomena of steels containing aluminum and titanium

NASA Astrophysics Data System (ADS)

Eldred, Benjamin Todd

This dissertation consists of two major sections. The first section concerns the wetting of single crystal mullite by borosilicate and yttrium-aluminosilicate glasses. The borosilicate glass showed poor wetting and interacted only moderately with the substrate. The yttrium-aluminosilicate glass interacted strongly with mullite and showed very good wetting. Balanced chemical equations between each glass and mullite were derived from EDS data. Wetting was found to be dependent on the crystallographic orientation of the substrate, in agreement with previous studies of the surface energy of mullite. The second section concerns the wetting phenomena of steels containing aluminum and titanium. A modified sessile drop technique was used to investigate the wetting of steels containing aluminum and/or titanium as a function of furnace atmosphere. It was found that the steel chemistry and furnace atmosphere had little effect on wetting except in the case of a particular ultra-low carbon steel containing both aluminum and titanium. This steel was found to show significantly lower contact angles than any other steel tested when it was in an atmosphere of pure hydrogen. As nitrogen was added to the atmosphere, the contact angle increased monotonically and irreversibly. The interaction between aluminum, titanium, and nitrogen is explained in terms of first-order interaction coefficients available in thermodynamic literature.

Identification of hydrophilic group formation on polymer surface during Ar{sup +} ion irradiation in O{sub 2} environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, J.S.; Choi, W.K.; Jung, H.J.

1997-12-01

Ar{sup +} ion irradiation on low density polyethylene (LDPE), and polystyrene (PS) was performed in an O{sub 2} environment in order to improve wettability of polymers to water and to identify the formation of hydrophilic groups originated from chemical reactions on the surface of polymers. Doses of a broad Ar{sup +} ion beam of 1 keV energy were changed from 5 {times} 10{sup 15} to 1 {times} 10{sup 17}/cm{sup 2} and the rate of oxygen gas flowing near the sample surface was varied from 0 to 7 ml/min. The contact angle of polymers was not reduced much by Ar{sup +}more » ion irradiation without oxygen gas. However, it dropped largely to a minimum of 35{degree} and 26{degree} for Ar{sup +} ion irradiation in the presence of flowing oxygen gas on LDPE and PS, respectively. From x-ray photoelectron spectroscopy analysis, it was observed that hydrophilic groups were formed on the surface of polymers through an ion-assisted chemical reaction between the ion-induced unstable chains and oxygen. The newly formed hydrophilic group was identified as {single_bond}(C{double_bond}){single_bond} bond and {single_bond}(C{double_bond}O){single_bond}O{single_bond} bond. The contact angle of polymer was greatly dependent on the hydrophilic group formed on the surface.« less

Ammonia modification for flotation separation of polycarbonate and polystyrene waste plastics.

PubMed

Wang, Chong-Qing; Wang, Hui; Gu, Guo-Hua; Lin, Qing-Quan; Zhang, Ling-Ling; Huang, Luo-Luo; Zhao, Jun-Yao

2016-05-01

A promising method, ammonia modification, was developed for flotation separation of polycarbonate (PC) and polystyrene (PS) waste plastics. Ammonia modification has little effect on flotation behavior of PS, while it changes significantly that of PC. The PC recovery in the floated product drops from 100% to 3.17% when modification time is 13min and then rises to 100% after longer modification. The mechanism of ammonia modification was studied by contact angle, and Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements. Contact angle of PC indicates the decline of PC recovery in the floated product is ascribed to an increase in surface wettability. FT-IR and XPS spectra suggest that ammonia modification causes chemical reactions occurred on PC surface. Flotation behavior of ammonia-modified PC and PS was investigated with respect to flotation time, frother concentration and particle sizes. Flotation separation of PC and PS waste plastics was conducted based on the flotation behavior of single plastic. PC and PS mixtures with different particle sizes are separated efficiently, implying that the technology possesses superior applicability to particle sizes of plastics. The purity of PS and PC is up to 99.53% and 98.21%, respectively, and the recovery of PS and PC is larger than 92.06%. A reliable, cheap and effective process is proposed for separation of PC and PS waste plastics. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ultralow contact angle hysteresis and no-aging effects in superhydrophobic tangled nanofiber structures generated by controlling the pore size of a 99.5% aluminum foil

NASA Astrophysics Data System (ADS)

Lee, Sangmin; Hwang, Woonbong

2009-03-01

Superhydrophobic surfaces designed to improve hydrophobicity have high advancing contact angles corresponding to the Cassie state, but these surfaces also exhibit high contact angle hysteresis. We report here a simple and inexpensive method for fabricating superhydrophobic tangled nanofiber structures with ultralow contact angle hysteresis and no-aging degradation, based on a widening process. The resulting nanostructures are suitable for diverse applications including microfluidic devices for biological studies and industrial self-cleaning products for automobiles, ships and houses.

Wettability Control of Gold Surfaces Modified with Benzenethiol Derivatives: Water Contact Angle and Thermal Stability.

PubMed

Tatara, Shingo; Kuzumoto, Yasutaka; Kitamura, Masatoshi

2016-04-01

The water wettability of Au surfaces has been controlled using various benzenethiol derivatives including 4-methylbenzenethiol, pentafluorobenzenethiol, 4-flubrobenzenethiol, 4-methoxy-benzenethiol, 4-nitrobenzenethiol, and 4-hydroxybenzenethiol. The water contact angle of the Au surface modified with the benzenethiol derivative was found to vary in the wide range of 30.9° to 88.3°. The contact angle of the modified Au films annealed was also measured in order to investigate their thermal stability. The change in the contact angle indicated that the modified surface is stable at temperatures below about 400 K. Meanwhile, the activation energy of desorption from the modified surface was estimated from the change in the contact angle. The modified Au surface was also examined using X-ray photoelectron spectroscopy.

Impact of air and water vapor environments on the hydrophobicity of surfaces.

PubMed

Weisensee, Patricia B; Neelakantan, Nitin K; Suslick, Kenneth S; Jacobi, Anthony M; King, William P

2015-09-01

Droplet wettability and mobility play an important role in dropwise condensation heat transfer. Heat exchangers and heat pipes operate at liquid-vapor saturation. We hypothesize that the wetting behavior of liquid water on microstructures surrounded by pure water vapor differs from that for water droplets in air. The static and dynamic contact angles and contact angle hysteresis of water droplets were measured in air and pure water vapor environments inside a pressure vessel. Pressures ranged from 60 to 1000 mbar, with corresponding saturation temperatures between 36 and 100°C. The wetting behavior was studied on four hydrophobic surfaces: flat Teflon-coated, micropillars, micro-scale meshes, and nanoparticle-coated with hierarchical micro- and nanoscale roughness. Static advancing contact angles are 9° lower in the water vapor environment than in air on a flat surface. One explanation for this reduction in contact angles is water vapor adsorption to the Teflon. On microstructured surfaces, the vapor environment has little effect on the static contact angles. In all cases, variations in pressure and temperature do not influence the wettability and mobility of the water droplets. In most cases, advancing contact angles increase and contact angle hysteresis decreases when the droplets are sliding or rolling down an inclined surface. Copyright © 2015 Elsevier Inc. All rights reserved.

In vitro evaluation of the contact angle formed between AH Plus, Hybrid Root Seal and mineral trioxide aggregate Plus sealer with dentin and gutta-percha.

PubMed

Nikhil, Vineeta; Jaiswal, Shikha; Bajpai, Gauravi

2018-01-01

The purpose of this study was evaluation and comparison of the contact angle of new root canal sealers - Hybrid Root Seal, mineral trioxide aggregate (MTA) Plus, and the conventional AH Plus sealer with dentin and gutta-percha. Two groups (Group D - dentin and Group G - gutta-percha) of 18 samples each were further randomly divided into 3 subgroups based on the type of sealer used, that is, AH Plus, Hybrid Root Seal, and MTA Plus. Contact angle measurement device (Phoenix 300) was used to measure the contact angle of the sealers on both dentin and gutta-percha. The results thus obtained were analyzed using one-way analysis of variance and Student's t -test. MTA Plus recorded significantly higher values of contact angle on both the substrates, that is, dentin and gutta-percha when compared to AH Plus and Hybrid root canal sealer. The lowest value of contact angle in gutta-percha and dentin was shown by Hybrid root canal sealer and AH Plus, respectively. Both AH Plus and Hybrid Root Seal exhibited lower contact angle values, and hence, better wettability on both dentin and gutta-percha as compared to MTA Plus.

Color-gradient lattice Boltzmann model for simulating droplet motion with contact-angle hysteresis.

PubMed

Ba, Yan; Liu, Haihu; Sun, Jinju; Zheng, Rongye

2013-10-01

Lattice Boltzmann method (LBM) is an effective tool for simulating the contact-line motion due to the nature of its microscopic dynamics. In contact-line motion, contact-angle hysteresis is an inherent phenomenon, but it is neglected in most existing color-gradient based LBMs. In this paper, a color-gradient based multiphase LBM is developed to simulate the contact-line motion, particularly with the hysteresis of contact angle involved. In this model, the perturbation operator based on the continuum surface force concept is introduced to model the interfacial tension, and the recoloring operator proposed by Latva-Kokko and Rothman is used to produce phase segregation and resolve the lattice pinning problem. At the solid surface, the color-conserving wetting boundary condition [Hollis et al., IMA J. Appl. Math. 76, 726 (2011)] is applied to improve the accuracy of simulations and suppress spurious currents at the contact line. In particular, we present a numerical algorithm to allow for the effect of the contact-angle hysteresis, in which an iterative procedure is used to determine the dynamic contact angle. Numerical simulations are conducted to verify the developed model, including the droplet partial wetting process and droplet dynamical behavior in a simple shear flow. The obtained results are compared with theoretical solutions and experimental data, indicating that the model is able to predict the equilibrium droplet shape as well as the dynamic process of partial wetting and thus permits accurate prediction of contact-line motion with the consideration of contact-angle hysteresis.

Pinning of the Contact Line during Evaporation on Heterogeneous Surfaces: Slowdown or Temporary Immobilization? Insights from a Nanoscale Study.

PubMed

Zhang, Jianguo; Müller-Plathe, Florian; Leroy, Frédéric

2015-07-14

The question of the effect of surface heterogeneities on the evaporation of liquid droplets from solid surfaces is addressed through nonequilibrium molecular dynamics simulations. The mechanism behind contact line pinning which is still unclear is discussed in detail on the nanoscale. Model systems with the Lennard-Jones interaction potential were employed to study the evaporation of nanometer-sized cylindrical droplets from a flat surface. The heterogeneity of the surface was modeled through alternating stripes of equal width but two chemical types. The first type leads to a contact angle of 67°, and the other leads to a contact angle of 115°. The stripe width was varied between 2 and 20 liquid-particle diameters. On the surface with the narrowest stripes, evaporation occurred at constant contact angle as if the surface was homogeneous, with a value of the contact angle as predicted by the regular Cassie-Baxter equation. When the width was increased, the contact angle oscillated during evaporation between two boundaries whose values depend on the stripe width. The evaporation behavior was thus found to be a direct signature of the typical size of the surface heterogeneity domains. The contact angle both at equilibrium and during evaporation could be predicted from a local Cassie-Baxter equation in which the surface composition within a distance of seven fluid-particle diameters around the contact line was considered, confirming the local nature of the interactions that drive the wetting behavior of droplets. More importantly, we propose a nanoscale explanation of pinning during evaporation. Pinning should be interpreted as a drastic slowdown of the contact line dynamics rather than a complete immobilization of it during a transition between two contact angle boundaries.

Effect of acetabular cup abduction angle on wear of ultrahigh-molecular-weight polyethylene in hip simulator testing.

PubMed

Korduba, Laryssa A; Essner, Aaron; Pivec, Robert; Lancin, Perry; Mont, Michael A; Wang, Aiguo; Delanois, Ronald E

2014-10-01

The effect of acetabular component positioning on the wear rates of metal-on-polyethylene articulations has not been extensively studied. Placement of acetabular cups at abduction angles of more than 40° has been noted as a possible reason for early failure caused by increased wear. We conducted a study to evaluate the effects of different acetabular cup abduction angles on polyethylene wear rate, wear area, contact pressure, and contact area. Our in vitro study used a hip joint simulator and finite element analysis to assess the effects of cup orientation at 4 angles (0°, 40°, 50°, 70°) on wear and contact properties. Polyethylene bearings with 28-mm cobalt-chrome femoral heads were cycled in an environment mimicking in vivo joint fluid to determine the volumetric wear rate after 10 million cycles. Contact pressure and contact area for each cup abduction angle were assessed using finite element analysis. Results were correlated with cup abduction angles to determine if there were any differences among the 4 groups. The inverse relationship between volumetric wear rate and acetabular cup inclination angle demonstrated less wear with steeper cup angles. The largest abduction angle (70°) had the lowest contact area, largest contact pressure, and smallest head coverage. Conversely, the smallest abduction angle (0°) had the most wear and most head coverage. Polyethylene wear after total hip arthroplasty is a major cause of osteolysis and aseptic loosening, which may lead to premature implant failure. Several studies have found that high wear rates for cups oriented at steep angles contributed to their failure. Our data demonstrated that larger cup abduction angles were associated with lower, not higher, wear. However, this potentially "protective" effect is likely counteracted by other complications of steep cup angles, including impingement, instability, and edge loading. These factors may be more relevant in explaining why implants fail at a higher rate if cups are oriented at more than 40° of abduction.

Spread of pathogens through rain drop impact

NASA Astrophysics Data System (ADS)

Kim, Seungho; Gruszewski, Hope; Gidley, Todd; Schmale, David G., III; Jung, Sunghwan

2017-11-01

Rain drop impact can disperse micron-sized pathogenic particles over long distances. In this study, we aim to elucidate mechanisms for disease dispersal when a rain drop impacts a particle-laden solid surface. Three different dispersal types were observed depending on whether the dispersed glass particles were dry or wet. For a dry particle dispersal, the movement of contact line made the particles initially jump off the surface with relatively high velocity. Then, air vortex was formed due to the air current entrained along with the falling drop, and advected the particles with relatively low velocity. For a wet particle dispersal, the contact line of a spreading liquid became unstable due to the presence of the particles on the substrate. This caused splashing at the contact line and ejected liquid droplets carrying the particles. Finally, we released a drop onto wheat plants infected with the rust fungus, Puccinia triticina, and found that nearly all of the satellite droplets from a single drop contained at least one rust spore. Also, we visualized such novel dispersal dynamics with a high-speed camera and characterized their features by scaling models. This research was partially supported by National Science Foundation Grant CBET-1604424.

Coffee-stain growth dynamics on dry and wet surfaces

NASA Astrophysics Data System (ADS)

Boulogne, François; Ingremeau, François; Stone, Howard A.

2017-02-01

The drying of a drop containing particles often results in the accumulation of the particles at the contact line. In this work, we investigate the drying of an aqueous colloidal drop surrounded by a hydrogel that is also evaporating. We combine theoretical and experimental studies to understand how the surrounding vapor concentration affects the particle deposit during the constant radius evaporation mode. In addition to the common case of evaporation on an otherwise dry surface, we show that in a configuration where liquid is evaporating from a flat surface around the drop, the singularity of the evaporative flux at the contact line is suppressed and the drop evaporation is homogeneous. For both conditions, we derive the velocity field and we establish the temporal evolution of the number of particles accumulated at the contact line. We predict the growth dynamics of the stain and the drying timescales. Thus, dry and wet conditions are compared with experimental results and we highlight that only the dynamics is modified by the evaporation conditions, not the final accumulation at the contact line.

Comparison of the replication and transmissibility of an infectious laryngotracheitis virus vaccine delivered via eye-drop or drinking-water.

PubMed

Coppo, Mauricio J C; Devlin, Joanne M; Noormohammadi, Amir H

2012-01-01

Live attenuated vaccines have been extensively used to control infectious laryngotracheitis (ILT). Most vaccines are registered/recommended for use via eye-drop although vaccination via drinking-water is commonly used in the field. Drinking-water vaccination has been associated with non-uniform protection. Bird-to-bird passage of chick-embryo-origin (CEO) ILT vaccines has been shown to result in reversion to virulence. The purpose of the present study was to examine the replication and transmission of a commercial CEO infectious laryngotracheitis virus (ILTV) vaccine strain following drinking-water or eye-drop inoculation. Two groups of 10 specific-pathogen-free chickens were each vaccinated with Serva ILTV vaccine strain either via eye-drop or drinking-water. Groups of four or five unvaccinated birds were placed in contact with vaccinated birds at regular intervals. Tracheal swabs were collected every 4 days from vaccinated and in-contact birds to assess viral replication and transmission using quantitative polymerase chain reaction. Compared with eye-drop-vaccinated birds, drinking-water-vaccinated birds showed delayed viral replication but had detectable viral DNA for a longer period of time. Transmission to chickens exposed by contact on day 0 of the experiments was similar in both groups. Birds exposed to ILTV by contact with eye-drop vaccinated birds on days 4, 8, 12 and 16 of the experiment had detectable ILTV for up to 8 days post exposure. ILTV was not detected in chickens that were exposed by contact with drinking-water vaccinated birds on day 12 of the experiment or later. Results from this study provide valuable practical information for the use of ILT vaccine.

Difluprednate Ophthalmic

MedlinePlus

... tell you that you should not wear contact lenses during your treatment with difluprednate eye drops.you should know that difluprednate eye drops ... your regular dosing schedule. Do not apply extra eye drops to make up for a missed dose.

Probing the nanoscale with high-speed interferometry of an impacting drop

NASA Astrophysics Data System (ADS)

Thoroddsen, S. T.; Li, E. Q.; Vakarelski, I. U.; Langley, K.

2017-02-01

The simple phenomenon of a water drop falling onto a glass plate may seem like a trivial fluid mechanics problem. However, detailed imaging has shown that this process is highly complex and a small air-bubble is always entrapped under the drop when it makes contact with the solid. This bubble can interfere with the uniformity of spray coatings and degrade inkjet fabrication of displays etc. We will describe how we use high-speed interferometry at 5 million frames per second to understand the details of this process. As the impacting drop approaches the solid, the dynamics are characterized by a balance between the lubrication pressure in the thin air layer and the inertia of the bot-tom of the drop. This deforms the drop, forming a dimple at its bottom and making the drop touch the surface along a ring, thereby entrapping the air-layer, which is typically 1-3 μm thick. This air-layer can be highly compressed and the deceleration of the bottom of the drop can be as large as 300,000 g. We describe how the thickness evolution of the lubricating air-layer is extracted from following the interference fringes between frames. Two-color interferometry is also used to extract absolute layer thicknesses. Finally, we identify the effects of nanometric surface roughness on the first contact of the drop with the substrate. Here we need to resolve the 100 nm thickness changes occurring during 200 ns intervals, requiring these state of the art high-speed cameras. Surprisingly, we see a ring of micro-bubbles marking the first contact of the drop with the glass, only for microscope slides, which have a typical roughness of 20 nm, while such rings are absent for drop impacts onto molecularly smooth mica surfaces.

Wettability and impact dynamics of water droplets on rice ( Oryza sativa L.) leaves

NASA Astrophysics Data System (ADS)

Kwon, Dae Hee; Huh, Hyung Kyu; Lee, Sang Joon

2014-03-01

We investigated the wettability and impact dynamics of water droplets on rice leaves at various leaf inclination angles and orientations. Contact angle, contact angle hysteresis (CAH), and roll-off angle ( α roll) of water droplets were measured quantitatively. Results showed that droplet motion exhibited less resistance along the longitudinal direction. Impact dynamic parameters, such as impact behaviors, maximum spreading factor, contact distance, and contact time were also investigated. Three different impact behaviors were categorized based on the normal component of Weber number irrespective of the inclination angle of the rice leaf. The asymmetric impact behavior induced by the tangential Weber number was also identified. Variation in the maximum spreading factor according to the normal Weber number was measured and compared with theoretical value obtained according to scaling law to show the wettability of the rice leaves. The contact distance of the impacting droplets depended on the inclination angle of the leaves. Along the longitudinal direction of rice leaves, contact distance was farther than that along the transverse direction. This result is consistent with the smaller values of CAH and α roll along the longitudinal direction.

Analysis of water microdroplet condensation on silicon surfaces

NASA Astrophysics Data System (ADS)

Honda, Takuya; Fujimoto, Kenya; Yoshimoto, Yuta; Mogi, Katsuo; Kinefuchi, Ikuya; Sugii, Yasuhiko; Takagi, Shu; Univ. of Tokyo Team; Tokyo Inst. of Tech. Team

2016-11-01

We observed the condensation process of water microdroplets on flat silicon (100) surfaces by means of the sequential visualization of the droplets using an environmental scanning electron microscope. As previously reported for nanostructured surfaces, the condensation process of water microdroplets on the flat silicon surfaces also exhibits two modes: the constant base (CB) area mode and the constant contact angle (CCA) mode. In the CB mode, the contact angle increases with time while the base diameter is constant. Subsequently, in the CCA mode, the base diameter increases with time while the contact angle remains constant. The dropwise condensation model regulated by subcooling temperature does not reproduce the experimental results. Because the subcooling temperature is not constant in the case of a slow condensation rate, this model is not applicable to the condensation of the long time scale ( several tens of minutes). The contact angle of water microdroplets ( several μm) tended to be smaller than the macro contact angle. Two hypotheses are proposed as the cause of small contact angles: electrowetting and the coalescence of sub- μm water droplets.

Magnetowetting and sliding motion of a sessile ferrofluid droplet in the presence of a permanent magnet.

PubMed

Nguyen, Nam-Trung; Zhu, Guiping; Chua, Yong-Chin; Phan, Vinh-Nguyen; Tan, Say-Hwa

2010-08-03

Motion of a droplet on a planar surface has applications in droplet-based lab on a chip technology. This paper reports the experimental results of the shape, contact angles, and motion of ferrofluid droplets driven by a permanent magnet on a planar homogeneous surface. The water-based ferrofluid in use is a colloidal suspension of single-domain magnetic nanoparticles. The effect of the magnetic field on the apparent contact angle of the ferrofluid droplet was first investigated. The results show that an increasing magnetic flux decreases the apparent contact angle of a sessile ferrofluid droplet. Next, the dynamic contact angle was investigated by observing the shape and the motion of a sessile ferrofluid droplet. The advancing and receding contact angles of the moving ferrofluid were measured at different moving speeds and magnetic field strengths. The measured contact angles were used to estimate the magnitude of the forces involved in the sliding motion. Scaling analysis was carried out to derive the critical velocity, beyond which the droplet is not able to catch up with the moving magnet.

Wettability of naturally aged silicone and EPDM composite insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubanski, S.M.; Vlastos, A.E.

1990-07-01

This paper reports the wettability of aged surfaces and of the bulk of naturally aged silicone and EPDM insulator housings and of silicone elastomer insulator coatings studied. The samples were taken either directly from the insulators or treated by exposing them to corona discharges and/or to saline pollution. The results show that the contact angles of the silicone rubber insulator surfaces are larger than the contact angles of the RTV silicone rubber coating and of the EPDM rubber insulator surfaces, especially when the surfaces are aged. When the insulators were exposed to corona discharges, the contact angles of the siliconemore » rubber insulators are reduced but after the exposure they recover with time. The contact angles of the EPDM rubber insulators, however, after the exposure, continue to reduce. When exposed to artificial saline pollution, the silicone rubber insulators show a limited recovery of their contact angles with time, while, when exposed to corona discharge, they show a recovery of the contact angle after the exposure. The time for recovery is dependent on the exposure time to the corona discharges.« less

Clinical investigation of the effect of topical anesthesia on intraocular pressure

PubMed Central

Almubrad, Turki M; Ogbuehi, Kelechi C

2007-01-01

Background/Aims: Contact tonometry is generally considered more accurate than non-contact tonometry in the assessment of intraocular pressure (IOP). This study was designed to investigate the effect of ocular anesthesia, a pre-requisite for contact tonometry, on the IOP in a sample of visually normal subjects. Method: In a random sample of 120 young visually normal subjects (divided equally among three groups), the Topcon CT80 non-contact tonometer was used to measure IOP before, at the second minute and at the fifth minute following instillation of one drop of one of three eyedrops – carboxymethylcellulose sodium 0.5% (control), oxybuprocaine hydrochloride 0.4% and proparacaine hydrochloride 0.5%. Results: The IOP measured before instilling the ophthalmic drops did not vary significantly among the three groups of subjects (p > 0.05). In the control group, the average IOP of 15.1 ± 2.6 mmHg did not vary significantly (p > 0.05) 2 minutes and 5 minutes following instillation of one drop of Carboxymethylcellulose sodium. There were statistically significant reductions of IOP 2 minutes (p < 0.01) and 5 minutes (p < 0.001) after the instillation of one drop of oxybuprocaine hydrochloride. One drop of proparacaine hydrochloride caused significant reductions in the average IOP after 2 minutes (p < 0.001) and after 5 minutes (p < 0.001). Conclusions: One drop of topical proparacaine or oxybuprocaine may cause a small but a statistically significant reduction in IOP which could lead to lower IOP readings. PMID:19668485

Clinical investigation of the effect of topical anesthesia on intraocular pressure.

PubMed

Almubrad, Turki M; Ogbuehi, Kelechi C

2007-09-01

Contact tonometry is generally considered more accurate than non-contact tonometry in the assessment of intraocular pressure (IOP). This study was designed to investigate the effect of ocular anesthesia, a pre-requisite for contact tonometry, on the IOP in a sample of visually normal subjects. In a random sample of 120 young visually normal subjects (divided equally among three groups), the Topcon CT80 non-contact tonometer was used to measure IOP before, at the second minute and at the fifth minute following instillation of one drop of one of three eyedrops - carboxymethylcellulose sodium 0.5% (control), oxybuprocaine hydrochloride 0.4% and proparacaine hydrochloride 0.5%. The IOP measured before instilling the ophthalmic drops did not vary significantly among the three groups of subjects (p > 0.05). In the control group, the average IOP of 15.1 +/- 2.6 mmHg did not vary significantly (p > 0.05) 2 minutes and 5 minutes following instillation of one drop of Carboxymethylcellulose sodium. There were statistically significant reductions of IOP 2 minutes (p < 0.01) and 5 minutes (p < 0.001) after the instillation of one drop of oxybuprocaine hydrochloride. One drop of proparacaine hydrochloride caused significant reductions in the average IOP after 2 minutes (p < 0.001) and after 5 minutes (p < 0.001). One drop of topical proparacaine or oxybuprocaine may cause a small but a statistically significant reduction in IOP which could lead to lower IOP readings.

Optical distortion correction of a liquid-gas interface and contact angle in cylindrical tubes

NASA Astrophysics Data System (ADS)

Darzi, Milad; Park, Chanwoo

2017-05-01

Objects inside cylindrical tubes appear distorted as seen outside the tube due to the refraction of the light passing through different media. Such an optical distortion may cause significant errors in geometrical measurements using optical observations of objects (e.g., liquid-gas interfaces, solid particles, gas bubbles) inside the tubes. In this study, an analytical method using a point-by-point correction of the optical distortion was developed. For an experimental validation, the method was used to correct the apparent profiles of the water-air interfaces (menisci) in cylindrical glass tubes with different tube diameters and wall thicknesses. Then, the corrected meniscus profiles were used to calculate the corrected static contact angles. The corrected contact angle shows an excellent agreement with the reference contact angles as compared to the conventional contact angle measurement using apparent meniscus profiles.

A review of factors that affect contact angle and implications for flotation practice.

PubMed

Chau, T T; Bruckard, W J; Koh, P T L; Nguyen, A V

2009-09-30

Contact angle and the wetting behaviour of solid particles are influenced by many physical and chemical factors such as surface roughness and heterogeneity as well as particle shape and size. A significant amount of effort has been invested in order to probe the correlation between these factors and surface wettability. Some of the key investigations reported in the literature are reviewed here. It is clear from the papers reviewed that, depending on many experimental conditions such as the size of the surface heterogeneities and asperities, surface cleanliness, and the resolution of measuring equipment and data interpretation, obtaining meaningful contact angle values is extremely difficult and such values are reliant on careful experimental control. Surface wetting behaviour depends on not only surface texture (roughness and particle shape), and surface chemistry (heterogeneity) but also on hydrodynamic conditions in the preparation route. The inability to distinguish the effects of each factor may be due to the interplay and/or overlap of two or more factors in each system. From this review, it was concluded that: Surface geometry (and surface roughness of different scales) can be used to tune the contact angle; with increasing surface roughness the apparent contact angle decreases for hydrophilic materials and increases for hydrophobic materials. For non-ideal surfaces, such as mineral surfaces in the flotation process, kinetics plays a more important role than thermodynamics in dictating wettability. Particle size encountered in flotation (10-200 microm) showed no significant effect on contact angle but has a strong effect on flotation rate constant. There is a lack of a rigid quantitative correlation between factors affecting wetting, wetting behaviour and contact angle on minerals; and hence their implication for flotation process. Specifically, universal correlation of contact angle to flotation recovery is still difficult to predict from first principles. Other advanced techniques and measures complementary to contact angle will be essential to establish the link between research and practice in flotation.

Measurement of contact-angle hysteresis for droplets on nanopillared surface and in the Cassie and Wenzel states: a molecular dynamics simulation study.

PubMed

Koishi, Takahiro; Yasuoka, Kenji; Fujikawa, Shigenori; Zeng, Xiao Cheng

2011-09-27

We perform large-scale molecular dynamics simulations to measure the contact-angle hysteresis for a nanodroplet of water placed on a nanopillared surface. The water droplet can be in either the Cassie state (droplet being on top of the nanopillared surface) or the Wenzel state (droplet being in contact with the bottom of nanopillar grooves). To measure the contact-angle hysteresis in a quantitative fashion, the molecular dynamics simulation is designed such that the number of water molecules in the droplets can be systematically varied, but the number of base nanopillars that are in direct contact with the droplets is fixed. We find that the contact-angle hysteresis for the droplet in the Cassie state is weaker than that in the Wenzel state. This conclusion is consistent with the experimental observation. We also test a different definition of the contact-angle hysteresis, which can be extended to estimate hysteresis between the Cassie and Wenzel state. The idea is motivated from the appearance of the hysteresis loop typically seen in computer simulation of the first-order phase transition, which stems from the metastability of a system in different thermodynamic states. Since the initial shape of the droplet can be controlled arbitrarily in the computer simulation, the number of base nanopillars that are in contact with the droplet can be controlled as well. We show that the measured contact-angle hysteresis according to the second definition is indeed very sensitive to the initial shape of the droplet. Nevertheless, the contact-angle hystereses measured based on the conventional and new definition seem converging in the large droplet limit. © 2011 American Chemical Society

Lattice Boltzmann modeling of contact angle and its hysteresis in two-phase flow with large viscosity difference.

PubMed

Liu, Haihu; Ju, Yaping; Wang, Ningning; Xi, Guang; Zhang, Yonghao

2015-09-01

Contact angle hysteresis is an important physical phenomenon omnipresent in nature and various industrial processes, but its effects are not considered in many existing multiphase flow simulations due to modeling complexity. In this work, a multiphase lattice Boltzmann method (LBM) is developed to simulate the contact-line dynamics with consideration of the contact angle hysteresis for a broad range of kinematic viscosity ratios. In this method, the immiscible two-phase flow is described by a color-fluid model, in which the multiple-relaxation-time collision operator is adopted to increase numerical stability and suppress unphysical spurious currents at the contact line. The contact angle hysteresis is introduced using the strategy proposed by Ding and Spelt [Ding and Spelt, J. Fluid Mech. 599, 341 (2008)JFLSA70022-112010.1017/S0022112008000190], and the geometrical wetting boundary condition is enforced to obtain the desired contact angle. This method is first validated by simulations of static contact angle and dynamic capillary intrusion process on ideal (smooth) surfaces. It is then used to simulate the dynamic behavior of a droplet on a nonideal (inhomogeneous) surface subject to a simple shear flow. When the droplet remains pinned on the surface due to hysteresis, the steady interface shapes of the droplet quantitatively agree well with the previous numerical results. Four typical motion modes of contact points, as observed in a recent study, are qualitatively reproduced with varying advancing and receding contact angles. The viscosity ratio is found to have a notable impact on the droplet deformation, breakup, and hysteresis behavior. Finally, this method is extended to simulate the droplet breakup in a microfluidic T junction, with one half of the wall surface ideal and the other half nonideal. Due to the contact angle hysteresis, the droplet asymmetrically breaks up into two daughter droplets with the smaller one in the nonideal branch channel, and the behavior of daughter droplets is significantly different in both branch channels. Also, it is found that the contact angle hysteresis is strengthened with decreasing the viscosity ratio, leading to an earlier droplet breakup and a decrease in the maximum length that the droplet can reach before the breakup. These simulation results manifest that the present multiphase LBM can be a useful substitute to Ba et al. [Phys. Rev. E 88, 043306 (2013)PLEEE81539-375510.1103/PhysRevE.88.043306] for modeling the contact angle hysteresis, and it can be easily implemented with higher computational efficiency.

Preparation of hydrophobic coatings

DOEpatents

Branson, Eric D [Albuquerque, NM; Shah, Pratik B [Albuquerque, NM; Singh, Seema [Rio Rancho, NM; Brinker, C Jeffrey [Albuquerque, NM

2009-02-03

A method for preparing a hydrophobic coating by preparing a precursor sol comprising a metal alkoxide, a solvent, a basic catalyst, a fluoroalkyl compound and water, depositing the precursor sol as a film onto a surface, such as a substrate or a pipe, heating, the film and exposing the film to a hydrophobic silane compound to form a hydrophobic coating with a contact angle greater than approximately 150.degree.. The contact angle of the film can be controlled by exposure to ultraviolet radiation to reduce the contact angle and subsequent exposure to a hydrophobic silane compound to increase the contact angle.

Approach to the determination of the contact angle in hydrophobic samples with simultaneous correction of the effect of the roughness

NASA Astrophysics Data System (ADS)

Domínguez, Noemí; Castilla, Pau; Linzoain, María Eugenia; Durand, Géraldine; García, Cristina; Arasa, Josep

2018-04-01

This work presents the validation study of a method developed to measure contact angles with a confocal device in a set of hydrophobic samples. The use of this device allows the evaluation of the roughness of the surface and the determination of the contact angle in the same area of the sample. Furthermore, a theoretical evaluation of the impact of the roughness of a nonsmooth surface in the calculation of the contact angle when it is not taken into account according to Wenzel's model is also presented.

Measurement of Critical Contact Angle in a Microgravity Space Experiment

NASA Technical Reports Server (NTRS)

Concus, P.; Finn, R.; Weislogel, M.

1998-01-01

Mathematical theory predicts that small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. This phenomenon was investigated in the Interface Configuration Experiment on board the USML-2 Space Shuttle flight. The experiment's "double proboscis" containers were designed to strike a balance between conflicting requirements of sizable volume of liquid shift (for ease of observation) and abruptness of the shift (for accurate determination of critical contact angle). The experimental results support the classical concept of macroscopic contact angle and demonstrate the role of hysteresis in impeding orientation toward equilibrium.

Measurement of Critical Contact Angle in a Microgravity Space Experiment

NASA Technical Reports Server (NTRS)

Concus, P.; Finn, R.; Weislogel, M.

1998-01-01

Mathematical theory predicts that small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. This phenomenon was investigated in the Interface Configuration Experiment on board the USMT,2 Space Shuttle flight. The experiment's "double proboscis" containers were designed to strike a balance between conflicting requirements of sizable volume of liquid shift (for ease of observation) and abruptness of the shift (for accurate determination of critical contact angle). The experimental results support the classical concept of macroscopic contact angle and demonstrate the role of hysteresis in impeding orientation toward equilibrium.

Investigating How Contact Angle Effects the Interaction between Water and a Hydrophobic Surface

NASA Astrophysics Data System (ADS)

Poynor, Adele; Neidig, Caitlyn

2012-02-01

By definition hydrophobic substances hate water. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density region forms near the surface. Contact angle is a measure of how hydrophobic a surface is. We have employed an automated home-built Surface Plasmon Resonance (SPR) apparatus to investigate the effect of varying the contact angle on the depletion layer

The influence of muscle pennation angle and cross-sectional area on contact forces in the ankle joint.

PubMed

Sopher, Ran S; Amis, Andrew A; Davies, D Ceri; Jeffers, Jonathan Rt

2017-01-01

Data about a muscle's fibre pennation angle and physiological cross-sectional area are used in musculoskeletal modelling to estimate muscle forces, which are used to calculate joint contact forces. For the leg, muscle architecture data are derived from studies that measured pennation angle at the muscle surface, but not deep within it. Musculoskeletal models developed to estimate joint contact loads have usually been based on the mean values of pennation angle and physiological cross-sectional area. Therefore, the first aim of this study was to investigate differences between superficial and deep pennation angles within each muscle acting over the ankle and predict how differences may influence muscle forces calculated in musculoskeletal modelling. The second aim was to investigate how inter-subject variability in physiological cross-sectional area and pennation angle affects calculated ankle contact forces. Eight cadaveric legs were dissected to excise the muscles acting over the ankle. The mean surface and deep pennation angles, fibre length and physiological cross-sectional area were measured. Cluster analysis was applied to group the muscles according to their architectural characteristics. A previously validated OpenSim model was used to estimate ankle muscle forces and contact loads using architecture data from all eight limbs. The mean surface pennation angle for soleus was significantly greater (54%) than the mean deep pennation angle. Cluster analysis revealed three groups of muscles with similar architecture and function: deep plantarflexors and peroneals, superficial plantarflexors and dorsiflexors. Peak ankle contact force was predicted to occur before toe-off, with magnitude greater than five times bodyweight. Inter-specimen variability in contact force was smallest at peak force. These findings will help improve the development of experimental and computational musculoskeletal models by providing data to estimate force based on both surface and deep pennation angles. Inter-subject variability in muscle architecture affected ankle muscle and contact loads only slightly. The link between muscle architecture and function contributes to the understanding of the relationship between muscle structure and function.

The Development of using the digital projection method to measure the contact angle of ball screw

NASA Astrophysics Data System (ADS)

Chen, Chun-Jen; Jywe, Wenyuh; Liu, Yu-Chun; Jwo, Hsin-Hong

The ball screw frequently used to drive or translate the parts on the precision machine, such as machine tool and motorized stage. Therefore they were most frequently used on the precision machine, semiconductor equipment, medical instrument and aero industry. The main parts of ball screw are screw, ball and nut. The contact angle between the screw, ball and nut will affect the performance (include loading and noise) and lifecycle of a ball screw. If the actual contact angle and the designed contact angle are not the same, the friction between the ball, screw and nut will increase and it will result in the thermal increase and lifecycle decrease. This paper combines the traditional profile projector and commercial digital camera to build an imaging based and noncontact measurements system. It can implement the contact angle measurement quickly and accurately. Three different pitch angles of ball screws were completed tests in this paper. The angle resolution of this measurement system is about 0.001 degree and its accuracy is about 0.05 degree.

The comparison between two irrigation regimens on the dentine wettability for an epoxy resin based sealer by measuring its contact angle formed to the irrigated dentine.

PubMed

Mohan, Rayapudi Phani; Pai, Annappa Raghavendra Vivekananda

2015-01-01

The aim was to assess the influence of two irrigation regimens having ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetraacetic acid with cetrimide (EDTAC) as final irrigants, respectively, on the dentine wettability for AH Plus sealer by comparing its contact angle formed to the irrigated dentine. Study samples were divided into two groups (n = 10). The groups were irrigated with 3% sodium hypochlorite (NaOCl) solution followed by either 17% EDTA or 17% EDTAC solution. AH Plus was mixed, and controlled volume droplet (0.1 mL) of the sealer was placed on the dried samples. The contact angle was measured using a Dynamic Contact Angle Analyzer and results were analyzed using SPSS 21.0 and 2 sample t-test. There was a significant difference in the contact angle of AH Plus formed to the dentine irrigated with the above two regimens. AH Plus showed significantly lower contact angle with the regimen having EDTAC as a final irrigant than the one with EDTA (P < 0.05). An irrigation regimen consisting of NaOCl with either EDTA or EDTAC solution as a final irrigant influences the dentine wettability and contact angle of a sealer. EDTAC as a final irrigant facilitates better dentin wettability than EDTA for AH Plus to promote its better flow and adhesion.

Dynamic Contact Angle at the Nanoscale: A Unified View.

PubMed

Lukyanov, Alex V; Likhtman, Alexei E

2016-06-28

Generation of a dynamic contact angle in the course of wetting is a fundamental phenomenon of nature. Dynamic wetting processes have a direct impact on flows at the nanoscale, and therefore, understanding them is exceptionally important to emerging technologies. Here, we reveal the microscopic mechanism of dynamic contact angle generation. It has been demonstrated using large-scale molecular dynamics simulations of bead-spring model fluids that the main cause of local contact angle variations is the distribution of microscopic force acting at the contact line region. We were able to retrieve this elusive force with high accuracy. It has been directly established that the force distribution can be solely predicted on the basis of a general friction law for liquid flow at solid surfaces by Thompson and Troian. The relationship with the friction law provides both an explanation of the phenomenon of dynamic contact angle and a methodology for future predictions. The mechanism is intrinsically microscopic, universal, and irreducible and is applicable to a wide range of problems associated with wetting phenomena.

Ergonomic factors related to drop-off detection with the long cane: effects of cane tips and techniques.

PubMed

Kim, Dae Shik; Emerson, Robert S Wall; Curtis, Amy B

2010-06-01

This study examined the effect of cane tips and cane techniques on drop-off detection with the long cane. Blind pedestrians depend on a long cane to detect drop-offs. Missing a drop-off may result in falls or collision with moving vehicles in the street. Although cane tips appear to affect a cane user's ability to detect drop-offs, few experimental studies have examined such effect. A repeated-measures design with block randomization was used for the study. Participants were 17 adults who were legally blind and had no other disabilities. Participants attempted to detect the drop-offs of varied depths using different cane tips and cane techniques. Drop-off detection rates were similar between the marshmallow tip (77.0%) and the marshmallow roller tip (79.4%) when both tips were used with the constant contact technique, p = .294. However, participants detected drop-offs at a significantly higher percentage when they used the constant contact technique with the marshmallow roller tip (79.4%) than when they used the two-point touch technique with the marshmallow tip (63.2%), p < .001. The constant contact technique used with a marshmallow roller tip (perceived as a less advantageous tip) was more effective than the two-point touch technique used with a marshmallow tip (perceived as a more advantageous tip) in detecting drop-offs. The findings of the study may help cane users and orientation and mobility specialists select appropriate cane techniques and cane tips in accordance with the cane user's characteristics and the nature of the travel environment.

Gunshot residue patterns on skin in angled contact and near contact gunshot wounds.

PubMed

Plattner, T; Kneubuehl, B; Thali, M; Zollinger, U

2003-12-17

The goal of this study was the reproduction of shape and pattern of gunshot residues in near contact and contact gunshot wounds by a series of experimental gunshots on a skin and soft tissue model. The aim was to investigate the shape and direction of soot deposits with regard to the muzzle according to different muzzle-target angles, firing distances, type of ammunition and weapon and barrel length. Based on a review of the literature and on the results of the experiments the authors could make the following statements of gunshot residues in angled contact and close contact gunshot: (1) gunshot residues on the target surface can be differentiated in a "inner" and "outer powder soot zone"; (2) the outer powder soot zone is much less visible than the inner powder soot zone and may lack on human skin; (3) with increasing muzzle target distance both inner and outer powder soot halo increase in size and decrease in density; (4) in angled shots the inner powder soot halo shows an eccentric, elliptic shape which points towards the muzzle, regardless of ammunition, calibre and barrel length; (5) the outer powder soot points away from the muzzle in angled contact and close contact shots.

Instruction and jump-landing kinematics in college-aged female athletes over time.

PubMed

Etnoyer, Jena; Cortes, Nelson; Ringleb, Stacie I; Van Lunen, Bonnie L; Onate, James A

2013-01-01

Instruction can be used to alter the biomechanical movement patterns associated with anterior cruciate ligament (ACL) injuries. To determine the effects of instruction through combination (self and expert) feedback or self-feedback on lower extremity kinematics during the box-drop-jump task, running-stop-jump task, and sidestep-cutting maneuver over time in college-aged female athletes. Randomized controlled clinical trial. Laboratory. Forty-three physically active women (age = 21.47 ± 1.55 years, height = 1.65 ± 0.08 m, mass = 63.78 ± 12.00 kg) with no history of ACL or lower extremity injuries or surgery in the 2 months before the study were assigned randomly to 3 groups: self-feedback (SE), combination feedback (CB), or control (CT). Participants performed a box-drop-jump task for the pretest and then received feedback about their landing mechanics. After the intervention, they performed an immediate posttest of the box-drop-jump task and a running-stop-jump transfer test. Participants returned 1 month later for a retention test of each task and a sidestep-cutting maneuver. Kinematic data were collected with an 8-camera system sampled at 500 Hz. The independent variables were feedback group (3), test time (3), and task (3). The dependent variables were knee- and hip-flexion, knee-valgus, and hip- abduction kinematics at initial contact and at peak knee flexion. For the box-drop-jump task, knee- and hip-flexion angles at initial contact were greater at the posttest than at the retention test (P < .001). At peak knee flexion, hip flexion was greater at the posttest than at the pretest (P = .003) and was greater at the retention test than at the pretest (P = .04); knee valgus was greater at the retention test than at the pretest (P = .03) and posttest (P = .02). Peak knee flexion was greater for the CB than the SE group (P = .03) during the box-drop-jump task at posttest. For the running-stop-jump task at the posttest, the CB group had greater peak knee flexion than the SE and CT (P ≤ .05). Our results suggest that feedback involving a combination of self-feedback and expert video feedback with oral instruction effectively improved lower extremity kinematics during jump-landing tasks.

Instruction and Jump-Landing Kinematics in College-Aged Female Athletes Over Time

PubMed Central

Etnoyer, Jena; Cortes, Nelson; Ringleb, Stacie I.; Van Lunen, Bonnie L.; Onate, James A.

2013-01-01

Context: Instruction can be used to alter the biomechanical movement patterns associated with anterior cruciate ligament (ACL) injuries. Objective: To determine the effects of instruction through combination (self and expert) feedback or self-feedback on lower extremity kinematics during the box–drop-jump task, running–stop-jump task, and sidestep-cutting maneuver over time in college-aged female athletes. Design: Randomized controlled clinical trial. Setting: Laboratory. Patients or Other Participants: Forty-three physically active women (age = 21.47 ± 1.55 years, height = 1.65 ± 0.08 m, mass = 63.78 ± 12.00 kg) with no history of ACL or lower extremity injuries or surgery in the 2 months before the study were assigned randomly to 3 groups: self-feedback (SE), combination feedback (CB), or control (CT). Intervention(s): Participants performed a box–drop-jump task for the pretest and then received feedback about their landing mechanics. After the intervention, they performed an immediate posttest of the box–drop-jump task and a running–stop-jump transfer test. Participants returned 1 month later for a retention test of each task and a sidestep-cutting maneuver. Kinematic data were collected with an 8-camera system sampled at 500 Hz. Main Outcome Measure(s): The independent variables were feedback group (3), test time (3), and task (3). The dependent variables were knee- and hip-flexion, knee-valgus, and hip- abduction kinematics at initial contact and at peak knee flexion. Results: For the box–drop-jump task, knee- and hip-flexion angles at initial contact were greater at the posttest than at the retention test (P < .001). At peak knee flexion, hip flexion was greater at the posttest than at the pretest (P = .003) and was greater at the retention test than at the pretest (P = .04); knee valgus was greater at the retention test than at the pretest (P = .03) and posttest (P = .02). Peak knee flexion was greater for the CB than the SE group (P = .03) during the box–drop-jump task at posttest. For the running–stop-jump task at the posttest, the CB group had greater peak knee flexion than the SE and CT (P ≤ .05). Conclusions: Our results suggest that feedback involving a combination of self-feedback and expert video feedback with oral instruction effectively improved lower extremity kinematics during jump-landing tasks. PMID:23672380

A Langevin model for fluctuating contact angle behaviour parametrised using molecular dynamics.

PubMed

Smith, E R; Müller, E A; Craster, R V; Matar, O K

2016-12-06

Molecular dynamics simulations are employed to develop a theoretical model to predict the fluid-solid contact angle as a function of wall-sliding speed incorporating thermal fluctuations. A liquid bridge between counter-sliding walls is studied, with liquid-vapour interface-tracking, to explore the impact of wall-sliding speed on contact angle. The behaviour of the macroscopic contact angle varies linearly over a range of capillary numbers beyond which the liquid bridge pinches off, a behaviour supported by experimental results. Nonetheless, the liquid bridge provides an ideal test case to study molecular scale thermal fluctuations, which are shown to be well described by Gaussian distributions. A Langevin model for contact angle is parametrised to incorporate the mean, fluctuation and auto-correlations over a range of sliding speeds and temperatures. The resulting equations can be used as a proxy for the fully-detailed molecular dynamics simulation allowing them to be integrated within a continuum-scale solver.

Visualization of the equilibrium position of colloidal particles at fluid-water interfaces by deposition of nanoparticles

NASA Astrophysics Data System (ADS)

Sabapathy, Manigandan; Kollabattula, Viswas; Basavaraj, Madivala G.; Mani, Ethayaraja

2015-08-01

We present a general yet simple method to measure the contact angle of colloidal particles at fluid-water interfaces. In this method, the particles are spread at the required fluid-water interface as a monolayer. In the water phase a chemical reaction involving reduction of a metal salt such as aurochloric acid is initiated. The metal grows as a thin film or islands of nanoparticles on the particle surface exposed to the water side of the interface. Analyzing the images of particles by high resolution scanning microscopy (HRSEM), we trace the three phase contact line up to which deposition of the metal film occurs. From geometrical relations, the three phase contact angle is then calculated. We report the measurements of the contact angle of silica and polystyrene (PS) particles at different interfaces such as air-water, decane-water and octanol-water. We have also applied this method to measure the contact angle of surfactant treated polystyrene particles at the air-water interface, and we find a non-monotonic change of the contact angle with the concentration of the surfactant. Our results are compared with the well-known gel trapping technique and we find good comparison with previous measurements.We present a general yet simple method to measure the contact angle of colloidal particles at fluid-water interfaces. In this method, the particles are spread at the required fluid-water interface as a monolayer. In the water phase a chemical reaction involving reduction of a metal salt such as aurochloric acid is initiated. The metal grows as a thin film or islands of nanoparticles on the particle surface exposed to the water side of the interface. Analyzing the images of particles by high resolution scanning microscopy (HRSEM), we trace the three phase contact line up to which deposition of the metal film occurs. From geometrical relations, the three phase contact angle is then calculated. We report the measurements of the contact angle of silica and polystyrene (PS) particles at different interfaces such as air-water, decane-water and octanol-water. We have also applied this method to measure the contact angle of surfactant treated polystyrene particles at the air-water interface, and we find a non-monotonic change of the contact angle with the concentration of the surfactant. Our results are compared with the well-known gel trapping technique and we find good comparison with previous measurements. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03369a

Estimation of dynamic stability parameters from drop model flight tests

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Iliff, K. W.

1981-01-01

The overall remotely piloted drop model operation, descriptions, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods are discussed. Static and dynamic stability derivatives were obtained for an angle attack range from -20 deg to 53 deg. It is indicated that the variations of the estimates with angle of attack are consistent for most of the static derivatives, and the effects of configuration modifications to the model were apparent in the static derivative estimates.

Assessment of water droplet evaporation mechanisms on hydrophobic and superhydrophobic substrates.

PubMed

Pan, Zhenhai; Dash, Susmita; Weibel, Justin A; Garimella, Suresh V

2013-12-23

Evaporation rates are predicted and important transport mechanisms identified for evaporation of water droplets on hydrophobic (contact angle ~110°) and superhydrophobic (contact angle ~160°) substrates. Analytical models for droplet evaporation in the literature are usually simplified to include only vapor diffusion in the gas domain, and the system is assumed to be isothermal. In the comprehensive model developed in this study, evaporative cooling of the interface is accounted for, and vapor concentration is coupled to local temperature at the interface. Conjugate heat and mass transfer are solved in the solid substrate, liquid droplet, and surrounding gas. Buoyancy-driven convective flows in the droplet and vapor domains are also simulated. The influences of evaporative cooling and convection on the evaporation characteristics are determined quantitatively. The liquid-vapor interface temperature drop induced by evaporative cooling suppresses evaporation, while gas-phase natural convection acts to enhance evaporation. While the effects of these competing transport mechanisms are observed to counterbalance for evaporation on a hydrophobic surface, the stronger influence of evaporative cooling on a superhydrophobic surface accounts for an overprediction of experimental evaporation rates by ~20% with vapor diffusion-based models. The local evaporation fluxes along the liquid-vapor interface for both hydrophobic and superhydrophobic substrates are investigated. The highest local evaporation flux occurs at the three-phase contact line region due to proximity to the higher temperature substrate, rather than at the relatively colder droplet top; vapor diffusion-based models predict the opposite. The numerically calculated evaporation rates agree with experimental results to within 2% for superhydrophobic substrates and 3% for hydrophobic substrates. The large deviations between past analytical models and the experimental data are therefore reconciled with the comprehensive model developed here.

Tracking the Effect of Adatom Electronegativity on Systematically Modified AlGaN/GaN Schottky Interfaces.

PubMed

Reiner, Maria; Pietschnig, Rudolf; Ostermaier, Clemens

2015-10-21

The influence of surface modifications on the Schottky barrier height for gallium nitride semiconductor devices is frequently underestimated or neglected in investigations thereof. We show that a strong dependency of Schottky barrier heights for nickel/aluminum-gallium nitride (0001) contacts on the surface terminations exists: a linear correlation of increasing barrier height with increasing electronegativity of superficial adatoms is observed. The negatively charged adatoms compete with the present nitrogen over the available gallium (or aluminum) orbital to form an electrically improved surface termination. The resulting modification of the surface dipoles and hence polarization of the surface termination causes observed band bending. Our findings suggest that the greatest Schottky barrier heights are achieved by increasing the concentration of the most polarized fluorine-gallium (-aluminum) bonds at the surface. An increase in barrier height from 0.7 to 1.1 eV after a 15% fluorine termination is obtained with ideality factors of 1.10 ± 0.05. The presence of surface dipoles that are changing the surface energy is proven by the sessile drop method as the electronegativity difference and polarization influences the contact angle. The extracted decrease in the Lifshitz-van-der-Waals component from 48.8 to 40.4 mJ/m(2) with increasing electronegativity and concentration of surface adatoms confirms the presence of increasing surface dipoles: as the polarizability of equally charged anions decreases with increasing electronegativity, the diiodomethane contact angles increase significantly from 14° up to 39° after the 15% fluorine termination. Therefore, a linear correlation between increasing anion electronegativity of the (Al)GaN termination and total surface energy within a 95% confidence interval is obtained. Furthermore, our results reveal a generally strong Lewis basicity of (Al)GaN surfaces explaining the high chemical inertness of the surfaces.

Dynamic Response in Nanoelectrowetting on a Dielectric.

PubMed

Choudhuri, Jyoti Roy; Vanzo, Davide; Madden, Paul Anthony; Salanne, Mathieu; Bratko, Dusan; Luzar, Alenka

2016-09-27

Droplet spreading at an applied voltage underlies the function of tunable optical devices including adjustable lenses and matrix display elements. Faster response and the enhanced resolution motivate research toward miniaturization of these devices to nanoscale dimensions. The response of an aqueous nanodroplet to an applied field can differ significantly from macroscopic predictions. Understanding these differences requires characterization at the molecular level. We describe the equilibrium and nonequilibrium molecular dynamics simulations of nanosized aqueous droplets on a hydrophobic surface with the embedded concentric electrodes. Constant electrode potential is enforced by a rigorous account of the metal polarization. We demonstrate that the reduction of the equilibrium contact angle is commensurate to, and adjusts reversibly with, the voltage change. For a droplet with O(10) nm diameter, a typical response time to the imposition of the field is of O(10(2)) ps. Drop relaxation is about twice as fast when the field is switched off. The friction coefficient obtained from the rate of the drop relaxation on the nonuniform surface, decreases when the droplet approaches equilibrium from either direction, that is, by spreading or receding. The strong dependence of the friction on the surface hydrophilicity points to the dominance of the liquid-surface friction at the drop's perimeter as described in the molecular kinetic theory. This approach enables correct predictions of trends in dynamic responses associated with varied voltage or substrate material.

Wetting of soap bubbles on hydrophilic, hydrophobic, and superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Arscott, Steve

2013-06-01

Wetting of sessile bubbles on various wetting surfaces (solid and liquid) has been studied. A model is presented for the apparent contact angle of a sessile bubble based on a modified Young's equation--the experimental results agree with the model. Wetting a hydrophilic surface results in a bubble contact angle of 90° whereas using a superhydrophobic surface one observes 134°. For hydrophilic surfaces, the bubble angle diminishes with bubble radius whereas on a superhydrophobic surface, the bubble angle increases. The size of the plateau borders governs the bubble contact angle, depending on the wetting of the surface.

Estimation of bearing contact angle in-situ by X-ray kinematography

NASA Technical Reports Server (NTRS)

Fowler, P. H.; Manders, F.

1982-01-01

The mounted, preloaded contact angle of the structural bearings in the assembled design mechanical assembly was measured. A modification of the Turns method is presented, based upon the clarity and definition of moving parts achieved with X-ray technique and cinematic display. Contact angle is estimated by counting the number of bearings passing a given point as a function of number of turns of the shaft. Ball and pitch diameter variations are discussed. Ball train and shaft angle uncertainties are also discussed.

Failure of chemotherapy in the first reported cases of Acanthamoeba keratitis in Pakistan

PubMed Central

Siddiqui, Ruqaiyyah; Chaudhry, Tanveer; Lakhundi, Sahreena; Ahmad, Khabir; Khan, Naveed Ahmed

2014-01-01

Acanthamoeba keratitis is a painful and progressive infection of the cornea that can result in loss of vision. Here, for the first time in Pakistan, we report two cases of Acanthamoeba keratitis. The first patient was a 37-year-old female who presented with severe itching, redness, pain, along with loss of vision. The patient was a regular soft contact lens wearer. The second patient was a 25-year-old female who had been using soft contact lenses for the past two years. She presented with a burning sensation and extreme pain, along with loss of vision. Both patients were treated for a possible microbial keratitis with topical moxifloxacin hydrochloride drops, vancomycin drops, propamidine isethionate ointment, amphotericin B drops, and amikacin drops. However, the response was inadequate and both patients were referred for corneal transplant. Acanthamoeba castellanii was isolated by placing contact lenses and contact lens cases on non-nutrient agar plates containing a lawn of non-invasive Escherichia coli K-12 HB101 bacteria. The polymerase chain reaction (PCR) using genus-specific probes confirmed the identity of Acanthamoeba spp., whereas the morphological characteristics of trophozoites and cysts were suggestive of A. castellanii in both cases. With growing use of contact lenses for vision correction/cosmetic use coupled with sub-standard lens care in this region and the possibility of non-contact lens-associated Acanthamoeba keratitis, a need for increased awareness of this sight-threatening infection is discussed further. PMID:24548160

Superhydrophobic floatability of a hydrophilic object driven by edge effect

NASA Astrophysics Data System (ADS)

Chang, Feng-Ming; Sheng, Yu-Jane; Tsao, Heng-Kwong

2009-11-01

It is generally believed that a water-repellent surface is necessary for small insects to stand on water. Through a combined experimental and theoretical study, we demonstrate that an object with hydrophilic surface can float with apparent contact angle greater than 90° due to edge effect. The apparent contact angle rises with increasing loading even to a value typically displayed only by superhydrophobic surfaces. On the basis of free energy minimization, two regimes are identified. When buoyancy controls, the meniscus meets the object with the intrinsic contact angle. As surface tension dominates, however, contact angle is regulated by total force balance.

Resonances, radiation pressure and optical scattering phenomena of drops and bubbles

NASA Technical Reports Server (NTRS)

Marston, P. L.; Goosby, S. G.; Langley, D. S.; Loporto-Arione, S. E.

1982-01-01

Acoustic levitation and the response of fluid spheres to spherical harmonic projections of the radiation pressure are described. Simplified discussions of the projections are given. A relationship between the tangential radiation stress and the Konstantinov effect is introduced and fundamental streaming patterns for drops are predicted. Experiments on the forced shape oscillation of drops are described and photographs of drop fission are displayed. Photographs of critical angle and glory scattering by bubbles and rainbow scattering by drops are displayed.

Repulsion-based model for contact angle saturation in electrowetting

PubMed Central

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results. PMID:25759748

Fabrication of zero contact angle ultra-super hydrophilic surfaces.

PubMed

Jothi Prakash, C G; Clement Raj, C; Prasanth, R

2017-06-15

Zero contact angle surfaces have been created with the combined effect of nanostructure and UV illumination. The contact angle of titanium surface has been optimized to 3.25°±1°. with nanotubular structures through electrochemical surface modification. The porosity and surface energy of tubular TiO 2 layer play critical role over the surface wettability and the hydrophilicity of the surface. The surface free energy has been enhanced from 23.72mJ/m 2 (bare titanium surface) to 87.11mJ/m 2 (nanotubular surface). Similar surface with TiO 2 nanoparticles coating shows superhydrophilicity with contact angle up to 5.63°±0.95°. This implies liquid imbibition and surface curvature play a crucial role in surface hydrophilicity. The contact angle has been further reduced to 0°±0.86° by illuminating the surface with UV radiation. Results shows that by tuning the nanotube morphology, highly porous surfaces can be fabricated to reduce contact angle and enhance wettability. This study provides an insight into the inter-relationship between surface structural factors and ultra-superhydrophilic surfaces which can help to optimize thermal hydraulic and self cleaning surfaces. Copyright © 2017. Published by Elsevier Inc.

Water Contact Angle Dependence with Hydroxyl Functional Groups on Silica Surfaces under CO2 Sequestration Conditions.

PubMed

Chen, Cong; Zhang, Ning; Li, Weizhong; Song, Yongchen

2015-12-15

Functional groups on silica surfaces under CO2 sequestration conditions are complex due to reactions among supercritical CO2, brine and silica. Molecular dynamics simulations have been performed to investigate the effects of hydroxyl functional groups on wettability. It has been found that wettability shows a strong dependence on functional groups on silica surfaces: silanol number density, space distribution, and deprotonation/protonation degree. For neutral silica surfaces with crystalline structure (Q(3), Q(3)/Q(4), Q(4)), as silanol number density decreases, contact angle increases from 33.5° to 146.7° at 10.5 MPa and 318 K. When Q(3) surface changes to an amorphous structure, water contact angle increases 20°. Water contact angle decreases about 12° when 9% of silanol groups on Q(3) surface are deprotonated. When the deprotonation degree increases to 50%, water contact angle decreases to 0. The dependence of wettability on silica surface functional groups was used to analyze contact angle measurement ambiguity in literature. The composition of silica surfaces is complicated under CO2 sequestration conditions, the results found in this study may help to better understand wettability of CO2/brine/silica system.

Repulsion-based model for contact angle saturation in electrowetting.

PubMed

Ali, Hassan Abdelmoumen Abdellah; Mohamed, Hany Ahmed; Abdelgawad, Mohamed

2015-01-01

We introduce a new model for contact angle saturation phenomenon in electrowetting on dielectric systems. This new model attributes contact angle saturation to repulsion between trapped charges on the cap and base surfaces of the droplet in the vicinity of the three-phase contact line, which prevents these surfaces from converging during contact angle reduction. This repulsion-based saturation is similar to repulsion between charges accumulated on the surfaces of conducting droplets which causes the well known Coulombic fission and Taylor cone formation phenomena. In our model, both the droplet and dielectric coating were treated as lossy dielectric media (i.e., having finite electrical conductivities and permittivities) contrary to the more common assumption of a perfectly conducting droplet and perfectly insulating dielectric. We used theoretical analysis and numerical simulations to find actual charge distribution on droplet surface, calculate repulsion energy, and minimize energy of the total system as a function of droplet contact angle. Resulting saturation curves were in good agreement with previously reported experimental results. We used this proposed model to predict effect of changing liquid properties, such as electrical conductivity, and system parameters, such as thickness of the dielectric layer, on the saturation angle, which also matched experimental results.

Designing Energy-Efficient Heat Exchangers--- Creating Micro-Channels on the Aluminum Fin Surface

NASA Astrophysics Data System (ADS)

Ying, Jia; Sommers, Andrew; Eid, Khalid

2010-03-01

In this research, a method for patterning micro-channels on aluminum surfaces is described for the purpose of exploiting those features to affect the surface wettability. Minimizing water retention on aluminum is important in the design of energy-efficient heat exchangers because water retention can deteriorate the performance of such devices. It increases the air-side pressure drop and can decrease the sensible heat transfer coefficient thereby increasing energy consumption and contributing to higher pollution levels in the environment. Photolithography is used to create the micro-scale channels and a hydrophobic polymer is used to reduce the surface energy of the aluminum plates. Droplets are both injected on the surface using a micro-syringe and condensed on the surface using an environmentally-controlled chamber. A ram'e-hart goniometer is used to determine the advancing and receding contact angles of water droplets on these modified surfaces, and a tilt-table assembly is used to measure the critical inclination angle for sliding. Our results show that droplets placed on these patterned surfaces not only have significantly lower critical inclination angles for sliding but are easier to remove from the surface at low air flow rates. Efforts to model the onset of droplet movement on these surfaces using a simple force balance relationship are currently underway.

Deposition of bi-dispersed particles in inkjet-printed evaporating colloidal drops

NASA Astrophysics Data System (ADS)

Sun, Ying; Joshi, Abhijit; Chhasatia, Viral

2010-11-01

In this study, the deposition behaviors of inkjet-printed evaporating colloidal drops consisting of bi-dispersed micro and nano-sized particles are investigated by fluorescence microscopy and SEM. The results on hydrophilic glass substrates show that, evaporatively-driven outward flow drives the nanoparticles to deposit close to the pinned contact line while an inner ring deposition is formed by microparticles. This size-induced particle separation is consistent with the existence of a wedge-shaped drop edge near the contact line region of an evaporating drop on a hydrophilic substrate. The replenishing evaporatively-driven flow assembles nanoparticles closer to the pinned contact line forming an outer ring of nanoparticles and this particle jamming further enhances the contact line pinning. Microparticles are observed to form an inner ring inside the nano-sized deposits. This size-induced particle separation presents a new challenge to the uniformity of functional materials in bioprinting applications where nanoparticles and micro-sized cells are mixed together. On the other hand, particle self-assembly based on their sizes provides enables easy and well-controlled pattern formation. The effects of particle size contrast, particle volume fraction, substrate surface energy, and relative humidity of the printing environment on particle separation are examined in detail.

Aluminum alloy/alumina-based ceramic interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lebeau, T.; Strom-Olsen, J.O.; Gruzleski, J.E.

1995-07-01

Wetting experiments were performed on eutectic ZrO{sub 2}/Al{sub 2}O{sub 3} (ZA), ZrO{sub 2}/Al{sub 2}O{sub 3}/TiO{sub 2} (ZAT), and ZrO{sub 2}/Al{sub 2}O{sub 3}/SiO{sub 2} (ZAS) ceramic substrates with different Al alloys. Four major variables were tested to study the wetting behavior of the different ceramic-metal systems. Variable include holding time, melt temperature, ally, and ceramic compositions. An experimental setup was designed to measure in situ contact angles using the sessile drop method. For any ceramic substrate, a temperature over 950 C was necessary to observe an equilibrium wetting angle of less than 90{degree} with pure Al; by alloying the aluminum, wettingmore » could be observed at lower temperatures ({theta} = 76--86{degree} at 900 C for Al-10 wt. % Si, {theta} {approximately}72{degree} at 850 C for Al-2.4 wt. % Mg) forming clean interfaces. Finally, ZAS specimens reacted with molten Al alloys over 900 C to produce Zr-Al based intermetallics at the metal-ceramic interface.« less

Heat transfer and pressure drop characteristics of a plate heat exchanger using water based Al2O3 nanofluid for 30° and 60° chevron angles

NASA Astrophysics Data System (ADS)

Elias, M. M.; Saidur, R.; Ben-Mansour, R.; Hepbasli, A.; Rahim, N. A.; Jesbains, K.

2018-04-01

Nanofluid is a new class of engineering fluid that has good heat transfer characteristics which is essential to increase the heat transfer performance in various engineering applications such as heat exchangers and cooling of electronics. In this study, experiments were conducted to compare the heat transfer performance and pressure drop characteristics in a plate heat exchanger (PHE) for 30° and 60° chevron angles using water based Al2O3 nanofluid at the concentrations from 0 to 0.5 vol.% for different Reynolds numbers. The thermo-physical properties has been determined and presented in this paper. At 0.5 vol% concentration, the maximum heat transfer coefficient, the overall heat transfer coefficient and the heat transfer rate for 60° chevron angle have attained a higher percentage of 15.14%, 7.8% and 15.4%, respectively in comparison with the base fluid. Consequently, when the volume concentration or Reynolds number increases, the heat transfer coefficient and the overall heat transfer coefficient as well as the heat transfer rate of the PHE (Plate Heat Exchangers) increases respectively. Similarly, the pressure drop increases with the volume concentration. 60° chevron angle showed better performance in comparison with 30° chevron angle.

"Insensitive" to touch: fabric-supported lubricant-swollen polymeric films for omniphobic personal protective gear.

PubMed

Damle, Viraj G; Tummala, Abhishiktha; Chandrashekar, Sriram; Kido, Cassidee; Roopesh, Ajay; Sun, Xiaoda; Doudrick, Kyle; Chinn, Jeff; Lee, James R; Burgin, Timothy P; Rykaczewski, Konrad

2015-02-25

The use of personal protective gear made from omniphobic materials that easily shed drops of all sizes could provide enhanced protection from direct exposure to most liquid-phase biological and chemical hazards and facilitate the postexposure decontamination of the gear. In recent literature, lubricated nanostructured fabrics are seen as attractive candidates for personal protective gear due to their omniphobic and self-healing characteristics. However, the ability of these lubricated fabrics to shed low surface tension liquids after physical contact with other objects in the surrounding, which is critical in demanding healthcare and military field operations, has not been investigated. In this work, we investigate the depletion of oil from lubricated fabrics in contact with highly absorbing porous media and the resulting changes in the wetting characteristics of the fabrics by representative low and high surface tension liquids. In particular, we quantify the loss of the lubricant and the dynamic contact angles of water and ethanol on lubricated fabrics upon repeated pressurized contact with highly absorbent cellulose-fiber wipes at different time intervals. We demonstrate that, in contrast to hydrophobic nanoparticle coated microfibers, fabrics encapsulated within a polymer that swells with the lubricant retain the majority of the oil and are capable of repelling high as well as low surface tension liquids even upon multiple contacts with the highly absorbing wipes. The fabric supported lubricant-swollen polymeric films introduced here, therefore, could provide durable and easy to decontaminate protection against hazardous biological and chemical liquids.

Reduction of Defects in Germanium-Silicon

NASA Technical Reports Server (NTRS)

2003-01-01

Crystals grown without contact with a container have far superior quality to otherwise similar crystals grown in direct contact with a container. In addition to float-zone processing, detached- Bridgman growth is a promising tool to improve crystal quality, without the limitations of float zoning or the defects introduced by normal Bridgman growth. Goals of this project include the development of the detached Bridgman process to be reproducible and well understood and to quantitatively compare the defect and impurity levels in crystals grown by these three methods. Germanium (Ge) and germanium-silicon (Ge-Si) alloys are being used. At MSFC, we are responsible for the detached Bridgman experiments intended to differentiate among proposed mechanisms of detachment, and to confirm or refine our understanding of detachment. Because the contact angle is critical to determining the conditions for detachment, the sessile drop method was used to measure the contact angles as a function of temperature and composition for a large number of substrates made of potential ampoule materials. Growth experiments have used pyrolytic boron nitride (pBN) and fused silica ampoules with the majority of the detached results occurring predictably in the pBN. Etch pit density (EPD) measurements of normal and detached Bridgman-grown Ge samples show a two order of magnitude improvement in the detached-grown samples. The nature and extent of detachment is determined by using profilometry in conjunction with optical and electron microscopy. The stability of detachment has been analyzed, and an empirical model for the conditions necessary to achieve sufficient stability to maintain detached growth for extended periods has been developed. We have investigated the effects on detachment of ampoule material, pressure difference above and below the melt, and Si concentration; samples that are nearly completely detached can be grown repeatedly in pBN. Current work is concentrated on developing a method to make in situ pressure measurements in the growth ampoules.

SU-E-T-44: Angular Dependence of Surface Dose Enhancement Measured On Several Inhomogeneities Using Radiochromic EBT3 Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jansen, A; Schoenfeld, A; Poppinga, D

Purpose: The quantification of the relative surface dose enhancement in dependence on the angle of incidence and the atomic number Z of the surface material. Methods: Experiments were performed with slabs made of aluminum, titanium, copper, silver, dental gold and lead. The metal slabs with equal sizes of 1.0×8.0×8.8mm{sup 3} were embedded in an Octavius 4D phantom (PTW Freiburg, Germany). Radiochromic EBT3 films were used to measure the surface dose for angles of incidence ranging from 0° to 90°. The setup with the metals slabs at the isocenter was irradiated with acceleration voltages of 6MV and 10MV. Water reference measurementsmore » were taken under equal conditions. Results: The surface dose enhancement is highest for angles of incidence below 30° and drops significantly for higher. The surface dose enhancement produced by lead and dental gold at 6MV showed a peak of 65%. At 90°, the surface dose enhancement dropped to 15% for both materials. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 32%, 22% and 12% at 0°, respectively. At an angle of incidence of 80°, the values dropped to 22%, 18%, 12% und 6%. The values for 10MV were very similar. Lead and dental gold showed peaks of 65% und 60%. Their values dropped to 18% at an angle of 90°. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 30%, 20% and 8% at 0°. At 80° the values dropped to 30%, 20%, 12% and 5%. A dependence of the magnitude of the surface dose enhancement on the atomic number of the surface material can be seen, which is in consistence with literature. Conclusion: The results show that the surface dose enhancements near implant materials with high Z-values should be taken into consideration in radio therapy, even when the angle of incidence is flat.« less

The behavior of surface tension on steady-state rotating fluids in the low gravity environments

NASA Technical Reports Server (NTRS)

Hung, R. J.; Leslie, Fred W.

1987-01-01

The effect of surface tension on steady-state rotating fluids in a low gravity environment is studied. All the values of the physical parameters used in these calculations, except in the low gravity environments, are based on the measurements carried out by Leslie (1985) in the low gravity environment of a free-falling aircraft. The profile of the interface of two fluids is derived from Laplace's equation relating the pressure drop across an interface to the radii of curvature which has been applied to a low gravity rotating bubble that contacts the container boundary. The interface shape depends on the ratio of gravity to surface tension forces, the ratio of centrifugal to surface tension forces, the contact radius of the interface to the boundary, and the contact angle. The shape of the bubble is symmetric about its equator in a zero-gravity environment. This symmetry disappears and gradually shifts to parabolic profiles as the gravity environment becomes non-zero. The location of the maximum radius of the bubble moves upward from the center of the depth toward the top boundary of the cylinder as gravity increases. The contact radius of interface to the boundary r0 at the top side of cylinder increases and r0 at the bottom side of the cylinder decreases as the gravity environment increases from zero to 1 g.

Wetting Behavior and Reactivity of Molten Silicon with h-BN Substrate at Ultrahigh Temperatures up to 1750 °C

NASA Astrophysics Data System (ADS)

Polkowski, Wojciech; Sobczak, Natalia; Nowak, Rafał; Kudyba, Artur; Bruzda, Grzegorz; Polkowska, Adelajda; Homa, Marta; Turalska, Patrycja; Tangstad, Merete; Safarian, Jafar; Moosavi-Khoonsari, Elmira; Datas, Alejandro

2017-12-01

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.

New GaN Schottky barrier diode employing a trench on AlGaN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Ha, Min-Woo; Lee, Seung-Chul; Choi, Young-Hwan; Kim, Soo-Seong; Yun, Chong-Man; Han, Min-Koo

2006-10-01

A new GaN Schottky barrier diode employing a trench structure, which is proposed and fabricated, successfully decreases a forward voltage drop without sacrificing any other electric characteristics. The trench is located in the middle of Schottky contact during a mesa etch. The Schottky metal of Pt/Mo/Ti/Au is e-gun evaporated on the 300 nm-deep trench as well as the surface of the proposed GaN Schottky barrier diode. The trench forms the vertical Au Schottky contact and lateral Pt Schottky contact due to the evaporation sequence of Schottky metal. The forward voltage drops of the proposed diode and conventional one are 0.73 V and 1.25 V respectively because the metal work function (5.15 eV) of the vertical Au Schottky contact is considerably less than that of the lateral Pt Schottky contact (5.65 eV). The proposed diode exhibits the low on-resistance of 1.58 mΩ cm 2 while the conventional one exhibits 8.20 mΩ cm 2 due to the decrease of a forward voltage drop.

Transmittance of transparent windows with non-absorbing cap-shaped droplets condensed on their backside

NASA Astrophysics Data System (ADS)

Zhu, Keyong; Huang, Yong; Pruvost, Jeremy; Legrand, Jack; Pilon, Laurent

2017-06-01

This study aims to quantify systematically the effect of non-absorbing cap-shaped droplets condensed on the backside of transparent windows on their directional-hemispherical transmittance and reflectance. Condensed water droplets have been blamed to reduce light transfer through windows in greenhouses, solar desalination plants, and photobioreactors. Here, the directional-hemispherical transmittance was predicted by Monte Carlo ray-tracing method. For the first time, both monodisperse and polydisperse droplets were considered, with contact angle between 0 and 180°, arranged either in an ordered hexagonal pattern or randomly distributed on the window backside with projected surface area coverage between 0 and 90%. The directional-hemispherical transmittance was found to be independent of the size and spatial distributions of the droplets. Instead, it depended on (i) the incident angle, (ii) the optical properties of the window and droplets, and on (iii) the droplet contact angle and (iv) projected surface area coverage. In fact, the directional-hemispherical transmittance decreased with increasing incident angle. Four optical regimes were identified in the normal-hemispherical transmittance. It was nearly constant for droplet contact angles either smaller than the critical angle θcr (predicted by Snell's law) for total internal reflection at the droplet/air interface or larger than 180°-θcr. However, between these critical contact angles, the normal-hemispherical transmittance decreased rapidly to reach a minimum at 90° and increased rapidly with increasing contact angles up to 180°-θcr. This was attributed to total internal reflection at the droplet/air interface which led to increasing reflectance. In addition, the normal-hemispherical transmittance increased slightly with increasing projected surface area coverage for contact angle was smaller than θcr. However, it decreased monotonously with increasing droplet projected surface area coverage for contact angle larger than θcr. These results can be used to select the material or surface coating with advantageous surface properties for applications when dropwise condensation may otherwise have a negative effect on light transmittance.

Effects of menarcheal age on the anterior cruciate ligament injury risk factors during single-legged drop landing in female artistic elite gymnasts.

PubMed

Kim, Kew-Wan; Lim, Bee-Oh

2014-11-01

Although numerous studies have demonstrated the relationship between maturation and lower extremity biomechanics during landing in team sport athletes, we are presently uninformed of any research that examined the single-legged drop landing biomechanics of gymnasts. The purpose of this study is to investigate the effects of the menarcheal age on the lower extremity biomechanics during a single-legged drop landing in female artistic elite gymnasts. Twenty-two female artistic elite gymnasts, between 9 and 36 years of age, participated in this study. The participants were divided into two groups pre- (n = 11) and post- (n = 11) menarche and asked to perform a single-legged drop landing on top of a 30 cm platform and land on a force plate. The statistical analysis consisted of the multivariate analysis with the level of significance set at p < 0.05. The post-menarche group showed a decrease in their maximum knee flexion angle and increase in their maximum knee abduction angle, maximum internal tibial rotation angle, maximum knee abduction moment, and hamstring-quadriceps muscle activity ratio compared with the pre-menarche group during the single-legged drop landing. The post-menarche group showed an increased noncontact anterior cruciate ligament injury risk, due to their greater knee loads, compared with the pre-menarche group.

Characterization of Tape Adhesion to Chemical Agent Resistant Coatings

DTIC Science & Technology

2015-01-01

use by OEM’s and depots. More specifically, each tape was tested on water dispersible and solvent borne polyurethane topcoats in the two most common...andGenerally, systems formulated to be water dispersible produced films that were slightly hydrophilic (water contact angle < 90°) whereas systems...8). Table 8: Average water contact angle of various CARC systems. advancing contact angle of water (degrees) waterborne polyurethane

Ergonomic Factors Related to Drop-Off Detection With the Long Cane: Effects of Cane Tips and Techniques

PubMed Central

Kim, Dae Shik; Wall Emerson, Robert S.; Curtis, Amy B.

2010-01-01

Objective This study examined the effect of cane tips and cane techniques on drop-off detection with the long cane. Background Blind pedestrians depend on a long cane to detect drop-offs. Missing a drop-off may result in falls or collision with moving vehicles in the street. Although cane tips appear to affect a cane user’s ability to detect drop-offs, few experimental studies have examined such effect. Method A repeated-measures design with block randomization was used for the study. Participants were 17 adults who were legally blind and had no other disabilities. Participants attempted to detect the drop-offs of varied depths using different cane tips and cane techniques. Results Drop-off detection rates were similar between the marshmallow tip (77.0%) and the marshmallow roller tip (79.4%) when both tips were used with the constant contact technique, p = .294. However, participants detected drop-offs at a significantly higher percentage when they used the constant contact technique with the marshmallow roller tip (79.4%) than when they used the two-point touch technique with the marshmallow tip (63.2%), p < .001. Conclusion The constant contact technique used with a marshmallow roller tip (perceived as a less advantageous tip) was more effective than the two-point touch technique used with a marshmallow tip (perceived as a more advantageous tip) in detecting drop-offs. Application The findings of the study may help cane users and orientation and mobility specialists select appropriate cane techniques and cane tips in accordance with the cane user’s characteristics and the nature of the travel environment. PMID:21077566

The influence of muscle pennation angle and cross-sectional area on contact forces in the ankle joint

PubMed Central

Sopher, Ran S; Amis, Andrew A; Davies, D Ceri; Jeffers, Jonathan RT

2016-01-01

Data about a muscle’s fibre pennation angle and physiological cross-sectional area are used in musculoskeletal modelling to estimate muscle forces, which are used to calculate joint contact forces. For the leg, muscle architecture data are derived from studies that measured pennation angle at the muscle surface, but not deep within it. Musculoskeletal models developed to estimate joint contact loads have usually been based on the mean values of pennation angle and physiological cross-sectional area. Therefore, the first aim of this study was to investigate differences between superficial and deep pennation angles within each muscle acting over the ankle and predict how differences may influence muscle forces calculated in musculoskeletal modelling. The second aim was to investigate how inter-subject variability in physiological cross-sectional area and pennation angle affects calculated ankle contact forces. Eight cadaveric legs were dissected to excise the muscles acting over the ankle. The mean surface and deep pennation angles, fibre length and physiological cross-sectional area were measured. Cluster analysis was applied to group the muscles according to their architectural characteristics. A previously validated OpenSim model was used to estimate ankle muscle forces and contact loads using architecture data from all eight limbs. The mean surface pennation angle for soleus was significantly greater (54%) than the mean deep pennation angle. Cluster analysis revealed three groups of muscles with similar architecture and function: deep plantarflexors and peroneals, superficial plantarflexors and dorsiflexors. Peak ankle contact force was predicted to occur before toe-off, with magnitude greater than five times bodyweight. Inter-specimen variability in contact force was smallest at peak force. These findings will help improve the development of experimental and computational musculoskeletal models by providing data to estimate force based on both surface and deep pennation angles. Inter-subject variability in muscle architecture affected ankle muscle and contact loads only slightly. The link between muscle architecture and function contributes to the understanding of the relationship between muscle structure and function. PMID:29805194

Determination of the Contact Angle Based on the Casimir Effect

NASA Technical Reports Server (NTRS)

Mazuruk, K.; Volz, M. P.

2015-01-01

In several crystal growth processed based on capillarity, a melt comes into contact with a crucible wall at an angle defined as the contact angle. For molten metals and semiconductors, this contact angle is dependent upon both the crucible and melt material and typical values fall in the range 80-170deg. However, on a microscopic scale, there does not exist a precise and sharp contact angle but rather the melt and solid surfaces merge smoothly and continuously over a distance of up to several micrometers. Accurate modeling requires a more advanced treatment of this interaction. The interaction between the melt and solid surfaces can be calculated by considering two forces: a short-range repulsive force and a longer range (up to a few micrometers) Casimir force. The Casimir force between the two bodies of complex geometry is calculated using a retarded temperature Green's function (Matsubara type) for the photon in the medium. The governing equations are cast in the form of a set of boundary integral equations which are then solved numerically for the case of molten Ge on SiO2. The shape of the molten surface approaching the flat solid body is determined, and the contact angle is defined as the angle between the two surfaces at the microscopically asymptotic distance of 1-2 micrometers. The formulation of this model and the results of the numerical calculations will be presented and discussed.

Contact Hamiltonian systems and complete integrability

NASA Astrophysics Data System (ADS)

Visinescu, Mihai

2017-12-01

We summarize recent results on the integrability of Hamiltonian systems on contact manifolds. We explain how to extend the classical formulation of action-angle variables to contact integrable systems. Using the Jacobi brackets defined on contact manifolds, we discuss the commutativity of first integrals for contact Hamiltonian systems and present the construction of generalized contact action-angle variables. We illustrate the integrability in the contact geometry on the five-dimensional Sasaki-Einstein spaces T1,1 and Yp,q.

Proper Brushing

MedlinePlus

... bristles along the gumline at a 45-degree angle. Bristles should contact both the tooth surface and the gumline. Gently ... A rolling motion is when the brush makes contact with the gumline and ... a 45-degree angle with bristles contacting the tooth surface and gumline. ...

Contact-angle hysteresis on periodic microtextured surfaces: Strongly corrugated liquid interfaces.

PubMed

Iliev, Stanimir; Pesheva, Nina

2016-06-01

We study numerically the shapes of a liquid meniscus in contact with ultrahydrophobic pillar surfaces in Cassie's wetting regime, when the surface is covered with identical and periodically distributed micropillars. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes when the cross-sections of the pillars are both of square and circular shapes, for a broad interval of pillar concentrations. The bending of the liquid interface in the area between the pillars is studied in the framework of the full capillary model and compared to the results of the heterogeneous approximation model. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of pillars. It is found that the contact angle hysteresis is proportional to the line fraction of the contact line on pillars tops in the block case and to the surface fraction for pillar concentrations 0.1-0.5 in the kink case. The contact angle hysteresis does not depend on the shape (circular or square) of the pillars cross-section. The expression for the proportionality of the receding contact angle to the line fraction [Raj et al., Langmuir 28, 15777 (2012)LANGD50743-746310.1021/la303070s] in the case of block depinning is theoretically substantiated through the capillary force, acting on the solid plate at the meniscus contact line.

Three-dimensional lattice Boltzmann simulations of microdroplets including contact angle hysteresis on topologically structured surfaces

DOE PAGES

Ba, Yan; Kang, Qinjun; Liu, Haihu; ...

2016-04-14

In this study, the dynamical behavior of a droplet on topologically structured surface is investigated by using a three-dimensional color-gradient lattice Boltzmann model. A wetting boundary condition is proposed to model fluid-surface interactions, which is advantageous to improve the accuracy of the simulation and suppress spurious velocities at the contact line. The model is validated by the droplet partial wetting test and reproduction of the Cassie and Wenzel states. A series of simulations are conducted to investigate the behavior of a droplet when subjected to a shear flow. It is found that in Cassie state, the droplet undergoes a transitionmore » from stationary, to slipping and finally to detachment states as the capillary number increases, while in Wenzel state, the last state changes to the breakup state. The critical capillary number, above which the droplet slipping occurs, is small for the Cassie droplet, but is significantly enhanced for the Wenzel droplet due to the increased contact angle hysteresis. In Cassie state, the receding contact angle nearly equals the prediction by the Cassie relation, and the advancing contact angle is close to 180°, leading to a small contact angle hysteresis. In Wenzel state, however, the contact angle hysteresis is extremely large (around 100°). Finally, high droplet mobility can be easily achieved for Cassie droplets, whereas in Wenzel state, extremely low droplet mobility is identified.« less

Creation of hydrophobic surfaces using a paint containing functionalized oxide particles

NASA Astrophysics Data System (ADS)

Sino, Paul Albert L.; Herrera, Marvin U.; Balela, Mary Donnabelle L.

2017-05-01

Hydrophobic surfaces were created by coating various substrates (aluminum sheet, soda-lime glass, silicon carbide polishing paper, glass with double-sided adhesive) with paint containing functionalized oxide particles. The paint was created by functionalizing oxide particles (ground ZnO, TiO2 nanoparticles, or TiO2 microparticles) with fluorosilane molecules in absolute ethanol. Water contact angle of samples shows that the coated substrate becomes hydrophobic (water contact angle ≥ 90°). Among the oxides that were used, ground ZnO yielded contact angle exemplifying superhydrophobicity (water contact angle ≥ 150°). Scanning electron micrograph of paint-containing TiO2 nanoparticles shows rough functionalized oxides structures which probably increase the hydrophobicity of the surface.

Smoothed particle hydrodynamics study of the roughness effect on contact angle and droplet flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shigorina, Elena; Kordilla, Jannes; Tartakovsky, Alexandre M.

We employ a pairwise force Smoothed Particle Hydrodynamics (PF-SPH) model to simulate sessile and transient droplets on rough hydrophobic and hydrophilic surfaces. PF-SPH allows for modeling of free surface flow without discretizing the air phase, which is achieved by imposing the surface tension and dynamic contact angles with pairwise interaction forces. We use the PF-SPH model to study the effect of surface roughness and microscopic contact angle on the effective contact angle and droplet dynamics. In the first part of this work, we investigate static contact angles of sessile droplets on rough surfaces in a shape of a sinusoidal functionmore » and made of rectangular bars placed on top of a flat surface. We find that the effective static contact angles of Cassie and Wenzel droplets on a rough surface are greater than the corresponding microscale static contact angles. As a result, microscale hydrophobic rough surfaces also show effective hydrophobic behavior. On the other hand, microscale hydrophilic surfaces may be macroscopically hydrophilic or hydrophobic, depending on the type of roughness. Next, we study the impact of the roughness orientation (i.e., an anisotropic roughness) and surface inclination on droplet flow velocities. Simulations show that droplet flow velocities are lower if the surface roughness is oriented perpendicular to the flow direction. If the predominant elements of surface roughness are in alignment with the flow direction, the flow velocities increase compared to smooth surfaces, which can be attributed to the decrease in fluid-solid contact area similar to the classical lotus effect. We demonstrate that linear scaling relationships between Bond and capillary number for droplet flow on flat surfaces also hold for flow on rough surfaces.« less

Calculation of gas turbine characteristic

NASA Astrophysics Data System (ADS)

Mamaev, B. I.; Murashko, V. L.

2016-04-01

The reasons and regularities of vapor flow and turbine parameter variation depending on the total pressure drop rate π* and rotor rotation frequency n are studied, as exemplified by a two-stage compressor turbine of a power-generating gas turbine installation. The turbine characteristic is calculated in a wide range of mode parameters using the method in which analytical dependences provide high accuracy for the calculated flow output angle and different types of gas dynamic losses are determined with account of the influence of blade row geometry, blade surface roughness, angles, compressibility, Reynolds number, and flow turbulence. The method provides satisfactory agreement of results of calculation and turbine testing. In the design mode, the operation conditions for the blade rows are favorable, the flow output velocities are close to the optimal ones, the angles of incidence are small, and the flow "choking" modes (with respect to consumption) in the rows are absent. High performance and a nearly axial flow behind the turbine are obtained. Reduction of the rotor rotation frequency and variation of the pressure drop change the flow parameters, the parameters of the stages and the turbine, as well as the form of the characteristic. In particular, for decreased n, nonmonotonic variation of the second stage reactivity with increasing π* is observed. It is demonstrated that the turbine characteristic is mainly determined by the influence of the angles of incidence and the velocity at the output of the rows on the losses and the flow output angle. The account of the growing flow output angle due to the positive angle of incidence for decreased rotation frequencies results in a considerable change of the characteristic: poorer performance, redistribution of the pressure drop at the stages, and change of reactivities, growth of the turbine capacity, and change of the angle and flow velocity behind the turbine.

Contact angle determination procedure and detection of an invisible surface film

NASA Technical Reports Server (NTRS)

Meyer, G.; Grat, R.

1990-01-01

The contact angle value, i.e., the tangent angle of liquid resting on a planar solid surface, is a basic parameter which can be applied to a wide range of applications. The goal is to provide a basic understanding of the contact angle measurement technique and to present a simple illustration that can be applied as a quality control method; namely, detection of a surface contaminant which exists on a surface that appears clean to the unaided eye. The equipment and experimental procedures are detailed.

Experimental study on pool boiling of distilled water and HFE7500 fluid under microgravity

NASA Astrophysics Data System (ADS)

Yang, Yan-jie; Chen, Xiao-qian; Huang, Yi-yong; Li, Guang-yu

2018-02-01

The experimental study on bubble behavior and heat transfer of pool boiling for distilled water and HFE7500 fluid under microgravity has been conducted by using drop tower in the National Microgravity Laboratory of China (NMLC). Two MCH ceramic plates of 20 mm(L) × 10 mm(W) × 1.2 mm(H) were used as the heaters. The nucleate boiling evolution under microgravity was observed during the experiment. It has been found that at the same heat flux, the bubbles of HFE7500 (which has smaller contact angle) grew faster and bigger, moved quickly on the heater surface, and were easier to merge into a central big bubble with other bubbles than that of distilled water. The whole process of bubbles coalescence from seven to one was recorded by using video camera. For distilled water (with bigger contact angle), the bubbles tended to keep at the nucleate location on heater surface, and the central big bubble evolved at its nucleate cite by absorbing smaller bubbles nearby. Compared with the bubbles under normal gravity, bubble radius of distilled water under microgravity was about 1.4 times bigger and of HFE7500 was about more than 6 times bigger till the end of experiment. At the beginning, pool boiling heat transfer of distilled water was advanced and then impeded under microgravity. As to HFE7500, the pool boiling impedes the heat transfer from heater to liquid under microgravity throughout the experiment.

Anisotropic wetting of microstructured surfaces as a function of surface chemistry.

PubMed

Neuhaus, Sonja; Spencer, Nicholas D; Padeste, Celestino

2012-01-01

In order to study the influence of surface chemistry on the wetting of structured surfaces, microstructures consisting of grooves or squares were produced via hot embossing of poly(ethylene-alt-tetrafluoroethylene) ETFE substrates. The structured substrates were modified with polymer brushes, thereby changing their surface functionality and wettability. Water droplets were most strongly pinned to the structure when the surface was moderately hydrophilic, as in the case of poly(4-vinylpyridine) (P4VP) or poly(vinyl(N-methyl-2-pyridone) (PVMP) brush-modified substrates. As a result, the droplet shape was determined by the features of the microstructure. The water contact angles (CA) were considerably higher than on flat surfaces and differed, in the most extreme case, by 37° when measured on grooved substrates, parallel and perpendicular to the grooves. On hydrophobic substrates (pristine ETFE), the same effects were observed but were much less pronounced. On very hydrophilic sampes (those modified with poly(N-methyl-vinylpyridinium) (QP4VP)), the microstructure had no influence on the drop shape. These findings are explained by significant differences in apparent and real contact angles at the relatively smooth edges of the embossed structures. Finally, the highly anisotropic grooved microstructure was combined with a gradient in polymer brush composition and wettability. In the case of a parallel alignment of the gradient direction to the grooves, the directed spreading of water droplets could be observed. © 2011 American Chemical Society

Molecular dynamics simulations study of nano bubble attachment at hydrophobic surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Jiaqi; Dang, Liem X.; Miller, Jan D.

Bubble attachment phenomena are examined using Molecular Dynamics Simulations (MDS) for the first time. The simulation involves a nitrogen nano bubble containing 906 nitrogen molecules in a water phase with 74,000 water molecules at molybdenite surfaces. During a simulation period of 1 ns, film rupture and displacement occurs. The attached nanobubble at the hydrophobic molybdenite face surface results in a contact angle of about 90º. This spontaneous attachment is due to a “water exclusion zone” at the molybdenite face surface and can be explained by a van der Waals (vdW) attractive force, as discussed in the literature. In contrast, themore » film is stable at the hydrophilic quartz (001) surface and the bubble does not attach. Contact angles determined from MD simulations are reported, and these results agree well with experimental and MDS sessile drop results. In this way, film stability and bubble attachment are described with respect to interfacial water structure for surfaces of different polarity. Interfacial water molecules at the hydrophobic molybdenite face surface have relatively weak interactions with the surface when compared to the hydrophilic quartz (001) surface, as revealed by the presence of a 3 Å “water exclusion zone” at the molybdenite/water interface. The molybdenite armchair-edge and zigzag-edge surfaces show a comparably slow process for film rupture and displacement when compared to the molybdenite face surface, which is consistent with their relatively weak hydrophobic character.« less

Low Voltage Electrowetting on Ferroelectric PVDF-HFP Insulator with Highly Tunable Contact Angle Range.

PubMed

Sawane, Yogesh B; Ogale, Satishchandra B; Banpurkar, Arun G

2016-09-14

We demonstrate a consistent electrowetting response on ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) insulator covered with a thin Teflon AF layer. This bilayer exhibits a factor of 3 enhancement in the contact angle modulation compared to that of conventional single-layered Teflon AF dielectric. On the basis of the proposed model the enhancement is attributed to the high value of effective dielectric constant (εeff ≈ 6) of the bilayer. Furthermore, the bilayer dielectric exhibits a hysteresis-free contact angle modulation over many AC voltage cycles. But the contact angle modulation for DC voltage shows a hysteresis because of the field-induced residual polarization in the ferroelectric layer. Finally, we show that a thin bilayer exhibits contact angle modulation of Δθ (U) ≈ 60° at merely 15 V amplitude of AC voltage indicating a potential dielectric for practical low voltage electrowetting applications. A proof of concept confirms electrowetting based rapid mixing of a fluorescent dye in aqueous glycerol solution for 15 V AC signal.

Bubble formation during drop impact on a heated pool

NASA Astrophysics Data System (ADS)

Tian, Yuansi; Alhazmi, Muath; Kouraytem, Nadia; Thoroddsen, Sigurdur

2017-11-01

Ultra high-speed video imaging, at up to 200 kfps, is used to investigate a drop impinging onto a high temperature pool. The room-temperature perfluorohexane drop, which has a boiling temperature as low as 56 °C impacts on the soybean oil pool heated up to around 200 °C, which is overwhelmingly higher than the boiling temperature of the drop. The bottom of the drop is therefore covered by a layer of vapor which prevents contact between the two immiscible liquid surfaces, akin to the Leidenfrost effect However, as the pool temperature is reduced, one starts seeing contact and the dynamics transition into the vapor explosion regime. At the boundary of this regime we observe some entrapment of scattered or a toroidal ring of small bubbles. Experimental video data will be presented to show this novel phenomenon and explain how these bubbles are formed and evolve.