The physics of water droplets on surfaces: exploring the effects of roughness and surface chemistry

NASA Astrophysics Data System (ADS)

Eid, K. F.; Panth, M.; Sommers, A. D.

2018-03-01

This paper explores the fluid property commonly called surface tension, its effect on droplet shape and contact angle, and the major influences of contact angle behaviour (i.e. surface roughness and surface chemistry). Images of water droplets placed on treated copper surfaces are used to measure the contact angles between the droplets and the surface. The surface wettability is manipulated either by growing a self-assembled monolayer on the surface to make it hydrophobic or by changing the surface roughness. The main activities in this experiment, then, are (1) preparing and studying surfaces with different surface wettability and roughness; (2) determining the shape and contact angles of water droplets on these surfaces; and (3) demonstrating the spontaneous motion of water droplets using surface tension gradients.

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.

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.

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

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.

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

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.

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.

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.

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

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.

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.

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.

Drop shape visualization and contact angle measurement on curved surfaces.

PubMed

Guilizzoni, Manfredo

2011-12-01

The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface-air and drop-air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop-surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces. Copyright © 2011 Elsevier Inc. All rights reserved.

Oil Contact Angles in a Water-Decane-Silicon Dioxide System: Effects of Surface Charge

NASA Astrophysics Data System (ADS)

Xu, Shijing; Wang, Jingyao; Wu, Jiazhong; Liu, Qingjie; Sun, Chengzhen; Bai, Bofeng

2018-04-01

Oil wettability in the water-oil-rock systems is very sensitive to the evolution of surface charges on the rock surfaces induced by the adsorption of ions and other chemical agents in water flooding. Through a set of large-scale molecular dynamics simulations, we reveal the effects of surface charge on the oil contact angles in an ideal water-decane-silicon dioxide system. The results show that the contact angles of oil nano-droplets have a great dependence on the surface charges. As the surface charge density exceeds a critical value of 0.992 e/nm2, the contact angle reaches up to 78.8° and the water-wet state is very apparent. The variation of contact angles can be confirmed from the number density distributions of oil molecules. With increasing the surface charge density, the adsorption of oil molecules weakens and the contact areas between nano-droplets and silicon dioxide surface are reduced. In addition, the number density distributions, RDF distributions, and molecular orientations indicate that the oil molecules are adsorbed on the silicon dioxide surface layer-by-layer with an orientation parallel to the surface. However, the layered structure of oil molecules near the silicon dioxide surface becomes more and more obscure at higher surface charge densities.

Oil Contact Angles in a Water-Decane-Silicon Dioxide System: Effects of Surface Charge.

PubMed

Xu, Shijing; Wang, Jingyao; Wu, Jiazhong; Liu, Qingjie; Sun, Chengzhen; Bai, Bofeng

2018-04-19

Oil wettability in the water-oil-rock systems is very sensitive to the evolution of surface charges on the rock surfaces induced by the adsorption of ions and other chemical agents in water flooding. Through a set of large-scale molecular dynamics simulations, we reveal the effects of surface charge on the oil contact angles in an ideal water-decane-silicon dioxide system. The results show that the contact angles of oil nano-droplets have a great dependence on the surface charges. As the surface charge density exceeds a critical value of 0.992 e/nm 2 , the contact angle reaches up to 78.8° and the water-wet state is very apparent. The variation of contact angles can be confirmed from the number density distributions of oil molecules. With increasing the surface charge density, the adsorption of oil molecules weakens and the contact areas between nano-droplets and silicon dioxide surface are reduced. In addition, the number density distributions, RDF distributions, and molecular orientations indicate that the oil molecules are adsorbed on the silicon dioxide surface layer-by-layer with an orientation parallel to the surface. However, the layered structure of oil molecules near the silicon dioxide surface becomes more and more obscure at higher surface charge densities.

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.

Smoothed particle hydrodynamics study of the roughness effect on contact angle and droplet flow.

PubMed

Shigorina, Elena; Kordilla, Jannes; Tartakovsky, Alexandre M

2017-09-01

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 modeling of free-surface flows 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 different types of rough surfaces. 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. We study the dependence of the transition between Cassie and Wenzel states on roughness and droplet size, which can be linked to the critical pressure for the given fluid-substrate combination. We observe good agreement between simulations and theoretical predictions. Finally, 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 lotus effect. We demonstrate that classical linear scaling relationships between Bond and capillary numbers for droplet flow on flat surfaces also hold for flow on rough surfaces.

[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

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.

Wetting of flat gradient surfaces.

PubMed

Bormashenko, Edward

2018-04-01

Gradient, chemically modified, flat surfaces enable directed transport of droplets. Calculation of apparent contact angles inherent for gradient surfaces is challenging even for atomically flat ones. Wetting of gradient, flat solid surfaces is treated within the variational approach, under which the contact line is free to move along the substrate. Transversality conditions of the variational problem give rise to the generalized Young equation valid for gradient solid surfaces. The apparent (equilibrium) contact angle of a droplet, placed on a gradient surface depends on the radius of the contact line and the values of derivatives of interfacial tensions. The linear approximation of the problem is considered. It is demonstrated that the contact angle hysteresis is inevitable on gradient surfaces. Electrowetting of gradient surfaces is discussed. Copyright © 2018 Elsevier Inc. All rights reserved.

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

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.

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

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.

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

Creation of superwetting surfaces with roughness structures.

PubMed

Garg, Varun; Qiao, Lei; Sarwate, Prasha; Luo, Cheng

2014-12-09

In this work, we explored the possibility of creating superwetting surfaces, which are defined here as those with apparent contact angles of <5°, using roughness structures for the purpose of eliminating the surface tension effect on a floating small plate, which is denser than the surrounding liquid. The roughness ratio is often thought to play a critical role in generating superwetting surfaces. However, we found that the top surface ratio had more influence on apparent contact angles. When this ratio was <0.013, the resulting apparent contact angle might be less than 5°, when the intrinsic contact angle was ≥40°. Accordingly, hybrid micro- and nanostructures, which had such a small ratio, were chosen to create the superwetting surfaces. These surfaces were subsequently applied to eliminate the surface tension effect on a small plate. As a result of this elimination, the small plate sank down to the bottom of the liquid.

Thermodynamics of Surface Nanobubbles.

PubMed

Zargarzadeh, Leila; Elliott, Janet A W

2016-11-01

In this paper, we examine the thermodynamic stability of surface nanobubbles. The appropriate free energy is defined for the system of nanobubbles on a solid surface submerged in a supersaturated liquid solution at constant pressure and temperature, under conditions where an individual nanobubble is not in diffusive contact with a gas phase outside of the system or with other nanobubbles on the time scale of the experiment. The conditions under which plots of free energy versus the radius of curvature of the nanobubbles show a global minimum, which denotes the stable equilibrium state, are explored. Our investigation shows that supersaturation and an anomalously high contact angle (measured through the liquid) are required to have stable surface nanobubbles. In addition, the anomalously high contact angle of surface nanobubbles is discussed from the standpoint of a framework recently proposed by Koch, Amirfazli, and Elliott that relates advancing and receding contact angles to thermodynamic equilibrium contact angles, combined with the existence of a gas enrichment layer.

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.

Detailed statistical contact angle analyses; "slow moving" drops on inclining silicon-oxide surfaces.

PubMed

Schmitt, M; Groß, K; Grub, J; Heib, F

2015-06-01

Contact angle determination by sessile drop technique is essential to characterise surface properties in science and in industry. Different specific angles can be observed on every solid which are correlated with the advancing or the receding of the triple line. Different procedures and definitions for the determination of specific angles exist which are often not comprehensible or reproducible. Therefore one of the most important things in this area is to build standard, reproducible and valid methods for determining advancing/receding contact angles. This contribution introduces novel techniques to analyse dynamic contact angle measurements (sessile drop) in detail which are applicable for axisymmetric and non-axisymmetric drops. Not only the recently presented fit solution by sigmoid function and the independent analysis of the different parameters (inclination, contact angle, velocity of the triple point) but also the dependent analysis will be firstly explained in detail. These approaches lead to contact angle data and different access on specific contact angles which are independent from "user-skills" and subjectivity of the operator. As example the motion behaviour of droplets on flat silicon-oxide surfaces after different surface treatments is dynamically measured by sessile drop technique when inclining the sample plate. The triple points, the inclination angles, the downhill (advancing motion) and the uphill angles (receding motion) obtained by high-precision drop shape analysis are independently and dependently statistically analysed. Due to the small covered distance for the dependent analysis (<0.4mm) and the dominance of counted events with small velocity the measurements are less influenced by motion dynamics and the procedure can be called "slow moving" analysis. The presented procedures as performed are especially sensitive to the range which reaches from the static to the "slow moving" dynamic contact angle determination. They are characterised by small deviations of the computed values. Additional to the detailed introduction of this novel analytical approaches plus fit solution special motion relations for the drop on inclined surfaces and detailed relations about the reactivity of the freshly cleaned silicon wafer surface resulting in acceleration behaviour (reactive de-wetting) are presented. Copyright © 2014 Elsevier Inc. All rights reserved.

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. ...

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.

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.

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.

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.

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.

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.

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

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.

Contact angles and wettability of ionic liquids on polar and non-polar surfaces.

PubMed

Pereira, Matheus M; Kurnia, Kiki A; Sousa, Filipa L; Silva, Nuno J O; Lopes-da-Silva, José A; Coutinho, João A P; Freire, Mara G

2015-12-21

Many applications involving ionic liquids (ILs) require the knowledge of their interfacial behaviour, such as wettability and adhesion. In this context, herein, two approaches were combined aiming at understanding the impact of the IL chemical structures on their wettability on both polar and non-polar surfaces, namely: (i) the experimental determination of the contact angles of a broad range of ILs (covering a wide number of anions of variable polarity, cations, and cation alkyl side chain lengths) on polar and non-polar solid substrates (glass, Al-plate, and poly-(tetrafluoroethylene) (PTFE)); and (ii) the correlation of the experimental contact angles with the cation-anion pair interaction energies generated by the Conductor-like Screening Model for Real Solvents (COSMO-RS). The combined results reveal that the hydrogen-bond basicity of ILs, and thus the IL anion, plays a major role through their wettability on both polar and non-polar surfaces. The increase of the IL hydrogen-bond accepting ability leads to an improved wettability of more polar surfaces (lower contact angles) while the opposite trend is observed on non-polar surfaces. The cation nature and alkyl side chain lengths have however a smaller impact on the wetting ability of ILs. Linear correlations were found between the experimental contact angles and the cation-anion hydrogen-bonding and cation ring energies, estimated using COSMO-RS, suggesting that these features primarily control the wetting ability of ILs. Furthermore, two-descriptor correlations are proposed here to predict the contact angles of a wide variety of ILs on glass, Al-plate, and PTFE surfaces. A new extended list is provided for the contact angles of ILs on three surfaces, which can be used as a priori information to choose appropriate ILs before a given application.

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.

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 and Contact Time on a Biomimetic Superhydrophobic Surface.

PubMed

Liang, Yunhong; Peng, Jian; Li, Xiujuan; Huang, Jubin; Qiu, Rongxian; Zhang, Zhihui; Ren, Luquan

2017-03-02

Inspired by the array microstructure of natural superhydrophobic surfaces (lotus leaf and cicada wing), an array microstructure was successfully constructed by high speed wire electrical discharge machining (HS-WEDM) on the surfaces of a 7075 aluminum alloy without any chemical treatment. The artificial surfaces had a high apparent contact angle of 153° ± 1° with a contact angle hysteresis less than 5° and showed a good superhydrophobic property. Wettability, contact time, and the corresponding superhydrophobic mechanism of artificial superhydrophobic surface were investigated. The results indicated that the micro-scale array microstructure was an important factor for the superhydrophobic surface, while different array microstructures exhibited different effects on the wettability and contact time of the artificial superhydrophobic surface. The length ( L ), interval ( S ), and height ( H ) of the array microstructure are the main influential factors on the wettability and contact time. The order of importance of these factors is H > S > L for increasing the apparent contact angle and reducing the contact time. The method, using HS-WEDM to fabricate superhydrophobic surface, is simple, low-cost, and environmentally friendly and can easily control the wettability and contact time on the artificial surfaces by changing the array microstructure.

Wettability and Contact Time on a Biomimetic Superhydrophobic Surface

PubMed Central

Liang, Yunhong; Peng, Jian; Li, Xiujuan; Huang, Jubin; Qiu, Rongxian; Zhang, Zhihui; Ren, Luquan

2017-01-01

Inspired by the array microstructure of natural superhydrophobic surfaces (lotus leaf and cicada wing), an array microstructure was successfully constructed by high speed wire electrical discharge machining (HS-WEDM) on the surfaces of a 7075 aluminum alloy without any chemical treatment. The artificial surfaces had a high apparent contact angle of 153° ± 1° with a contact angle hysteresis less than 5° and showed a good superhydrophobic property. Wettability, contact time, and the corresponding superhydrophobic mechanism of artificial superhydrophobic surface were investigated. The results indicated that the micro-scale array microstructure was an important factor for the superhydrophobic surface, while different array microstructures exhibited different effects on the wettability and contact time of the artificial superhydrophobic surface. The length (L), interval (S), and height (H) of the array microstructure are the main influential factors on the wettability and contact time. The order of importance of these factors is H > S > L for increasing the apparent contact angle and reducing the contact time. The method, using HS-WEDM to fabricate superhydrophobic surface, is simple, low-cost, and environmentally friendly and can easily control the wettability and contact time on the artificial surfaces by changing the array microstructure. PMID:28772613

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.

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.

Evaporation kinetics of sessile water droplets on micropillared superhydrophobic surfaces.

PubMed

Xu, Wei; Leeladhar, Rajesh; Kang, Yong Tae; Choi, Chang-Hwan

2013-05-21

Evaporation modes and kinetics of sessile droplets of water on micropillared superhydrophobic surfaces are experimentally investigated. The results show that a constant contact radius (CCR) mode and a constant contact angle (CCA) mode are two dominating evaporation modes during droplet evaporation on the superhydrophobic surfaces. With the decrease in the solid fraction of the superhydrophobic surfaces, the duration of a CCR mode is reduced and that of a CCA mode is increased. Compared to Rowan's kinetic model, which is based on the vapor diffusion across the droplet boundary, the change in a contact angle in a CCR (pinned) mode shows a remarkable deviation, decreasing at a slower rate on the superhydrophobic surfaces with less-solid fractions. In a CCA (receding) mode, the change in a contact radius agrees well with the theoretical expectation, and the receding speed is slower on the superhydrophobic surfaces with lower solid fractions. The discrepancy between experimental results and Rowan's model is attributed to the initial large contact angle of a droplet on superhydrophobic surfaces. The droplet geometry with a large contact angle results in a narrow wedge region of air along the contact boundary, where the liquid-vapor diffusion is significantly restricted. Such an effect becomes minor as the evaporation proceeds with the decrease in a contact angle. In both the CCR and CCA modes, the evaporative mass transfer shows the linear relationship between mass(2/3) and evaporation time. However, the evaporation rate is slower on the superhydrophobic surfaces, which is more significant on the surfaces with lower solid fractions. As a result, the superhydrophobic surfaces slow down the drying process of a sessile droplet on them.

Static friction between rigid fractal surfaces

NASA Astrophysics Data System (ADS)

Alonso-Marroquin, Fernando; Huang, Pengyu; Hanaor, Dorian A. H.; Flores-Johnson, E. A.; Proust, Gwénaëlle; Gan, Yixiang; Shen, Luming

2015-09-01

Using spheropolygon-based simulations and contact slope analysis, we investigate the effects of surface topography and atomic scale friction on the macroscopically observed friction between rigid blocks with fractal surface structures. From our mathematical derivation, the angle of macroscopic friction is the result of the sum of the angle of atomic friction and the slope angle between the contact surfaces. The latter is obtained from the determination of all possible contact slopes between the two surface profiles through an alternative signature function. Our theory is validated through numerical simulations of spheropolygons with fractal Koch surfaces and is applied to the description of frictional properties of Weierstrass-Mandelbrot surfaces. The agreement between simulations and theory suggests that for interpreting macroscopic frictional behavior, the descriptors of surface morphology should be defined from the signature function rather than from the slopes of the contacting surfaces.

Geometrical effect, optimal design and controlled fabrication of bio-inspired micro/nanotextures for superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Ma, F. M.; Li, W.; Liu, A. H.; Yu, Z. L.; Ruan, M.; Feng, W.; Chen, H. X.; Chen, Y.

2017-09-01

Superhydrophobic surfaces with high water contact angles and low contact angle hysteresis or sliding angles have received tremendous attention for both academic research and industrial applications in recent years. In general, such surfaces possess rough microtextures, particularly, show micro/nano hierarchical structures like lotus leaves. Now it has been recognized that to achieve the artificial superhydrophobic surfaces, the simple and effective strategy is to mimic such hierarchical structures. However, fabrications of such structures for these artificial surfaces involve generally expensive and complex processes. On the other hand, the relationships between structural parameters of various surface topography and wetting properties have not been fully understood yet. In order to provide guidance for the simple fabrication and particularly, to promote practical applications of superhydrophobic surfaces, the geometrical designs of optimal microtextures or patterns have been proposed. In this work, the recent developments on geometrical effect, optimal design and controlled fabrication of various superhydrophobic structures, such as unitary, anisotropic, dual-scale hierarchical, and some other surface geometries, are reviewed. The effects of surface topography and structural parameters on wetting states (composite and noncomposite) and wetting properties (contact angle, contact angle hysteresis and sliding angle) as well as adhesive forces are discussed in detail. Finally, the research prospects in this field are briefly addressed.

Capillary surfaces in a wedge: Differing contact angles

NASA Technical Reports Server (NTRS)

Concus, Paul; Finn, Robert

1994-01-01

The possible zero-gravity equilibrium configurations of capillary surfaces u(x, y) in cylindrical containers whose sections are (wedge) domains with corners are investigated mathematically, for the case in which the contact angles on the two sides of the wedge may differ. In such a situation the behavior can depart in significant qualitative ways from that for which the contact angles on the two sides are the same. Conditions are described under which such qualitative changes must occur. Numerically computed surfaces are depicted to indicate the behavior.

On the equilibrium contact angle of sessile liquid drops from molecular dynamics simulations.

PubMed

Ravipati, Srikanth; Aymard, Benjamin; Kalliadasis, Serafim; Galindo, Amparo

2018-04-28

We present a new methodology to estimate the contact angles of sessile drops from molecular simulations by using the Gaussian convolution method of Willard and Chandler [J. Phys. Chem. B 114, 1954-1958 (2010)] to calculate the coarse-grained density from atomic coordinates. The iso-density contour with average coarse-grained density value equal to half of the bulk liquid density is identified as the average liquid-vapor (LV) interface. Angles between the unit normal vectors to the average LV interface and unit normal vector to the solid surface, as a function of the distance normal to the solid surface, are calculated. The cosines of these angles are extrapolated to the three-phase contact line to estimate the sessile drop contact angle. The proposed methodology, which is relatively easy to implement, is systematically applied to three systems: (i) a Lennard-Jones (LJ) drop on a featureless LJ 9-3 surface; (ii) an SPC/E water drop on a featureless LJ 9-3 surface; and (iii) an SPC/E water drop on a graphite surface. The sessile drop contact angles estimated with our methodology for the first two systems are shown to be in good agreement with the angles predicted from Young's equation. The interfacial tensions required for this equation are computed by employing the test-area perturbation method for the corresponding planar interfaces. Our findings suggest that the widely adopted spherical-cap approximation should be used with caution, as it could take a long time for a sessile drop to relax to a spherical shape, of the order of 100 ns, especially for water molecules initiated in a lattice configuration on a solid surface. But even though a water drop can take a long time to reach the spherical shape, we find that the contact angle is well established much faster and the drop evolves toward the spherical shape following a constant-contact-angle relaxation dynamics. Making use of this observation, our methodology allows a good estimation of the sessile drop contact angle values even for moderate system sizes (with, e.g., 4000 molecules), without the need for long simulation times to reach the spherical shape.

On the equilibrium contact angle of sessile liquid drops from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Ravipati, Srikanth; Aymard, Benjamin; Kalliadasis, Serafim; Galindo, Amparo

2018-04-01

We present a new methodology to estimate the contact angles of sessile drops from molecular simulations by using the Gaussian convolution method of Willard and Chandler [J. Phys. Chem. B 114, 1954-1958 (2010)] to calculate the coarse-grained density from atomic coordinates. The iso-density contour with average coarse-grained density value equal to half of the bulk liquid density is identified as the average liquid-vapor (LV) interface. Angles between the unit normal vectors to the average LV interface and unit normal vector to the solid surface, as a function of the distance normal to the solid surface, are calculated. The cosines of these angles are extrapolated to the three-phase contact line to estimate the sessile drop contact angle. The proposed methodology, which is relatively easy to implement, is systematically applied to three systems: (i) a Lennard-Jones (LJ) drop on a featureless LJ 9-3 surface; (ii) an SPC/E water drop on a featureless LJ 9-3 surface; and (iii) an SPC/E water drop on a graphite surface. The sessile drop contact angles estimated with our methodology for the first two systems are shown to be in good agreement with the angles predicted from Young's equation. The interfacial tensions required for this equation are computed by employing the test-area perturbation method for the corresponding planar interfaces. Our findings suggest that the widely adopted spherical-cap approximation should be used with caution, as it could take a long time for a sessile drop to relax to a spherical shape, of the order of 100 ns, especially for water molecules initiated in a lattice configuration on a solid surface. But even though a water drop can take a long time to reach the spherical shape, we find that the contact angle is well established much faster and the drop evolves toward the spherical shape following a constant-contact-angle relaxation dynamics. Making use of this observation, our methodology allows a good estimation of the sessile drop contact angle values even for moderate system sizes (with, e.g., 4000 molecules), without the need for long simulation times to reach the spherical shape.

Contact angles and wettability of ionic liquids on polar and non-polar surfaces†

PubMed Central

Sousa, Filipa L.; Silva, Nuno J. O.; Lopes-da-Silva, José A.; Coutinho, João A. P.; Freire, Mara G.

2016-01-01

Many applications involving ionic liquids (ILs) require the knowledge of their interfacial behaviour, such as wettability and adhesion. In this context, herein, two approaches were combined aiming at understanding the impact of the IL chemical structures on their wettability on both polar and non-polar surfaces, namely: (i) the experimental determination of the contact angles of a broad range of ILs (covering a wide number of anions of variable polarity, cations, and cation alkyl side chain lengths) on polar and non-polar solid substrates (glass, Al-plate, and poly-(tetrafluoroethylene) (PTFE)); and (ii) the correlation of the experimental contact angles with the cation–anion pair interaction energies generated by the Conductor-like Screening Model for Real Solvents (COSMO-RS). The combined results reveal that the hydrogen-bond basicity of ILs, and thus the IL anion, plays a major role through their wettability on both polar and non-polar surfaces. The increase of the IL hydrogen-bond accepting ability leads to an improved wettability of more polar surfaces (lower contact angles) while the opposite trend is observed on non-polar surfaces. The cation nature and alkyl side chain lengths have however a smaller impact on the wetting ability of ILs. Linear correlations were found between the experimental contact angles and the cation–anion hydrogen-bonding and cation ring energies, estimated using COSMO-RS, suggesting that these features primarily control the wetting ability of ILs. Furthermore, two-descriptor correlations are proposed here to predict the contact angles of a wide variety of ILs on glass, Al-plate, and PTFE surfaces. A new extended list is provided for the contact angles of ILs on three surfaces, which can be used as a priori information to choose appropriate ILs before a given application. PMID:26554705

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.

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.

Effect of Stratification on Surface Properties of Corneal Epithelial Cells

PubMed Central

Yáñez-Soto, Bernardo; Leonard, Brian C.; Raghunathan, Vijay Krishna; Abbott, Nicholas L.; Murphy, Christopher J.

2015-01-01

Purpose The purpose of this study was to determine the influence of mucin expression in an immortalized human corneal epithelial cell line (hTCEpi) on the surface properties of cells, such as wettability, contact angle, and surface heterogeneity. Methods hTCEpi cells were cultured to confluence in serum-free medium. The medium was then replaced by stratification medium to induce mucin biosynthesis. The mucin expression profile was analyzed using quantitative PCR and Western blotting. Contact angles were measured using a two-immiscible liquid method, and contact angle hysteresis was evaluated by tilting the apparatus and recording advancing and receding contact angles. The spatial distribution of mucins was evaluated with fluorescently labeled lectin. Results hTCEpi cells expressed the three main ocular mucins (MUC1, MUC4, and MUC16) with a maximum between days 1 and 3 of the stratification process. Upon stratification, cells caused a very significant increase in contact angle hysteresis, suggesting the development of spatially discrete and heterogeneously distributed surface features, defined by topography and/or chemical functionality. Although atomic force microscopy measurements showed no formation of appreciable topographic features on the surface of the cells, we observed a significant increase in surface chemical heterogeneity. Conclusions The surface chemical heterogeneity of the corneal epithelium may influence the dynamic behavior of tear film by “pinning” the contact line between the cellular surface and aqueous tear film. Engineering the surface properties of corneal epithelium could potentially lead to novel treatments in dry eye disease. PMID:26747762

Surface roughness effects on contact line motion with small capillary number

NASA Astrophysics Data System (ADS)

Yang, Feng-Chao; Chen, Xiao-Peng; Yue, Pengtao

2018-01-01

In this work, we investigate how surface roughness influences contact line dynamics by simulating forced wetting in a capillary tube. The tube wall is decorated with microgrooves and is intrinsically hydrophilic. A phase-field method is used to capture the fluid interface and the moving contact line. According to the numerical results, a criterion is proposed to judge whether the grooves are entirely wetted or not at vanishing capillary numbers. When the contact line moves over a train of grooves, the apparent contact angle exhibits a periodic nature, no matter whether the Cassie-Baxter or the Wenzel state is achieved. The oscillation amplitude of apparent contact angle is analyzed and found to be inversely proportional to the interface area. The contact line motion can be characterized as stick-jump-slip in the Cassie-Baxter state and stick-slip in the Wenzel state. By comparing to the contact line dynamics on smooth surfaces, equivalent microscopic contact angles and slip lengths are obtained. The equivalent slip length in the Cassie-Baxter state agrees well with the theoretical model in the literature. The equivalent contact angles are, however, much greater than the predictions of the Cassie-Baxter model and the Wenzel model for equilibrium stable states. Our results reveal that the pinning of the contact line at surface defects effectively enhances the hydrophobicity of rough surfaces, even when the surface material is intrinsically hydrophilic and the flow is under the Wenzel state.

Drop impact and wettability: From hydrophilic to superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Antonini, Carlo; Amirfazli, Alidad; Marengo, Marco

2012-10-01

Experiments to understand the effect of surface wettability on impact characteristics of water drops onto solid dry surfaces were conducted. Various surfaces were used to cover a wide range of contact angles (advancing contact angle from 48° to 166°, and contact angle hysteresis from 5° to 56°). Several different impact conditions were analyzed (12 impact velocities on 9 different surfaces, among which 2 were superhydrophobic). Results from impact tests with millimetric drops show that two different regimes can be identified: a moderate Weber number regime (30 < We < 200), in which wettability affects both drop maximum spreading and spreading characteristic time; and a high Weber number regime (We > 200), in which wettability effect is secondary, because capillary forces are overcome by inertial effects. In particular, results show the role of advancing contact angle and contact angle hysteresis as fundamental wetting parameters to allow understanding of different phases of drop spreading and beginning of recoiling. It is also shown that drop spreading on hydrophilic and superhydrophobic surfaces occurs with different time scales. Finally, if the surface is superhydrophobic, eventual impalement, i.e., transition from Cassie to Wenzel wetting state, which might occur in the vicinity of the drop impact area, does not influence drop maximum spreading.

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.

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.

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.

High contact angle hysteresis of superhydrophobic surfaces: Hydrophobic defects

NASA Astrophysics Data System (ADS)

Chang, Feng-Ming; Hong, Siang-Jie; Sheng, Yu-Jane; Tsao, Heng-Kwong

2009-08-01

A typical superhydrophobic surface is essentially nonadhesive and exhibits very low water contact angle (CA) hysteresis, so-called Lotus effect. However, leaves of some plants such as scallion and garlic with an advancing angle exceeding 150° show very serious CA hysteresis. Although surface roughness and epicuticular wax can explain the very high advancing CA, our analysis indicates that the unusual hydrophobic defect, diallyl disulfide, is the key element responsible for contact line pinning on allium leaves. After smearing diallyl disulfide on an extended polytetrafluoroethylene (PTFE) film, which is originally absent of CA hysteresis, the surface remains superhydrophobic but becomes highly adhesive.

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.

Superhydrophobic aluminum alloy surfaces by a novel one-step process.

PubMed

Saleema, N; Sarkar, D K; Paynter, R W; Chen, X-G

2010-09-01

A simple one-step process has been developed to render aluminum alloy surfaces superhydrophobic by immersing the aluminum alloy substrates in a solution containing NaOH and fluoroalkyl-silane (FAS-17) molecules. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements have been performed to characterize the morphological features, chemical composition and superhydrophobicity of the surfaces. The resulting surfaces provided a water contact angle as high as ∼162° and a contact angle hysteresis as low as ∼4°. The study indicates that it is possible to fabricate superhydrophobic aluminum surfaces easily and effectively without involving the traditional two-step processes.

The estimation of dynamic contact angle of ultra-hydrophobic surfaces using inclined surface and impinging droplet methods

NASA Astrophysics Data System (ADS)

Jasikova, Darina; Kotek, Michal

2014-03-01

The development of industrial technology also brings with optimized surface quality, particularly where there is contact with food. Application ultra-hydrophobic surface significantly reduces the growth of bacteria and facilitates cleaning processes. Testing and evaluation of surface quality are used two methods: impinging droplet and inclined surface method optimized with high speed shadowgraphy, which give information about dynamic contact angle. This article presents the results of research into new methods of measuring ultra-hydrophobic patented technology.

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.

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.

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.

Surface energy changes produced by ultraviolet-ozone irradiation of poly(methylmethacrylate), polycarbone and polytetrafluoroethylene

NASA Technical Reports Server (NTRS)

Ponter, A. B.; Jones, W. R., Jr.; Jansen, R. H.

1994-01-01

Contact angles of water and methylene iodide were measured as a function of UV/O3 treatment time for three polymers: poly(methylmethacrylate) (PMMA), polycarbonate, and polytetrafluoroethylene (PTFE). Surface roughnesses were also measured. Surface free energies were then calculated using relationships developed by Kaelble and Neumann. The surface energy of polycarbonate was found to increase (60 percent) during UV/O3 treatment. However, calculations on PMMA were hampered by the formation of a water soluble surface product. On PTFE surfaces, the UV/O3 treatment etched the surface causing large increases in surface roughness, rendering contact angle measurements impossible. It is concluded that care must be taken in interpreting contact angle measurements and surface energy calculations on UV/O3 treated polymer surfaces.

Study of role of meniscus and viscous forces during liquid-mediated contacts separation

NASA Astrophysics Data System (ADS)

Dhital, Prabin

Menisci may form between two solid surfaces with the presence of an ultra-thin liquid film. When the separation operation is needed, meniscus and viscous forces contribute to an adhesion leading stiction, high friction, possibly high wear and potential failure of the contact systems, for instance microdevices, magnetic head disks and diesel fuel injectors. The situation may become more pronounced when the contacting surfaces are ultra-smooth and the normal load is small. Various design parameters, such as contact angle, initial separation height, surface tension and liquid viscosity, have been investigated during liquid-mediated contact separation. However, how the involved forces will change roles for various liquid is of interest and is necessary to be studied. In this study, meniscus and viscous forces due to water and liquid lubricants during separation of two flat surfaces are studied. Previously established mathematical model for meniscus and viscous forces during flat on flat contact separation is simulated. The effect of meniscus and viscous force on critical meniscus area at which those forces change role is studied with different liquid properties for flat on flat contact surfaces. The roles of the involved forces at various meniscus areas are analyzed. Experiments are done in concerns to studying the effect of surface roughness on contact angle. The impact of liquid properties, initial separation heights and contact angle on critical meniscus area for different liquid properties are analyzed. The study provides a fundamental understanding of the forces of the separation process and its value for the design of interfaces. The effect of surface roughness and liquid properties on contact angle are studied.

Spontaneous Spreading of a Droplet: The Role of Solid Continuity and Advancing Contact Angle.

PubMed

Jiang, Youhua; Sun, Yujin; Drelich, Jaroslaw W; Choi, Chang-Hwan

2018-05-01

Spontaneous spreading of a droplet on a solid surface is poorly understood from a macroscopic level down to a molecular level. Here, we investigate the effect of surface topography and wettability on spontaneous spreading of a water droplet. Spreading force is measured for a suspended droplet that minimizes interference of kinetic energy in the spontaneous spreading during its contact with solid surfaces of discontinuous (pillar) and continuous (pore) patterns with various shapes and dimensions. Results show that a droplet cannot spread spontaneously on pillared surfaces regardless of their shapes or dimensions because of the solid discontinuity. On the contrary, a droplet on pored surfaces can undergo spontaneous spreading whose force increases with a decrease in the advancing contact angle. Theoretical models based on both the system free energy and capillary force along the contact line validate the direct and universal dependency of the spontaneous spreading force on the advancing contact angle.

High-precision drop shape analysis on inclining flat surfaces: introduction and comparison of this special method with commercial contact angle analysis.

PubMed

Schmitt, Michael; Heib, Florian

2013-10-07

Drop shape analysis is one of the most important and frequently used methods to characterise surfaces in the scientific and industrial communities. An especially large number of studies, which use contact angle measurements to analyse surfaces, are characterised by incorrect or misdirected conclusions such as the determination of surface energies from poorly performed contact angle determinations. In particular, the characterisation of surfaces, which leads to correlations between the contact angle and other effects, must be critically validated for some publications. A large number of works exist concerning the theoretical and thermodynamic aspects of two- and tri-phase boundaries. The linkage between theory and experiment is generally performed by an axisymmetric drop shape analysis, that is, simulations of the theoretical drop profiles by numerical integration onto a number of points of the drop meniscus (approximately 20). These methods work very well for axisymmetric profiles such as those obtained by pendant drop measurements, but in the case of a sessile drop onto real surfaces, additional unknown and misunderstood effects on the dependence of the surface must be considered. We present a special experimental and practical investigation as another way to transition from experiment to theory. This procedure was developed to be especially sensitive to small variations in the dependence of the dynamic contact angle on the surface; as a result, this procedure will allow the properties of the surface to be monitored with a higher precession and sensitivity. In this context, water drops onto a 111 silicon wafer are dynamically measured by video recording and by inclining the surface, which results in a sequence of non-axisymmetric drops. The drop profiles are analysed by commercial software and by the developed and presented high-precision drop shape analysis. In addition to the enhanced sensitivity for contact angle determination, this analysis technique, in combination with innovative fit algorithms and data presentations, can result in enhanced reproducibility and comparability of the contact angle measurements in terms of the material characterisation in a comprehensible way.

High-precision drop shape analysis on inclining flat surfaces: Introduction and comparison of this special method with commercial contact angle analysis

NASA Astrophysics Data System (ADS)

Schmitt, Michael; Heib, Florian

2013-10-01

Drop shape analysis is one of the most important and frequently used methods to characterise surfaces in the scientific and industrial communities. An especially large number of studies, which use contact angle measurements to analyse surfaces, are characterised by incorrect or misdirected conclusions such as the determination of surface energies from poorly performed contact angle determinations. In particular, the characterisation of surfaces, which leads to correlations between the contact angle and other effects, must be critically validated for some publications. A large number of works exist concerning the theoretical and thermodynamic aspects of two- and tri-phase boundaries. The linkage between theory and experiment is generally performed by an axisymmetric drop shape analysis, that is, simulations of the theoretical drop profiles by numerical integration onto a number of points of the drop meniscus (approximately 20). These methods work very well for axisymmetric profiles such as those obtained by pendant drop measurements, but in the case of a sessile drop onto real surfaces, additional unknown and misunderstood effects on the dependence of the surface must be considered. We present a special experimental and practical investigation as another way to transition from experiment to theory. This procedure was developed to be especially sensitive to small variations in the dependence of the dynamic contact angle on the surface; as a result, this procedure will allow the properties of the surface to be monitored with a higher precession and sensitivity. In this context, water drops onto a 111 silicon wafer are dynamically measured by video recording and by inclining the surface, which results in a sequence of non-axisymmetric drops. The drop profiles are analysed by commercial software and by the developed and presented high-precision drop shape analysis. In addition to the enhanced sensitivity for contact angle determination, this analysis technique, in combination with innovative fit algorithms and data presentations, can result in enhanced reproducibility and comparability of the contact angle measurements in terms of the material characterisation in a comprehensible way.

Increasing light coupling in a photovoltaic film by tuning nanoparticle shape with substrate surface energy

NASA Astrophysics Data System (ADS)

Kataria, Devika; Krishnamoorthy, Kothandam; Iyer, S. Sundar Kumar

2017-08-01

Tuning metal nanoparticle (MNP) contact angle on the surface it is formed can help maximise the useful optical coupling in photovoltaic films by localized surface plasmon (LSP) resonance—opening up the possibility of building improved photovoltaic cells. In this work experimental demonstration of optical absorption increase in copper phthalocyanine (CuPc) films by tuning silver MNP shape by changing its contact angles with substrate has been reported. Thin films of poly3,4 ethylenedioxythiophene: sodium dodecycl sulphate (PEDOT:SDS) with different surface energies were formed on indium tin oxide (ITO) coated glass by electro-deposition. Silver MNPs thermally evaporated directly on ozonised ITO as well as on the PEDOT:SDS films showed contact angles ranging from 60° to 125°. The CuPc layer was deposited on top of the MNPs. For the samples studied, best optical absorption in the CuPc layer was for a contact angle of 110°.

Poly(styrene-co-butadiene) random copolymer thin films and nanostructures on a mica surface: morphology and contact angles of nanodroplets.

PubMed

McClements, Jake; Buffone, Cosimo; Shaver, Michael P; Sefiane, Khellil; Koutsos, Vasileios

2017-09-20

The self-assembly of poly(styrene-co-butadiene) random copolymers on mica surfaces was studied by varying solution concentrations and polymer molecular weights. Toluene solutions of the poly(styrene-co-butadiene) samples were spin coated onto a mica surface and the resulting polymer morphology was investigated by atomic force microscopy. At higher concentrations, thin films formed with varying thicknesses; some dewetting was observed which depended on the molecular weight. Total dewetting did not occur despite the polymer's low glass transition temperature. Instead, partial dewetting was observed suggesting that the polymer was in a metastable equilibrium state. At lower concentrations, spherical cap shaped nanodroplets formed with varying sizes from single polymer chains to aggregates containing millions of chains. As the molecular weight was increased, fewer aggregates were observed on the surface, albeit with larger sizes resulting from increased solution viscosities and more chain entanglements at higher molecular weights. The contact angles of the nanodroplets were shown to be size dependent. A minimum contact angle occurs for droplets with radii of 100-250 nm at each molecular weight. Droplets smaller than 100 nm showed a sharp increase in contact angle; attributed to an increase in the elastic modulus of the droplets, in addition, to a positive line tension value. Droplets larger than 250 nm also showed an increased contact angle due to surface heterogeneities which cannot be avoided for larger droplets. This increase in contact angle plateaus as the droplet size reaches the macroscopic scale.

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.

Thermal management of metallic surfaces: evaporation of sessile water droplets on polished and patterned stainless steel

NASA Astrophysics Data System (ADS)

Czerwiec, T.; Tsareva, S.; Andrieux, A.; Bortolini, G. A.; Bolzan, P. H.; Castanet, G.; Gradeck, M.; Marcos, G.

2017-10-01

This communication focus on the evaporation of sessile water droplets on different states of austenitic stainless steel surfaces: mirror polished, mirror polished and aged and patterned by sputtering. The evolution of the contact angle and of the droplet diameter is presented as a function of time at room temperature. For all the surface states, a constant diameter regime (CCR) is observed. An important aging effect on the contact angle is measured on polished surfaces due to atmospheric contamination. The experimental observations are compared to a quasi-static evaporation model assuming spherical caps. The evolution of the droplet volume as a function of time is almost linear with the evaporation time for all the observed surfaces. This is in accordance with the model prediction for the CCR mode for small initial contact angles. In our experiments, the evaporation time is found to be linearly dependent on the initial contact angle. This dependence is not correctly described by the evaporation model

Equilibrium contact angle or the most-stable contact angle?

PubMed

Montes Ruiz-Cabello, F J; Rodríguez-Valverde, M A; Cabrerizo-Vílchez, M A

2014-04-01

It is well-established that the equilibrium contact angle in a thermodynamic framework is an "unattainable" contact angle. Instead, the most-stable contact angle obtained from mechanical stimuli of the system is indeed experimentally accessible. Monitoring the susceptibility of a sessile drop to a mechanical stimulus enables to identify the most stable drop configuration within the practical range of contact angle hysteresis. Two different stimuli may be used with sessile drops: mechanical vibration and tilting. The most stable drop against vibration should reveal the changeless contact angle but against the gravity force, it should reveal the highest resistance to slide down. After the corresponding mechanical stimulus, once the excited drop configuration is examined, the focus will be on the contact angle of the initial drop configuration. This methodology needs to map significantly the static drop configurations with different stable contact angles. The most-stable contact angle, together with the advancing and receding contact angles, completes the description of physically realizable configurations of a solid-liquid system. Since the most-stable contact angle is energetically significant, it may be used in the Wenzel, Cassie or Cassie-Baxter equations accordingly or for the surface energy evaluation. © 2013 Elsevier B.V. All rights reserved.

Numerical Study for a Large-Volume Droplet on the Dual-Rough Surface: Apparent Contact Angle, Contact Angle Hysteresis, and Transition Barrier.

PubMed

Dong, Jian; Jin, Yanli; Dong, He; Liu, Jiawei; Ye, Senbin

2018-06-26

The profile, apparent contact angle (ACA), contact angle hysteresis (CAH), and wetting state transmission energy barrier (WSTEB) are important static and dynamic properties of a large-volume droplet on the hierarchical surface. Understanding them can provide us with important insights into functional surfaces and promote the application in corresponding areas. In this paper, we establish three theoretical models (models 1-3) and the corresponding numerical methods, which were obtained by the free energy minimization and the nonlinear optimization algorithm, to predict the profile, ACA, CAH, and WSTEB of a large-volume droplet on the horizontal regular dual-rough surface. In consideration of the gravity, the energy barrier on the contact circle, the dual heterogeneous structures and their roughness on the surface, the models are more universal and accurate than the previous models. It showed that the predictions of the models were in good agreement with the results from the experiment or literature. The models are promising to become novel design approaches of functional surfaces, which are frequently applied in microfluidic chips, water self-catchment system, and dropwise condensation heat transfer system.

Stability of surface nanobubbles

NASA Astrophysics Data System (ADS)

Maheshwari, Shantanu; van der Hoef, Martin; Zhang, Xuehua; Lohse, Detlef

2015-11-01

We have studied the stability and dissolution of surface nanobubbles on the chemical heterogenous surface by performing Molecular Dynamics (MD) simulations of binary mixture consists of Lennard-Jones (LJ) particles. Recently our group has derived the exact expression for equilibrium contact angle of surface nanobubbles as a function of oversaturation of the gas concentration in bulk liquid and the lateral length of bubble. It has been showed that the contact line pinning and the oversaturation of gas concentration in bulk liquid is crucial in the stability of surface nanobubbles. Our simulations showed that how pinning of the three-phase contact line on the chemical heterogenous surface lead to the stability of the nanobubble. We have calculated the equilibrium contact angle by varying the gas concentration in bulk liquid and the lateral length of the bubble. Our results showed that the equilibrium contact angle follows the expression derived analytically by our group. We have also studied the bubble dissolution dynamics and showed the ''stick-jump'' mechanism which was also observed experimentally in case of dissolution of nanodrops.

Fabrication of highly hydrophobic two-component thermosetting polyurethane surfaces with silica nanoparticles

NASA Astrophysics Data System (ADS)

Yang, Guang; Song, Jialu; Hou, Xianghui

2018-05-01

Highly hydrophobic thermosetting polyurethane (TSU) surfaces with micro-nano hierarchical structures were developed by a simple process combined with sandpaper templates and nano-silica embellishment. Sandpapers with grit sizes varying from 240 to 7000 grit were used to obtain micro-scale roughness on an intrinsic hydrophilic TSU surface. The surface wettability was investigated by contact angle measurement. It was found that the largest contact angle of the TSU surface without nanoparticles at 102 ± 3° was obtained when the template was 240-grit sandpaper and the molding progress started after 45 min curing of TSU. Silica nanoparticles modified with polydimethylsiloxane were scattered onto the surfaces of both the polymer and the template to construct the desirable nanostructures. The influences of the morphology, surface composition and the silica content on the TSU surface wettability were studied by scanning electron microscopy (SEM), attenuated total reflection (ATR) infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The surface of the TSU/SiO2 nanocomposites containing 4 wt% silica nanoparticles exhibited a distinctive dual-scale structure and excellent hydrophobicity with the contact angle above 150°. The mechanism of wettability was also discussed by Wenzel model and Cassie-Baxter model.

Mechanism of Hydrophilicity by Radiation-Induced Surface Activation

NASA Astrophysics Data System (ADS)

Honjo, Yoshio; Furuya, Masahiro; Takamasa, Tomoji; Okamoto, Koji

When a metal oxide is irradiated by gamma rays, the irradiated surface becomes hydrophilic. This surface phenomenon is called as radiation-induced surface activation (RISA) hydrophilicity. In order to investigate gamma ray-induced and photoinduced hydrophilicity, the contact angles of water droplets on a titanium dioxide surface were measured in terms of irradiation intensity and time for gamma rays of cobalt-60 and for ultraviolet rays. Reciprocals of the contact angles increased in proportion to the irradiation time before the contact angles reached its super-hydrophilic state. The irradiation time dependency is equal to each other qualitatively. In addition, an effect of ambient gas was investigated. In pure argon gas, the contact angle remains the same against the irradiation time. This clearly indicates that certain humidity is required in ambient gas to take place of RISA hydrophilicity. A single crystal titanium dioxide (100) surface was analyzed by X-ray photoelectron spectrometry (XPS). After irradiation with gamma rays, a peak was found in the O1s spectrum, which indicates the adsorption of dissociative water to a surface 5-fold coordinate titanium site, and the formation of a surface hydroxyl group. We conclude that the RISA hydrophilicity is caused by chemisorption of the hydroxyl group on the surface.

A reliable method of manufacturing metallic hierarchical superhydrophobic surfaces

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

Pogreb, Roman; Whyman, Gene; Barayev, Reuven

2009-06-01

A method of manufacturing hierarchical metallic surfaces demonstrating superhydrophobic properties is presented. The surfaces showed apparent contact angles as high as 153 deg. and sliding angles of 10 deg. for 50-100 {mu}l droplets. The Cassie-like model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)], considering the hierarchical topography of the relief, predicts apparent contact angles in a satisfactory agreement with the measured values.

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

Correlation of Cell Surface Biomarker Expression Levels with Adhesion Contact Angle Measured by Lateral Microscopy.

PubMed

Walz, Jenna A; Mace, Charles R

2018-06-05

Immunophenotyping is typically achieved using flow cytometry, but any influence a biomarker may have on adhesion or surface recognition cannot be determined concurrently. In this manuscript, we demonstrate the utility of lateral microscopy for correlating cell surface biomarker expression levels with quantitative descriptions of cell morphology. With our imaging system, we observed single cells from two T cell lines and two B cell lines adhere to antibody-coated substrates and quantified this adhesion using contact angle measurements. We found that SUP-T1 and CEM CD4+ cells, both of which express similar levels of CD4, experienced average changes in contact angle that were not statistically different from one another on surfaces coated in anti-CD4. However, MAVER-1 and BJAB K20 cells, both of which express different levels of CD20, underwent average changes in contact angle that were significantly different from one another on surfaces coated in anti-CD20. Our results indicate that changes in cell contact angles on antibody-coated substrates reflect the expression levels of corresponding antigens on the surfaces of cells as determined by flow cytometry. Our lateral microscopy approach offers a more reproducible and quantitative alternative to evaluate adhesion compared to commonly used wash assays and can be extended to many additional immunophenotyping applications to identify cells of interest within heterogeneous populations.

Wettability of graphitic-carbon and silicon surfaces: MD modeling and theoretical analysis

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

Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.

2015-07-28

The wettability of graphitic carbon and silicon surfaces was numerically and theoretically investigated. A multi-response method has been developed for the analysis of conventional molecular dynamics (MD) simulations of droplets wettability. The contact angle and indicators of the quality of the computations are tracked as a function of the data sets analyzed over time. This method of analysis allows accurate calculations of the contact angle obtained from the MD simulations. Analytical models were also developed for the calculation of the work of adhesion using the mean-field theory, accounting for the interfacial entropy changes. A calibration method is proposed to providemore » better predictions of the respective contact angles under different solid-liquid interaction potentials. Estimations of the binding energy between a water monomer and graphite match those previously reported. In addition, a breakdown in the relationship between the binding energy and the contact angle was observed. The macroscopic contact angles obtained from the MD simulations were found to match those predicted by the mean-field model for graphite under different wettability conditions, as well as the contact angles of Si(100) and Si(111) surfaces. Finally, an assessment of the effect of the Lennard-Jones cutoff radius was conducted to provide guidelines for future comparisons between numerical simulations and analytical models of wettability.« less

Determination of the Contact Angle Based on the Casimir Effect

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Volz, Martin P.

2015-01-01

On a macroscopic scale, a nonreactive liquid partially covering a homogeneous solid surface will intersect the solid at an angle called the contact angle. For molten metals and semiconductors, the contact angle is materially dependent upon both the solid and liquid and typical values fall in the range 80-170 deg, depending on the crucible material. On a microscopic scale, there does not exist a precise and sharp contact angle but rather the liquid and solid surfaces merge smoothly and continuously. Consider the example of the so called detached Bridgman crystal growth process. In this technique, a small gap is formed between the growing crystal and the crucible. At the crystal/melt interface, a meniscus ring is formed. Its width can be in the range of a few micrometers, approaching a microscopic scale. It then becomes questionable to describe the shape of this meniscus by the contact angle. A more advanced treatment of the interface is needed and here we propose such a refined model. The interaction of the liquid surface with the solid can be calculated by considering two forces: a short-range repulsive force and a longer range (up to a few micrometers) Casimir or van der Waals force.

Effect of microstructure and surface features on wetting angle of a Fe-3.2 wt%C.E. cast iron with water

NASA Astrophysics Data System (ADS)

Riahi, Samira; Niroumand, Behzad; Dorri Moghadam, Afsaneh; Rohatgi, Pradeep K.

2018-05-01

In the present study, variation in surface wetting behavior of a hypoeutectic cast iron with its microstructural features and surface roughness was investigated. Samples with an identical composition, i.e. Fe-3.2 wt%C.E., and different microstructures (a gray cast iron with A-type flake graphite and a white cast iron) were fabricated by gravity casting of molten cast iron in a chill mold at different cooling rates. A variation of surface roughness was also developed by polishing, a four-stage electroetching and a four-stage mechanical abrading on the samples. Roughness and water contact angles of all surfaces were then measured. The surface roughness factor and the solid fraction in contact with water by the Wenzel and Cassie-Baxter contact models were also calculated and compared with the corresponding measured contact angles to find out which regime was active. Results indicated that the surface microstructure and the type of constituents present at the surface influenced the cast iron surface wettability and that it was possible to change the surface contact angle by modification of the surface microstructure. The mechanically abraded gray cast iron followed the Wenzel-type regime while the electroetched surfaces of gray cast iron exhibited a transition from Wenzel to Cassie-Baxter type regime. In white cast iron, the results indicated Wenzel type behavior in the electroetched samples while for the mechanically abraded samples, none of these two models could predict the wetting behavior. Furthermore, the wetting angles of both gray and white cast irons were measured after 1, 2, 3 and 4 weeks of air exposure. The results showed that the wetting angles of both samples increased to above 90° after one week of air exposure which was likely due to adsorption of low surface energy hydrocarbons on the surfaces.

Influence of Contact Angle, Growth Angle and Melt Surface Tension on Detached Solidification of InSb

NASA Technical Reports Server (NTRS)

Wang, Yazhen; Regel, Liya L.; Wilcox, William R.

2000-01-01

We extended the previous analysis of detached solidification of InSb based on the moving meniscus model. We found that for steady detached solidification to occur in a sealed ampoule in zero gravity, it is necessary for the growth angle to exceed a critical value, the contact angle for the melt on the ampoule wall to exceed a critical value, and the melt-gas surface tension to be below a critical value. These critical values would depend on the material properties and the growth parameters. For the conditions examined here, the sum of the growth angle and the contact angle must exceed approximately 130, which is significantly less than required if both ends of the ampoule are open.

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.

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.

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

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.

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

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

Hydrophobic and optical characteristics of graphene and graphene oxide films transferred onto functionalized silica particles deposited glass surface

NASA Astrophysics Data System (ADS)

Yilbas, B. S.; Ibrahim, A.; Ali, H.; Khaled, M.; Laoui, T.

2018-06-01

Hydrophobic and optical transmittance characteristics of the functionalized silica particles on the glass surface prior and after transfer of graphene and graphene oxide films on the surface are examined. Nano-size silica particles are synthesized and functionalized via chemical grafting and deposited onto a glass surface. Graphene film, grown on copper substrate, was transferred onto the functionalized silica particles surface through direct fishing method. Graphene oxide layer was deposited onto the functionalized silica particles surface via spin coating technique. Morphological, hydrophobic, and optical characteristics of the functionalized silica particles deposited surface prior and after graphene and graphene oxide films transfer are examined using the analytical tools. It is found that the functionalized silica particles are agglomerated at the surface forming packed structures with few micro/nano size pores. This arrangement gives rise to water droplet contact angle and contact angle hysteresis in the order of 163° and 2°, respectively, and remains almost uniform over the entire surface. Transferring graphene and depositing graphene oxide films over the functionalized silica particles surface lowers the water droplet contact angle slightly (157-160°) and increases the contact angle hysteresis (4°). The addition of the graphene and graphene oxide films onto the surface of the deposited functionalized silica particles improves the optical transmittance.

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.

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

Wettability of Y2O3: A Relative Analysis of Thermally Oxidized, Reactively Sputtered and Template Assisted Nanostructured Coatings

PubMed Central

Barshilia, Harish C.; Chaudhary, Archana; Kumar, Praveen; Manikandanath, Natarajan T.

2012-01-01

The wettability of reactively sputtered Y2O3, thermally oxidized Y-Y2O3 and Cd-CdO template assisted Y2O3 coatings has been studied. The wettability of as-deposited Y2O3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y2O3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y2O3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y2O3 and thermally oxidized Y-Y2O3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y2O3 coatings, the surface roughness was improved by depositing a thin film of Y2O3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y2O3 (54 mJ/m2) and thermally oxidized Y-Y2O3 coatings (43 mJ/m2) compared to the Cd-CdO template assisted Y2O3 coating (7 mJ/m2). PMID:28348296

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.

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.

Packing the silica colloidal crystal beads: a facile route to superhydrophobic surfaces.

PubMed

Sun, Cheng; Gu, Zhong-Ze; Xu, Hua

2009-11-03

To mimic the structure of the lotus leaf, we present a facile route to prepare superhydrophobic surfaces by depositing nanoparticle clusters onto a solid surface. These clusters were fabricated via solidification of an emulsion droplet containing a nanoparticle in silicone oil. Thus, the microsized clusters and nanoparticles form dual-scale roughness structures. The surface is modified by fluoroalkylsilane and exhibits superhydrophobicity, with a contact angle greater than 165 degrees as well as a sliding angle less than 1 degrees . On the basis of size tuning of the nano/microstructures, various contact angles and sliding angles were investigated. Furthermore, the influence of micro/nanostructures on superhydrophobicity is discussed.

Fabrication of hierarchical polymer surfaces with superhydrophobicity by injection molding from nature and function-oriented design

NASA Astrophysics Data System (ADS)

Weng, Can; Wang, Fei; Zhou, Mingyong; Yang, Dongjiao; Jiang, Bingyan

2018-04-01

A comparison of processes and wettability characteristics was presented for injection molded superhydrophobic polypropylene surfaces from two fabricating strategies. One is the biomimetic replication of patterns from indocalamus leaf in nature. The contact angle of water sitting on this PP surface was measured as 152 ± 2°, with comparable wetting behavior to natural indocalamus leaf surface. The other strategy is the fabrication of superhydrophobic structure by combining methods that produce structures at different length scales. Regarding both the machinability of mold inserts and function-oriented design, three micro-quadrangular arrays and one hierarchical micro-nano cylinder array were designed with the goal of superhydrophobicity. Particularly, a simple approach to the fabrication of hierarchical structures was proposed by combining the anodized plate and the punching plate. The function-oriented design targets as superhydrophobicity were all reached for the designed four structures. The measured contact angles of droplet for these structures were almost consistent with the calculated equilibrium contact angles from thermodynamic analysis. Among them, the contact angle of droplet on the surface of designed hierarchical structure reached about 163° with the sliding angle of 5°, resulting in self-cleaning characteristic. The superhydrophobicity of function-oriented designed polymer surfaces could be modified and controlled, which is exactly the limitation of replicating from natural organisms.

Lattice Boltzmann simulation of immiscible displacement in the cavity with different channel configurations

NASA Astrophysics Data System (ADS)

Lou, Qin; Zang, Chenqiang; Yang, Mo; Xu, Hongtao

In this work, the immiscible displacement in a cavity with different channel configurations is studied using an improved pseudo-potential lattice Boltzmann equation (LBE) model. This model overcomes the drawback of the dependence of the fluid properties on the grid size, which exists in the original pseudo-potential LBE model. The approach is first validated by the Laplace law. Then, it is employed to study the immiscible displacement process. The influences of different factors, such as the surface wettability, the distance between the gas cavity and liquid cavity and the surface roughness of the channel are investigated. Numerical results show that the displacement efficiency increases and the displacement time decreases with the increase of the surface contact angle. On the other hand, the displacement efficiency increases with increasing distance between the gas cavity and the liquid cavity at first and finally reaches a constant value. As for the surface roughness, two structures (a semicircular cavity and a semicircular bulge) are studied. The comprehensive results show that although the displacement processes for both the structures depend on the surface wettability, they present quite different behaviors. Specially, for the roughness structure constituted by the semicircular cavity, the displacement efficiency decreases and displacement time increases evidently with the size of the semicircular cavity for the small contact angle. The trend slows down as the increase of the contact angle. Once the contact angle exceeds a certain value, the size of the semicircular cavity almost has no influence on the displacement process. While for the roughness structure of a semicircular bulge, the displacement efficiency increases with the size of bulge first and then it decreases for the small contact angle. The displacement efficiency increases first and finally reaches a constant for the large contact angle. The results also show that the displacement time has an extreme value in these cases for the small contact angles.

In situ measurement of contact angles and surface tensions of interfacial nanobubbles in ethanol aqueous solutions.

PubMed

Zhao, Binyu; Wang, Xingya; Wang, Shuo; Tai, Renzhong; Zhang, Lijuan; Hu, Jun

2016-04-14

The astonishing long lifetime and large contact angles of interfacial nanobubbles are still in hot debate despite numerous experimental and theoretical studies. One hypothesis to reconcile the two abnormalities of interfacial nanobubbles is that they have low surface tensions. However, few studies have been reported to measure the surface tensions of nanobubbles due to the lack of effective measurements. Herein, we investigate the in situ contact angles and surface tensions of individual interfacial nanobubbles immersed in different ethanol aqueous solutions using quantitative nanomechanical atomic force microscopy (AFM). The results showed that the contact angles of nanobubbles in the studied ethanol solutions were also much larger than the corresponding macroscopic counterparts on the same substrate, and they decreased with increasing ethanol concentrations. More significantly, the surface tensions calculated were much lower than those of the gas-liquid interfaces of the solutions at the macroscopic scale but have similar tendencies with increasing ethanol concentrations. Those results are expected to be helpful in further understanding the stability of interfacial nanobubbles in complex solutions.

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.

An energy-based equilibrium contact angle boundary condition on jagged surfaces for phase-field methods.

PubMed

Frank, Florian; Liu, Chen; Scanziani, Alessio; Alpak, Faruk O; Riviere, Beatrice

2018-08-01

We consider an energy-based boundary condition to impose an equilibrium wetting angle for the Cahn-Hilliard-Navier-Stokes phase-field model on voxel-set-type computational domains. These domains typically stem from μCT (micro computed tomography) imaging of porous rock and approximate a (on μm scale) smooth domain with a certain resolution. Planar surfaces that are perpendicular to the main axes are naturally approximated by a layer of voxels. However, planar surfaces in any other directions and curved surfaces yield a jagged/topologically rough surface approximation by voxels. For the standard Cahn-Hilliard formulation, where the contact angle between the diffuse interface and the domain boundary (fluid-solid interface/wall) is 90°, jagged surfaces have no impact on the contact angle. However, a prescribed contact angle smaller or larger than 90° on jagged voxel surfaces is amplified. As a remedy, we propose the introduction of surface energy correction factors for each fluid-solid voxel face that counterbalance the difference of the voxel-set surface area with the underlying smooth one. The discretization of the model equations is performed with the discontinuous Galerkin method. However, the presented semi-analytical approach of correcting the surface energy is equally applicable to other direct numerical methods such as finite elements, finite volumes, or finite differences, since the correction factors appear in the strong formulation of the model. Copyright © 2018 Elsevier Inc. All rights reserved.

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.

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.

Dynamic wetting and spreading and the role of topography.

PubMed

McHale, Glen; Newton, Michael I; Shirtcliffe, Neil J

2009-11-18

The spreading of a droplet of a liquid on a smooth solid surface is often described by the Hoffman-de Gennes law, which relates the edge speed, v(e), to the dynamic and equilibrium contact angles θ and θ(e) through [Formula: see text]. When the liquid wets the surface completely and the equilibrium contact angle vanishes, the edge speed is proportional to the cube of the dynamic contact angle. When the droplets are non-volatile this law gives rise to simple power laws with time for the contact angle and other parameters in both the capillary and gravity dominated regimes. On a textured surface, the equilibrium state of a droplet is strongly modified due to the amplification of the surface chemistry induced tendencies by the topography. The most common example is the conversion of hydrophobicity into superhydrophobicity. However, when the surface chemistry favors partial wetting, topography can result in a droplet spreading completely. A further, frequently overlooked consequence of topography is that the rate at which an out-of-equilibrium droplet spreads should also be modified. In this report, we review ideas related to the idea of topography induced wetting and consider how this may relate to dynamic wetting and the rate of droplet spreading. We consider the effect of the Wenzel and Cassie-Baxter equations on the driving forces and discuss how these may modify power laws for spreading. We relate the ideas to both the hydrodynamic viscous dissipation model and the molecular-kinetic theory of spreading. This suggests roughness and solid surface fraction modified Hoffman-de Gennes laws relating the edge speed to the dynamic and equilibrium contact angle. We also consider the spreading of small droplets and stripes of non-volatile liquids in the capillary regime and large droplets in the gravity regime. In the case of small non-volatile droplets spreading completely, a roughness modified Tanner's law giving the dependence of dynamic contact angle on time is presented. We review existing data for the spreading of small droplets of polydimethylsiloxane oil on surfaces decorated with micro-posts. On these surfaces, the initial droplet spreads with an approximately constant volume and the edge speed-dynamic contact angle relationship follows a power law [Formula: see text]. As the surface texture becomes stronger the exponent goes from p = 3 towards p = 1 in agreement with a Wenzel roughness driven spreading and a roughness modified Hoffman-de Gennes power law. Finally, we suggest that when a droplet spreads to a final partial wetting state on a rough surface, it approaches its Wenzel equilibrium contact angle in an exponential manner with a time constant dependent on roughness.

Characterization of the Intrinsic Water Wettability of Graphite Using Contact Angle Measurements: Effect of Defects on Static and Dynamic Contact Angles.

PubMed

Kozbial, Andrew; Trouba, Charlie; Liu, Haitao; Li, Lei

2017-01-31

Elucidating the intrinsic water wettability of the graphitic surface has increasingly attracted research interests, triggered by the recent finding that the well-established hydrophobicity of graphitic surfaces actually results from airborne hydrocarbon contamination. Currently, static water contact angle (WCA) is often used to characterize the intrinsic water wettability of graphitic surfaces. In the current paper, we show that because of the existence of defects, static WCA does not necessarily characterize the intrinsic water wettability. Freshly exfoliated graphite of varying qualities, characterized using atomic force microscopy and Raman spectroscopy, was studied using static, advancing, and receding WCA measurements. The results showed that graphite of different qualities (i.e., defect density) always has a similar advancing WCA, but it could have very different static and receding WCAs. This finding indicates that defects play an important role in contact angle measurements, and the static contact angle does not always represent the intrinsic water wettability of pristine graphite. On the basis of the experimental results, a qualitative model is proposed to explain the effect of defects on static, advancing, and receding contact angles. The model suggests that the advancing WCA reflects the intrinsic water wettability of pristine (defect-free) graphite. Our results showed that the advancing WCA for pristine graphite is 68.6°, which indicates that graphitic carbon is intrinsically mildly hydrophilic.

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.

Thermally Induced Silane Dehydrocoupling on Silicon Nanostructures (International ed.)

DTIC Science & Technology

2016-07-29

grafted. When performed on a mesopo- rous Si wafer, the perfluoro reagent yields a superhydrophobic surface (contact angle 1518). The bromo-derivative... superhydrophobic behavior, with a water contact angle of 1508 (Figure S13 and S14). As with the octadecylsilane derivative, these surface chemistries were not

Study on stair-step liquid triggered capillary valve for microfluidic systems

NASA Astrophysics Data System (ADS)

Zhang, Lei; Jones, Ben; Majeed, Bivragh; Nishiyama, Yukari; Okumura, Yasuaki; Stakenborg, Tim

2018-06-01

In lab-on-a-chip systems, various microfluidic technologies are being developed to handle fluids at very small quantities, e.g. in the scale of nano- or pico-liter. To achieve autonomous fluid handling at a low cost, passive fluidic control, based on the capillary force between the liquid and microchannel surface, is of the utmost interest in the microsystem. Valves are an essential component for flow control in many microfluidic systems, which enables a sequence of fluidic operations to be performed. In this paper, we present a new passive valve structure for a capillary driven microfluidic device. It is a variation of a capillary trigger valve that is amenable to silicon microfabrication; it will be referred to as a stair-step liquid triggered valve. In this paper, the valve functionality and its dependencies on channel geometry, surface contact angle, and surface roughness are studied both experimentally and with numerical modeling. The effect of the contact angle was explored in experiments on the silicon microfabricated valve structure; a maximal working contact angle, above which the valve fails to be triggered, was demonstrated. The fluidic behavior in the stair-step channel structure was further explored computationally using the finite volume method with the volume-of-fluid approach. Surface roughness due to scalloping of the sidewall during the Bosch etch process was hypothesized to reduce the sidewall contact angle. The reduced contact angle has considerable impacts on the capillary pressure as the liquid vapor interface traverses the stair-step structure of the valve. An improved match in the maximal working contact angle between the experiments and model was obtained when considering this surface roughness effect.

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

Nearly Perfect Durable Superhydrophobic Surfaces Fabricated by a Simple One-Step Plasma Treatment.

PubMed

Ryu, Jeongeun; Kim, Kiwoong; Park, JooYoung; Hwang, Bae Geun; Ko, YoungChul; Kim, HyunJoo; Han, JeongSu; Seo, EungRyeol; Park, YongJong; Lee, Sang Joon

2017-05-16

Fabrication of superhydrophobic surfaces is an area of great interest because it can be applicable to various engineering fields. A simple, safe and inexpensive fabrication process is required to fabricate applicable superhydrophobic surfaces. In this study, we developed a facile fabrication method of nearly perfect superhydrophobic surfaces through plasma treatment with argon and oxygen gases. A polytetrafluoroethylene (PTFE) sheet was selected as a substrate material. We optimized the fabrication parameters to produce superhydrophobic surfaces of superior performance using the Taguchi method. The contact angle of the pristine PTFE surface is approximately 111.0° ± 2.4°, with a sliding angle of 12.3° ± 6.4°. After the plasma treatment, nano-sized spherical tips, which looked like crown-structures, were created. This PTFE sheet exhibits the maximum contact angle of 178.9°, with a sliding angle less than 1°. As a result, this superhydrophobic surface requires a small external force to detach water droplets dripped on the surface. The contact angle of the fabricated superhydrophobic surface is almost retained, even after performing an air-aging test for 80 days and a droplet impacting test for 6 h. This fabrication method can provide superb superhydrophobic surface using simple one-step plasma etching.

Multicomponent Droplet Evaporation on Chemical Micro-Patterned Surfaces

PubMed Central

He, Minghao; Liao, Dong; Qiu, Huihe

2017-01-01

The evaporation and dynamics of a multicomponent droplet on a heated chemical patterned surface were presented. Comparing to the evaporation process of a multicomponent droplet on a homogenous surface, it is found that the chemical patterned surface can not only enhance evaporation by elongating the contact line, but also change the evaporation process from three regimes for the homogenous surface including constant contact line (CCL) regime, constant contact angle (CCA) regime and mix mode (MM) to two regimes, i.e. constant contact line (CCL) and moving contact line (MCL) regimes. The mechanism of contact line stepwise movement in MCL regimes in the microscopic range is investigated in detail. In addition, an improved local force model on the contact line was employed for analyzing the critical receding contact angles on homogenous and patterned surfaces. The analysis results agree well for both surfaces, and confirm that the transition from CCL to MCL regimes indicated droplet composition changes from multicomponent to monocomponent, providing an important metric to predict and control the dynamic behavior and composition of a multicomponent droplet using a patterned surface. PMID:28157229

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.

Eccentricity effect of micropatterned surface on contact angle.

PubMed

Kashaninejad, Navid; Chan, Weng Kong; Nguyen, Nam-Trung

2012-03-13

This article experimentally shows that the wetting property of a micropatterned surface is a function of the center-to-center offset distance between successive pillars in a column, referred to here as eccentricity. Studies were conducted on square micropatterns which were fabricated on a silicon wafer with pillar eccentricity ranging from 0 to 6 μm for two different pillar diameters and spacing. Measurement results of the static as well as the dynamic contact angles on these surfaces revealed that the contact angle decreases with increasing eccentricity and increasing relative spacing between the pillars. Furthermore, quantification of the contact angle hysteresis (CAH) shows that, for the case of lower pillar spacing, CAH could increase up to 41%, whereas for the case of higher pillar spacing, this increment was up to 35%, both corresponding to the maximum eccentricity of 6 μm. In general, the maximum obtainable hydrophobicity corresponds to micropillars with zero eccentricity. As the pillar relative spacing decreases, the effect of eccentricity on hydrophobicity becomes more pronounced. The dependence of the wettability conditions of the micropatterned surface on the pillar eccentricity is attributed to the contact line deformation resulting from the changed orientation of the pillars. This finding provides additional insights in design and fabrication of efficient micropatterned surfaces with controlled wetting properties.

Surface and capillary forces encountered by zinc sulfide microspheres in aqueous electrolyte.

PubMed

Gillies, Graeme; Kappl, Michael; Butt, Hans-Jürgen

2005-06-21

The colloid probe technique was used to investigate the interactions between individual zinc sulfide (ZnS) microspheres and an air bubble in electrolyte solution. Incorporation of zinc ions into the electrolyte solution overcomes the disproportionate zinc ion dissolution and mimics high-volume-fraction conditions common in flotation. Determined interaction forces revealed a distinct lack of long-ranged hydrophobic forces, indicated by the presence of a DLVO repulsion prior to particle engulfment. Single microsphere contact angles were determined from particle-bubble interactions. Contact angles increased with decreasing radii and with surface oxidation. Surface modification by the absorption of copper and subsequently potassium O-ethyldithiocarbonate (KED) reduced repulsive forces and strongly increased contact angles.

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.

An investigation of selected factors that influence hardwood wettability

Treesearch

Todd F. Shupe; Chung-Yun Hse; Wan H. Wang

2001-01-01

Wettability of sanded and non-sanded transverse and tangential sections of 22 southern hardwoods species was judged by measurement of contact angles using phenol formaldehyde resins. As expected, contact angle values on transverse sections were higher than those on tangential sections for both sanded and non-sanded surfaces. On sanded surfaces, hackberry had the...

The method of synthesizing of superhydrophobic surfaces by PECVD

NASA Astrophysics Data System (ADS)

Orazbayev, Sagi; Gabdullin, Maratbek; Ramazanov, Tlekkabul; Dosbolayev, Merlan; Zhunisbekov, Askar; Omirbekov, Dulat; Otarbay, Zhuldyz

2018-03-01

The aim of this work was to obtain superhydrophobic surfaces in a plasma medium. The experiment was carried out using the PECVD method in two different modes: constant and pulsing. The surface roughness was obtained by applying nanoparticles synthesized in plasma in a mixture of argon and methane. The resulting particles were deposited on the surface of silicon and glass materials. The contact angle increased linearly depending on the number of cycles, until it reached 160° at 150-160th cycles, after that the increase in cycles does not affect the contact angle, since the saturation process is in progress. Also the effect of the working gas composition on the hydrophobicity of the surface was studied. At low concentrations of methane (1%) only particles are synthesized in the working gas, and hydrophobicity is unstable, with an increase in methane concentration (7%) nanofilms are synthesized from nanoclusters, and surface hydrophobicity is relatively stable. In addition, a pulsing plasma mode was used to obtain superhydrophobic surfaces. The hydrophobicity of the sample showed that the strength of the nanofilm was stable in comparison with the sample obtained in the first mode, but the contact angle was lower. The obtained samples were examined using SEM, SPM, optical analysis, and their contact angles were determined.

Surface fluorination of zirconia: adhesive bond strength comparison to commercial primers.

PubMed

Piascik, Jeffrey R; Swift, Edward J; Braswell, Krista; Stoner, Brian R

2012-06-01

This study evaluated contact angle and shear bond strength of three commercial zirconia primers and compared them to a recently developed fluorination pre-treatment. Earlier investigations reported that plasma fluorinated zirconia modifies the chemical bonding structure creating a more reactive surface. Yttria-stabilized zirconia (LAVA, 3M ESPE) plates were highly polished using 3μm diamond paste (R(a) ∼200nm) prior to pretreatments. After primer and fluorination treatment, contact angles were measured to quantify surface hydrophobicity before and after ethanol clean. Additionally, simple shear bond tests were performed to measure the adhesion strength to a composite resin. Plasma fluorination produced the lowest contact angle (7.8°) and the highest shear bond strength (37.3MPa) suggesting this pretreatment facilitates a more "chemically" active surface for adhesive bonding. It is hypothesized that plasma fluorination increase hydroxylation at the surface, making it more reactive, thus allowing for covalent bonding between zirconia surface and resin cement. A strong correlation was observed between contact angle and adhesion strength for all specimens; a relationship which may help understand the frequency and modes of failures, clinically. It is also believed that this surface treatment can increase long-term viability of zirconia restorations over other adhesive techniques. Copyright © 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Superhydrophilicity of a nanofiber-covered aluminum surface fabricated via pyrophosphoric acid anodizing

NASA Astrophysics Data System (ADS)

Nakajima, Daiki; Kikuchi, Tatsuya; Natsui, Shungo; Suzuki, Ryosuke O.

2016-12-01

A superhydrophilic aluminum surface covered by numerous alumina nanofibers was fabricated via pyrophosphoric acid anodizing. High-density anodic alumina nanofibers grow on the bottom of a honeycomb oxide via anodizing in concentrated pyrophosphoric acid. The water contact angle on the nanofiber-covered aluminum surface decreased with time after a 4 μL droplet was placed on the surface, and a superhydrophilic behavior with a contact angle measuring 2.2° was observed within 2 s; this contact angle is considerably lower than those observed for electropolished and porous alumina-covered aluminum surfaces. There was no dependence of the superhydrophilicity on the density of alumina nanofibers fabricated via different constant voltage anodizing conditions. The superhydrophilic property of the surface covered by anodic alumina nanofibers was maintained during an exposure test for 359 h. The quick-drying and snow-sliding behaviors of the superhydrophilic aluminum covered with anodic alumina nanofibers were demonstrated.

Wetting characteristic of ceramic to water and adhesive resin.

PubMed

Oh, Won-Suck; Shen, Chiayi; Alegre, Brandon; Anusavice, Kenneth J

2002-12-01

Maximum wetting of ceramic by adhesive resin is required to achieve optimal adhesion of the resin to ceramic. It is unknown whether the adhesion of the resin to the ceramic is affected by the surface topography and wetting by water or the adhesive resin. This study was designed to characterize the effect of surface topography on the wetting of ceramics by water and adhesive resin. Three materials, a veneering ceramic, Eris (ERV), and 2 core ceramics, Empress 1 core ceramic (E1C) and an experimental core ceramic (EXC), were used. Four surface-roughening procedures were used. They included polishing through 1200-grit SiC paper (P), air abrasion with 50 microm Al(2)O(3) (A), etching with 5% hydrofluoric acid gel (E), and a combination of airborne particle abrasion and etching (A/E). Forty bar specimens (15 x 10 x 1.5 mm) were prepared from each material (N=120). Twelve groups of 10 specimens each were prepared for the 4 surface-roughening procedures. Advancing (theta(A)) and receding (theta(R)) contact angles were measured with a CAHN Dynamic Contact Analyzer, on the basis of the Wilhelmy plate technique, with water and adhesive resin. The work of adhesion (W(A)) by the probing media was calculated by use of advancing contact angle data. The data were analyzed by t testing, analysis of variance, and Duncan's tests (alpha=0.05) to determine the statistical significance of differences in the contact angles between ceramic and water or resin as a function of surface roughening. In general, the mean theta(A) values were higher than the mean theta(R) values except for groups of E or A/E specimens with water used as a probing medium. E and A/E treatments yielded the lowest contact angle values, followed by A and P treatments (P<.001). The E1C exhibited the highest mean contact angles, whereas EXC exhibited the lowest mean contact angle except for the theta(R) with resin. The corresponding values for ERV were between those of E1C and EXC except for theta(R) values with resin. The resin medium yielded higher mean contact angles than the water medium for the same surfaces. W(A) ranged from 62.9 to 145.2 mJ/m(2). Within the limitations of this study, etching or a combination of air abrasion and etching were comparably effective in increasing the surface area for bonding. The most wettable surface as measured by the resin medium was EXC, followed by ERV and E1C.

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.

Incorporating contact angles in the surface tension force with the ACES interface curvature scheme

NASA Astrophysics Data System (ADS)

Owkes, Mark

2017-11-01

In simulations of gas-liquid flows interacting with solid boundaries, the contact line dynamics effect the interface motion and flow field through the surface tension force. The surface tension force is directly proportional to the interface curvature and the problem of accurately imposing a contact angle must be incorporated into the interface curvature calculation. Many commonly used algorithms to compute interface curvatures (e.g., height function method) require extrapolating the interface, with defined contact angle, into the solid to allow for the calculation of a curvature near a wall. Extrapolating can be an ill-posed problem, especially in three-dimensions or when multiple contact lines are near each other. We have developed an accurate methodology to compute interface curvatures that allows for contact angles to be easily incorporated while avoiding extrapolation and the associated challenges. The method, known as Adjustable Curvature Evaluation Scale (ACES), leverages a least squares fit of a polynomial to points computed on the volume-of-fluid (VOF) representation of the gas-liquid interface. The method is tested by simulating canonical test cases and then applied to simulate the injection and motion of water droplets in a channel (relevant to PEM fuel cells).

Effect of airborne contaminants on the wettability of supported graphene and graphite

NASA Astrophysics Data System (ADS)

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P.; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

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.

Effect of airborne contaminants on the wettability of supported graphene and graphite.

PubMed

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

Controlled growth of standing Ag nanorod arrays on bare Si substrate using glancing angle deposition for self-cleaning applications

NASA Astrophysics Data System (ADS)

Singh, Dhruv P.; Singh, J. P.

2014-03-01

A facile approach to manipulate the hydrophobicity of surface by controlled growth of standing Ag nanorod arrays is presented. Instead of following the complicated conventional method of the template-assisted growth, the morphology or particularly average diameter and number density (nanorods cm-2) of nanorods were controlled on bare Si substrate by simply varying the deposition rate during glancing angle deposition. The contact angle measurements showed that the evolution of Ag nanorods reduces the surface energy and makes an increment in the apparent water contact angle compared to the plain Ag thin film. The contact angle was found to increase for the Ag nanorod samples grown at lower deposition rates. Interestingly, the morphology of the nanorod arrays grown at very low deposition rate (1.2 Å sec-1) results in a self-cleaning superhydrophobic surface of contact angle about 157° and a small roll-off angle about 5°. The observed improvement in hydrophobicity with change in the morphology of nanorod arrays is explained as the effect of reduction in solid fraction within the framework of Cassie-Baxter model. These self-cleaning Ag nanorod arrays could have a significant impact in wide range of applications such as anti-icing coatings, sensors and solar panels.

Superhydrophobicity of hierarchical nanostructure of candle soot films

NASA Astrophysics Data System (ADS)

Hankhuntond, A.; Singjai, P.; Sakulsermsuk, S.

2017-09-01

Candle soot containing carbon nanoparticles can form hierarchical structure films. We prepared soot films by using glass slides blocking candle flame in the middle of the flame. The hierarchical nanostructures of the carbon nanoparticles films were confirmed by scanning electron microscopy and transmission electron microscopy. Carbon nanoparticle size was 49.2 ± 9.0 nm from SEM, which agrees to 37.9 ± 8.5 nm from TEM. The contact angles of water droplets on these films are more than 150°, indicating superhydrophobic surface. Decrease contact angles of water droplets were observed with an increase deposition time. The decrease of contact angle was saturated at about 150° when the deposition time reaches 180 s. Cassie-Baxter state was attributed to describe superhydrophobicity of carbon nanoparticles films because the hierarchical nanostructures of the surface provide a large fraction of hollows on the surface. We proposed that the contact angle dependence on deposition time was governed by the increase of the distance between nanopillars in carbon nanoparticles films.

From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

PubMed Central

Kanduč, Matej; Netz, Roland R.

2015-01-01

Using all-atom molecular dynamics (MD) simulations at constant water chemical potential in combination with basic theoretical arguments, we study hydration-induced interactions between two overall charge-neutral yet polar planar surfaces with different wetting properties. Whether the water film between the two surfaces becomes unstable below a threshold separation and cavitation gives rise to long-range attraction, depends on the sum of the two individual surface contact angles. Consequently, cavitation-induced attraction also occurs for a mildly hydrophilic surface interacting with a very hydrophobic surface. If both surfaces are very hydrophilic, hydration repulsion dominates at small separations and direct attractive force contribution can—if strong enough—give rise to wet adhesion in this case. In between the regimes of cavitation-induced attraction and hydration repulsion we find a narrow range of contact angle combinations where the surfaces adhere at contact in the absence of cavitation. This dry adhesion regime is driven by direct surface–surface interactions. We derive simple laws for the cavitation transition as well as for the transition between hydration repulsion and dry adhesion, which favorably compare with simulation results in a generic adhesion state diagram as a function of the two surface contact angles. PMID:26392526

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.

A low-cost, high-efficiency and high-flexibility surface modification technology for a black bisphenol A polycarbonate board

NASA Astrophysics Data System (ADS)

Wang, Suhuan; Liu, Jianguo; Lv, Ming; Zeng, Xiaoyan

2014-09-01

In this paper, a low-cost, high-efficiency and high-flexibility surface modification technology for polymer materials was achieved at high laser scanning speeds (600-1000 mm s-1) and using an all-solid state, Q-switched, high-average power, and nanosecond pulse ultraviolet (355 nm wavelength) laser. During the surface modification of a very important engineering plastic, i.e., black bisphenol A polycarbonate (BAPC) board, it was found that different laser parameters (e.g., laser fluence and pulse frequency) were able to result in different surface microstructures (e.g., many tiny protuberances or a porous microstructure with periodical V-type grooves). After the modification, although the total relative content of the oxygen-containing groups (e.g., Csbnd O and COO-) on the BAPC surface increased, however, the special microstructures played a deciding role in the surface properties (e.g., contact angle and surface energy) of the BAPC. The change trend of the water contact angle on the BAPC surface was with an obvious increase, that of the diiodomethane contact angle was with a most decrease, and that of the ethylene glycol contact angle was between the above two. It showed that the wetting properties of the three liquids on the modified BAPC surface were different. Basing on the measurements of the contact angles of the three liquids, and according to the Young equation and the Lifshitz van der Waals and Lewis acid-base theory, the BAPC surface energy after the modification was calculated. The results were that, in a broad range of laser fluences, pulse frequencies and scanning speeds, the surface energy had a significant increase (e.g., from the original of about 44 mJ m-2 to the maximum of about 70 mJ m-2), and the higher the laser pulse frequency, the more significant the increase. This would be very advantageous to fabricate the high-quality micro-devices and micro-systems on the modified surface.

An oilspill trajectory analysis model with a variable wind deflection angle

USGS Publications Warehouse

Samuels, W.B.; Huang, N.E.; Amstutz, D.E.

1982-01-01

The oilspill trajectory movement algorithm consists of a vector sum of the surface drift component due to wind and the surface current component. In the U.S. Geological Survey oilspill trajectory analysis model, the surface drift component is assumed to be 3.5% of the wind speed and is rotated 20 degrees clockwise to account for Coriolis effects in the Northern Hemisphere. Field and laboratory data suggest, however, that the deflection angle of the surface drift current can be highly variable. An empirical formula, based on field observations and theoretical arguments relating wind speed to deflection angle, was used to calculate a new deflection angle at each time step in the model. Comparisons of oilspill contact probabilities to coastal areas calculated for constant and variable deflection angles showed that the model is insensitive to this changing angle at low wind speeds. At high wind speeds, some statistically significant differences in contact probabilities did appear. ?? 1982.

Fabrication and icing property of superhydrophilic and superhydrophobic aluminum surfaces derived from anodizing aluminum foil in a sodium chloride aqueous solution

NASA Astrophysics Data System (ADS)

Song, Meirong; Liu, Yuru; Cui, Shumin; Liu, Long; Yang, Min

2013-10-01

An aluminum foil with a rough surface was first prepared by anodic treatment in a neutral aqueous solution with the help of pitting corrosion of chlorides. First, the hydrophobic Al surface (contact angle around 79°) became superhydrophilic (contact angle smaller than 5°) after the anodizing process. Secondly, the superhydrophilic Al surface became superhydrophobic (contact angle larger than 150°) after being modified by oleic acid. Finally, the icing property of superhydrophilic, untreated, and superhydrophobic Al foils were investigated in a refrigerated cabinet at -12 °C. The mean total times to freeze a water droplet (6 μL) on the three foils were 17 s, 158 s and 1604 s, respectively. Thus, the superhydrophilic surface accelerates the icing process, while the superhydrophobic surface delays the process. The main reason for this transition might mainly result from the difference of the contact area of the water droplet with Al substrate: the increase in contact area with Al substrate will accelerate the heat conduct process, as well as the icing process; the decrease in contact area with Al substrate will delay the heat conduct process, as well as the icing process. Compared to the untreated Al foil, the contact area of the water droplet with the Al substrate was higher on superhydrophilic surface and smaller on the superhydrophobic surface, which led to the difference of the heat transfer time as well as the icing time.

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

Spray-deposition and photopolymerization of organic-inorganic thiol-ene resins for fabrication of superamphiphobic surfaces.

PubMed

Xiong, Li; Kendrick, Laken L; Heusser, Hannele; Webb, Jamie C; Sparks, Bradley J; Goetz, James T; Guo, Wei; Stafford, Christopher M; Blanton, Michael D; Nazarenko, Sergei; Patton, Derek L

2014-07-09

Superamphiphobic surfaces, exhibiting high contact angles and low contact angle hysteresis to both water and low surface tension liquids, have attracted a great deal attention in recent years because of the potential of these materials in practical applications such as liquid-resistant textiles, self-cleaning surfaces, and antifouling/anticorrosion coatings. In this work, we present a simple strategy for fabricating of superamphiphobic coatings based on photopolymerization of hybrid thiol-ene resins. Spray-deposition and UV photopolymerization of thiol-ene resins containing hydrophobic silica nanoparticles and perfluorinated thiols provide a multiscale topography and low-energy surface that endows the surface with superamphiphobicity. The wettability and chemical composition of the surfaces were characterized by contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The hierarchical roughness features of the thiol-ene surfaces were investigated with field-emission scanning electron microscopy. Droplet impact and sandpaper abrasion tests indicate the coatings respectively possess a robust antiwetting behavior and good mechanical durability.

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.

Formation and composition of adsorbates on hydrophobic carbon surfaces from aqueous laccase-maltodextrin mixture suspension

NASA Astrophysics Data System (ADS)

Corrales Ureña, Yendry Regina; Lisboa-Filho, Paulo Noronha; Szardenings, Michael; Gätjen, Linda; Noeske, Paul-Ludwig Michael; Rischka, Klaus

2016-11-01

A robust procedure for the surface bio-functionalization of carbon surfaces was developed. It consists on the modification of carbon materials in contact with an aqueous suspension of the enzyme laccase from Trametes versicolor and the lyophilization agent maltodextrin, with the pH value adjusted close to the isoelectric point of the enzyme. We report in-situ investigations applying Quartz Crystal Microbalance with Dissipation (QCM-D) for carbon-coated sensor surfaces and, moreover, ex-situ measurements with static contact angle measurements, X-ray Photoelectron Spectroscopy (XPS) and Scanning Force Microscopy (SFM) for smooth Highly Oriented Pyrolytic Graphite (HOPG) substrates, for contact times between the enzyme formulation and the carbon material surface ranging from 20 s to 24 h. QCM-D studies reveals the formation of rigid layer of biomaterial, a few nanometers thin, which shows a strongly improved wettability of the substrate surface upon contact angle measurements. Following spectroscopic characterization, these layers are composed of mixtures of laccase and maltodextrin. The formation of these adsorbates is attributed to attractive interactions between laccase, the maltodextrin-based lyophilization agent and the hydrophobic carbon surfaces; a short-term contact between the aqueous laccase mixture suspension and HOPG surfaces is shown to merely result in de-wetting patterns influencing the results of contact angle measurements. The new enzyme-based surface modification of carbon-based materials is suggested to be applicable for the improvement of not only the wettability of low energy substrate surfaces with fluid formulations like coatings or adhesives, but also their adhesion in contact with hardened polymers.

Stability of Atmospheric-Pressure Plasma Induced Changes on Polycarbonate Surfaces

NASA Technical Reports Server (NTRS)

Sharma, Rajesh; Holcomb, Edward; Trigwell, Steve

2006-01-01

Polycarbonate films are subjected to plasma treatment in a number of applications such as improving adhesion between polycarbonate and silicon alloy in protective and optical coatings. The changes in surface chemistry due to plasma treatment have tendency to revert back. Thus stability of the plasma induced changes on polymer surfaces over desired time period is very important. The objective of this study was to examine the effect of ageing on atmospheric pressure helium-plasma treated polycarbonate (PC) sample as a function of treatment time. The ageing effects were studied over a period of 10 days. The samples were plasma treated for 0.5, 2, 5 and 10 minutes. Contact angle measurements were made to study surface energy changes. Modification of surface chemical structure was examined using, X-ray Photoelectron Spectroscopy (XPS). Contact angle measurements on untreated and plasma treated surfaces were made immediately, 24, 48, 72 and 96 hrs after treatment. Contact angle decreased from 93 deg for untreated sample to 30 deg for sample plasma treated for 10 minutes. After 10 days the contact angles for the 10 minute plasma treated sample increased to 67 deg, but it never reverted back to that of untreated surface. Similarly the O/C ratio increased from 0.136 for untreated sample to 0.321 for 10 minute plasma treated sample indication increase in surface energy.

Method of drying passivated micromachines by dewetting from a liquid-based process

DOEpatents

Houston, Michael R.; Howe, Roger T.; Maboudian, Roya; Srinivasan, Uthara

2000-01-01

A method of fabricating a micromachine includes the step of constructing a low surface energy film on the micromachine. The micromachine is then rinsed with a rinse liquid that has a high surface energy, relative to the low surface energy film, to produce a contact angle of greater than 90.degree. between the low surface energy film and the rinse liquid. This relatively large contact angle causes any rinse liquid on the micromachine to be displaced from the micromachine when the micromachine is removed from the rinse liquid. In other words, the micromachine is dried by dewetting from a liquid-based process. Thus, a separate evaporative drying step is not required, as the micromachine is removed from the liquid-based process in a dry state. The relatively large contact angle also operates to prevent attractive capillary forces between micromachine components, thereby preventing contact and adhesion between adjacent microstructure surfaces. The low surface energy film may be constructed with a fluorinated self-assembled monolayer film. The processing of the invention avoids the use of environmentally harmful, health-hazardous chemicals.

Wettability control of droplet deposition and detachment.

PubMed

Baret, Jean-Christophe; Brinkmann, Martin

2006-04-14

The conditions for droplet deposition on plane substrates are studied using electrowetting to continuously modulate the surface wettability. Droplets of controlled volume attached to the tip of a pipette are brought into contact with the surface. During retraction of the pipette the droplets are deposited or detach completely depending on volume and contact angle. The experimental limit of deposition in the contact angle or volume plane is in good agreement with analytical and numerical predictions obtained within the capillary model.

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.

Method for laser welding a fin and a tube

DOEpatents

Fuerschbach, Phillip W.; Mahoney, A. Roderick; Milewski, John O

2001-01-01

A method of laser welding a planar metal surface to a cylindrical metal surface is provided, first placing a planar metal surface into approximate contact with a cylindrical metal surface to form a juncture area to be welded, the planar metal surface and cylindrical metal surface thereby forming an acute angle of contact. A laser beam, produced, for example, by a Nd:YAG pulsed laser, is focused through the acute angle of contact at the juncture area to be welded, with the laser beam heating the juncture area to a welding temperature to cause welding to occur between the planar metal surface and the cylindrical metal surface. Both the planar metal surface and cylindrical metal surface are made from a reflective metal, including copper, copper alloys, stainless steel alloys, aluminum, and aluminum alloys.

Effect of Surface Oxidation on Interfacial Water Structure at a Pyrite (100) Surface as Studied by Molecular Dynamics Simulation

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

Jin, Jiaqi; Miller, Jan D.; Dang, Liem X.

2015-06-01

In the first part of this paper, a Scanning Electron Microscopy and contact angle study of a pyrite surface (100) is reported describing the relationship between surface oxidation and the hydrophilic surface state. In addition to these experimental results, the following simulated surface states were examined using Molecular Dynamics Simulation (MDS): fresh unoxidized (100) surface; polysulfide at the (100) surface; elemental sulfur at the (100) surface. Crystal structures for the polysulfide and elemental sulfur at the (100) surface were simulated using Density Functional Theory (DFT) quantum chemical calculations. The well known oxidation mechanism which involves formation of a metal deficientmore » layer was also described with DFT. Our MDS results of the behavior of interfacial water at the fresh and oxidized pyrite (100) surfaces without/with the presence of ferric hydroxide include simulated contact angles, number density distribution for water, water dipole orientation, water residence time, and hydrogen-bonding considerations. The significance of the formation of ferric hydroxide islands in accounting for the corresponding hydrophilic surface state is revealed not only from experimental contact angle measurements but also from simulated contact angle measurements using MDS. The hydrophilic surface state developed at oxidized pyrite surfaces has been described by MDS, on which basis the surface state is explained based on interfacial water structure. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the DOE funded work performed by Liem X. Dang. Battelle operates the Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.« less

Determination of contact angle from the maximum height of enlarged drops on solid surfaces

NASA Astrophysics Data System (ADS)

Behroozi, F.

2012-04-01

Measurement of the liquid/solid contact angle provides useful information on the wetting properties of fluids. In 1870, the German physicist Georg Hermann Quincke (1834-1924) published the functional relation between the maximum height of an enlarged drop and its contact angle. Quincke's relation offered an alternative to the direct measurement of contact angle, which in practice suffers from several experimental uncertainties. In this paper, we review Quincke's original derivation and show that it is based on a hidden assumption. We then present a new derivation that exposes this assumption and clarifies the conditions under which Quincke's relation is valid. To explore Quincke's relation experimentally, we measure the maximum height of enlarged water drops on several substrates and calculate the contact angle in each case. Our results are in good agreement with contact angles measured directly from droplet images.

Wetting of nanophases: Nanobubbles, nanodroplets and micropancakes on hydrophobic surfaces.

PubMed

An, Hongjie; Liu, Guangming; Craig, Vincent S J

2015-08-01

The observation by Atomic Force Microscopy of a range of nanophases on hydrophobic surfaces poses some challenging questions, not only related to the stability of these objects but also regarding their wetting properties. Spherical capped nanobubbles are observed to exhibit contact angles that far exceed the macroscopic contact angle measured for the same materials, whereas nanodroplets exhibit contact angles that are much the same as the macroscopic contact angle. Micropancakes are reported to consist of gas, in which case their wetting properties are mysterious. They should only be stable when the van der Waals forces act to thicken the film whereas for a gas, the van der Waals forces will always act to thin the film. Here we examine the available evidence and contribute some additional experiments in order to review our understanding of the wetting properties of these nanophases. We demonstrate that if in fact micropancakes consist of a contaminant their wetting properties can be explained, though the very high contact angles of nanobubbles remain unexplained. Copyright © 2014 Elsevier B.V. All rights reserved.

Dependency of the apparent contact angle on nonisothermal conditions

NASA Astrophysics Data System (ADS)

Krahl, Rolf; Gerstmann, Jens; Behruzi, Philipp; Bänsch, Eberhard; Dreyer, Michael E.

2008-04-01

The dynamic behavior of liquids in partly filled containers is influenced to a large extend by the angle between the gas-liquid phase boundary and the solid container wall at the contact line. This contact angle in turn is influenced by nonisothermal conditions. In the case of a cold liquid meniscus spreading over a hot solid wall, the contact angle apparently becomes significantly larger. In this paper we want to establish a quantitative equation for this enlargement, both from experimental and numerical data. Our findings can be used to build a subgrid model for computations, where the resolution is not sufficient to resolve the boundary layers. This might be the case for large containers which are exposed to low accelerations and where the contact angle boundary condition determines the position of the free surface. These types of computation are performed, for example, to solve propellant management problems in launcher and satellite tanks. In this application, the knowledge of the position of the free surface is very important for the withdrawal of liquid and the calculation of heat and mass transfer.

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.

Evaporation dynamics of a sessile droplet on glass surfaces with fluoropolymer coatings: focusing on the final stage of thin droplet evaporation.

PubMed

Gatapova, Elizaveta Ya; Shonina, Anna M; Safonov, Alexey I; Sulyaeva, Veronica S; Kabov, Oleg A

2018-03-07

The evaporation dynamics of a water droplet with an initial volume of 2 μl from glass surfaces with fluoropolymer coatings are investigated using the shadow technique and an optical microscope. The droplet profile for a contact angle of less than 5° is constructed using an image-analyzing interference technique, and evaporation dynamics are investigated at the final stage. We coated the glass slides with a thin film of a fluoropolymer by the hot-wire chemical vapor deposition method at different deposition modes depending on the deposition pressure and the temperature of the activating wire. The resulting surfaces have different structures affecting the wetting properties. Droplet evaporation from a constant contact radius mode in the early stage of evaporation was found followed by the mode where both contact angle and contact radius simultaneously vary in time (final stage) regardless of wettability of the coated surfaces. We found that depinning occurs at small contact angles of 2.2-4.7° for all samples, which are smaller than the measured receding contact angles. This is explained by imbibition of the liquid into the developed surface of the "soft" coating that leads to formation of thin droplets completely wetting the surface. The final stage, which is little discussed in the literature, is also recorded. We have singled out a substage where the contact line velocity is abruptly increasing for all coated and uncoated surfaces. The critical droplet height corresponding to the transition to this substage is about 2 μm with R/h = 107. The duration of this substage is the same for all coated and uncoated surfaces. Droplets observed at this substage for all the tested surfaces are axisymmetric. The specific evaporation rate clearly demonstrates an abrupt increase at the final substage of the droplet evaporation. The classical R 2 law is justified for the complete wetting situation where the droplet is disappearing in an axisymmetric manner.

Correlation between surface properties and wettability of multi-scale structured biocompatible surfaces

NASA Astrophysics Data System (ADS)

Gorodzha, S. N.; Surmeneva, M. A.; Prymak, O.; Wittmar, A.; Ulbricht, M.; Epple, M.; Teresov, A.; Koval, N.; Surmenev, R. A.

2015-11-01

The influence of surface properties of radio-frequency (RF) magnetron deposited hydroxyapatite (HA) and Si-containing HA coatings on wettability was studied. The composition and morphology of the coatings fabricated on titanium (Ti) were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The surface wettability was studied using contact angle analysis. Different geometric parameters of acid-etched (AE) and pulse electron beam (PEB)-treated Ti substrates and silicate content in the HA films resulted in the different morphology of the coatings at micro- and nano- length scales. Water contact angles for the HA coated Ti samples were evaluated as a combined effect of micro roughness of the substrate and nano-roughness of the HA films resulting in higher water contact angles compared with acid-etched (AE) or pulse electron beam (PEB) treated Ti substrates.

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.

Wetting, adhesion and friction of superhydrophobic and hydrophilic leaves and fabricated micro/nanopatterned surfaces

NASA Astrophysics Data System (ADS)

Bhushan, Bharat; Jung, Yong Chae

2008-06-01

Superhydrophobic surfaces have considerable technological potential for various applications due to their extreme water-repellent properties. When two hydrophilic bodies are brought into contact, any liquid present at the interface forms menisci, which increases adhesion/friction and the magnitude is dependent upon the contact angle. Certain plant leaves are known to be superhydrophobic in nature due to their roughness and the presence of a thin wax film on the leaf surface. Various leaf surfaces on the microscale and nanoscale have been characterized in order to separate out the effects of the microbumps and nanobumps and the wax on the hydrophobicity. The next logical step in realizing superhydrophobic surfaces that can be produced is to design surfaces based on understanding of the leaves. The effect of micropatterning and nanopatterning on the hydrophobicity was investigated for two different polymers with micropatterns and nanopatterns. Scale dependence on adhesion was also studied using atomic force microscope tips of various radii. Studies on silicon surfaces patterned with pillars of varying diameter, height and pitch values and deposited with a hydrophobic coating were performed to demonstrate how the contact angles vary with the pitch. The effect of droplet size on contact angle was studied by droplet evaporation and a transition criterion was developed to predict when air pockets cease to exist. Finally, an environmental scanning electron microscope study on the effect of droplet size of about 20 µm radius on the contact angle of patterned surfaces is presented. The importance of hierarchical roughness structure on destabilization of air pockets is discussed.

Effect of plasma treatment (He/CH4) on glass surface for the reduction of powder flux adhesion in the spray drying process

NASA Astrophysics Data System (ADS)

Ramlan, Nadiah; Zamri, Nazirah Wahidah Mohd; Maskat, Mohd Yusof; Hoong, Chin Oi; Theng, Lau Yen; Zubairi, Saiful Irwan

2018-04-01

A 50Hz glow discharge He/CH4 plasma was generated and applied for the modification of glass surface to reduce powder adhesion on the wall of spray dryer. The hydrophobicity of the glass samples determined by the water droplet contact angle and adhesion weight on glass, dependent on the CH4 flow rate and plasma exposure time. There was a peak that appeared at 1470 cm-1 on the surface of treated glass indicating the presence of CH3 groups from ATR-FTIR data. Surface morphology analysis using scanning electron microscopy (SEM) showed changes of roughness in the surface-treated glass. The presence of alkyl group (CH3) that deposited on the glass surface is one of the factors that contribute to the increase in the surface roughness. The surface roughness will reflect the value of contact angle where hydrophobic surface are rougher compared to hydrophilic surface. The plasma treatment could enhance the value of the contact angle and thus reduced the adhesion on the spray dryer glass surface.

Closer look at the effect of AFM imaging conditions on the apparent dimensions of surface nanobubbles.

PubMed

Walczyk, Wiktoria; Schönherr, Holger

2013-01-15

To date, TM AFM (tapping mode or intermittent contact mode atomic force microscopy) is the most frequently applied direct imaging technique to visualize surface nanobubbles at the solid-aqueous interface. On one hand, AFM is the only profilometric technique that provides estimates of the bubbles' nanoscopic dimensions. On the other hand, the nanoscopic contact angles of surface nanobubbles estimated from their apparent dimensions that are deduced from AFM "height" images of nanobubbles differ markedly from the macrocopic water contact angles on the identical substrates. Here we show in detail how the apparent bubble height and width of surface nanobubbles on highly oriented pyrolytic graphite (HOPG) depend on the free amplitude of the cantilever oscillations and the amplitude setpoint ratio. (The role of these two AFM imaging parameters and their interdependence has not been studied so far for nanobubbles in a systematic way.) In all experiments, even with optimal scanning parameters, nanobubbles at the HOPG-water interface appeared to be smaller in the AFM images than their true size, which was estimated using a method presented herein. It was also observed that the severity of the underestimate increased with increasing bubble height and radius of curvature. The nanoscopic contact angle of >130° for nanobubbles on HOPG extrapolated to zero interaction force was only slightly overestimated and hence significantly higher than the macroscopic contact angle of water on HOPG (63 ± 2°). Thus, the widely reported contact angle discrepancy cannot be solely attributed to inappropriate AFM imaging conditions.

Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior.

PubMed

Harikrishnan, A R; Dhar, Purbarun; Agnihotri, Prabhat K; Gedupudi, Sateesh; Das, Sarit Kumar

2017-06-22

Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations.

Contact Angle and Adhesion Dynamics and Hysteresis on Molecularly Smooth Chemically Homogeneous Surfaces.

PubMed

Chen, Szu-Ying; Kaufman, Yair; Schrader, Alex M; Seo, Dongjin; Lee, Dong Woog; Page, Steven H; Koenig, Peter H; Isaacs, Sandra; Gizaw, Yonas; Israelachvili, Jacob N

2017-09-26

Measuring truly equilibrium adhesion energies or contact angles to obtain the thermodynamic values is experimentally difficult because it requires loading/unloading or advancing/receding boundaries to be measured at rates that can be slower than 1 nm/s. We have measured advancing-receding contact angles and loading-unloading adhesion energies for various systems and geometries involving molecularly smooth and chemically homogeneous surfaces moving at different but steady velocities in both directions, ±V, focusing on the thermodynamic limit of ±V → 0. We have used the Bell Theory (1978) to derive expressions for the dynamic (velocity-dependent) adhesion energies and contact angles suitable for both (i) dynamic adhesion measurements using the classic Johnson-Kendall-Roberts (JKR, 1971) theory of "contact mechanics" and (ii) dynamic contact angle hysteresis measurements of both rolling droplets and syringe-controlled (sessile) droplets on various surfaces. We present our results for systems that exhibited both steady and varying velocities from V ≈ 10 mm/s to 1 nm/s, where in all cases but one, the advancing (V > 0) and receding (V < 0) adhesion energies and/or contact angles converged toward the same theoretical (thermodynamic) values as V → 0. Our equations for the dynamic contact angles are similar to the classic equations of Blake & Haynes (1969) and fitted the experimental adhesion data equally well over the range of velocities studied, although with somewhat different fitting parameters for the characteristic molecular length/dimension or area and characteristic bond formation/rupture lifetime or velocity. Our theoretical and experimental methods and results unify previous kinetic theories of adhesion and contact angle hysteresis and offer new experimental methods for testing kinetic models in the thermodynamic, quasi-static, limit. Our analyses are limited to kinetic effects only, and we conclude that hydrodynamic, i.e., viscous, and inertial effects do not play a role at the interfacial velocities of our experiments, i.e., V < (1-10) mm/s (for water and hexadecane, but for viscous polymers it may be different), consistent with previously reported studies.

Preliminary Study of Water Repellent Properties of Red Pepper Seed Oil

NASA Astrophysics Data System (ADS)

Kurniawan, F.; Madurani, K. A.; Wahyulis, N. C.

2017-03-01

The water-repellent properties of red pepper seed oil (capsicol) have been studied. The oil was coated on the glass surface by spray technique. Water repellent properties were performed by measuring the contact angle of water droplets. The measurement was conducted by varying the drying time of the oil coating at room temperature. The optimum contact angle of the droplets on the glass with capsicol coating is 46.77°, which can be achieved in 30 min of drying time. It also obtained the smallest diameter of the droplets (0.47 cm). The longer drying time decrease the contact angles and increases the diameter. The results were compared with the bare glass and commercial water repellent. The contact angle of the droplets on the glass surface with capsicol coating is higher than bare glass, but lower than glass with commercial water repellent coating. It means that capsicol has the water-repellent properties.

Contact angle change during evaporation of near-critical liquids

NASA Astrophysics Data System (ADS)

Nikolayev, Vadim; Hegseth, John; Beysens, Daniel

1998-03-01

An unexpected change of the dynamic contact angle was recently observed in a near-critical liquid-gas system in a space experiment. While the near-critical liquid completely wets a solid under equilibrium conditions, the apparent contact angle changed from 0^circ to about 120^circ during evaporation. We propose an explanation for this phenomenon by taking into account vapor recoil due to evaporation (motion of the vapor from the free liquid surface). This force is normal to the vapor-liquid interface and is directed towards the liquid. It increases sharply near the triple contact line. Near the critical point, where the surface tension force is very weak, the vapor recoil force can be important enough to change the apparent contact angle. A similar effect can also explain the drying of a heater during boiling at high heat flux. The drying greatly reduces the heat transfer to the liquid causing the heater to melt. This phenomenon is called ``boiling crisis", ``burnout" or ``Departure from Nuclear Boiling".

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.

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

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.

On the uniqueness of the receding contact angle: effects of substrate roughness and humidity on evaporation of water drops.

PubMed

Pittoni, Paola G; Lin, Chia-Hui; Yu, Teng-Shiang; Lin, Shi-Yow

2014-08-12

Could a unique receding contact angle be indicated for describing the wetting properties of a real gas-liquid-solid system? Could a receding contact angle be defined if the triple line of a sessile drop is not moving at all during the whole measurement process? To what extent is the receding contact angle influenced by the intrinsic properties of the system or the measurement procedures? In order to answer these questions, a systematic investigation was conducted in this study on the effects of substrate roughness and relative humidity on the behavior of pure water drops spreading and evaporating on polycarbonate (PC) surfaces characterized by different morphologies. Dynamic, advancing, and receding contact angles were found to be strongly affected by substrate roughness. Specifically, a receding contact angle could not be measured at all for drops evaporating on the more rugged PC surfaces, since the drops were observed strongly pinning to the substrate almost until their complete disappearance. Substrate roughness and system relative humidity were also found responsible for drastic changes in the depinning time (from ∼10 to ∼60 min). Thus, for measurement observations not sufficiently long, no movement of the triple line could be noted, with, again, the failure to find a receding contact angle. Therefore, to keep using concepts such as the receding contact angle as meaningful specifications of a given gas-liquid-solid system, the imperative to carefully investigate and report the inner characteristics of the system (substrate roughness, topography, impurities, defects, chemical properties, etc.) is pointed out in this study. The necessity of establishing methodological standards (drop size, measurement method, system history, observation interval, relative humidity, etc.) is also suggested.

Hydrophobization of track membrane surface by ion-plasma sputtering method

NASA Astrophysics Data System (ADS)

Kuklin, I. E.; Khlebnikov, N. A.; Barashev, N. R.; Serkov, K. V.; Polyakov, E. V.; Zdorovets, M. V.; Borgekov, D. B.; Zhidkov, I. S.; Cholakh, S. O.; Kozlovskiy, A. L.

2017-09-01

This article reviews the possibility of applying inorganic coatings of metal compounds on PTM by ion-plasma sputtering. The main aim of this research is to increase the contact angle of PTM surfaces and to impart the properties of a hydrophobic material to it. After the modification, the initial contact angle increased from 70° to 120°.

Effects of surface roughness and energy on ice adhesion strength

NASA Astrophysics Data System (ADS)

Zou, M.; Beckford, S.; Wei, R.; Ellis, C.; Hatton, G.; Miller, M. A.

2011-02-01

The aim of this study is to investigate the effects of surface roughness and surface energy on ice adhesion strength. Sandblasting technique was used to prepare samples with high roughness. Silicon-doped hydrocarbon and fluorinated-carbon thin films were employed to alter the surface energy of the samples. Silicon-doped hydrocarbon films were deposited by plasma-enhanced chemical vapor deposition, while fluorinated-carbon films were produced using deep reactive ion etching equipment by only activating the passivation step. Surface topographies were characterized using scanning electron microscopy and a stylus profilometer. The surface wetting properties were characterized by a video-based contact angle measurement system. The adhesion strength of ice formed from a water droplet on these surfaces was studied using a custom-built shear force test apparatus. It was found that the ice adhesion strength is correlated to the water contact angles of the samples only for surfaces with similar roughness: the ice adhesion strength decreases with the increase in water contact angle. The study also shows that smoother as-received sample surfaces have lower ice adhesion strength than the much rougher sandblasted surfaces.

Bacterial adhesion capacity on food service contact surfaces.

PubMed

Fink, Rok; Okanovič, Denis; Dražič, Goran; Abram, Anže; Oder, Martina; Jevšnik, Mojca; Bohinc, Klemen

2017-06-01

The aim of this study was to analyse the adhesion of E. coli, P. aeruginosa and S. aureus on food contact materials, such as polyethylene terephthalate, silicone, aluminium, Teflon and glass. Surface roughness, streaming potential and contact angle were measured. Bacterial properties by contact angle and specific charge density were characterised. The bacterial adhesion analysis using staining method and scanning electron microscopy showed the lowest adhesion on smooth aluminium and hydrophobic Teflon for most of the bacteria. However, our study indicates that hydrophobic bacteria with high specific charge density attach to those surfaces more intensively. In food services, safety could be increased by selecting material with low adhesion to prevent cross contamination.

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.

Surface Nanobubbles in Nonaqueous Media: Looking for Nanobubbles in DMSO, Formamide, Propylene Carbonate, Ethylammonium Nitrate, and Propylammonium Nitrate.

PubMed

An, Hongjie; Liu, Guangming; Atkin, Rob; Craig, Vincent S J

2015-07-28

Surface nanobubbles produced by supersaturation during the exchange of ethanol for water are routinely observed on hydrophobic surfaces, are stable for days, and have contact angles that are very much greater than observed macroscopically. Here, we test the hypothesis that nanobubbles can also be observed in nonaqueous solvents in order to ascertain if their anomalous lifetimes and contact angles are related to properties of the solvent. Nanobubbles were seen in the protic solvents formamide, ethylammonium nitrate, and propylammonium nitrate, but not in propylene carbonate or dimethyl sulfoxide. Solvents in which nanobubbles were observed exhibit a three-dimensional hydrogen-bonding network. Like in aqueous systems, the nanobubbles were stable for days and exhibited high contact angles (∼165°).

Microstructured Polymer Blend Surfaces Produced by Spraying Functional Copolymers and Their Blends

PubMed Central

Vargas-Alfredo, Nelson; Rodríguez Hernández, Juan

2016-01-01

We described the fabrication of functional and microstructured surfaces from polymer blends by spray deposition. This simple technique offers the possibility to simultaneously finely tune the microstructure as well as the surface chemical composition. Whereas at lower polymer concentration, randomly distributed surface micropatterns were observed, an increase of the concentration leads to significant changes on these structures. On the one hand, using pure homopolystyrene fiber-like structures were observed when the polymer concentration exceeded 30 mg/mL. Interestingly, the incorporation of 2,3,4,5,6-pentafluorostyrene changed the morphology, and, instead of fibers, micrometer size particles were identified at the surface. These fluorinated microparticles provide superhydrophobic properties leading to surfaces with contact angles above 165°. Equally, in addition to the microstructures provided by the spray deposition, the use of thermoresponsive polymers to fabricate interfaces with responsive properties is also described. Contact angle measurements revealed variations on the surface wettability upon heating when blends of polystyrene and polystyrene-b-poly(dimethylaminoethyl methacrylate) are employed. Finally, the use of spraying techniques to fabricate gradient surfaces is proposed. Maintaining a constant orientation, the surface topography and thus the contact angle varies gradually from the center to the edge of the film depending on the spray angle. PMID:28773555

CO2 adhesion on hydrated mineral surfaces.

PubMed

Wang, Shibo; Tao, Zhiyuan; Persily, Sara M; Clarens, Andres F

2013-10-15

Hydrated mineral surfaces in the environment are generally hydrophilic but in certain cases can strongly adhere CO2, which is largely nonpolar. This adhesion can significantly alter the wettability characteristics of the mineral surface and consequently influence capillary/residual trapping and other multiphase flow processes in porous media. Here, the conditions influencing adhesion between CO2 and homogeneous mineral surfaces were studied using static pendant contact angle measurements and captive advancing/receding tests. The prevalence of adhesion was sensitive to both surface roughness and aqueous chemistry. Adhesion was most widely observed on phlogopite mica, silica, and calcite surfaces with roughness on the order of ~10 nm. The incidence of adhesion increased with ionic strength and CO2 partial pressure. Adhesion was very rarely observed on surfaces equilibrated with brines containing strong acid or base. In advancing/receding contact angle measurements, adhesion could increase the contact angle by a factor of 3. These results support an emerging understanding of adhesion of, nonpolar nonaqueous phase fluids on mineral surfaces influenced by the properties of the electrical double layer in the aqueous phase film and surface functional groups between the mineral and CO2.

Transparent, superhydrophobic, and wear-resistant surfaces using deep reactive ion etching on PDMS substrates.

PubMed

Ebert, Daniel; Bhushan, Bharat

2016-11-01

Surfaces that simultaneously exhibit superhydrophobicity, low contact angle hysteresis, and high transmission of visible light are of interest for many applications, such as optical devices, solar panels, and self-cleaning windows. Superhydrophobicity could also find use in medical devices where antifouling characteristics are desirable. These applications also typically require mechanical wear resistance. The fabrication of such surfaces is challenging due to the competing goals of superhydrophobicity and transmittance in terms of the required degree of surface roughness. In this study, deep reactive ion etching (DRIE) was used to create rough surfaces on PDMS substrates using a O2/CF4 plasma. Surfaces then underwent an additional treatment with either octafluorocyclobutane (C4F8) plasma or vapor deposition of perfluorooctyltrichlorosilane (PFOTCS) following surface activation with O2 plasma. The effects of surface roughness and the additional surface modifications were examined with respect to the contact angle, contact angle hysteresis, and optical transmittance. To examine wear resistance, a sliding wear experiment was performed using an atomic force microscope (AFM). Copyright © 2016 Elsevier Inc. All rights reserved.

Wetting behavior and drainage of water droplets on microgrooved brass surfaces.

PubMed

Rahman, M Ashiqur; Jacobi, Anthony M

2012-09-18

In the present study, contact angle hysteresis and sliding behavior of water droplets on parallel, periodic microgrooved brass surfaces are investigated experimentally for enhancement of water drainage and compared to that on flat baseline surfaces. The surfaces (a total of 17 microgrooved samples, with a range of groove depth of 22 to 109 μm, pillar width of 26 to 190 μm, and groove width of 103 and 127 μm) are fabricated using a mechanical micromachining process. The wetting state and shape/elongation of deposited water droplets, anisotropy of the contact angle hysteresis, and the drainage behavior of water droplets on the microgrooved surfaces are found to be strongly dependent on the topography of the groove geometry, which is analyzed in detail. The wetting state is found to be Wenzel for microgrooved surfaces with very low aspect ratio (<0.2) and narrow pillars (pillar width to groove width ratio of ≈0.2), and also for the two deepest grooved surfaces of two different sample series, all of which exhibit high contact angle hysteresis. Mechanisms of the advancing and receding motions are identified. The critical sliding angle (the angle from horizontal at incipient motion of the advancing confluence) for the microgrooved surfaces is found to be significantly smaller than for flat surfaces. The sliding angle exhibits significant groove geometry dependence and is found to increase with pillar width and decrease with groove depth. The findings of this study may be useful in a broad range of applications where water retention plays an important role.

Tribological interaction between polytetrafluoroethylene and silicon oxide surfaces

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

Uçar, A.; Çopuroğlu, M.; Suzer, S., E-mail: suzer@fen.bilkent.edu.tr

2014-10-28

We investigated the tribological interaction between polytetrafluoroethylene (PTFE) and silicon oxide surfaces. A simple rig was designed to bring about a friction between the surfaces via sliding a piece of PTFE on a thermally oxidized silicon wafer specimen. A very mild inclination (∼0.5°) along the sliding motion was also employed in order to monitor the tribological interaction in a gradual manner as a function of increasing contact force. Additionally, some patterns were sketched on the silicon oxide surface using the PTFE tip to investigate changes produced in the hydrophobicity of the surface, where the approximate water contact angle was 45°more » before the transfer. The nature of the transferred materials was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS results revealed that PTFE was faithfully transferred onto the silicon oxide surface upon even at the slightest contact and SEM images demonstrated that stable morphological changes could be imparted onto the surface. The minimum apparent contact pressure to realize the PTFE transfer is estimated as 5 kPa, much lower than reported previously. Stability of the patterns imparted towards many chemical washing processes lead us to postulate that the interaction is most likely to be chemical. Contact angle measurements, which were carried out to characterize and monitor the hydrophobicity of the silicon oxide surface, showed that upon PTFE transfer the hydrophobicity of the SiO{sub 2} surface could be significantly enhanced, which might also depend upon the pattern sketched onto the surface. Contact angle values above 100° were obtained.« less

[Study of Interaction between Fluorinated Coating Glass and the Medicines].

PubMed

Kawano, Yayoi; Otsu, Saki; Bamba, Takao; Hanawa, Takehisa

2017-11-01

 The adsorption of active pharmaceutical ingredients on the surface of medical devices such as polyvinl chloride, ethylene-vinyl acetate copolymer and glass often prevent the acuurate dose of drug. At dispensing of pharmaceuticals, mètre glass (MG) has been widely used for dispensing syrup. When measuring the viscous syrup, it often takes long time to dispense the accurate volume due to their adhesiveness on the glass surface. In this study, we investigate the adhesion of various syrups to MG made with uncoated glass or glass with a strongly hydrophobic silicone or fluorinated coating in terms of the following formulation parameters: viscosity, surface tension, contact angle, and surface free energy. The contact angles for syrups on the coated glass surfaces were significantly higher than those on the uncoated glass surface. In addition, the relationship between surface tension and contact angle was examined. We found that the contact angle was independent of surface tension for the uncoated glass, while it increased with increasing surface tension for the coated glasses. These results can be explained as follows: the silicone or fluorinated coatings inhibit the hydrogen bonding that usually takes place between water and silanol and siloxane groups at glass surfaces. The coatings reduced the surface free energy and increased the hydrophobicity of the glass, reduced its wettability by the syrups, and thus reduced the adhesion loss for the syrups. It was considered that as for the hydrophobic action, properties of matter of sample influence the coated device by coating in order that it is reinforced.

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.

Wetting and phase separation in soft adhesion

PubMed Central

Jensen, Katharine E.; Sarfati, Raphael; Style, Robert W.; Boltyanskiy, Rostislav; Chakrabarti, Aditi; Chaudhury, Manoj K.; Dufresne, Eric R.

2015-01-01

In the classic theory of solid adhesion, surface energy drives deformation to increase contact area whereas bulk elasticity opposes it. Recently, solid surface stress has been shown also to play an important role in opposing deformation of soft materials. This suggests that the contact line in soft adhesion should mimic that of a liquid droplet, with a contact angle determined by surface tensions. Consistent with this hypothesis, we observe a contact angle of a soft silicone substrate on rigid silica spheres that depends on the surface functionalization but not the sphere size. However, to satisfy this wetting condition without a divergent elastic stress, the gel phase separates from its solvent near the contact line. This creates a four-phase contact zone with two additional contact lines hidden below the surface of the substrate. Whereas the geometries of these contact lines are independent of the size of the sphere, the volume of the phase-separated region is not, but rather depends on the indentation volume. These results indicate that theories of adhesion of soft gels need to account for both the compressibility of the gel network and a nonzero surface stress between the gel and its solvent. PMID:26553989

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.

A numerical investigation of the effect of surface wettability on the boiling curve.

PubMed

Hsu, Hua-Yi; Lin, Ming-Chieh; Popovic, Bridget; Lin, Chii-Ruey; Patankar, Neelesh A

2017-01-01

Surface wettability is recognized as playing an important role in pool boiling and the corresponding heat transfer curve. In this work, a systematic study of pool boiling heat transfer on smooth surfaces of varying wettability (contact angle range of 5° - 180°) has been conducted and reported. Based on numerical simulations, boiling curves are calculated and boiling dynamics in each regime are studied using a volume-of-fluid method with contact angle model. The calculated trends in critical heat flux and Leidenfrost point as functions of surface wettability are obtained and compared with prior experimental and theoretical predictions, giving good agreement. For the first time, the effect of contact angle on the complete boiling curve is shown. It is demonstrated that the simulation methodology can be used for studying pool boiling and related dynamics and providing more physical insights.

A numerical investigation of the effect of surface wettability on the boiling curve

PubMed Central

Lin, Ming-Chieh; Popovic, Bridget; Lin, Chii-Ruey; Patankar, Neelesh A.

2017-01-01

Surface wettability is recognized as playing an important role in pool boiling and the corresponding heat transfer curve. In this work, a systematic study of pool boiling heat transfer on smooth surfaces of varying wettability (contact angle range of 5° − 180°) has been conducted and reported. Based on numerical simulations, boiling curves are calculated and boiling dynamics in each regime are studied using a volume-of-fluid method with contact angle model. The calculated trends in critical heat flux and Leidenfrost point as functions of surface wettability are obtained and compared with prior experimental and theoretical predictions, giving good agreement. For the first time, the effect of contact angle on the complete boiling curve is shown. It is demonstrated that the simulation methodology can be used for studying pool boiling and related dynamics and providing more physical insights. PMID:29125847

Facile hydrophobicity/hydrophilicity modification of SMP surface based on metal constrained cracking

NASA Astrophysics Data System (ADS)

Han, Yu; Li, Peng; Zhao, Liangyu; Wang, Wenxin; Leng, Jinsong; Jin, Peng

2015-04-01

This study demonstrates an easy way to change surface characteristics, the water contact angle on styrene based shape memory polymer (SMP) surface alters before and after cracking formation and recovery. The contact angle of water on the original SMP surface is about 85 degree, after coating with Al and then kneading from side face at glass transition temperature Tg, cracking appeared both on Al film and SMP; cooling down and removing the Al film, cracks remain on SMP surface while the contact angle reduced to about 25 degree. When reheated above Tg, the cracks disappeared, and the contact angle go back to about 85 degree. The thin Al film bonded on SMP surface was coated by spurting, that constrains the deformation of SMP. Heating above Tg, there are complex interactions between soft SMP and hard metal film under kneading. The thin metal film cracked first with the considerable deformation of soft polymer, whereafter, the polymer was ripped by the metal cracks thus polymer cracked as well. Cracks on SMP can be fixed cooling down Tg, while reheated, cracks shrinking and the SMP recovers to its original smooth surface. Surface topography changed dramatically while chemical composition showed no change during the deformation and recovery cycle, as presented by SEM and EDS. Furthermore, the wetting cycle is repeatable. This facile method can be easily extended to the hydropobicity/hydrophilicity modification of other stimuli-responsive polymers and put forward many potential applications, such as microfluidic switching and molecule capture and release.

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

Sarshar, Mohammad Amin; Swarctz, Christopher; Hunter, Scott Robert

In this paper, the iceophobic properties of superhydrophobic surfaces are investigated under dynamic flow conditions by using a closed loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared by coating the substrates of aluminum and steel plates with nano-structured hydrophobic particles. The superhydrophobic plates along with uncoated control ones were exposed to an air flow of 12 m/s and 20 F accompanying micron-sized water droplets in the icing wind tunnel and the ice formation and accretion were probed by high-resolution CCD cameras. Results show that the superhydrophobic coatings significantly delay the ice formation and accretion even under the dynamic flow conditionmore » of the highly energetic impingement of accelerated super-cooled water droplets. It is found that there is a time scale for this phenomenon (delay of the ice formation) which has a clear correlation with the contact angle hysteresis and the length scale of surface roughness of the superhydrophobic surface samples, being the highest for the plate with the lowest contact angle hysteresis and finer surface roughness. The results suggest that the key parameter for designing iceophobic surfaces is to retain a low contact angle hysteresis (dynamic property) and the non-wetting superhydrophobic state under the hydrodynamic pressure of impinging droplets, rather than to only have a high contact angle (static property), in order to result in efficient anti-icing properties under dynamic conditions such as forced flows.« less

Growth Angle: A Microscopic View

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Croll, Arne; Volz, Martin P.

2017-01-01

A microscopic continuum mechanical model of the growth angle is proposed. It is based on the van der Waals type framework that is used for surface force phenomena. The obtained augmented Laplace type integro-differential equations are, in general, difficult to analyze. Here we focused primarily on the particular case of equal melt and crystal surface energies. We derived an approximate equation for the meniscus shape, and obtained an analytical relationship between the contact and the growth angle. Interestingly, the same result can be obtained using the macroscopic model of Herring. The case of a macroscopically sharp corner is also considered. For this case, the macroscopic angle is not defined and it can be any angle between the contact angles of both flat surfaces. The microscopic model yields the smooth shape for the meniscus that also is not unique, but depends on the initial position of the meniscus.

Correlating contact line capillarity and dynamic contact angle hysteresis in surfactant-nanoparticle based complex fluids

NASA Astrophysics Data System (ADS)

Harikrishnan, A. R.; Dhar, Purbarun; Agnihotri, Prabhat K.; Gedupudi, Sateesh; Das, Sarit K.

2018-04-01

Dynamic wettability and contact angle hysteresis can be correlated to shed insight onto any solid-liquid interaction. Complex fluids are capable of altering the expected hysteresis and dynamic wetting behavior due to interfacial interactions. We report the effect of capillary number on the dynamic advancing and receding contact angles of surfactant-based nanocolloidal solutions on hydrophilic, near hydrophobic, and superhydrophobic surfaces by performing forced wetting and de-wetting experiments by employing the embedded needle method. A segregated study is performed to infer the contributing effects of the constituents and effects of particle morphology. The static contact angle hysteresis is found to be a function of particle and surfactant concentrations and greatly depends on the nature of the morphology of the particles. An order of estimate of line energy and a dynamic flow parameter called spreading factor and the transient variations of these parameters are explored which sheds light on the dynamics of contact line movement and response to perturbation of three-phase contact. The Cox-Voinov-Tanner law was found to hold for hydrophilic and a weak dependency on superhydrophobic surfaces with capillary number, and even for the complex fluids, with a varying degree of dependency for different fluids.

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

Superhydrophobic coatings on wood substrate for self-cleaning and EMI shielding

NASA Astrophysics Data System (ADS)

Xing, Yingjie; Xue, Yaping; Song, Jinlong; Sun, Yankui; Huang, Liu; Liu, Xin; Sun, Jing

2018-04-01

A layer of superhydrophobic coating having good electromagnetic shielding and self-cleaning performance was fabricated on a wood surface through an electroless copper plated process. The superhydrophobic property of the wood surface was measured by contact angle (CA) and roll-off angle (RA) measurements. The microstructure and chemical composition of the superhydrophobic coating were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The analysis revealed that the microscale particles were uniformly distributed on the wood surface and the main component of the coating is metallic copper. The as-prepared Cu coatings on wood substrate exhibit a good superhydrophobicity with water contact angle about 160° and rolling angle less than 5°.

Evaporation and Degradation of a Sessile Droplet of VX on an Impermeable Surface

DTIC Science & Technology

2017-09-01

NOTES 14. ABSTRACT: This report highlights experimental studies into the combined physical and chemical processes that occur when a sessile droplet...resulting chemical change causes a corresponding change in the contact angle and evaporation rate of the sessile droplet on an impermeable surface...for phase separation. 15. SUBJECT TERMS Chemical degradation Phase separation Contact angle 2-(diisopropylamino)ethyl-O-ethyl

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.

Wettability measurement under high P-T conditions using X-ray imaging with application to the brine-supercritical CO2 system

NASA Astrophysics Data System (ADS)

Chaudhary, Kuldeep; Guiltinan, Eric J.; Cardenas, M. Bayani; Maisano, Jessica A.; Ketcham, Richard A.; Bennett, Philip C.

2015-09-01

We present a new method for measuring wettability or contact angle of minerals at reservoir pressure-temperature conditions using high-resolution X-ray computed tomography (HRXCT) and radiography. In this method, a capillary or a narrow slot is constructed from a mineral or a rock sample of interest wherein two fluids are allowed to form an interface that is imaged using X-rays. After some validation measurements at room pressure-temperature conditions, we illustrate this method by measuring the contact angle of CO2-brine on quartz, muscovite, shale, borosilicate glass, polytetrafluoroethylene (PTFE or Teflon), and polyether ether ketone (PEEK) surfaces at 60-71°C and 13.8-22.8 MPa. At reservoir conditions, PTFE and PEEK surfaces were found to be CO2-wet with contact angles of 140° and 127°, respectively. Quartz and muscovite were found to be water-wet with contact angles of 26° and 58°, respectively, under similar conditions. Borosilicate glass-air-brine at room conditions showed strong water-wet characteristics with a contact angle of 9°, whereas borosilicate glass-CO2-brine at 13.8 MPa and 60°C showed a decrease in its water-wetness with contact angle of 54°. This method provides a new application for X-ray imaging and an alternative to other methods.

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.

Effect of surface roughness on contact line dynamics of a thin droplet

NASA Astrophysics Data System (ADS)

Bhattacharjee, Debanik; Soltannia, Babak; Nazaripoor, Hadi; Sadrzadeh, Mohtada

2017-11-01

Any surface possesses inherent roughness. Droplet spreading on a surface is an example of a contact line problem. The tri-phase contact line is prone to stress singularity which can be relieved by using precursor film assumption and disjoining pressure. In this study, an axisymmetric, incompressible, Newtonian droplet spreading on a surface was investigated. An evolution equation which tracks the droplet height over time was obtained considering the lubrication approximation. The nonlinear PDE of evolution equation was solved using finite difference scheme. A simplified Gaussian model was used as a starting point to assess the role of roughness in the dynamics of contact line. The preliminary results revealed that, for both impermeable and permeable surfaces, the apparent contact angle increased in the presence of defects whereas the equilibrium stage remained unaffected. The apparent contact angle, however, was more strongly dependent on the nature and density of defects for impermeable surfaces due to the longer droplet lifetime. Furthermore, random self-affine and non-Gaussian models are employed. The mathematical model results are finally compared with theoretical models like the Cassie-Baxter, Wenzel, and Penetration modes. NSERC.

Dynamic contact angle cycling homogenizes heterogeneous surfaces.

PubMed

Belibel, R; Barbaud, C; Mora, L

2016-12-01

In order to reduce restenosis, the necessity to develop the appropriate coating material of metallic stent is a challenge for biomedicine and scientific research over the past decade. Therefore, biodegradable copolymers of poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) were prepared in order to develop a new coating exhibiting different custom groups in its side chain and being able to carry a drug. This material will be in direct contact with cells and blood. It consists of carboxylic acid and hexylic groups used for hydrophilic and hydrophobic character, respectively. The study of this material wettability and dynamic surface properties is of importance due to the influence of the chemistry and the potential motility of these chemical groups on cell adhesion and polymer kinetic hydrolysis. Cassie theory was used for the theoretical correction of contact angles of these chemical heterogeneous surfaces coatings. Dynamic Surface Analysis was used as practical homogenizer of chemical heterogeneous surfaces by cycling during many cycles in water. In this work, we confirmed that, unlike receding contact angle, advancing contact angle is influenced by the difference of only 10% of acidic groups (%A) in side-chain of polymers. It linearly decreases with increasing acidity percentage. Hysteresis (H) is also a sensitive parameter which is discussed in this paper. Finally, we conclude that cycling provides real information, thus avoiding theoretical Cassie correction. H(10)is the most sensible parameter to %A. Copyright © 2016 Elsevier B.V. All rights reserved.

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.

Surface Properties and Permeability of Poly(Vinylidene Fluoride)-Clays (PVDF/Clays) Composite Membranes

NASA Astrophysics Data System (ADS)

Pramono, E.; Ahdiat, M.; Simamora, A.; Pratiwi, W.; Radiman, C. L.; Wahyuningrum, D.

2017-07-01

Surface properties are important factors that determine the performance of ultrafiltration membranes. This study aimed to investigate the effects of clay addition on the surface properties and membrane permeability of PVDF (poly-vinylidene fluoride) membranes. Three types of clay with different particle size were used in this study, namely montmorillonite-MMT, bentonite-BNT and cloisite 15A-CLS. The PVDF-clay composite membranes were prepared by phase inversion method using PEG as additive. The hydrophobicity of membrane surface was characterized by contact angle. The membrane permeability was determined by dead- end ultrafiltration with a trans-membrane pressure of 2 bars. In contact angle measurement, water contact angle of composite membranes is higher than PVDF membrane. The addition of clays decreased water flux but increased of Dextran rejection. The PVDF-BNT composite membranes reach highest Dextran rejection value of about 93%. The type and particle size of clay affected the hydrophobicity of membrane surface and determined the resulting membrane structure as well as the membrane performance.

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

Wetting properties of phospholipid dispersion on tunable hydrophobic SiO2-glass plates.

PubMed

Alexandrova, Lidia; Karakashev, Stoyan I; Grigorov, L; Phan, Chi M; Smoukov, Stoyan K

2015-06-01

We study the wetting properties of very small droplets of salty aqueous suspensions of unilamellar liposomes of DMPC (dimyristoylphosphatidylcholine), situated on SiO2-glass surfaces with different levels of hydrophobicity. We evaluated two different measures of hydrophobicity of solid surfaces - receding contact angles and the thickness of wetting films trapped between an air bubble and the solid surface at different levels of hydrophobicity. We established a good correlation between methods which differ significantly in measurement difficulty and experimental setup. We also reveal details of the mechanism of wetting of different surfaces by the DMPC liposome suspension. Hydrophilic surfaces with water contact angles in the range of 0° to 35° are readily hydrophobized by the liposomes and only showed corresponding contact angles in the range 27°-43°. For same range of surface hydrophobicities, there was a clear reduction of the thickness of the wetting films between the surface and a bubble, reaching a minimum in the 35°-40° range. At higher levels of hydrophobicity both pure water and the liposome suspension show similar contact angles, and the thickness of wetting films between a bubble and those surfaces increases in parallel. Our analysis showed that the only force able to stabilize the film under these experimental conditions is steric repulsion. The latter suggests that nanobubbles adsorbed on hydrophobic parts of the surface, and coated with a DMPC layer, may be the cause of the 40-70 nm thickness of wetting films we observe. Copyright © 2014 Elsevier B.V. All rights reserved.

Comparison of Tibiofemoral Contact Mechanics After Various Transtibial and All-Inside Fixation Techniques for Medial Meniscus Posterior Root Radial Tears in a Porcine Model.

PubMed

Chung, Kyu Sung; Choi, Choong Hyeok; Bae, Tae Soo; Ha, Jeong Ku; Jun, Dal Jae; Wang, Joon Ho; Kim, Jin Goo

2018-04-01

To compare tibiofemoral contact mechanics after fixation for medial meniscus posterior root radial tears (MMPRTs). Seven fresh knees from mature pigs were used. Each knee was tested under 5 conditions: normal knee, MMPRT, pullout fixation with simple sutures, fixation with modified Mason-Allen sutures, and all-inside fixation using Fastfix 360. The peak contact pressure and contact surface area were evaluated using a capacitive sensor positioned between the meniscus and tibial plateau, under a 1,000-N compression force, at different flexion angles (0°, 30°, 60°, and 90°). The peak contact pressure was significantly higher in MMPRTs than in normal knees (P = .018). Although the peak contact pressure decreased significantly after fixation at all flexion angles (P = .031), it never recovered to the values noted in the normal meniscus. No difference was observed among fixation groups (P = .054). The contact surface area was significantly lower in MMPRTs than in the normal meniscus (P = .018) and increased significantly after fixation at all flexion angles (P = .018) but did not recover to within normal limits. For all flexion angles except 60°, the contact surface area was significantly higher for fixation with Mason-Allen sutures than for fixation with simple sutures or all-inside fixation (P = .027). At 90° of flexion, the contact surface area was significantly better for fixation with simple sutures than for all-inside fixation (P = .031). The peak contact pressure and contact surface area improved significantly after fixation, regardless of the fixation method, but did not recover to the levels noted in the normal meniscus after any type of fixation. Among the fixation methods evaluated in this time 0 study, fixation using modified Mason-Allen sutures provided a superior contact surface area compared with that noted after fixation using simple sutures or all-inside fixation, except at 60° of flexion. However, this study had insufficient power to accurately detect the differences between the outcomes of various fixation methods. Our results in a porcine model suggest that fixation can restore tibiofemoral contact mechanics in MMPRT and that fixation with a locking mechanism leads to superior biomechanical properties. Copyright © 2017 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Discontinuous contact line motion of evaporating particle-laden droplet on superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Yamada, Yutaka; Horibe, Akihiko

2018-04-01

The three-phase contact line motion on a superhydrophobic surface through particle-laden sessile droplet evaporation was investigated. Sample surfaces with micro- and nanoscale structures were generated by various durations of chemical treatment and Si O2 spherical particles with different sizes were used as additives of test liquid. The contact angle and contact radius profiles were studied, and the discontinuous motion of those profiles on micro- and nanostructured hierarchical surfaces was observed, while it was not observed on a nanostructured superhydrophobic surface. Suspensions with low particle concentration induced a relatively large contact radius jump compared to the high-concentrated condition; in contrast, the previous report showed the opposite trend for flat surfaces. In order to explain this result, a simple explanation was provided—that the stacked particles at the contact line region suppressed to the deformation of the liquid-vapor interface near the contact line. This is confirmed by side-view images of the deposition results because the contact line region after evaporation of the dense suspension showed a large contact angle compared to that of the diluted suspension. In addition, deposition at the contact line region was observed by scanning electron microscopy to discuss the effect of the characteristic length scale of the surface structure and particles on the contact line motion. We believe that these results will help one to understand the deposition phenomenon during particle-laden droplet evaporation on the superhydrophobic surface and its applications such as evaporation-driven materials deposition.

Survey of Thermal-Fluids Evaluation and Confirmatory Experimental Validation Requirements of Accident Tolerant Cladding Concepts with Focus on Boiling Heat Transfer Characteristics

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

Brown, Nicholas R.; Wysocki, Aaron J.; Terrani, Kurt A.

The U.S. Department of Energy Office of Nuclear Energy (DOE-NE) Advanced Fuels Campaign (AFC) is working closely with the nuclear industry to develop fuel and cladding candidates with potentially enhanced accident tolerance, also known as accident tolerant fuel (ATF). Thermal-fluids characteristics are a vital element of a holistic engineering evaluation of ATF concepts. One vital characteristic related to boiling heat transfer is the critical heat flux (CHF). CHF plays a vital role in determining safety margins during normal operation and also in the progression of potential transient or accident scenarios. This deliverable is a scoping survey of thermal-fluids evaluation andmore » confirmatory experimental validation requirements of accident tolerant cladding concepts with a focus on boiling heat transfer characteristics. The key takeaway messages of this report are: 1. CHF prediction accuracy is important and the correlations may have significant uncertainty. 2. Surface conditions are important factors for CHF, primarily the wettability that is characterized by contact angle. Smaller contact angle indicates greater wettability, which increases the CHF. Surface roughness also impacts wettability. Results in the literature for pool boiling experiments indicate changes in CHF by up to 60% for several ATF cladding candidates. 3. The measured wettability of FeCrAl (i.e., contact angle and roughness) indicates that CHF should be investigated further through pool boiling and flow boiling experiments. 4. Initial measurements of static advancing contact angle and surface roughness indicate that FeCrAl is expected to have a higher CHF than Zircaloy. The measured contact angle of different FeCrAl alloy samples depends on oxide layer thickness and composition. The static advancing contact angle tends to decrease as the oxide layer thickness increases.« less

Determination of wood wettability properties of oil palm trunk, Shorea sp. and Paraserianthes falcataria by contact angle method

NASA Astrophysics Data System (ADS)

Sucipto, T.; Hartono, R.; Dwianto, W.

2018-02-01

The aim of this study was to determine the wettability of the inner part of oil palm trunk (OPT), the outer part of OPT, OPT that densified 50%, Shorea sp. and Paraserianthes falcataria wood, as raw material for laminated beams. The wettability of the wood was measured by using cosine-contact angle (CCA) method, which is measuring the angle between dripped resin liquid and the wood surface. The resins that used in this study is phenol formaldehyde (PF) and urea formaldehyde (UF). The results showed that the Shorea sp. and P. falcataria woods have the smallest contact angle or the best wettability properties than OPT. Shorea sp. has the best wettability on PF resin (83.00°), while P. falcataria on UF resin (90.89°), this is due to the levels of starch and extractive substances in Shorea sp. and P. falcataria wood are smaller than OPT. Furthermore, Shorea sp. and P. falcataria wood surfaces are flatter and smoother than OPT, so that the resin will flow easier and wetting the wood surface. In this condition, the liquid resin will flow easier and formed a smaller contact angle. The good wettability of wood will enhance the adhesion properties of laminated beams.

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.

Contact angle change during evaporation of near-critical liquids

NASA Astrophysics Data System (ADS)

Nikolayev, Vadim; Hegseth, John; Beysens, Daniel

1998-11-01

An unexpected change of the dynamic contact angle was recently observed in a near-critical liquid-gas system in a space experiment. While the near-critical liquid completely wets a solid under equilibrium conditions, the apparent contact angle changed from 0^circ to about 120^circ during evaporation. We propose an explanation for this phenomenon by taking into account vapor recoil due to evaporation (motion of the vapor from the free liquid surface). This force is normal to the vapor-liquid interface and is directed towards the liquid. It increases sharply near the triple contact line. Near the critical point, where the surface tension force is very weak, the vapor recoil force can be important enough to change the apparent contact angle. A similar effect can also explain the drying of a heater during boiling at high heat flux. The drying greatly reduces the heat transfer to the liquid causing the heater to melt. This phenomenon is called ``boiling crisis", ``burnout" or ``Departure from Nuclear Boiling". We report the preliminary results of the numerical simulation of the liquid evaporation by the Boundary Element method.

Effect of solution and leaf surface polarity on droplet spread area and contact angle.

PubMed

Nairn, Justin J; Forster, W Alison; van Leeuwen, Rebecca M

2016-03-01

How much an agrochemical spray droplet spreads on a leaf surface can significantly influence efficacy. This study investigates the effect solution polarity has on droplet spreading on leaf surfaces and whether the relative leaf surface polarity, as quantified using the wetting tension dielectric (WTD) technique, influences the final spread area. Contact angles and spread areas were measured using four probe solutions on 17 species. Probe solution polarity was found to affect the measured spread area and the contact angle of the droplets on non-hairy leaves. Leaf hairs skewed the spread area measurement, preventing investigation of the influence of surface polarity on hairy leaves. WTD-measured leaf surface polarity of non-hairy leaves was found to correlate strongly with the effect of solution polarity on spread area. For non-polar leaf surfaces the spread area decreases with increasing solution polarity, for neutral surfaces polarity has no effect on spread area and for polar leaf surfaces the spread area increases with increasing solution polarity. These results attest to the use of the WTD technique as a means to quantify leaf surface polarity. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.

Silane Modification of Glass and Silica Surfaces to Obtain Equally Oil-Wet Surfaces in Glass-Covered Silicon Micromodel Applications

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

Grate, Jay W.; Warner, Marvin G.; Pittman, Jonathan W.

2013-08-05

The wettability of silicon and glass surfaces can be modified by silanization. However, similar treatments of glass and silica surfaces using the same silane do not necessarily yield the same wettability as determined by the oil-water contact angle. In this technical note, surface cleaning pretreatments were investigated to determine conditions that would yield oil-wet surfaces on glass with similar wettability to silica surfaces treated with the same silane, and both air-water and oil-water contact angles were determined. Air-water contact angles were less sensitive to differences between silanized silica and glass surfaces, often yielding similar values while the oil-water contact anglesmore » were quite different. Borosilicate glass surfaces cleaned with standard cleaning solution 1 (SC1) yield intermediate-wet surfaces when silanized with hexamethyldisilazane, while the same cleaning and silanization yields oil-wet surfaces on silica. However, cleaning glass in boiling concentrated nitric acid creates a surface that can be silanized to obtain oil-wet surfaces using HDMS. Moreover, this method is effective on glass with prior thermal treatment at an elevated temperature of 400oC. In this way, silica and glass can be silanized to obtain equally oil-wet surfaces using HMDS. It is demonstrated that pretreatment and silanization is feasible in silicon-silica/glass micromodels previously assembled by anodic bonding, and that the change in wettability has a significant observable effect on immiscisble fluid displacements in the pore network.« less

Rapid and Clean Covalent Attachment of Methylsiloxane Polymers and Oligomers to Silica Using B(C6F5)3 Catalysis.

PubMed

Flagg, Daniel H; McCarthy, Thomas J

2017-08-22

The rapid, room-temperature covalent attachment of alkylhydridosilanes (R 3 Si-H) to silicon oxide surfaces to form monolayers using tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 , BCF) catalysis has recently been described. This method, unlike alternative routes to monolayers, produces only unreactive H 2 gas as a byproduct and reaches completion within minutes. We report the use of this selective reaction between surface silanols and hydridosilanes to prepare surface-grafted poly(dimethylsiloxane)s (PDMSs) with various graft architectures that are controlled by the placement of hydridosilane functionality at one end, both ends, or along the chain of PDMS samples of controlled molecular weight. We also report studies of model methylsiloxane monolayers prepared from pentamethyldisiloxane, heptamethyltrisiloxane (two isomers), heptamethylcyclotetrasiloxane, and tris(trimethylsiloxy)silane. These modified silica surfaces with structurally defined methylsiloxane groups are not accessible by conventional silane surface chemistry and proved to be useful in exploring the steric limitations of the reaction. Linear monohydride- and dihydride-terminated PDMS-grafted surfaces exhibit increasing thickness and decreasing contact angle hysteresis with increasing molecular weight up to a particular molecular weight value. Above this value, the hysteresis increases with increasing molecular weight of end-grafted polymers. Poly(hydridomethyl-co-dimethylsiloxane)s with varied hydride content (3-100 mol %) exhibit decreasing thickness, decreasing contact angle, and increasing contact angle hysteresis with increasing hydride content. These observations illustrate the importance of molecular mobility in three-phase contact line dynamics on low-hysteresis surfaces. To calibrate our preparative procedure against both monolayers prepared by conventional approaches as well as the recent reports, a series of trialkylsilane (mostly, n-alkyldimethylsilane) monolayers was prepared to determine the reaction time required to achieve the maximum bonding density using dynamic contact angle analysis. Monolayers prepared from hydridosilanes with BCF catalysis have lower bonding densities than those derived from chlorosilanes, and the reactions are more sensitive to alkyl group sterics. This lower bonding density renders greater flexibility to the n-alkyl groups in monolayers and can decrease the contact angle hysteresis.

Improvement of mechanical robustness of the superhydrophobic wood surface by coating PVA/SiO2 composite polymer

NASA Astrophysics Data System (ADS)

Liu, Feng; Wang, Shuliang; Zhang, Ming; Ma, Miaolian; Wang, Chengyu; Li, Jian

2013-09-01

Improvement of the robustness of superhydrophobic surfaces is crucial for the purpose of achieving commercial applications of these surfaces in such various areas as self-cleaning, water repellency and corrosion resistance. We have investigated a fabrication of polyvinyl alcohol (PVA)/silica (SiO2) composite polymer coating on wooden substrates with super repellency toward water, low sliding angles, low contact angle hysteresis, and relatively better mechanical robustness. The composite polymer slurry, consisting of well-mixing SiO2 particles and PVA, is prepared simply and subsequently coated over wooden substrates with good adhesion. In this study, the mechanical robustness of superhydrophobic wood surfaces was evaluated. The effect of petaloid structures of the composite polymer on robustness was investigated using an abrasion test and the results were compared with those of superhydrophobic wood surfaces fabricated by other processes. The produced wood surfaces exhibited promising superhydrophobic properties with a contact angle of 159̊ and a sliding angle of 4̊, and the relatively better mechanical robustness.

Spontaneous imbibition of water and determination of effective contact angles in the Eagle Ford Shale Formation using neutron imaging

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

DiStefano, Victoria H.; Cheshire, Michael C.; McFarlane, Joanna

Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extraction. Although, the modern analytical and computational models can capture fracture growth, there is a lack of experimental data on spontaneous imbibition and wettability in oil and gas reservoirs for the validation of further model development. In this work, we used neutron imaging to measure the spontaneous imbibition of water into fractures of Eagle Ford Shale with known geometries and fracture orientations. An analytical solution for a set of nonlinear second-order differential equationsmore » was applied to the measured imbibition data to determine effective contact angles. The analytical solution fit the measured imbibition data reasonably well and determined effective contact angles were slightly higher than static contact angles due to effects of in-situ changes in velocity, surface roughness, and heterogeneity of mineral surfaces on the fracture surface. Additionally, small fracture widths may have retarded imbibition and affected model fits, which suggests that average fracture widths are not satisfactory for modeling imbibition in natural systems.« less

Surface wettability of silicon substrates enhanced by laser ablation

NASA Astrophysics Data System (ADS)

Tseng, Shih-Feng; Hsiao, Wen-Tse; Chen, Ming-Fei; Huang, Kuo-Cheng; Hsiao, Sheng-Yi; Lin, Yung-Sheng; Chou, Chang-Pin

2010-11-01

Laser-ablation techniques have been widely applied for removing material from a solid surface using a laser-beam irradiating apparatus. This paper presents a surface-texturing technique to create rough patterns on a silicon substrate using a pulsed Nd:YAG laser system. The different degrees of microstructure and surface roughness were adjusted by the laser fluence and laser pulse duration. A scanning electron microscope (SEM) and a 3D confocal laser-scanning microscope are used to measure the surface micrograph and roughness of the patterns, respectively. The contact angle variations between droplets on the textured surface were measured using an FTA 188 video contact angle analyzer. The results indicate that increasing the values of laser fluence and laser pulse duration pushes more molten slag piled around these patterns to create micro-sized craters and leads to an increase in the crater height and surface roughness. A typical example of a droplet on a laser-textured surface shows that the droplet spreads very quickly and almost disappears within 0.5167 s, compared to a contact angle of 47.9° on an untextured surface. This processing technique can also be applied to fabricating Si solar panels to increase the absorption efficiency of light.

Detection of surface mobility of poly (2, 3, 4, 5, 6-pentafluorostyrene) films by in situ variable-temperature ToF-SIMS and contact angle measurements.

PubMed

Fu, Yi; Lau, Yiu-Ting R; Weng, Lu-Tao; Ng, Kai-Mo; Chan, Chi-Ming

2014-10-01

Poly (2, 3, 4, 5, 6-pentafluorostyrene) (5FPS) was prepared by bulk radical polymerization. The spin-cast films of this polymer were analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) at various temperatures ranging from room temperature to 120°C. Principal component analysis (PCA) of the ToF-SIMS data revealed a transition temperature (T(T)) at which the surface structure of 5FPS was rearranged. A comparison between the results of the PCA of ToF-SIMS spectra obtained on 5FPS and polystyrene (PS) indicate that the pendant groups of 5FPS and PS moved in exactly opposite directions as the temperature increased. More pendant groups of 5FPS and PS migrated from the bulk to the surface and verse versa, respectively, as the temperature increased. These results clearly support the view that the abrupt changes in the normalized principal component 1 value was caused by the surface reorientation of the polymers and not by a change in the ion fragmentation mechanism at temperatures above the T(T). Contact angle measurement, which is another extremely surface sensitive technique, was used to monitor the change in the surface tension as a function of temperature. A clear T(T) was determined by the contact angle measurements. The T(T) values determined by contact angle measurements and ToF-SIMS were very similar. Copyright © 2014 Elsevier Inc. All rights reserved.

Time-Dependent Wetting Behavior of PDMS Surfaces with Bioinspired, Hierarchical Structures.

PubMed

Mishra, Himanshu; Schrader, Alex M; Lee, Dong Woog; Gallo, Adair; Chen, Szu-Ying; Kaufman, Yair; Das, Saurabh; Israelachvili, Jacob N

2016-03-01

Wetting of rough surfaces involves time-dependent effects, such as surface deformations, nonuniform filling of surface pores within or outside the contact area, and surface chemistries, but the detailed impact of these phenomena on wetting is not entirely clear. Understanding these effects is crucial for designing coatings for a wide range of applications, such as membrane-based oil-water separation and desalination, waterproof linings/windows for automobiles, aircrafts, and naval vessels, and antibiofouling. Herein, we report on time-dependent contact angles of water droplets on a rough polydimethylsiloxane (PDMS) surface that cannot be completely described by the conventional Cassie-Baxter or Wenzel models or the recently proposed Cassie-impregnated model. Shells of sand dollars (Dendraster excentricus) were used as lithography-free, robust templates to produce rough PDMS surfaces with hierarchical, periodic features ranging from 1 × 10(-7) to 1 × 10(-4) m. Under saturated vapor conditions, we found that in the short term (<1 min), the contact angle of a sessile water droplet on the templated PDMS, θ(SDT) = 140 ± 3°, was accurately described by the Cassie-Baxter model (predicted θ(SDT) = 137°); however, after 90 min, θ(SDT) fell to 110°. Fluorescent confocal microscopy confirmed that the initial reduction in θ(SDT) to 110° (the Wenzel limit) was primarily a Cassie-Baxter to Wenzel transition during which pores within the contact area filled gradually, and more rapidly for ethanol-water mixtures. After 90 min, the contact line of the water droplet became pinned, perhaps caused by viscoelastic deformation of the PDMS around the contact line, and a significant volume of water began to flow from the droplet to pores outside the contact region, causing θ(SDT) to decrease to 65° over 48 h on the rough surface. The system we present here to explore the concept of contact angle time dependence (dynamics) and modeling of natural surfaces provides insights into the design and development of long- and short-lived coatings.

Surface studies of low molecular weight photolysis products from UV-ozone oxidised polystyrene

NASA Astrophysics Data System (ADS)

Davidson, M. R.; Mitchell, S. A.; Bradley, R. H.

2005-05-01

The production of low molecular weight oxidised material during UV-ozone treatment of polystyrene has been studied by XPS, GC-MS, FTIR and UV/visible spectroscopy. XPS analysis of the oxidised polystyrene surfaces before and after washing with water or methanol indicates that the removal of oxidation products and the surface that remains after washing is strongly dependent on the choice of solvent. Methanol washing removes a greater proportion of the more highly oxidised carbonyl and carboxyl groups resulting in a surface with a lower oxygen content than that remaining after water washing. Extended exposure to UV-ozone treatment reveals a two-stage oxidation process with mono-substituted benzene rings such as benzaldehyde, acetophenone and benzoic acid being produced at exposure times less than 15 min. Compounds, more typical of those formed via dehydration reactions of existing oxidised species, are produced at longer exposure times. UV-visible spectroscopy and Fourier transform infrared spectroscopy also confirm the presence of carboxylic acid, aromatic ketones and esters. Measurements of water contact angle on a 10 min treated surface reveals that methanol washing produces a more hydrophilic surface than water washing, the resulting water contact angles being 47° and 62° respectively. Ageing of methanol washed surfaces for 24 h leads to a recovery of the water contact angle back to 62° which suggests some form of post-washing surface relaxation process. Since XPS analyses show no increase in the oxygen concentration of the methanol washed surfaces after a 24 h ageing period, the increase in contact angle found with ageing is attributed to the reorientation of very near-surface functional groups i.e. within the XPS sampling depth.

Superhydrophobic, carbon-infiltrated carbon nanotubes on Si and 316L stainless steel with tunable geometry

NASA Astrophysics Data System (ADS)

Stevens, Kimberly A.; Esplin, Christian D.; Davis, Taylor M.; Butterfield, D. Jacob; Ng, Philip S.; Bowden, Anton E.; Jensen, Brian D.; Iverson, Brian D.

2018-05-01

The use of carbon nanotubes to create superhydrophobic coatings has been considered due to their ability to offer a relatively uniform nanostructure. However, carbon nanotubes (CNTs) may be considered delicate with a typical diameter of tens of nanometers for a multi-walled CNT; as-grown carbon nanotubes often require the addition of a thin-film hydrophobic coating to render them superhydrophobic. Furthermore, fine control over the diameter of the as-grown CNTs or the overall nanostructure is difficult. This work demonstrates the utility of using carbon infiltration to layer amorphous carbon on multi-walled nanotubes to improve structural integrity and achieve superhydrophobic behavior with tunable geometry. These carbon-infiltrated carbon nanotube (CICNT) surfaces exhibit an increased number of contact points between neighboring tubes, resulting in a composite structure with improved mechanical stability. Additionally, the native surface can be rendered superhydrophobic with a vacuum pyrolysis treatment, with contact angles as high as 160° and contact angle hysteresis on the order of 1°. The CICNT diameter, static contact angle, sliding angle, and contact angle hysteresis were examined for varying levels of carbon-infiltration to determine the effect of infiltration on superhydrophobicity. The same superhydrophobic behavior and tunable geometry were also observed with CICNTs grown directly on stainless steel without an additional catalyst layer. The ability to tune the geometry while maintaining superhydrophobic behavior offers significant potential in condensation heat transfer, anti-icing, microfluidics, anti-microbial surfaces, and other bio-applications where control over the nanostructure is beneficial.

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

Yang, Lu; Hanson, David E

Here we present the results on the study of surface properties of {beta}-HMX crystal utilizing molecular simulations. The surface polarity of three principal crystal surfaces are investigated by measuring the water contact angles. The calculated contact angles agree excellently with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain with and without nitroplasticizer from the three principal crystal surfaces were calculated using umbrella sampling technique. We find that the detaching free energy/force increases with the increasing HMX surface polarity. In addition, ourmore » results also show that nitroplasticizer plays an important role in the adhesion forces between Estane and HMX surfaces.« less

Wettability measurement under high P-T conditions using X-ray imaging with application to the brine-supercritical CO 2 system: WETTABILITY MEASUREMENT USING X-RAY

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

Chaudhary, Kuldeep; Guiltinan, Eric J.; Cardenas, M. Bayani

2015-08-30

We present a new method for measuring wettability or contact angle of minerals at reservoir pressure-temperature conditions using high-resolution X-ray computed tomography (HRXCT) and radiography. In this method, a capillary or a narrow slot is constructed from a mineral or a rock sample of interest wherein two fluids are allowed to form an interface that is imaged using X-rays. After some validation measurements at room pressure-temperature conditions, we illustrate this method by measuring the contact angle of CO 2-brine on quartz, muscovite, shale, borosilicate glass, polytetrafluoroethylene (PTFE or Teflon), and polyether ether ketone (PEEK) surfaces at 60–71°C and 13.8–22.8 MPa.more » At reservoir conditions, PTFE and PEEK surfaces were found to be CO 2-wet with contact angles of 140° and 127°, respectively. Quartz and muscovite were found to be water-wet with contact angles of 26° and 58°, respectively, under similar conditions. Borosilicate glass-air-brine at room conditions showed strong water-wet characteristics with a contact angle of 9°, whereas borosilicate glass-CO 2-brine at 13.8 MPa and 60°C showed a decrease in its water-wetness with contact angle of 54°. This method provides a new application for X-ray imaging and an alternative to other methods.« less

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.

Constructing a superhydrophobic surface on polydimethylsiloxane via spin coating and vapor-liquid sol-gel process.

PubMed

Peng, Yu-Ting; Lo, Kuo-Feng; Juang, Yi-Je

2010-04-06

In this study, a superhydrophobic surface on polydimethylsiloxane (PDMS) substrate was constructed via the proposed vapor-liquid sol-gel process in conjunction with spin coating of dodecyltrichlorosilane (DTS). Unlike the conventional sol-gel process where the reaction takes place in the liquid phase, layers of silica (SiO(2)) particles were formed through the reaction between the reactant spin-coated on the PDMS surface and vapor of the acid solution. This led to the SiO(2) particles inlaid on the PDMS surface. Followed by subsequent spin coating of DTS solution, the wrinkle-like structure was formed, and the static contact angle of the water droplet on the surface could reach 162 degrees with 2 degrees sliding angle and less than 5 degrees contact angle hysteresis. The effect of layers of SiO(2) particles, concentrations of DTS solution and surface topography on superhydrophobicity of the surface is discussed.

Surface modification of EPDM rubber by plasma treatment.

PubMed

Grythe, Kai Frode; Hansen, Finn Knut

2006-07-04

The effect of argon, oxygen, and nitrogen plasma treatment of solvent cast EPDM rubber films has been investigated by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface energy measurements. Plasma treatment leads to changes in the surface energy from 25 to 70 mN/m. Treatment conditions influenced both the changes in surface energy and the stability, and it became more difficult to obtain good contact angle measurements after longer (> ca. 4 min) treatment times, probably because of an increasingly uneven surface structure. XPS analyses revealed that up to 20 at. % oxygen can be easily incorporated and that variations of approximately 5% can be controlled by the plasma conditions. Oxygen was mainly found in hydroxyl groups, but also as carbonyl and carboxyl. XPS analyses showed more stable surfaces than expected from contact angles, probably because XPS analysis is less surface sensitive than contact angle measurements. AFM measurements revealed different surface structures with the three gases. The surface roughness increased generally with treatment time, and dramatic changes could be observed at longer times. At short times, surface energy changes were much faster than the changes in surface structure, showing that plasma treatment conditions can be utilized to tailor both surface energies and surface structure of EPDM rubber.

Flexible Teflon nanocone array surfaces with tunable superhydrophobicity for self-cleaning and aqueous droplet patterning.

PubMed

Toma, Mana; Loget, Gabriel; Corn, Robert M

2014-07-23

Tunable hydrophobic/hydrophilic flexible Teflon nanocone array surfaces were fabricated over large areas (cm(2)) by a simple two-step method involving the oxygen plasma etching of a colloidal monolayer of polystyrene beads on a Teflon film. The wettability of the nanocone array surfaces was controlled by the nanocone array dimensions and various additional surface modifications. The resultant Teflon nanocone array surfaces were hydrophobic and adhesive (a "gecko" type of surface on which a water droplet has a high contact angle but stays in place) with a contact angle that correlated with the aspect ratio/sharpness of the nanocones. The surfaces switched to a superhydrophobic or "lotus" type of surface when hierarchical nanostructures were created on Teflon nanocones by modifying them with a gold nanoparticle (AuNPs) film. The nanocone array surfaces could be made superhydrophobic with a maximum contact angle of 160° by the further modification of the AuNPs with an octadecanethiol (C18SH) monolayer. Additionally, these nanocone array surfaces became hydrophilic when the nanocone surfaces were sequentially modified with AuNPs and hydrophilic polydopamine (PDA) layers. The nanocone array surfaces were tested for two potential applications: self-cleaning superhydrophobic surfaces and for the passive dispensing of aqueous droplets onto hybrid superhydrophobic/hydrophilic microarrays.

Superomniphobic Surfaces for Military Applications: Nano- and Micro-Fabrication Methods. Chapter 1: Lithographic Fabrication of Surfaces with Different Microgeometries and Investigation of Their Wetting Behaviour

DTIC Science & Technology

2011-01-01

plus important, comparativement à une échelle plus large. Les résultats indiquent qu’un effet de cette nature est attribuable à des facteurs...par un angle de contact à l’avancement plus petit et un angle de contact au retrait plus important, comparativement à une échelle plus large. Les...Methods ............................................................................................................ 10 3.1 Experimental Design

Effective Wettability of Heterogenous Fracture Surfaces Using the Lattice-Boltzmann Method

NASA Astrophysics Data System (ADS)

E Santos, J.; Prodanovic, M.; Landry, C. J.

2017-12-01

Fracture walls in the subsurface are often structured by minerals of different composition (potentially further altered in contact with fluids during hydrocarbon extraction or CO2 sequestration), this yields in a heterogeneous wettability of the surface in contact with the fluids. The focus of our work is to study how surfaces presenting different mineralogy and roughness affect multiphase flow in fractures. Using the Shan-Chen model of the lattice-Boltzmann method (LBM) we define fluid interaction and surface attraction parameters to simulate a system of a wetting and a non-wetting fluid. In this work, we use synthetically created fractures presenting different arrangements of wetting and non-wetting patches, and with or without roughness; representative of different mineralogy, similar workflow can be applied to fractures extracted from X-ray microtomography images of fractures porous media. The results from the LBM simulations provide an insight on how the distribution of mineralogy and surface roughness are related with the observed macroscopic contact angle. We present a comparison between the published analytical models, and our results based on surface areas, spatial distribution and local fracture aperture. The understanding of the variables that affect the contact angle is useful for the comprehension of multiphase processes in naturally fractured reservoirs like primary oil production, enhanced oil recovery and CO2 sequestration. The macroscopic contact angle analytical equations for heterogeneous surfaces with variable roughness are no longer valid in highly heterogeneous systems; we quantify the difference thus offering an alternative to analytical models.

A lattice Boltzmann model for substrates with regularly structured surface roughness

NASA Astrophysics Data System (ADS)

Yagub, A.; Farhat, H.; Kondaraju, S.; Singh, T.

2015-11-01

Superhydrophobic surface characteristics are important in many industrial applications, ranging from the textile to the military. It was observed that surfaces fabricated with nano/micro roughness can manipulate the droplet contact angle, thus providing an opportunity to control the droplet wetting characteristics. The Shan and Chen (SC) lattice Boltzmann model (LBM) is a good numerical tool, which holds strong potentials to qualify for simulating droplets wettability. This is due to its realistic nature of droplet contact angle (CA) prediction on flat smooth surfaces. But SC-LBM was not able to replicate the CA on rough surfaces because it lacks a real representation of the physics at work under these conditions. By using a correction factor to influence the interfacial tension within the asperities, the physical forces acting on the droplet at its contact lines were mimicked. This approach allowed the model to replicate some experimentally confirmed Wenzel and Cassie wetting cases. Regular roughness structures with different spacing were used to validate the study using the classical Wenzel and Cassie equations. The present work highlights the strength and weakness of the SC model and attempts to qualitatively conform it to the fundamental physics, which causes a change in the droplet apparent contact angle, when placed on nano/micro structured surfaces.

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.

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

Wang, Yang; Liu, Xiao Wei; Zhang, Hai Feng, E-mail: wy3121685@163.com

In this work, we present a method of fabricating super-hydrophobic surface on aluminum alloy substrate. The etching of aluminum surfaces has been performed using Beck's dislocation etchant for different time to create micrometer-sized irregular steps. An optimised etching time of 50 s is found to be essential before polytetrafluoroethylene (PTFE) coating, to obtain a highest water contact angle of 165±2° with a lowest contact angle hysteresis as low as 5±2°. The presence of patterned microstructure as revealed by scanning electron microscopy (SEM) together with the low surface energy ultrathin RF-sputtered PTFE films renders the aluminum alloy surfaces highly super-hydrophobic.

Wetting Hysteresis at the Molecular Scale

NASA Technical Reports Server (NTRS)

Jin, Wei; Koplik, Joel; Banavar, Jayanth R.

1996-01-01

The motion of a fluid-fluid-solid contact line on a rough surface is well known to display hysteresis in the contact angle vs. velocity relationship. In order to understand the phenomenon at a fundamental microscopic level, we have conducted molecular dynamics computer simulations of a Wilhelmy plate experiment in which a solid surface is dipped into a liquid bath, and the force-velocity characteristics are measured. We directly observe a systematic variation of force and contact angle with velocity, which is single-valued for the case of an atomically smooth solid surface. In the microscopically rough case, however, we find (as intuitively expected) an open hysteresis loop. Further characterization of the interface dynamics is in progress.

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

Ba, Yan; Kang, Qinjun; Liu, Haihu

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

Contact angle and detachment energy of shape anisotropic particles at fluid-fluid interfaces.

PubMed

Anjali, Thriveni G; Basavaraj, Madivala G

2016-09-15

The three phase contact angle of particles, a measure of its wettability, is an important factor that greatly influences their behaviour at interfaces. It is one of the principal design parameters for potential applications of particles as emulsion/foam stabilizers, functional coatings and other novel materials. In the present work, the effect of size, shape and surface chemistry of particles on their contact angle is investigated using the gel trapping technique, which facilitates the direct visualization of the equilibrium position of particles at interfaces. The contact angle of hematite particles of spherocylindrical, peanut and cuboidal shapes, hematite-silica core-shell and silica shells is reported at a single particle level. The spherocylindrical and peanut shaped particles are always positioned with their major axis parallel to the interface. However, for cuboidal particles at air-water as well as decane-water interfaces, different orientations namely - face-up, edge-up and the vertex-up - are observed. The influence of gravity on the equilibrium position of the colloidal particles at the interface is studied using the hematite-silica core-shell particles and the silica shells. The measured contact angle values are utilized in the calculations of the detachment and surface energies of the hematite particles adsorbed at the interface. Copyright © 2016 Elsevier Inc. All rights reserved.

Further studies of propellant sloshing under low-gravity conditions

NASA Technical Reports Server (NTRS)

Dodge, F. T.

1971-01-01

A variational integral is formulated from Hamilton's Principle and is proved to be equivalent to the usual differential equations of low-gravity sloshing in ellipsoidal tanks. It is shown that for a zero-degree contact angle the contact line boundary condition corresponds to the stuck condition, a result that is due to the linearization of the equations and the ambiguity in the definition of the wave height at the wall. The variational integral is solved by a Rayleigh-Ritz technique. Results for slosh frequency when the free surface is not bent-over compare well with previous numerical solutions. When the free surface is bent over, however, the results for slosh frequency are considerably larger than those predicted by previous finite-difference, numerical approaches: the difference may be caused by the use of a zero degree contact angle in the present theory in contrast to the nonzero contact angle used in the numerical approaches.

Investigation of porous silicon obtained under different conditions by the contact angle method

NASA Astrophysics Data System (ADS)

Belorus, A. O.; Bukina, Y. V.; Pastukhov, A. I.; Stebko, D. S.; Spivak, Yu M.; Moshnikov, V. A.

2017-11-01

This paper investigates a hydrophobicity/hydrophilicity of porous silicon by the contact angle method. Porous silicon series were obtained by electrochemical anodic etching of n-Si (100) and (111) under the current anodization density range of 5-120 mA/cm2. For this purpose the original laboratory installation and the software «Measurement of contact angle» were developed. It is shown that, the contact angle can vary significantly (up to 80 degrees for (100)) depending on the current anodization Discussion of the results is carried out taking in account the composition of the functional groups and of surface morphology of the porous silicon. These results are important for developing porous silicon particles as nanocontainers in the targeted drug delivery.

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.

Preparation and properties of ZnS superhydrophobic surface with hierarchical structure

NASA Astrophysics Data System (ADS)

Yao, Lujun; Zheng, Maojun; He, Shuanghu; Ma, Li; Li, Mei; Shen, Wenzhong

2011-01-01

A novel ZnS hierarchical structure composed of nanorod arrays with branched nanosheets and nanowires grown on their upside walls, was synthesized over Au-coated silicon substrate via chemical vapor deposition technique. Contact angle and sliding angle of this hierarchical film with no surface modification were measured to be about 153.8° and 9.1° for 5 μl water droplets. Self-cleaning behavior and dynamic water-repelling performance were clearly demonstrated. In addition, electrowetting transition phenomenon from superhydrophobic to hydrophilic state happened when a critical bias ∼7.0 V was applied. Below this threshold voltage, the contact angle change is little. This work for the first time reports the creation of ZnS superhydrophobic surface and could enrich its research field as surface functional materials.

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.

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

Wetting characteristics of 3-dimensional nanostructured fractal surfaces

NASA Astrophysics Data System (ADS)

Davis, Ethan; Liu, Ying; Jiang, Lijia; Lu, Yongfeng; Ndao, Sidy

2017-01-01

This article reports the fabrication and wetting characteristics of 3-dimensional nanostructured fractal surfaces (3DNFS). Three distinct 3DNFS surfaces, namely cubic, Romanesco broccoli, and sphereflake were fabricated using two-photon direct laser writing. Contact angle measurements were performed on the multiscale fractal surfaces to characterize their wetting properties. Average contact angles ranged from 66.8° for the smooth control surface to 0° for one of the fractal surfaces. The change in wetting behavior was attributed to modification of the interfacial surface properties due to the inclusion of 3-dimensional hierarchical fractal nanostructures. However, this behavior does not exactly obey existing surface wetting models in the literature. Potential applications for these types of surfaces in physical and biological sciences are also discussed.

49 CFR 571.219 - Standard No. 219; Windshield zone intrusion.

Code of Federal Regulations, 2010 CFR

2010-10-01

... contact with the windshield, shall penetrate the protected zone template, affixed according to S6, to a... simultaneously contacts the inner surface of the windshield glazing and the surface of the instrument panel... surface of the windshield. (c) The locus of lines forming a 45° angle with the outer surface of the...

Wettability of modified silica layers deposited on glass support activated by plasma

NASA Astrophysics Data System (ADS)

Terpiłowski, Konrad; Rymuszka, Diana; Goncharuk, Olena V.; Sulym, Iryna Ya.; Gun'ko, Vladimir M.

2015-10-01

Fumed silica modified by hexamethyldisilazane [HDMS] and polydimethylsiloxane [PDMS] was dispersed in a polystyrene/chloroform solution. To increase adhesion between deposited silica layers and a glass surface, the latter was pretreated with air plasma for 30 s. The silica/polystyrene dispersion was deposited on the glass support using a spin coater. After deposition, the plates were dried in a desiccator for 24 h. Water advancing and receding contact angles were measured using the tilted plate method. The apparent surface free energy (γS) was evaluated using the contact angle hysteresis approach. The surface topography was determined using the optical profilometry method. Contact angles changed from 59.7° ± 4.4 (at surface coverage with trimethylsilyl groups Θ = 0.14) to 155° ± 3.1 at Θ = 1. The value of γS decreased from 51.3 ± 2.8 mJ/m2 (for the sample at the lowest value of Θ) to 1.0 ± 0.4 mJ/m2 for the most hydrophobic sample. Thus, some systems with a high degree of modification by HDMS showed superhydrophobicity, and the sliding angle amounted to about 16° ± 2.1.

Superhydrophobic surfaces: From nature to biomimetic through VOF simulation.

PubMed

Liu, Chunbao; Zhu, Ling; Bu, Weiyang; Liang, Yunhong

2018-04-01

The contact angle, surface structure and chemical compositions of Canna leaves were investigated. According to the surface structure of Canna leaves which observed by Scanning Electron Microscopy(SEM), the CFD (Computational Fluid Dynamics)model was established and the method of volume of fluid (VOF) was used to simulate the process of droplet impacting on the surface and established a smooth surface for comparison to verify that the surface structure was an important factor of the superhydrophobic properties. Based on the study of Canna leaf and VOF simulation of its surface structure, the superhydrophobic samples were processed successfully and showed a good superhydrophobic property with a contact angle of 156 ± 1 degrees. A high-speed camera (5000 frames per second) was used to assess droplet movement and determine the contact time of the samples. The contact time for the sample was 13.1 ms. The results displayed that the artificial superhydrophobic surface is perfect for the performance of superhydrophobic properties. The VOF simulation method was efficient, accurate and low cost before machining artificial superhydrophobic samples. Copyright © 2018 Elsevier Ltd. All rights reserved.

Free-surface phenomena under low- and zero-gravity conditions

NASA Technical Reports Server (NTRS)

Coles, D.

1985-01-01

An apparatus to measure contact angle was constructed to exploit the proposed internal-corner criterion. If 2 alfa is the internal angle between two intersecting vertical planes and gamma is the contact angle, a meniscus at the corner rises to a finite height if alfa + gamma pi/2 and to an infinite height if alfa + gamma pi/2. The apparatus operates by decreasing the angle alfa from pi/2 until the meniscus height changes abruptly. A number of liquids are tested on glass and plexiglas.

Evaluation of the surface properties of PTFE foam coating filter media using XPS and contact angle measurements

NASA Astrophysics Data System (ADS)

Park, Byung Hyun; Lee, Myong-Hwa; Kim, Sang Bum; Jo, Young Min

2011-02-01

A newly developed PTFE foam coating filter was developed which can be used for hot gas cleaning at temperatures up to 250 °C. The emulsion-type PTFE was coated onto a woven glass fiber using a foam coating method. The filter surface was closely examined using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The XPS results were used to determine the binding force between the carbon and fluorine of PTFE, which imparts coating stability to the filter medium. More than 95% of the bonds of the PTFE foam coating filter were between carbon and fluorine, and this filter demonstrated excellent hydrophobic and good oleophobic properties at the same time. The contact angles of liquid droplets on the filter surface were used to predict the potential wetability of the filter against water or oil. In addition, the very low surface free energy of the filter medium, which was evaluated using the Owens-Wendt method, demonstrates a very stable surface and a high de-dusting quality.

Wetting Transition of Water

NASA Astrophysics Data System (ADS)

Friedman, Serah; Khalil, Matt; Taborek, Peter

2013-03-01

Pure liquid water does not wet most solid surfaces. Liquid water on these surfaces beads up and forms droplets with a finite contact angle. General thermodynamic principles suggest that as the temperature approaches the critical point, the contact angle should go to zero, marking the wetting transition. We have made an optical cell which can operate near the critical point of water (Tc =373C, Pc =217 atm) to study this phenomenon on sapphire, graphite and silicon. We have used two methods to measure the wetting temperature of water on these surfaces. Firstly, we studied a single droplet on a horizontal surface and optically measured the change in contact angle as a function of increasing temperature. Second, we studied the condensation of droplets on a vertical plate as a function of temperature. As the temperature approached the wetting temperature in both cases, the droplets spread and eventually form a smooth film along the surface of the plate. The wetting temperature on sapphire is near 240C and is considerably higher on graphite. Our observed values of Tw are significantly higher than the predictions made by the sharp-kink approximation and recent molecular dynamics simulations.

Effect of dielectric barrier discharge treatment on surface nanostructure and wettability of polylactic acid (PLA) nonwoven fabrics

NASA Astrophysics Data System (ADS)

Ren, Yu; Xu, Lin; Wang, Chunxia; Wang, Xiaona; Ding, Zhirong; Chen, Yuyue

2017-12-01

Polylactic acid (PLA) nonwoven fabrics are treated with atmospheric dielectric barrier discharge (DBD) plasma to improve surface wettability. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that micro- to nano-scale textures appear on the treated PLA surfaces dependent on the treatment time. X-ray photoelectron spectroscopy (XPS) analysis reveals that the DBD plasma treatments result in decreased carbon contents and increased oxygen contents as well as slightly increased nitrogen contents. The water contact angle decreases sharply with the increase of the DBD plasma treatment time. The super hydrophilic PLA surfaces (the water contact angle reached 0°) are obtained when the treatment time is longer than 90 s. Ninety days after the DBD plasma treatment, the XPS analysis shows that Csbnd O/Csbnd N and Cdbnd O/Osbnd Cdbnd O percentages decline for all treatment groups. However, the water contact angle is kept constant at 0° for the groups treated above 90 s, which could be due to the oxidized nano-structured layer on the DBD plasma treated PLA surfaces.

Hydrophobic interactions between dissimilar surfaces

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

Yoon, R.H.; Flinn, D.H.; Rabinovich, Y.I.

1997-01-15

An atomic force microscope (AFM) was used to measure surface forces between a glass sphere and a silica plate. When the measurements were conducted between untreated surfaces, a short-range hydration force with decay lengths of 0.4 and 3.0 nm was observed. When the surfaces were hydrophobized with octadecyltrichlorosilane (OTS), on the other hand, long-range hydrophobic forces with decay lengths in the range of 2--32 nm were observed. The force measurements were conducted between surfaces having similar and dissimilar hydrophobicities so that the results may be used for deriving an empirical combining rule. It was found that the power law forcemore » constants for asymmetric interactions are close to the geometric means of those for symmetric interactions. Thus, hydrophobic force constants can be combined in the same manner as the Hamaker constants. A plot of the power law force constants versus water contact angles suggests that the hydrophobic force is uniquely determined by contact angle. These results will be useful in predicting hydrophobic forces for asymmetric interactions and in estimating hydrophobic forces from contact angles.« less

Topography and surface free energy of DPPC layers deposited on a glass, mica, or PMMA support.

PubMed

Jurak, Malgorzata; Chibowski, Emil

2006-08-15

An investigation of energetic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on glass, mica, and PMMA (poly(methyl methacrylate)) surfaces was carried out by means of contact angles measurements (advancing and receding) for three probe liquids (diiodomethane, water, and formamide). DPPC was deposited on the surfaces from water (on glass and mica) or methanol (on PMMA) solutions. The topography of the tested surfaces was determined with a help of scanning electron microscopy (SEM) and atomic force microscopy (AFM). Using the measured contact angles, the total apparent surface free energy and its components of the studied layers were determined from van Oss et al.'s (Lifshitz-van der Waals and acid-base components, LWAB) and contact angle hysteresis (CAH) approaches. It allowed us to learn about changes in the surface free energy of the layers (hydrophobicity/hydrophilicity) depending on their number and kind of support. It was found that the changes in the energy greatly depended on the surface properties of the substrate as well as the statistical number of monolayers of DPPC. However, principal changes took place for first three monolayers.

A Facile All-Solution-Processed Surface with High Water Contact Angle and High Water Adhesive Force.

PubMed

Chen, Mei; Hu, Wei; Liang, Xiao; Zou, Cheng; Li, Fasheng; Zhang, Lanying; Chen, Feiwu; Yang, Huai

2017-07-12

A series of sticky superhydrophobicity surfaces with high water contact angle and high water adhesive force is facilely prepared via an all-solution-processed method based on polymerization-induced phase separation between liquid crystals (LCs) and epoxy resin, which produces layers of epoxy microspheres (EMSs) with nanofolds on the surface of a substrate. The morphologies and size distributions of EMSs are confirmed by scanning electron microscopy. Results reveal that the obtained EMS coated-surface exhibits high apparent contact angle of 152.0° and high water adhesive force up to 117.6 μN. By varying the composition of the sample or preparing conditions, the sizes of the produced EMSs can be artificially regulated and, thus, control the wetting properties and water adhesive behaviors. Also, the sticky superhydrophobic surface exhibits excellent chemical stability, as well as long-term durability. Water droplet transportation experiments further prove that the as-made surface can be effectively used as a mechanical hand for water transportation applications. Based on this, it is believed that the simple method proposed in this paper will pave a new way for producing a sticky superhydrophobic surface and obtain a wide range of use.

A New Approach to Measure Contact Angle and Evaporation Rate with Flow Visualization in a Sessile Drop

NASA Technical Reports Server (NTRS)

Zhang, Nengli; Chao, David F.

1999-01-01

The contact angle and the spreading process of sessile droplet are very crucial in many technological processes, such as painting and coating, material processing, film-cooling applications, lubrication, and boiling. Additionally, as it is well known that the surface free energy of polymers cannot be directly, measured for their elastic and viscous restraints. The measurements of liquid contact angle on the polymer surfaces become extremely important to evaluate the surface free energy of polymers through indirect methods linked with the contact angle data. Due to the occurrence of liquid evaporation is inevitable, the effects of evaporation on the contact angle and the spreading become very important for more complete understanding of these processes. It is of interest to note that evaporation can induce Marangoni-Benard convection in sessile drops. However, the impacts of the inside convection on the wetting and spreading processes are not clear. The experimental methods used by previous investigators cannot simultaneously measure the spreading process and visualize the convection inside. Based on the laser shadowgraphic system used by the present author, a very simple optical procedure has been developed to measure the contact angle, the spreading speed, the evaporation rate, and to visualize inside convection of a sessile drop simultaneously. Two CCD cameras were used to synchronously record the real-time diameter of the sessile drop, which is essential for determination of both spreading speed and evaporation rate, and the shadowgraphic image magnified by the sessile drop acting as a thin plano-convex lens. From the shadowgraph, the inside convection of the drop can be observed if any and the image outer diameter, which linked to the drop profile, can be measured. Simple equations have been derived to calculate the drop profile, including the instantaneous contact angle, height, and volume of the sessile drop, as well as the evaporation rate. The influence of the inside convection on the wetting and spreading processes can be figured out through comparison of the drop profiles with and without inside convection when the sessile drop is placed at different evaporation conditions.

Fabrication and anisotropic wettability of titanium-coated microgrooves

NASA Astrophysics Data System (ADS)

Gui, N.; Xu, W.; Tian, J.; Rosengarten, G.; Brandt, M.; Qian, M.

2018-03-01

Surface wettability plays a critical role in a variety of key areas including orthopaedic implants and chemical engineering. Anisotropy in wettability can arise from surface grooves, which are of particular relevance to orthopaedic implants because they can mimic collagen fibrils that are the basic components of the extracellular matrix. Titanium (Ti) and its alloys have been widely used for orthopaedic and dental implant applications. This study is concerned with the fabrication of Ti-coated microgrooves with different groove widths and the characterisation of the anisotropy in wettability through measuring water contact angles, compared with both the Wenzel and Cassie models. Experimental results revealed that there existed significant anisotropy in the wettability of Ti-coated microgrooves, and the degree of anisotropy (Δθ) increased with an increasing groove width from 5 μm to 20 μm. On average, the contact angle measured parallel to the groove direction (θ//) was about 50°-60° smaller than that measured perpendicular to the groove direction (θ⊥). In general, the Wenzel model predicted the contact angles along the surface groove direction reasonably, and so did the Cassie model for the contact angles perpendicular to the groove direction. Osteoblast spreading was affected by the anisotropy in wettability, which occurred preferably along, rather than perpendicular to, the groove direction. These findings are informative for the design of Ti implant surfaces when anisotropy in wettability matters.

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.

Preliminary Tests for Ti-Mo-Zr-Ta Alloys as Potential Biomaterials

NASA Astrophysics Data System (ADS)

Bălţatu, M. S.; Vizureanu, P.; Bălan, T.; Lohan, M.; Ţugui, C. A.

2018-06-01

Nowadays, there is a continuing concern for the research and development of alloys for medical and biomedical applications. In order to check the biocompatible character of a new Ti-Mo-Zr-Ta alloys, it is necessary to carry out preliminary laboratory tests to follow how a biomaterial surface would interact with the host. The paper presents tests for Ti-Mo-Zr-Ta alloys like contact angle and DSC test to identify biocompatible character. Contact angle measurement is an experimental technique used to assess the hydrophilic or hydrophobic character of surfaces by reference to the 90º contact angle value and to characterize the thermal behavior, for temperature range between 36.5-37.2ºC, interval which a biomaterial works inside the healthy human body, was used DSC test.

Contact angle and surface free energy of experimental resin-based dental restorative materials after chewing simulation.

PubMed

Rüttermann, Stefan; Beikler, Thomas; Janda, Ralf

2014-06-01

To investigate contact angle and surface free energy of experimental dental resin composites containing novel delivery systems of polymeric hollow beads and low-surface tension agents after chewing simulation test. A delivery system of novel polymeric hollow beads differently loaded with two low-surface tension agents was used in different amounts to modify commonly formulated experimental dental resin composites. The non-modified resin was used as standard. Surface roughness Ra, contact angle Θ, total surface free energy γS, its apolar γS(LW), polar γS(AB), Lewis acid γS(+) and base γS(-) terms were determined and the results prior to and after chewing simulation test were compared. Significance was p<0.05. After chewing simulation Ra increased, Θ decreased, Ra increased for two test materials and γS decreased or remained constant for the standard or the test materials after chewing simulation. Ra of one test material was higher than of the standard, Θ and γS of the test materials remained lower than of the standard and, indicating their highly hydrophobic character (Θ≈60-75°, γS≈30mJm(-2)). γS(LW), and γS(-) of the test materials were lower than of the standard. Some of the test materials had lower γS(AB) and γS(+) than of the standard. Delivery systems based on novel polymeric hollow beads highly loaded with low-surface tension agents were found to significantly increase contact angle and thus to reduce surface free energy of experimental dental resin composites prior to and after chewing simulation test. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Automatic measurement of contact angle in pore-space images

NASA Astrophysics Data System (ADS)

AlRatrout, Ahmed; Raeini, Ali Q.; Bijeljic, Branko; Blunt, Martin J.

2017-11-01

A new approach is presented to measure the in-situ contact angle (θ) between immiscible fluids, applied to segmented pore-scale X-ray images. We first identify and mesh the fluid/fluid and fluid/solid interfaces. A Gaussian smoothing is applied to this mesh to eliminate artifacts associated with the voxelized nature of the image, while preserving large-scale features of the rock surface. Then, for the fluid/fluid interface we apply an additional smoothing and adjustment of the mesh to impose a constant curvature. We then track the three-phase contact line, and the two vectors that have a direction perpendicular to both surfaces: the contact angle is found from the dot product of these vectors where they meet at the contact line. This calculation can be applied at every point on the mesh at the contact line. We automatically generate contact angle values representing each invaded pore-element in the image with high accuracy. To validate the approach, we first study synthetic three-dimensional images of a spherical droplet of oil residing on a tilted flat solid surface surrounded by brine and show that our results are accurate to within 3° if the sphere diameter is 2 or more voxels. We then apply this method to oil/brine systems imaged at ambient temperature and reservoir pressure (10MPa) using X-ray microtomography (Singh et al., 2016). We analyse an image volume of diameter approximately 4.6 mm and 10.7 mm long, obtaining hundreds of thousands of values from a dataset with around 700 million voxels. We show that in a system of altered wettability, contact angles both less than and greater than 90° can be observed. This work provides a rapid method to provide an accurate characterization of pore-scale wettability, which is important for the design and assessment of hydrocarbon recovery and carbon dioxide storage.

Facile method for preparing superoleophobic surfaces with hierarchical microcubic/nanowire structures

NASA Astrophysics Data System (ADS)

Kwak, Wonshik; Hwang, Woonbong

2016-02-01

To facilitate the fabrication of superoleophobic surfaces having hierarchical microcubic/nanowire structures (HMNS), even for low surface tension liquids including octane (surface tension = 21.1 mN m-1), and to understand the influences of surface structures on the oleophobicity, we developed a convenient method to achieve superoleophobic surfaces on aluminum substrates using chemical acid etching, anodization and fluorination treatment. The liquid repellency of the structured surface was validated through observable experimental results the contact and sliding angle measurements. The etching condition required to ensure high surface roughness was established, and an optimal anodizing condition was determined, as a critical parameter in building the superoleophobicity. The microcubic structures formed by acid etching are essential for achieving the formation of the hierarchical structure, and therefore, the nanowire structures formed by anodization lead to an enhancement of the superoleophobicity for low surface tension liquids. Under optimized morphology by microcubic/nanowire structures with fluorination treatment, the contact angle over 150° and the sliding angle less than 10° are achieved even for octane.

Dynamics of contact line depinning during droplet evaporation based on thermodynamics.

PubMed

Yu, Dong In; Kwak, Ho Jae; Doh, Seung Woo; Ahn, Ho Seon; Park, Hyun Sun; Kiyofumi, Moriyama; Kim, Moo Hwan

2015-02-17

For several decades, evaporation phenomena have been intensively investigated for a broad range of applications. However, the dynamics of contact line depinning during droplet evaporation has only been inductively inferred on the basis of experimental data and remains unclear. This study focuses on the dynamics of contact line depinning during droplet evaporation based on thermodynamics. Considering the decrease in the Gibbs free energy of a system with different evaporation modes, a theoretical model was developed to estimate the receding contact angle during contact line depinning as a function of surface conditions. Comparison of experimentally measured and theoretically modeled receding contact angles indicated that the dynamics of contact line depinning during droplet evaporation was caused by the most favorable thermodynamic process encountered during constant contact radius (CCR mode) and constant contact angle (CCA mode) evaporation to rapidly reach an equilibrium state during droplet evaporation.

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

Lazauskas, A., E-mail: Algirdas.LAZAUSKAS@stud.ktu.lt; Guobienė, A., E-mail: Asta.GUOBIENE@ktu.lt; Prosyčevas, I., E-mail: IGORPROS@mail.ru

This work investigates water droplet behavior on superhydrophobic (water contact angle value of 162 ± 1°) SiO{sub 2} nanocomposite films subjected to repetitive icing/deicing treatments, changes in SiO{sub 2} nanocomposite film surface morphology and their non-wetting characteristics. During the experiment, water droplets on SiO{sub 2} nanocomposite film surface are subjected to a series of icing and deicing cycles in a humid (∼ 70% relative humidity) atmosphere and the resulting morphological changes are monitored and characterized using atomic force microscopy (AFM) and contact angle measurements. Our data show that the formation of the frozen or thawed water droplet, with no furthermore » shape change, on superhydrophobic SiO{sub 2} nanocomposite film, is obtained faster within each cycle as the number of the icing/deicing cycles increases. After 10 icing and deicing cycles, the superhydrophobic SiO{sub 2} nanocomposite film had a water contact angle value of 146 ± 2° which is effectively non-superhydrophobic. AFM analysis showed that the superhydrophobic SiO{sub 2} nanocomposite film surface area under the water droplet undergoes gradual mechanical damage during the repetitive icing/deicing cycles. We propose a possible mechanism of the morphological changes to the film surface that take place during the consecutive icing/deicing experiments. - Highlights: • Superhydrophobic film is subjected to repetitive icing/deicing treatments. • Water droplet shape transition is recorded and characterized thereafter. • Atomic force microscopy and contact angle measurements are performed. • The surface undergoes gradual mechanical damage during repetitive icing/deicing. • Mechanism for the observed surface morphological changes is suggested.« less

Changes in Wetting Hysteresis During Bioremediation: Changes in fluid flow behavior monitored with low-frequency seismic attenuation

NASA Astrophysics Data System (ADS)

Wempe, W.; Spetzler, H.; Kittleson, C.; Pursley, J.

2003-12-01

We observed significant reduction in wetting hysteresis with time while a diesel-contaminated quartz crystal was dipped in and out of an oil-reducing bacteria solution. This wetting hysteresis is significantly greater than the wetting hysteresis when the diesel-contaminated quartz crystal is dipped in and out of (1) water, (2) diesel and (3) the bacterial food solution that does not contain bacteria. The reduction in wetting hysteresis of the bacteria solution on the quartz surface results from a reduction in the advancing contact angle formed at the air-liquid-quartz contact with time; the receding contact angle remains the same with time. Our results suggest that the bacteria solution moves across the quartz surface with less resistance after bioremediation has begun. These results imply that bioremediation may influence fluid flow behavior with time. For many fluid-solid systems there is a difference between the contact angle while a contact line advances and recedes across a solid surface; this difference is known as wetting hysteresis. Changes in wetting hysteresis can occur from changes in surface tension or the surface topography. Low contact angle values indicate that the liquid spreads or wets well, while high values indicate poor wetting or non-wetting. Contact angles are estimated in the lab by measuring the weight of the meniscus formed at the air-liquid-quartz interface and by knowing the fluid surface tension. In the lab, we have been able to use low-frequency seismic attenuation data to detect changes in the wetting characteristics of glass plates and of Berea sandstone. The accepted seismic attenuation mechanism is related to the loss of seismic energy due to the hysteresis of meniscus movement (wetting hysteresis) when a pore containing two fluids is stressed at very low frequencies (< 10 Hz). When fluid-fluid-solid systems that exhibit wettability hysteresis are stressed at low frequencies, we observe seismic attenuation, whereas in a system that does not exhibit wettability hysteresis we do not. From our wettability hysteresis results, we conclude that we may be able to monitor bioremediation progress using seismic attenuation data. We are measuring low-frequency seismic attenuation in the lab while flowing bacteria solution through Berea sandstone and we are testing this application in the field.

New Method Developed to Measure Contact Angles of a Sessile Drop

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Nengli

2002-01-01

The spreading of an evaporating liquid on a solid surface occurs in many practical processes and is of importance in a number of practical situations such as painting, textile dyeing, coating, gluing, and thermal engineering. Typical processes involving heat transfer where the contact angle plays an important role are film cooling, boiling, and the heat transfer through heat pipes. The biological phenomenon of cell spreading also is analogous to a drop spreading (ref. 1). In the study of spreading, the dynamic contact angle describes the interfacial properties on solid substrates and, therefore, has been studied by physicists and fluid mechanics investigators. The dynamic contact angle of a spreading nonvolatile liquid drop provides a simple tool in the study of the free-boundary problem, but the study of the spreading of a volatile liquid drop is of more practical interest because the evaporation of common liquids is inevitable in practical processes. The most common method to measure the contact angle, the contact radius, and the height of a sessile drop on a solid surface is to view the drop from its edge through an optical microscope. However, this method gives only local information in the view direction. Zhang and Yang (ref. 2) developed a laser shadowgraphy method to investigate the evaporation of sessile drop on a glass plate. As described here, Zhang and Chao (refs. 3 and 4) improved the method and suggested a new optical arrangement to measure the dynamic contact angle and the instant evaporation rate of a sessile drop with much higher accuracy (less than 1 percent). With this method, any fluid motion in the evaporating drop can be visualized through shadowgraphy without using a tracer, which often affects the field under investigation.

Controlled surface morphology and hydrophilicity of polycaprolactone toward human retinal pigment epithelium cells.

PubMed

Shahmoradi, Saleheh; Yazdian, Fatemeh; Tabandeh, Fatemeh; Soheili, Zahra-Soheila; Hatamian Zarami, Ashraf Sadat; Navaei-Nigjeh, Mona

2017-04-01

Applying scaffolds as a bed to enhance cell proliferation and even differentiation is one of the treatment of retina diseases such as age-related macular degeneration (AMD) which deteriorating photoreceptors and finally happening blindness. In this study, aligned polycaprolactone (PCL) nanofibers were electrospun and at different conditions and their characteristics were measured by scanning electron microscope (SEM) and contact angle. Response surface methodology (RSM) was used to optimize the diameter of fabricated nanofibers. Two factors as solution concentration and voltage value were considered as independent variables and their effects on nanofibers' diameters were evaluated by central composite design and the optimum conditions were obtained as 0.12g/mL and 20kV, respectively. In order to decrease the hydrophobicity of PCL, the surface of the fabricated scaffolds was modified by alkaline hydrolysis method. Contact time of the scaffolds and alkaline solution and concentration of alkaline solution were optimized using Box Behnken design and (120min and 5M were the optimal, respectively). Contact angle measurement showed the high hydrophilicity of treated scaffolds (with contact angle 7.48°). Plasma surface treatment was applied to compare the effect of using two kinds of surface modification methods simultaneously on hydrolyzed scaffolds. The RPE cells grown on scaffolds were examined by immunocytochemistry (ICC), MTT and continuous inspection of cellular morphology. Interestingly, Human RPE cells revealed their characteristic morphology on hydrolyzed scaffold well. As a result, we introduced a culture substrate with low diameter (185.8nm), high porosity (82%) and suitable hydrophilicity (with contact angle 7.48 degree) which can be promising for hRPE cell transplantation. Copyright © 2016. Published by Elsevier B.V.

Confinement Correction to Mercury Intrusion Capillary Pressure of Shale Nanopores

PubMed Central

Wang, Sen; Javadpour, Farzam; Feng, Qihong

2016-01-01

We optimized potential parameters in a molecular dynamics model to reproduce the experimental contact angle of a macroscopic mercury droplet on graphite. With the tuned potential, we studied the effects of pore size, geometry, and temperature on the wetting of mercury droplets confined in organic-rich shale nanopores. The contact angle of mercury in a circular pore increases exponentially as pore size decreases. In conjunction with the curvature-dependent surface tension of liquid droplets predicted from a theoretical model, we proposed a technique to correct the common interpretation procedure of mercury intrusion capillary pressure (MICP) measurement for nanoporous material such as shale. Considering the variation of contact angle and surface tension with pore size improves the agreement between MICP and adsorption-derived pore size distribution, especially for pores having a radius smaller than 5 nm. The relative error produced in ignoring these effects could be as high as 44%—samples that contain smaller pores deviate more. We also explored the impacts of pore size and temperature on the surface tension and contact angle of water/vapor and oil/gas systems, by which the capillary pressure of water/oil/gas in shale can be obtained from MICP. This information is fundamental to understanding multiphase flow behavior in shale systems. PMID:26832445

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.

On the physically based modeling of surface tension and moving contact lines with dynamic contact angles on the continuum scale

NASA Astrophysics Data System (ADS)

Huber, M.; Keller, F.; Säckel, W.; Hirschler, M.; Kunz, P.; Hassanizadeh, S. M.; Nieken, U.

2016-04-01

The description of wetting phenomena is a challenging problem on every considerable length-scale. The behavior of interfaces and contact lines on the continuum scale is caused by intermolecular interactions like the Van der Waals forces. Therefore, to describe surface tension and the resulting dynamics of interfaces and contact lines on the continuum scale, appropriate formulations must be developed. While the Continuum Surface Force (CSF) model is well-engineered for the description of interfaces, there is still a lack of treatment of contact lines, which are defined by the intersection of an ending fluid interface and a solid boundary surface. In our approach we use a balance equation for the contact line and extend the Navier-Stokes equations in analogy to the extension of a two-phase interface in the CSF model. Since this model depicts a physically motivated approach on the continuum scale, no fitting parameters are introduced and the deterministic description leads to a dynamical evolution of the system. As verification of our theory, we show a Smoothed Particle Hydrodynamics (SPH) model and simulate the evolution of droplet shapes and their corresponding contact angles.

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.

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

Chen, Yu; School of Mechanical and Electrical Engineering, Wuhan Institute of Technology, Wuhan 430073; Guo, Zhiguang, E-mail: zguo@licp.cas.cn

Graphical abstract: A double-metal-assisted chemical etching method is employed to fabricate superhydrophobic surfaces, showing a good superhydrophobicity with the contact angle of about 170°, and the sliding angle of about 0°. Meanwhile, the potential formation mechanism about it is also presented. Highlights: ► A double-metal-assisted chemical etching method is employed to fabricate superhydrophobic surfaces. ► The obtained surfaces show good superhydrophobicity with a high contact angle and low sliding angle. ► The color of the etched substrate dark brown or black and it is so-called black silicon. -- Abstract: Silicon substrates treated by metal-assisted chemical etching have been studied formore » many years since they could be employed in a variety of electronic and optical devices such as integrated circuits, photovoltaics, sensors and detectors. However, to the best of our knowledge, the chemical etching treatment on the same silicon substrate with the assistance of two or more kinds of metals has not been reported. In this paper, we mainly focus on the etching time and finally obtain a series of superhydrophobic silicon surfaces with novel etching structures through two successive etching processes of Cu-assisted and Ag-assisted chemical etching. It is shown that large-scale homogeneous but locally irregular wire-like structures are obtained, and the superhydrophobic surfaces with low hysteresis are prepared after the modifications with low surface energy materials. It is worth noting that the final silicon substrates not only possess high static contact angle and low hysteresis angle, but also show a black color, indicating that the superhydrophobic silicon substrate has an extremely low reflectance in a certain range of wavelengths. In our future work, we will go a step further to discuss the effect of temperature, the size of Cu nanoparticles and solution concentration on the final topography and superhydrophobicity.« less

Influence of surface contamination on the wettability of heat transfer surfaces

DOE PAGES

Forrest, Eric Christopher; Schulze, Roland; Liu, Cheng; ...

2015-08-08

In this study, the wettability of heat transfer surfaces plays an important role in liquid–vapor phase change phenomena, including boiling incipience, the critical heat flux, the Leidenfrost transition, and condensation. The influence of adsorbed surface contamination at the nanoscale, though seldom considered, can have a profound impact on wetting behavior. This study quantitatively investigates the impact of contaminant layer thickness on wettability. Various cleaning treatments are explored on zirconium and 6061 aluminum to determine the effect on contaminant and oxide layer thickness. Angle-resolved X-ray photoelectron spectroscopy can be used to measure the thickness of oxide and contaminant layers, which ismore » then correlated to wettability by measuring the equilibrium contact angle. Results indicate that even after solvent cleaning, the contact angle of water on practical heat transfer surfaces is dominated by a hydrocarbon contaminant overlayer around five nanometers thick.« less

Influence of surface contamination on the wettability of heat transfer surfaces

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

Forrest, Eric Christopher; Schulze, Roland; Liu, Cheng

In this study, the wettability of heat transfer surfaces plays an important role in liquid–vapor phase change phenomena, including boiling incipience, the critical heat flux, the Leidenfrost transition, and condensation. The influence of adsorbed surface contamination at the nanoscale, though seldom considered, can have a profound impact on wetting behavior. This study quantitatively investigates the impact of contaminant layer thickness on wettability. Various cleaning treatments are explored on zirconium and 6061 aluminum to determine the effect on contaminant and oxide layer thickness. Angle-resolved X-ray photoelectron spectroscopy can be used to measure the thickness of oxide and contaminant layers, which ismore » then correlated to wettability by measuring the equilibrium contact angle. Results indicate that even after solvent cleaning, the contact angle of water on practical heat transfer surfaces is dominated by a hydrocarbon contaminant overlayer around five nanometers thick.« less

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.

Fast modification on wheat straw outer surface by water vapor plasma and its application on composite material.

PubMed

Chen, Weimin; Xu, Yicheng; Shi, Shukai; Cao, Yizhong; Chen, Minzhi; Zhou, Xiaoyan

2018-02-02

The presence of non-poplar extracts, cutin, and wax layer in the wheat straw outer surface (WOS) greatly limit its application in bio-composite preparation. In this study, a dielectric-barrier-discharge plasma using water vapor as feeding gas was used to fast modify the WOS. The morphology, free radical concentrations, surface chemical components, and contact angles of WOS before and after plasma modification were investigated. Wheat straw was further prepared into wheat straw-based composites (WSC) and its bonding strength was evaluated by a paper tension meter. The results showed that water vapor plasma leads to the appearance of surface roughness, the generation of massive free radicals, and the introduction of oxygen-containing groups. In addition, both initial and equilibrium contact angle and the surface total free energy were significantly increased after plasma modification. These results synergistically facilitate the spread and permeation of adhesive onto the WOS and thus improve the bonding strength of all prepared WSCs. A good linear relationship between bonding strength and surface roughness parameters, contact angles, and total free energy were observed. In general, this study provided a time-saving and cost-effective modification method to realize WSC manufacture.

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.

Effect of contact angle and contact angle hysteresis on the floatability of spheres at the air-water interface.

PubMed

Feng, Dong-Xia; Nguyen, Anh V

2017-10-01

The floatability of solid particles on the water surface governs many natural phenomena and industrial processes including film flotation and froth flotation separation of coal and valuable minerals. For many years, the contact angle (CA) has been postulated as the key factor in determining the particle floatability. Indeed, the maximum force (tenacity) supporting the flotation of fine spheres was conjectured to occur when the apical angle of the contact circle is equal to the contact angle. In this paper, the model predictions are reviewed and compared with experimental results. It is shown that CA can be affected by many physical and chemical factors such as surface roughness and chemical heterogeneity and can have a range of values known as the CA hysteresis. This multiple-valued CA invalidates the available theories on the floatability of spheres. Even the intuitive replacement of CA by the advancing (maximum) CA in the classical theories can be wrong. A few new examples are also reviewed and analyzed to demonstrate the significance of CA variation in controlling the particle floatability. They include the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, and the nearby interaction among floating particles, known as lateral inter-particle interaction. It is concluded that our quantitative understanding of the floatability of real particles being irregular and heterogeneous both morphologically and chemically is still far from being satisfactory. Copyright © 2017 Elsevier B.V. All rights reserved.

Dynamic Chemically Driven Dewetting, Spreading, and Self-Running of Sessile Droplets on Crystalline Silicon.

PubMed

Arscott, Steve

2016-12-06

A chemically driven dewetting effect is demonstrated using sessile droplets of dilute hydrofluoric acid on chemically oxidized silicon wafers. The dewetting occurs as the thin oxide is slowly etched by the droplet and replaced by a hydrogen-terminated surface; the result of this is a gradual increase in the contact angle of the droplet with time. The time-varying work of adhesion is calculated from the time-varying contact angle; this corresponds to the changing chemical nature of the surface during dewetting and can be modeled by the well-known logistic (sigmoid) function often used for the modeling of restricted growth, in this case, the transition from an oxidized surface to a hydrogen-terminated silicon surface. The observation of the time-varying contact angle allows one to both measure the etch rate of the silicon oxide and estimate the hydrogenation rate as a function of HF concentration and wafer type. In addition to this, at a certain HF concentration, a self-running droplet effect is observed. In contrast, on hydrogen-terminated silicon wafers, a chemically induced spreading effect is observed using sessile droplets of nitric acid. The droplet spreading can also be modeled using a logistical function, where the restricted growth is the transition from hydrogen-terminated to a chemically induced oxidized silicon surface. The chemically driven dewetting and spreading observed here add to the methods available to study dynamic wetting (e.g., the moving three-phase contact line) of sessile droplets on surfaces. By slowing down chemical kinetics of the wetting, one is able to record the changing profile of the sessile droplet with time and gather information concerning the time-varying surface chemistry. The data also indicates a chemical interface hysteresis (CIH) that is compared to contact angle hysteresis (CAH). The approach can also be used to study the chemical etching and deposition behavior of thin films using liquids by monitoring the macroscopic droplet profile and relating this to the time-varying physical and chemical interface phenomena.

Switchable Super-Hydrophilic/Hydrophobic Indium Tin Oxide (ITO) Film Surfaces on Reactive Ion Etching (RIE) Textured Si Wafer.

PubMed

Kim, Hwa-Min; Litao, Yao; Kim, Bonghwan

2015-11-01

We have developed a surface texturing process for pyramidal surface features along with an indium tin oxide (ITO) coating process to fabricate super-hydrophilic conductive surfaces. The contact angle of a water droplet was less than 5 degrees, which means that an extremely high wettability is achievable on super-hydrophilic surfaces. We have also fabricated a super-hydrophobic conductive surface using an additional coating of polytetrafluoroethylene (PTFE) on the ITO layer coated on the textured Si surface; the ITO and PTFE films were deposited by using a conventional sputtering method. We found that a super-hydrophilic conductive surface is produced by ITO coated on the pyramidal Si surface (ITO/Si), with contact angles of approximately 0 degrees and a resistivity of 3 x 10(-4) Ω x cm. These values are highly dependent on the substrate temperature during the sputtering process. We also found that the super-hydrophobic conductive surface produced by the additional coating of PTFE on the pyramidal Si surface with an ITO layer (PTFE/ITO/Si) has a contact angle of almost 160 degrees and a resistivity of 3 x 10(-4) Ω x cm, with a reflectance lower than 9%. Therefore, these processes can be used to fabricate multifunctional features of ITO films for switchable super-hydrophilic and super-hydrophobic surfaces.

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.

The low salinity effect at high temperatures

DOE PAGES

Xie, Quan; Brady, Patrick V.; Pooryousefy, Ehsan; ...

2017-04-05

The mechanism(s) of low salinity water flooding (LSWF) must be better understood at high temperatures and pressures if the method is to be applied in high T/P kaolinite-bearing sandstone reservoirs. We measured contact angles between a sandstone and an oil (acid number, AN = 3.98 mg KOH/g, base number, BN = 1.3 mg KOH/g) from a reservoir in the Tarim Field in western China in the presence of various water chemistries. We examined the effect of aqueous ionic solutions (formation brine, 100X diluted formation brine, and softened water), temperature (60, 100 and 140 °C) and pressure (20, 30, 40, andmore » 50 MPa) on the contact angle. We also measured the zeta potential of the oil/water and water/rock interfaces to calculate oil/brine/rock disjoining pressures. A surface complexation model was developed to interpret contact angle measurements and compared with DLVO theory predictions. Contact angles were greatest in formation water, followed by the softened water, and low salinity water at the same pressure and temperature. Contact angles increased slightly with temperature, whereas pressure had little effect. DLVO and surface complexation modelling predicted similar wettability trends and allow reasonably accurate interpretation of core-flood results. Water chemistry has a much larger impact on LSWF than reservoir temperature and pressure. As a result, low salinity water flooding should work in high temperature and high pressure kaolinite-bearing sandstone reservoirs.« less

The low salinity effect at high temperatures

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

Xie, Quan; Brady, Patrick V.; Pooryousefy, Ehsan

The mechanism(s) of low salinity water flooding (LSWF) must be better understood at high temperatures and pressures if the method is to be applied in high T/P kaolinite-bearing sandstone reservoirs. We measured contact angles between a sandstone and an oil (acid number, AN = 3.98 mg KOH/g, base number, BN = 1.3 mg KOH/g) from a reservoir in the Tarim Field in western China in the presence of various water chemistries. We examined the effect of aqueous ionic solutions (formation brine, 100X diluted formation brine, and softened water), temperature (60, 100 and 140 °C) and pressure (20, 30, 40, andmore » 50 MPa) on the contact angle. We also measured the zeta potential of the oil/water and water/rock interfaces to calculate oil/brine/rock disjoining pressures. A surface complexation model was developed to interpret contact angle measurements and compared with DLVO theory predictions. Contact angles were greatest in formation water, followed by the softened water, and low salinity water at the same pressure and temperature. Contact angles increased slightly with temperature, whereas pressure had little effect. DLVO and surface complexation modelling predicted similar wettability trends and allow reasonably accurate interpretation of core-flood results. Water chemistry has a much larger impact on LSWF than reservoir temperature and pressure. As a result, low salinity water flooding should work in high temperature and high pressure kaolinite-bearing sandstone reservoirs.« less

Surface cleaning for enhanced adhesion to packaging surfaces: Effect of oxygen and ammonia plasma

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

Gaddam, Sneha; Dong, Bin; Driver, Marcus

2015-03-15

The effects of direct plasma chemistries on carbon removal from silicon nitride (SiN{sub x}) and oxynitride (SiO{sub x}N{sub y}) surfaces have been studied by in-situ x-ray photoelectron spectroscopy (XPS) and ex-situ contact angle measurements. The data indicate that O{sub 2} and NH{sub 3} capacitively coupled plasmas are effective at removing adventitious carbon from silicon nitride (SiN{sub x}) and Si oxynitride (SiO{sub x}N{sub y}) surfaces. O{sub 2} plasma treatment results in the formation of a silica overlayer. In contrast, the exposure to NH{sub 3} plasma results in negligible additional oxidation of the SiN{sub x} or SiO{sub x}N{sub y} surface. Ex-situ contactmore » angle measurements show that SiN{sub x} and SiO{sub x}N{sub y} surfaces exposed to oxygen plasma are initially more hydrophilic than surfaces exposed to NH{sub 3} plasma, indicating that the O{sub 2} plasma-induced SiO{sub 2} overlayer is highly reactive toward ambient. At longer ambient exposures (≳10 h), however, surfaces treated by either O{sub 2} or NH{sub 3} plasma exhibit similar steady state contact angles, correlated with rapid uptake of adventitious carbon, as determined by XPS. Surface passivation by exposure to molecular hydrogen prior to ambient exposure significantly retards the increase in contact angle upon exposure to ambient. The results suggest a practical route to enhancing the time available for effective bonding to surfaces in microelectronics packaging applications.« less

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.

Contact angle studies on anodic porous alumina.

PubMed

Redón, Rocío; Vázquez-Olmos, A; Mata-Zamora, M E; Ordóñez-Medrano, A; Rivera-Torres, F; Saniger, J M

2005-07-15

The preparation of nanostructures using porous anodic aluminum oxide (AAO) as templates involves the introduction of dissolved materials into the pores of the membranes; one way to determine which materials are preferred to fill the pores involves the measurement of the contact angles (theta) of different solvents or test liquids on the AAOs. Thus, we present measurements of contact angles of nine solvents on four different AAO sheets by tensiometric and goniometric methods. From the solvents tested, we found dimethyl sulfoxide (DMSO) and N,N(')-dimethylformamide (DMF) to interact with the AAOs, the polarity of the solvents and the surfaces being the driving force.

Is an electric field always a promoter of wetting? Electro-dewetting of metals by electrolytes probed by in situ X-ray nanotomography

DOE PAGES

Nave, Maryana I.; Gu, Yu; Karen Chen-Wiegart, Yu-Chen; ...

2017-01-05

We developed a special electrochemical cell enabling quantitative analysis andin situX-ray nanotomography of metal/electrolyte interfaces subject to corrosion. Using this cell and applying the nodoid model to describe menisci formed on tungsten wires during anodization, the evolution of the electrolyte surface tension, the concentration of reaction products, and the meniscus contact angle were studied. In contrast to the electrowetting effect, where the applied electric field decreases the contact angle of electrolytes, anodization of the tungsten wires increases the contact angle of the meniscus. Hence, an electric field favors dewetting rather than wetting of the newly formed surface. Finally, the discoveredmore » effect opens up new opportunities for the control of wetting phenomena and calls for the revision of existing theories of electrowetting.« less

Microelectrofluidic lens for variable curvature

NASA Astrophysics Data System (ADS)

Chang, Jong-hyeon; Lee, Eunsung; Jung, Kyu-Dong; Lee, Seungwan; Choi, Minseog; Kim, Woonbae

2012-10-01

This paper presents a tunable liquid lens based on microelectrofluidic technology which integrates electrowetting and microfluidics. In the novel microelectrofluidic lens (MEFL), electrowetting in the hydrophobic surface channel induces the Laplace pressure difference between two fluidic interfaces on the lens aperture and the surface channel. Then, the pressure difference makes the lens curvature tunable. The previous electrowetting lens in which the contact angle changes at the side wall has a certain limitation of the curvature variation because of the contact angle saturation. Although the contact angle saturation also appears in the surface channel of the MEFL, the low surface channel increases the Laplace pressure and it makes the MEFL to have full variation of the optical power possible. The magnitude of the applied voltage determines the lens curvature in the analog mode MEFL as well as the electrowetting lens. Digital operation is also possible when the control electrodes of the MEFL are patterned to have an array. It is expected that the proposed MEFL is able to be widely used because of its full variation of the optical power without the use of oil and digital operation with fast response.

Influence of handrim wheelchair propulsion training in adolescent wheelchair users, a pilot study.

PubMed

Dysterheft, Jennifer L; Rice, Ian M; Rice, Laura A

2015-01-01

Ten full-time adolescent wheelchair users (ages 13-18) completed a total of three propulsion trials on carpet and tile surfaces, at a self-selected velocity, and on a concrete surface, at a controlled velocity. All trials were performed in their personal wheelchair with force and moment sensing wheels attached bilaterally. The first two trials on each surface were used as pre-intervention control trials. The third trial was performed after receiving training on proper propulsion technique. Peak resultant force, contact angle, stroke frequency, and velocity were recorded during all trials for primary analysis. Carpet and tile trials resulted in significant increases in contact angle and peak total force with decreased stroke frequency after training. During the velocity controlled trials on concrete, significant increases in contact angle occurred, as well as decreases in stroke frequency after training. Overall, the use of a training video and verbal feedback may help to improve short-term propulsion technique in adolescent wheelchair users and decrease the risk of developing upper limb pain and injury.

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.

The Influence of Structure Heights and Opening Angles of Micro- and Nanocones on the Macroscopic Surface Wetting Properties

NASA Astrophysics Data System (ADS)

Schneider, Ling; Laustsen, Milan; Mandsberg, Nikolaj; Taboryski, Rafael

2016-02-01

We discuss the influence of surface structure, namely the height and opening angles of nano- and microcones on the surface wettability. We show experimental evidence that the opening angle of the cones is the critical parameter on sample superhydrophobicity, namely static contact angles and roll-off angles. The textured surfaces are fabricated on silicon wafers by using a simple one-step method of reactive ion etching at different processing time and gas flow rates. By using hydrophobic coating or hydrophilic surface treatment, we are able to switch the surface wettability from superhydrophilic to superhydrophobic without altering surface structures. In addition, we show examples of polymer replicas (polypropylene and poly(methyl methacrylate) with different wettability, fabricated by injection moulding using templates of the silicon cone-structures.

Spreading of a pendant liquid drop underneath a textured substrate

NASA Astrophysics Data System (ADS)

Mistry, Aashutosh; Muralidhar, K.

2018-04-01

A pendant drop spreading underneath a partially wetting surface from an initial shape to its final equilibrium configuration and contact angle is studied. A mathematical formulation that quantifies spreading behavior of liquid drops over textured surfaces is discussed. The drop volume and the equilibrium contact angle are treated as parameters in the study. The unbalanced force at the three-phase contact line is modeled as being proportional to the degree of departure from the equilibrium state. Model predictions are verified against the available experimental data in the literature. Results show that the flow dynamics is strongly influenced by the fluid properties, drop volume, and contact angle of the liquid with the partially wetting surface. The drop exhibits rich dynamical behavior including inertial oscillations and gravitational instability, given that gravity tries to detach the drop against wetting contributions. Flow characteristics of drop motion, namely, the radius of the footprint, slip length, and dynamic contact angle in the pendant configuration are presented. Given the interplay among the competing time-dependent forces, a spreading drop can momentarily be destabilized and not achieve a stable equilibrium shape. Instability is then controlled by the initial drop shape as well. The spreading model is used to delineate stable and unstable regimes in the parameter space. Predictions of the drop volume based on the Young-Laplace equation are seen to be conservative relative to the estimates of the dynamical model discussed in the present study.

Measurement of nanoscale molten polymer droplet spreading using atomic force microscopy

NASA Astrophysics Data System (ADS)

Soleymaniha, Mohammadreza; Felts, Jonathan R.

2018-03-01

We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures using atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μm diameters at 115-175 °C on sapphire, silicon oxide, and mica. Custom image processing algorithms determine the droplet height, radius, volume, and contact angle of each AFM image over time to calculate the droplet spreading dynamics. The contact angle evolution follows a power law with time with experimentally determined values of -0.29 ± 0.01, -0.08 ± 0.02, and -0.21 ± 0.01 for sapphire, silicon oxide, and mica, respectively. The non-zero steady state contact angles result in a slower evolution of contact angle with time consistent with theories combining molecular kinetic and hydrodynamic models. Monitoring the cantilever phase provides additional information about the local mechanics of the droplet surface. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 °C to 175 °C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means.

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.

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.

Mixed-phase aerosol particles

NASA Astrophysics Data System (ADS)

Corti, T.; Krieger, U. K.; Koop, T.; Peter, T.

2003-04-01

Within a liquid aerosol particle a solid phase may coexist with the liquid over a wide range of ambient conditions. The optical properties of such particles are of interest for a number of reasons. They will affect the scattering albedo of atmospheric aerosols, may cause depolarisation in lidar measurements, and potentially open a window for studying the internal morphology and physical properties (e.g. wetting properties, diffusion constants) of composite particles in laboratory experiments. In this contribution, we will present results of experimental and theoretical work on mixed-phase aerosol particles. The optical properties of mixed-phase particles depend on the location of the inclusion in the liquid phase, which is determined by the surface tensions of the involved interfaces. In the case of complete wetting, the energetically favoured position of the inclusion is in the volume of the liquid phase. For partial wetting, a position at the surface of the liquid phase is favoured, with the contact angle between the solid, liquid and air being described by Young's equation. For systems with small contact angles, the difference in energy between an inclusion situated at the droplets surface and in its volume may be so small that the thermal energy kT is sufficient to displace the inclusion from the droplet surface into its volume. The critical contact angle depends on the size of the inclusion and the droplet and ranges from 0.1 to 10 degrees. Examples of mixed-phase aerosol particles are aged soot particles and sea salt particles at low relative humidity. For aged soot, contact angles on sulphuric acid clearly above 10 degrees have been reported, so that soot inclusions are expected to be located at the surface of aerosol particles. For mixed-phase sea salt particles, consisting of a solid NaCl inclusion and an aqueous solution of mainly NaCl and MgCl2, our measurements on macroscopic NaCl crystals show a contact angle clearly below 10 degrees and possibly as low as 0.1 degrees. An experimental method - based on measuring photon count statistics - is developed to distinguish in single levitated aerosol particle whether a solid inclusion is located in the volume of the particle or at its surface.

Thermal singularity and contact line motion in pool boiling: Effects of substrate wettability.

PubMed

Taylor, M T; Qian, Tiezheng

2016-03-01

The dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)] is employed to model the growth of a single vapor bubble in a superheated liquid on a flat homogeneous substrate. The bubble spreading dynamics in the pool boiling regime has been numerically investigated for one-component van der Waals fluids close to the critical point, with a focus on the effect of the substrate wettability on bubble growth and contact line motion. The substrate wettability is found to control the apparent contact angle and the rate of bubble growth (the rate of total evaporation), through which the contact line speed is determined. An approximate expression is derived for the contact line speed, showing good agreement with the simulation results. This demonstrates that the contact line speed is primarily governed by (1) the circular shape of interface (for slow bubble growth), (2) the constant apparent contact angle, and (3) the constant bubble growth rate. It follows that the contact line speed has a sensitive dependence on the substrate wettability via the apparent contact angle which also determines the bubble growth rate. Compared to hydrophilic surfaces, hydrophobic surfaces give rise to a thinner shape of bubble and a higher rate of total evaporation, which combine to result in a much faster contact line speed. This can be linked to the earlier formation of a vapor film and hence the onset of boiling crisis.

Surface modification of amorphous substrates by disulfide derivatives: A photo-assisted route to direct functionalization of chalcogenide glasses

NASA Astrophysics Data System (ADS)

Amalric, Julien; Marchand-Brynaert, Jacqueline

2011-12-01

A novel route for chalcogenide glass surface modification is disclosed. The formation of an organic monolayer from disulfide derivatives is studied on two different glasses of formula GexAsySez by water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR). The potential anchoring group is the disulfide functionality. Since thioctic acid derivatives absorb around 335 nm, an irradiation step is included, in order to favor S-S disruption. Three types of disulfide compounds are grafted onto small glass breaks for contact angle and XPS analyses. The results show effective changes of surface state. According to contact angle measurement, the deposited organic layer functionalized by a small polyethylene glycol chain leads to a more hydrophilic surface, long alkyl chain or a perfluorinated carbon chain leads to a more hydrophobic surface. XPS shows the presence at the surface of an organic layer with sulfur and ethylene oxide chains, or augmentation of organic carbons or fluorine and Csbnd F bonds. The photo-assisted grafting of the disulfides onto an ATR prism made of chalcogenide glass shows that this surface modification process does not affect infrared transparency, despite UV treatment, and accurate structural analysis can be performed.

Fabrication of flower-like micro/nano dual scale structured copper oxide surfaces: Optimization of self-cleaning properties via Taguchi design

NASA Astrophysics Data System (ADS)

Moosavi, Saeideh Sadat; Norouzbeigi, Reza; Velayi, Elmira

2017-11-01

In the present work, copper oxide superhydrophobic surface is fabricated on a copper foil via the chemical bath deposition (CBD) method. The effects of some influential factors such as initial concentrations of Cu (II) ions and the surface energy modifier, solution pH, reaction and modification steps time on the wettability property of copper oxide surface were evaluated using Taguchi L16 experimental design. Results showed that the initial concentration of Cu (II) has the most significant impact on the water contact angle and wettability characteristics. The XRD, SEM, AFM and FTIR analyses were used to characterize the copper oxide surfaces. The Water contact angle (WCA) and contact angle hysteresis (CAH) were also measured. The SEM results indicated the formation of a flower-like micro/nano dual-scale structure of copper oxide on the substrate. This structure composed of numerous nano-petals with a thickness of about 50 nm. As a result, a copper oxide hierarchical surface with WCA of 168.4°± 3.5° and CAH of 2.73° exhibited the best superhydrophobicity under proposed optimum condition. This result has been obtained just by 10 min hydrolysis reaction. Besides, this surface showed a good stability under acidic and saline conditions.

Mixed carboranethiol self-assembled monolayers on gold surfaces

NASA Astrophysics Data System (ADS)

Yavuz, Adem; Sohrabnia, Nima; Yilmaz, Ayşen; Danışman, M. Fatih

2017-08-01

Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.

Fabrication of surface micro- and nanostructures for superhydrophobic surfaces in electric and electronic applications

NASA Astrophysics Data System (ADS)

Xiu, Yonghao

In our study, the superhydrophobic surface based on biomimetic lotus leave is explored to maintain the desired properties for self-cleaning. Parameters in controlling bead-up and roll-off characteristics of water droplets were investigated on different model surfaces. The governing equations were proposed. Heuristic study is performed. First, the fundamental understanding of the effect of roughness on superhydrophobicity is performed. The effect of hierarchical roughness, i.e., two scale roughness effect on roughness is investigated using systems of (1) monodisperse colloidal silica sphere (submicron) arrays and Au nanoparticle on top and (2) Si micrometer pyramids and Si nanostructures on top from KOH etching and metal assisted etching of Si. The relation between the contact area fraction and water droplet contact angles are derived based on Wenzel and Cassie-Baxter equation for the systems and the two scale effect is explained regarding the synergistic combination of two scales. Previously the microscopic three-phase-contact line is thought to be the key factor in determining contact angles and hystereses. In our study, Laplace pressure was brought up and related to the three-phase-contact line and taken as a key figure of merit in determining superhydrophobicity. In addition, we are one of the first to study the effect of tapered structures (wall inclination). Combining with a second scale roughness on the tapered structures, stable Cassie state for both water and low surface energy oil may be achieved. This is of great significance for designing both superhydrophobicity and superoleophobicity. Regarding the origin of contact angle hysteresis, study of superhydrophobicity on micrometer Si pillars was performed. The relation between the interface work of function and contact angle hysteresis was proposed and derived mathematically based on the Young-Dupre equation. The three-phase-contact line was further related to a secondary scale roughness induced. Based on our understanding of the roughness effect on superhydrophobicity (both contact angle and hysteresis), structured surfaces from polybutadiene, polyurethane, silica, and Si etc. were successfully prepared. For engineering applications of superhydrophobic surfaces, stability issues regarding UV, mechanical robustness and humid environment need to be investigated. Among these factors, UV stability is the first one to be studied. However, most polymer surfaces we prepared failed the purpose. Silica surfaces with excellent UV stability were prepared. This method consists of preparation of rough silica surfaces, thermal treatment and the following surface hydrophobization by fluoroalkyl silane treatment. Fluoroalkyl groups are UV stable and the underlying species are silica which is also UV stable (UV transparent). UV stability on the surface currently is 5,500 h according the standard test method of ASTM D 4329. No degradation on surface superhydrophobicity was observed. New methods for preparing superhydrophobic and transparent silica surfaces were investigated using urea-choline chloride eutectic liquid to generate fine roughness and reduce the cost for preparation of surface structures. Another possible application for self-cleaning in photovoltaic panels was investigated on Si surfaces by construction of the two-scale rough structures followed by fluoroalkyl silane treatment. Metal (Au) assisted etching was employed to fabricate nanostructures on micrometer pyramid surfaces. The light reflection on the prepared surfaces was investigated. After surface texturing using KOH etching for micrometer pyramids and the following nanostructure using metal assisted etching, surface light reflection reduced to a minimum value which shows that this surface texturing technique is highly promising for improving the photovoltaic efficiency while imparting photovoltaics the self-cleaning feature. This surface is also expected to be UV stable due to the same fluoroalkyl silane used. Regarding the mechanical robustness, epoxy-silica superhydrophobic surfaces were prepared by O2 plasma etching to generate enough surface roughness of silica spheres followed by fluoroalkyl silane treatment. A robustness test method was proposed and the test results showed that the surface is among the most robust surfaces for the superhydrophobic surfaces we prepared and currently reported in literature.

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.

Adsorption of modified dextrins on molybdenite: AFM imaging, contact angle, and flotation studies.

PubMed

Beaussart, Audrey; Parkinson, Luke; Mierczynska-Vasilev, Agnieszka; Beattie, David A

2012-02-15

The adsorption of three dextrins (a regular wheat dextrin, Dextrin TY, carboxymethyl (CM) Dextrin, and hydroxypropyl (HP) Dextrin) on molybdenite has been investigated using adsorption isotherms, tapping mode atomic force microscopy (TMAFM), contact angle measurements, and dynamic bubble-surface collisions. In addition, the effect of the polymers on the flotation recovery of molybdenite has been determined. The isotherms revealed the importance of molecular weight in determining the adsorbed amounts of the polymers on molybdenite at plateau coverage. TMAFM revealed the morphology of the three polymers, which consisted of randomly dispersed domains with a higher area fraction of surface coverage for the substituted dextrins. The contact angle of polymer-treated molybdenite indicated that polymer layer coverage and hydration influenced the mineral surface hydrophobicity. Bubble-surface collisions indicated that the polymers affected thin film rupture and dewetting rate differently, correlating with differences in the adsorbed layer morphology. Direct correlations were found between the surface coverage of the adsorbed layers, their impact on thin film rupture time, and their impact on flotation recovery, highlighting the paramount role of the polymer morphology in the bubble/particle attachment process and subsequent flotation. Copyright © 2011 Elsevier Inc. All rights reserved.

Modeling and experimental study of oil/water contact angle on biomimetic micro-parallel-patterned self-cleaning surfaces of selected alloys used in water industry

NASA Astrophysics Data System (ADS)

Nickelsen, Simin; Moghadam, Afsaneh Dorri; Ferguson, J. B.; Rohatgi, Pradeep

2015-10-01

In the present study, the wetting behavior of surfaces of various common metallic materials used in the water industry including C84400 brass, commercially pure aluminum (99.0% pure), Nickle-Molybdenum alloy (Hastelloy C22), and 316 Stainless Steel prepared by mechanical abrasion and contact angles of several materials after mechanical abrasion were measured. A model to estimate roughness factor, Rf, and fraction of solid/oil interface, ƒso, for surfaces prepared by mechanical abrasion is proposed based on the assumption that abrasive particles acting on a metallic surface would result in scratches parallel to each other and each scratch would have a semi-round cross-section. The model geometrically describes the relation between sandpaper particle size and water/oil contact angle predicted by both the Wenzel and Cassie-Baxter contact type, which can then be used for comparison with experimental data to find which regime is active. Results show that brass and Hastelloy followed Cassie-Baxter behavior, aluminum followed Wenzel behavior and stainless steel exhibited a transition from Wenzel to Cassie-Baxter. Microstructural studies have also been done to rule out effects beyond the Wenzel and Cassie-Baxter theories such as size of structural details.

Effect of Cutting Tool Properties and Depth of Cut in Rock Cutting: An Experimental Study

NASA Astrophysics Data System (ADS)

Rostamsowlat, Iman

2018-06-01

The current paper is designed to investigate the effect of worn (blunt) polycrystalline diamond compact cutter properties on both the contact stress (σ) and friction coefficient ( μ) mobilized at the wear flat-rock interface at different inclination angles of the wear flat surface and at a wide range of depths of cut. An extensive and comprehensive set of cutting experiments is carried out on two sedimentary rocks (one limestone and one sandstone) using a state-of-the-art rock cutting equipment (Wombat) and various blunt cutters. Experiments with blunt cutters are characterized by different wear flat inclination angles (β), different wear flat surface roughness (Ra), different wear flat material, and different cutting tool velocities ({\\varvec{v}}) were conducted. The experimental results show that both the contact stress and friction coefficient are predominantly affected by the wear flat roughness at all inclination angles of the wear flat; however, the cutting tool velocity has a negligible influence on both the contact stress and friction coefficient. Further investigations suggest that the contact stress is greatly affected by the depth of cut within the plastic regime of frictional contact while the contact stress is insensitive to the depth of cut within the elastic regime.

Atomic Oxygen Textured Polymers

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Rutledge, Sharon K.; Hunt, Jason D.; Drobotij, Erin; Cales, Michael R.; Cantrell, Gidget

1995-01-01

Atomic oxygen can be used to microscopically alter the surface morphology of polymeric materials in space or in ground laboratory facilities. For polymeric materials whose sole oxidation products are volatile species, directed atomic oxygen reactions produce surfaces of microscopic cones. However, isotropic atomic oxygen exposure results in polymer surfaces covered with lower aspect ratio sharp-edged craters. Isotropic atomic oxygen plasma exposure of polymers typically causes a significant decrease in water contact angle as well as altered coefficient of static friction. Such surface alterations may be of benefit for industrial and biomedical applications. The results of atomic oxygen plasma exposure of thirty-three (33) different polymers are presented, including typical morphology changes, effects on water contact angle, and coefficient of static friction.

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.

Enhancement on the Surface Hydrophobicity and Oleophobicity of an Organosilicon Film by Conformity Deposition and Surface Fluorination Etching.

PubMed

Xu, Zheng-Wen; Zhang, Yu-Kai; Chen, Tai-Hong; Chang, Jin-How; Lee, Tsung-Hsin; Li, Pei-Yu; Liu, Day-Shan

2018-06-26

In this work, the surface morphology of a hydrophobic organosilicon film was modified as it was deposited onto a silver seed layer with nanoparticles. The surface hydrophobicity evaluated by the water contact angle was significantly increased from 100° to 128° originating from the surface of the organosilicon film becoming roughened, and was deeply relevant to the Ag seed layer conform deposition. In addition, the organosilicon film became surface oleophobic and the surface hydrophobicity was improved due to the formation of the inactive C-F chemical on the surface after the carbon tetrafluoride glow discharge etching. The surface hydrophobicity and oleophobicity of the organosilicon film could be further optimized with water and oleic contact angles of about 138° and 61°, respectively, after an adequate fluorination etching.

Surface polarity of beta-HMX crystal and the related adhesive forces with Estane binder.

PubMed

Yang, Lu

2008-12-02

Here I present the results on the study of surface properties of beta-HMX crystal utilizing molecular dynamics simulations. The surface polarity of three principal crystal surfaces, (011), (010), and (110), is investigated by measuring the water contact angles. The calculated contact angles are in excellent agreement with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain (with and without surrounding nitroplasticizer molecules) from the three principal crystal surfaces are also calculated using the umbrella sampling method. I find that the force for Estane detachment increases with the increasing HMX surface polarity. In addition, my results show that the nitroplasticizer also plays an important role in the adhesion between Estane and HMX surfaces.

Mirror-finished superhydrophobic aluminum surfaces modified by anodic alumina nanofibers and self-assembled monolayers

NASA Astrophysics Data System (ADS)

Nakajima, Daiki; Kikuchi, Tatsuya; Natsui, Shungo; Suzuki, Ryosuke O.

2018-05-01

We demonstrate mirror-finished superhydrophobic aluminum surfaces fabricated via the formation of anodic alumina nanofibers and subsequent modification with self-assembled monolayers (SAMs). High-density anodic alumina nanofibers were formed on the aluminum surface via anodizing in a pyrophosphoric acid solution. The alumina nanofibers became tangled and bundled by further anodizing at low temperature because of their own weight, and the aluminum surface was completely covered by the long falling nanofibers. The nanofiber-covered aluminum surface exhibited superhydrophilic behavior, with a contact angle measuring less than 10°. As the nanofiber-covered aluminum surface was modified with n-alkylphosphonic acid SAMs, the water contact angle drastically shifted to superhydrophobicity, measuring more than 150°. The contact angle increased with the applied voltage during pyrophosphoric acid anodizing, the anodizing time, and the number of carbon atoms contained in the SAM molecules modified on the alumina nanofibers. By optimizing the anodizing and SAM-modification conditions, superhydrophobic behavior could be achieved with only a brief pyrophosphoric acid anodizing period of 3 min and subsequent simple immersion in SAM solutions. The superhydrophobic aluminum surface exhibited a high reflectance, measuring approximately 99% across most of the visible spectrum, similar to that of an electropolished aluminum surface. Therefore, our mirror-finished superhydrophobic aluminum surface based on anodic alumina nanofibers and SAMs can be used as a reflective mirror in various optical applications such as concentrated solar power systems.

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%.

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.

Superhydrophobic surfaces using selected zinc oxide microrod growth on ink-jetted patterns.

PubMed

Myint, Myo Tay Zar; Kitsomboonloha, Rungrot; Baruah, Sunandan; Dutta, Joydeep

2011-02-15

The synthesis and properties of superhydrophobic surfaces based on binary surface topography made of zinc oxide (ZnO) microrod-decorated micropatterns are reported. ZnO is intrinsically hydrophilic but can be utilized to create hydrophobic surfaces by creating artificial roughness via microstructuring. Micron scale patterns consisting of nanocrystalline ZnO seed particles were applied to glass substrates with a modified ink-jet printer. Microrods were then grown on the patterns by a hydrothermal process without any further chemical modification. Water contact angle (WCA)(1) up to 153° was achieved. Different micro array patterned surfaces with varying response of static contact angle or sessile droplet analysis are reported. Copyright © 2010 Elsevier Inc. All rights reserved.

Canopy storage capacity and wettability of leaves and needles: The effect of water temperature changes

NASA Astrophysics Data System (ADS)

Klamerus-Iwan, Anna; Błońska, Ewa

2018-04-01

The canopy storage capacity (S) is a major component of the surface water balance. We analysed the relationship between the tree canopy water storage capacity and leaf wettability under changing simulated rainfall temperature. We estimated the effect of the rain temperature change on the canopy storage capacity and contact angle of leave and needle surfaces based on two scenarios. Six dominant forest trees were analysed: English oak (Quercus roburL.), common beech (Fagus sylvatica L.), small-leaved lime (Tilia cordata Mill), silver fir (Abies alba), Scots pine (Pinus sylvestris L.),and Norway spruce (Picea abies L.). Twigs of these species were collected from Krynica Zdrój, that is, the Experimental Forestry unit of the University of Agriculture in Cracow (southern Poland). Experimental analyses (simulations of precipitation) were performed in a laboratory under controlled conditions. The canopy storage capacity and leaf wettability classification were determined at 12 water temperatures and a practical calculator to compute changes of S and contact angles of droplets was developed. Among all species, an increase of the rainfall temperature by 0.7 °C decreases the contact angle between leave and needle surfaces by 2.41° and increases the canopy storage capacity by 0.74 g g-1; an increase of the rain temperature by 2.7 °C decreases the contact angle by 9.29° and increases the canopy storage capacity by 2.85 g g-1. A decreased contact angle between a water droplet and leaf surface indicates increased wettability. Thus, our results show that an increased temperature increases the leaf wettability in all examined species. The comparison of different species implies that the water temperature has the strongest effect on spruce and the weakest effect on oak. These data indicate that the rainfall temperature influences the canopy storage capacity.

Fabrication of anti-adhesion surfaces on aluminium substrates of rubber plastic moulds using electrolysis plasma treatment

NASA Astrophysics Data System (ADS)

Meng, Jianbing; Dong, Xiaojuan; Wei, Xiuting; Yin, Zhanmin

2015-04-01

An anti-adhesion surface with a water contact angle of 167° was fabricated on aluminium samples of rubber plastic moulds by electrolysis plasma treatment using mixed electrolytes of C6H5O7(NH4)3 and Na2SO4, followed by fluorination. To optimise the fabrication conditions, several important processing parameters such as the discharge voltage, discharge time, concentrations of supporting electrolyte and stearic acid ethanol solution were examined systematically. Using scanning electron microscopy (SEM) to analyse surfaces morphology, micrometer scale pits, and protrusions were found on the surface, with numerous nanometer mastoids contained in the protrusions. These binary micro/nano-scale structures, which are similar to the micro-structures of soil-burrowing animals, play a critical role in achieving low adhesion properties. Otherwise, the anti-adhesion behaviours of the resulting samples were analysed by the atomic force microscope (AFM), Fourier-transform infrared spectrophotometer (FTIR), electrons probe micro-analyzer (EPMA), optical contact angle meter, digital Vickers microhardness (Hv) tester, and electronic universal testing. The results show that the electrolysis plasma treatment does not require complex processing parameters, using a simple device, and is an environment-friendly and effective method. Under the optimised conditions, the contact angle (CA) for the modified anti-adhesion surface is up to 167°, the sliding angle (SA) is less than 2°, roughness of the sample surface is only 0.409μm. Moreover, the adhesion force and Hv are 0. 9KN and 385, respectively.

A "Conveyor Belt" Model for the Dynamic Contact Angle

ERIC Educational Resources Information Center

Della Volpe, C.; Siboni, S.

2011-01-01

The familiar Young contact angle measurement of a liquid at equilibrium on a solid is a fundamental aspect of capillary phenomena. But in the real world it is not so easy to observe it. This is due to the roughness and/or heterogeneity of real surfaces, which typically are not perfectly planar and chemically homogeneous. What can be easily…

Photo Initiated Chemical Vapour Deposition To Increase Polymer Hydrophobicity

NASA Astrophysics Data System (ADS)

Bérard, Ariane; Patience, Gregory S.; Chouinard, Gérald; Tavares, Jason R.

2016-08-01

Apple growers face new challenges to produce organic apples and now many cover orchards with high-density polyethylene (HDPE) nets to exclude insects, rather than spraying insecticides. However, rainwater- associated wetness favours the development of apple scabs, Venturia inaequalis, whose lesions accumulate on the leaves and fruit causing unsightly spots. Treating the nets with a superhydrophobic coating should reduce the amount of water that passes through the net. Here we treat HDPE and polyethylene terephthalate using photo-initiated chemical vapour deposition (PICVD). We placed polymer samples in a quartz tube and passed a mixture of H2 and CO through it while a UVC lamp (254 nm) illuminated the surface. After the treatment, the contact angle between water droplets and the surface increased by an average of 20°. The contact angle of samples placed 70 cm from the entrance of the tube was higher than those at 45 cm and 20 cm. The PICVD-treated HDPE achieved a contact angle of 124°. Nets spray coated with a solvent-based commercial product achieved 180° but water ingress was, surprisingly, higher than that for nets with a lower contact angle.

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.

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

Collapse of surface nanobubbles.

PubMed

Chan, Chon U; Chen, Longquan; Arora, Manish; Ohl, Claus-Dieter

2015-03-20

Surface attached nanobubbles populate surfaces submerged in water. These nanobubbles have a much larger contact angle and longer lifetime than predicted by classical theory. Moreover, it is difficult to distinguish them from hydrophobic droplets, e.g., polymeric contamination, using standard atomic force microscopy. Here, we report fast dynamics of a three phase contact line moving over surface nanobubbles, polymeric droplets, and hydrophobic particles. The dynamics is distinct: across polymeric droplets the contact line quickly jumps and hydrophobic particles pin the contact line, while surface nanobubbles rapidly shrink once merging with the contact line, suggesting a method to differentiate nanoscopic gaseous, liquid, and solid structures. Although the collapse process of surface nanobubbles occurs within a few milliseconds, we show that it is dominated by microscopic dynamics rather than bulk hydrodynamics.

Investigating the wetting behavior of a surface with periodic reentrant structures using integrated microresonators

NASA Astrophysics Data System (ADS)

Klingel, S.; Oesterschulze, E.

2017-08-01

The apparent contact angle is frequently used as an indicator of the wetting state of a surface in contact with a liquid. However, the apparent contact angle is subject to hysteresis that depends furthermore strongly on both the material properties and the roughness and structure of the sample surface. In this work, we show that integrated microresonators can be exploited to determine the wetting state by measuring both the frequency shift caused by the hydrodynamic mass of the liquid and the change in the quality factor as a result of damping. For this, we integrated electrically driven hybrid bridge resonators (HBRs) into a periodically structured surface intended for wetting experiments. We could clearly differentiate between the Wenzel state and the Cassie-Baxter state because the resonant frequency and quality factor of the HBR changed by over 35% and 40%, respectively. This offers the capability to unambiguously distinguish between the different wetting states.

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.

Yeast Droplets

NASA Astrophysics Data System (ADS)

Nguyen, Baochi; Upadhyaya, Arpita; van Oudenaarden, Alexander; Brenner, Michael

2002-11-01

It is well known that the Young's law and surface tension govern the shape of liquid droplets on solid surfaces. Here we address through experiments and theory the shape of growing aggregates of yeast on agar substrates, and assess whether these ideas still hold. Experiments are carried out on Baker's yeast, with different levels of expressions of an adhesive protein governing cell-cell and cell-substrate adhesion. Changing either the agar concentration or the expression of this protein modifies the local contact angle of a yeast droplet. When the colony is small, the shape is a spherical cap with the contact angle obeying Young's law. However, above a critical volume this structure is unstable, and the droplet becomes nonspherical. We present a theoretical model where this instability is caused by bulk elastic effects. The model predicts that the transition depends on both volume and contact angle, in a manner quantitatively consistent with our experiments.

How Does the Gibbs Inequality Condition Affect the Stability and Detachment of Floating Spheres from the Free Surface of Water?

PubMed

Feng, Dong-xia; Nguyen, Anh V

2016-03-01

Floating objects on the air-water interfaces are central to a number of everyday activities, from walking on water by insects to flotation separation of valuable minerals using air bubbles. The available theories show that a fine sphere can float if the force of surface tension and buoyancies can support the sphere at the interface with an apical angle subtended by the circle of contact being larger than the contact angle. Here we show that the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, also plays a significant role in controlling the stability and detachment of floating spheres. Specifically, we truncated the spheres with different angles and used a force sensor device to measure the force of pushing the truncated spheres from the interface into water. We also developed a theoretical modeling to calculate the pushing force that in combination with experimental results shows different effects of the Gibbs inequality condition on the stability and detachment of the spheres from the water surface. For small angles of truncation, the Gibbs inequality condition does not affect the sphere detachment, and hence the classical theories on the floatability of spheres are valid. For large truncated angles, the Gibbs inequality condition determines the tenacity of the particle-meniscus contact and the stability and detachment of floating spheres. In this case, the classical theories on the floatability of spheres are no longer valid. A critical truncated angle for the transition from the classical to the Gibbs inequality regimes of detachment was also established. The outcomes of this research advance our understanding of the behavior of floating objects, in particular, the flotation separation of valuable minerals, which often contain various sharp edges of their crystal faces.

Use of high L.E.T. radiation to improve adhesion of metals to polytetrafluoroethylene

NASA Technical Reports Server (NTRS)

Wheeler, D. R.; Pepper, S. V.

1982-01-01

MgK alpha X-rays (1254 eV) and 2 keV electrons irradiate the surface of polytetrafluoro ethylene (PTFE). The damage is confined to a few tenths of a micron below the surface, and the doses exceed 10 to the eight power rad. X-ray Photoelectron Spectroscopy (XPS) of the irradiated surfaces and mass spectroscopy of the gaseous products of irradiation indicate that the damaged layer is crosslinked or branched PTFE. After either type of irradiation, the surface has enhanced affinity for metals and a lower contact angle with hexadecane. Tape pull tests show that evaporated Ni and Au films adhere better to the irradiated surface. XPS shows the Ni interacts chemically with PTFE forming NiF2 and possibly NiC. However, the gold adhesion and contact angle results indicate that the interaction is, at least in part, chemically nonspecific. Decreased contact angles on FEP Teflon crystallized against gold were attributed to either the presence of a polar oxygen layer or increased physical forces due to greater density. In the case of irradiated PTFE, no oxygen on the surface was observed. The crosslinked structure might, however, have a greater density, thus accounting for the observed increase in adhesion and wettability.

Fast enhancement on hydrophobicity of poplar wood surface using low-pressure dielectric barrier discharges (DBD) plasma

NASA Astrophysics Data System (ADS)

Chen, Weimin; Zhou, Xiaoyan; Zhang, Xiaotao; Bian, Jie; Shi, Shukai; Nguyen, Thiphuong; Chen, Minzhi; Wan, Jinglin

2017-06-01

The hydrophilicity of woody products leads to deformation and cracks, which greatly limits its applications. Low-pressure dielectric barrier discharge (DBD) plasma using hexamethyldisiloxane was applied in poplar wood surface to enhance the hydrophobicity. The chemical properties, micro-morphology, and contact angles of poplar wood surface before and after plasma treatment were investigated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), x-ray photoelectron spectroscopy (XPS), scanning electron microscope and energy dispersive analysis of X-ray (SEM-EDX), atomic force microscopy (AFM), and optical contact angle measurement (OCA). Moreover, tinfoil film was used as the base to reveal the enhancement mechanism. The results showed that hexamethyldisiloxane monomer is first broken into several fragments with active sites and hydrophobic chemical groups. Meanwhile, plasma treatment results in the formation of free radicals and active sites in the poplar wood surface. Then, the fragments are reacted with free radicals and incorporated into the active sites to form a network structure based on the linkages of Si-O-Si and Sisbnd Osbnd C. Plasma treatment also leads to the formation of acicular nano-structure in poplar wood surface. These facts synergistically enhance the hydrophobicity of poplar wood surface, demonstrating the dramatically increase in the equilibrium contact angle by 330%.

Morphological study of polymer surfaces exposed to non-thermal plasma based on contact angle and the use of scaling laws

NASA Astrophysics Data System (ADS)

Felix, T.; Cassini, F. A.; Benetoli, L. O. B.; Dotto, M. E. R.; Debacher, N. A.

2017-05-01

The experiments presented in this communication have the purpose to elaborate an explanation for the morphological evolution of the growth of polymeric surfaces provided by the treatment of non-thermal plasma. According to the roughness analysis and the model proposed by scaling laws it is possible relate to a predictable or merely random effect. Polyethylene terephthalate (PET) and poly(etherether)ketone (PEEK) samples were exposed to a non-thermal plasma discharge and the resulting surfaces roughness were analyzed based on the measurements from contact angle, scanning electron microscopy and atomic force microscopy coupled with scaling laws analysis which can help to describe and understand the dynamic of formation of a wide variety of rough surfaces. The roughness, RRMS (RMS- Root Mean Square) values for polymer surface range between 19.8 nm and 110.9 nm. The contact angle and the AFM (Atomic Force Microscopy) measurements as a function of the plasma exposure time were in agreement with both polar and dispersive components according to the surface roughness and also with the morphology evaluated described by Wolf-Villain model, with proximate values of α between 0.91(PET) and 0.88(PEEK), β = 0.25(PET) and z = 3,64(PET).

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.

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).

Wetting behavior on hexagonally close-packed polystyrene bead arrays with different topographies.

PubMed

Park, Yi-Seul; Yoon, Seo Young; Lee, Jin Seok

2016-01-21

Herein, we investigated the wetting behavior of hexagonally close-packed polystyrene bead arrays with different bead diameters and surface flatness. The contact angle was found to be influenced by the surface roughness as well as the contact area of the polystyrene bead array with a water droplet.

Surfaces wettability and morphology modulation in a fluorene derivative self-assembly system

NASA Astrophysics Data System (ADS)

Cao, Xinhua; Gao, Aiping; Zhao, Na; Yuan, Fangyuan; Liu, Chenxi; Li, Ruru

2016-04-01

A new organogelator based on fluorene derivative (gelator 1) was designed and synthesized. Organogels could be obtained via the self-assembly of the derivative in acetone, toluene, ethyl acetate, hexane, DMSO and petroleum ether. The self-assembly process was thoroughly characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV-vis, FT-IR and the contact angle. Surfaces with different morphologies and wetting properties were formed via the self-assembly of gelator 1 in the six different solvents. Interestingly, a superhydrophobic surface with a contact angle of 150° was obtained from organogel 1 in DMSO and exhibited the lotus-effect. The sliding angle necessary for a water droplet to move on the glass was only 15°. Hydrogen bonding and van der Waals forces were attributed as the main driving forces for gel formation.

Effects of Evaporation/Condensation on Spreading and Contact Angle of a Volatile Liquid Drop

NASA Technical Reports Server (NTRS)

Zhang, Nengli; Chao, David F.; Singh, Bhim S. (Technical Monitor)

2000-01-01

Effects of evaporation/condensation on spreading and contact angle were experimentally studied. A sessile drop of R-113 was tested at different vapor environments to determine the effects of evaporation/condensation on the evolution of contact diameter and contact angle of the drop. Condensation on the drop surface occurs at both the saturated and a nonsaturated vapor environments and promotes the spreading. When the drop is placed in the saturated vapor environment it tends to completely wetting and spreads rapidly. In a nonsaturated vapor environment, the evolution of the sessile drop is divided three stages: condensation-spreading stage, evaporation-retracting stage and rapid contracting stage. In the first stage the drop behaves as in the saturated environment. In the evaporation -retracting stage, the competition between spreading and evaporation of the drop determines the evolution characteristics of the contact diameter and the contact angle. A lower evaporation rate struggles against the spreading power to turn the drop from spreading to retracting with a continuous increase of the contact angle. The drop placed in open air has a much higher evaporation rate. The strong evaporation suppresses the spreading and accelerates the retraction of the drop with a linear decrease of the contact diameter. The contraction of the evaporating drops is gradually accelerated when the contact diameter decreases to 3 min and less till drying up, though the evaporation rate is gradually slowing down.

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.

Direct Measurement of the Wettability of Minerals Using Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Deng, Y.; Xu, L.; Lu, H.; Wang, H.; Shi, Y.

2016-12-01

The wettability of reservoir rock plays an essential role in affecting the states of fluids (water, oil, etc) in pores which are constructed with various minerals. The contact angle method, which is based on the optical microscope photographs of millimeter-sized droplets on a smooth mineral surface, is one of the most widely employed methods to evaluate the wettability of a rock. However, the real reservoir rocks are composed of several kinds of minerals and thus nonhomogeneous, which leads to different wettability at different location of the rock. The mineral grains are usually micrometer-sized so that the traditional optical contact angle method cannot obtain the wettability of different minerals in the rock. Here we used a tapping-mode atomic force microscopy (TM-AFM, MFP-3D-BIO, Asylum Research) to measure the contact angles of micrometer-sized water droplets on different minerals in a tight sand rock which is mainly composed of quartz, albite, potash feldspar and anorthite. The water droplets varied from submicron to several tens micron in diameter. With the optimization of tool and operation parameters, the AFM tip was well controlled so that the nanoscale morphology of the contact configuration between water film and the mineral surface can be obtained at high resolution without disturbing the liquid surface. The AFM results showed that the contact angles of water on quartz and albite were 30-40 ° and 37-45 °, respectively. The AFM method provides a new measure for the wettability evaluation of reservoir rocks, and it is with potential to be applied to oil and gas hydrate studies.

Determination of Hydrophobic Contact Angle of Epoxy Resin Compound Silicon Rubber and Silica

NASA Astrophysics Data System (ADS)

Syakur, Abdul; Hermawan; Sutanto, Heri

2017-04-01

Epoxy resin is a thermosetting polymeric material which is very good for application of high voltage outdoor insulator in electrical power system. This material has several advantages, i.e. high dielectric strength, light weight, high mechanical strength, easy to blend with additive, and easy maintenance if compared to that of porcelain and glass outdoor insulators which are commonly used. However, this material also has several disadvantages, i.e. hydrophilic property, very sensitive to aging and easily degraded when there is a flow of contaminants on its surface. The research towards improving the performance of epoxy resin insulation materials were carried out to obtain epoxy resin insulating material with high water repellent properties and high surface tracking to aging. In this work, insulating material was made at room temperature vulcanization, with material composition: Diglycidyl Ether Bisphenol A (DGEBA), Metaphenylene Diamine (MPDA) as hardener with stoichiometric value of unity, and nanosilica mixed with Silicon Rubber (SiR) with 10% (RTV21), 20% (RTV22), 30% (RTV23), 40% (RTV24) and 50% (RTV25) variation. The usage of nanosilica and Silicon Rubber (SIR) as filler was expected to provide hydrophobic properties and was able to increase the value of surface tracking of materials. The performance of the insulator observed were contact angle of hydrophobic surface materials. Tests carried out using Inclined Plane Tracking procedure according to IEC 60-587: 1984 with Ammonium Chloride (NH4Cl) as contaminants flowed using peristaltic pumps. The results show that hydrophobic contact angle can be determined from each sample, and RTV25 has maximum contact angle among others.

Engineered Film Surfaces Via Spontaneous Phase Segregation

DTIC Science & Technology

2004-12-01

constituents of a Langmuir Blodgett thin Figure 1: Contact angles w/ H2O Contact angles determined from cast films of TPU with (right) 1% wt/wt...Synn, D.; Stelzle, M.; Rabolt, J. F., 2000: Characterization of Orientation of Perfluorostearic Acid Langmuir - Blodgett Multilayers by Infrared...Natick Soldier Center Materials Science Team Natick, MA 01760 ABSTRACT A series of hyperbranched materials have been developed that allow

A Rapid One-Step Process for Fabrication of Biomimetic Superhydrophobic Surfaces by Pulse Electrodeposition.

PubMed

Jiang, Shuzhen; Guo, Zhongning; Liu, Guixian; Gyimah, Glenn Kwabena; Li, Xiaoying; Dong, Hanshan

2017-10-25

Inspired by some typical plants such as lotus leaves, superhydrophobic surfaces are commonly prepared by a combination of low surface energy materials and hierarchical micro/nano structures. In this work, superhydrophobic surfaces on copper substrates were prepared by a rapid, facile one-step pulse electrodepositing process, with different duty ratios in an electrolyte containing lanthanum chloride (LaCl₃·6H₂O), myristic acid (CH₃(CH₂) 12 COOH), and ethanol. The equivalent electrolytic time was only 10 min. The surface morphology, chemical composition and superhydrophobic property of the pulse electrodeposited surfaces were fully investigated with SEM, EDX, XRD, contact angle meter and time-lapse photographs of water droplets bouncing method. The results show that the as-prepared surfaces have micro/nano dual scale structures mainly consisting of La[CH₃(CH₂) 12 COO]₃ crystals. The maximum water contact angle (WCA) is about 160.9°, and the corresponding sliding angle is about 5°. This method is time-saving and can be easily extended to other conductive materials, having a great potential for future applications.

A Rapid One-Step Process for Fabrication of Biomimetic Superhydrophobic Surfaces by Pulse Electrodeposition

PubMed Central

Jiang, Shuzhen; Guo, Zhongning; Liu, Guixian; Gyimah, Glenn Kwabena; Li, Xiaoying; Dong, Hanshan

2017-01-01

Inspired by some typical plants such as lotus leaves, superhydrophobic surfaces are commonly prepared by a combination of low surface energy materials and hierarchical micro/nano structures. In this work, superhydrophobic surfaces on copper substrates were prepared by a rapid, facile one-step pulse electrodepositing process, with different duty ratios in an electrolyte containing lanthanum chloride (LaCl3·6H2O), myristic acid (CH3(CH2)12COOH), and ethanol. The equivalent electrolytic time was only 10 min. The surface morphology, chemical composition and superhydrophobic property of the pulse electrodeposited surfaces were fully investigated with SEM, EDX, XRD, contact angle meter and time-lapse photographs of water droplets bouncing method. The results show that the as-prepared surfaces have micro/nano dual scale structures mainly consisting of La[CH3(CH2)12COO]3 crystals. The maximum water contact angle (WCA) is about 160.9°, and the corresponding sliding angle is about 5°. This method is time-saving and can be easily extended to other conductive materials, having a great potential for future applications. PMID:29068427

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.

Effect of Gold on the Corrosion Behavior of an Electroless Nickel/Immersion Gold Surface Finish

NASA Astrophysics Data System (ADS)

Bui, Q. V.; Nam, N. D.; Yoon, J. W.; Choi, D. H.; Kar, A.; Kim, J. G.; Jung, S. B.

2011-09-01

The performance of surface finishes as a function of the pH of the utilized plating solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. In addition, the surface finishes were examined by x-ray diffraction (XRD), and the contact angle of the liquid/solid interface was recorded. NiP films on copper substrates with gold coatings exhibited their highest coating performance at pH 5. This was attributed to the films having the highest protective efficiency and charge transfer resistance, lowest porosity value, and highest contact angle among those examined as a result of the strongly preferred Au(111) orientation and the improved surface wettability.

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.

Effect of polymer surface modification on polymer-protein interaction via hydrophilic polymer grafting.

PubMed

Liu, S X; Kim, J-T; Kim, S

2008-04-01

Surface modification of flat sheet ultrafiltration membranes, polyethersulfone (PES), was investigated to improve the hydrophilicity of the membrane surface thereby reducing adsorption of the proteins onto the membrane. Grafting of hydrophilic polymers onto UV/ozone-treated PES was used to improve the hydrophilicity of the commercial PES membranes. Hydrophilic polymers, that is, poly(vinyl alcohol) (PVA), polyethylene glycol (PEG), and chitosan, were employed to graft onto PES membrane surfaces because of their excellent hydrophilic property. The surfaces of modified PES membranes were characterized by contact angle measurement, FTIR, and AFM. The FTIR spectra indicated that PES membranes were successfully modified by grafting of the hydrophilic polymers. The modified PES membranes showed 20% to 50% reduction in contact angle measurements in comparison with those of the virgin PES membrane. The tapping mode AFM technique was employed to investigate the changes of surface topography, cross-section, and root mean square roughness of the modified PES membrane surfaces. The modified PES membranes showed elevated roughness (ranging from 7.0 to 25.7 nm) compared with that of the virgin PES membrane (2.1 nm). It is concluded that grafting of PVA, PEG, or chitosan onto UV/ozone-treated PES membranes increases hydrophilicity and lowers protein adsorption by 20% to 60% compared to the virgin PES membrane. Among the 3 hydrophilic polymers studied, PEG showed the most favorable result in terms of contact angle and protein adsorption.

Annealing temperature dependent reversible wettability switching of micro/nano structured ZnO superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Velayi, Elmira; Norouzbeigi, Reza

2018-05-01

Superhydrophobic ZnO surfaces with reversibly tunable wettability were fabricated on stainless steel meshes via a facile chemical bath deposition method just by regulating the micro/nano structured ZnO needles without using chemical post modifications. The obtained surfaces can be easily and reversibly switched between superhydrophobic and superhydrophilic/underwater superoleophobic characteristics by altering the annealing temperatures. As-prepared sample exhibited long-term superhydrophobic properties with a water contact angle (WCA) of 163.8° ± 1.8° and contact angle hysteresis (CAH) of 1.1° ± 0.8°. The SEM, XRD, XPS and Raman analyses were employed to characterize the morphological features and surface chemistry of the prepared samples. SEM images showed the formation of ZnO micro/nanoneedles with a diameter of ∼90 nm on the substrate. The superhydrophobic ZnO surface was switched to highly hydrophilic and underwater superoleophobic properties with an oil contact angle (OCA) of about 172.5° after being annealed at 400 °C in air for 30 min and restored to superhydrophobic state again by altering the annealing temperature to 150 °C. Mechanical durability of the ZnO superhydrophobic surface was tested by an abrasion test. Results confirmed that the prepared surface exhibited an excellent robustness after 20 abrasion cycles under the pressure of 4.7 kPa.

Preparation of enhanced hydrophobic poly(L-lactide-co-ɛ-caprolactone) films surface and its blood compatibility

NASA Astrophysics Data System (ADS)

Kim, Seung Il; Lim, Jin Ik; Jung, Youngmee; Mun, Cho Hay; Kim, Ji Heung; Kim, Soo Hyun

2013-07-01

Hydrophobicity-enhanced poly(L-lactide-co-ɛ-caprolactone) (PLCL) (50:50) films were cast by using the solvent-nonsolvent casting method. PLCL (50:50) was synthesized by the well-known random copolymerization process and confirmed by 1H NMR analysis. The molecular weight of the synthesized PLCL was measured by gel permeation chromatography (GPC). Number-average (Mn), weight-average (Mw) molecular weights and polydispersity (Mw/Mn) were 7 × 104, 1.2 × 105, and 1.7, respectively. PLCL films were cast in vacuum condition with various nonsolvents and nonsolvent ratios. Tetrahydrofuran (THF) was used as the solvent and three different alcohols were used as the nonsolvent: methanol, ethanol, and isopropyl alcohol (IPA). Surface hydrophobicity was confirmed by water contact angle. The water contact angle was increased from 81° ± 2° to 107° ± 2°. Water contact angle was influenced by surface porosity and topography. The prepared film surfaces were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The change of crystalline property was characterized by X-ray diffraction (XRD). Platelet adhesion tests on the modified PLCL film surfaces were evaluated by platelet-rich plasma (PRP). The modified film surface exhibited enhanced hydrophobicity and reduced platelet adhesion ratio depending on the surface topography. One of the candidate products proposed as a potential blood compatible material showed a markedly reduced platelet adhesion property.

Reaction Force of Micro-scale Liquid Droplets Constrained Between Parallel Plates through CFD

NASA Astrophysics Data System (ADS)

Free, Robert; Hekiri, Haider; Hawa, Takumi

2012-02-01

Micro-scale liquid droplets responding to depression between parallel plates are investigated analytically and numerically. The functional dependence of the reaction force accrued in such droplets on droplet size, surface tension, depression amount, and contact angle is explored. For both the 2D and 3D case, an analytical model is developed based on first principles. Computational fluid dynamics is then utilized to evaluate the validity of these models. The reaction force is highly nonlinear, initially increasing very slowly with increasing depression of the droplet, but eventually moving asymptotically to infinity. The force scales linearly with both the droplet free radius and surface tension of the liquid, but has a much more complicated dependence on the contact angle and depression. Explicit expressions for the reaction force have been determined, showing these dependencies. The 3D model has been largely supported by the CFD results. It very accurately predicts the reaction force on the upper plate as the droplet is crushed, accounting for the effect of contact angle, surface tension, and droplet size.

Influence of Handrim Wheelchair Propulsion Training in Adolescent Wheelchair Users, A Pilot Study

PubMed Central

Dysterheft, Jennifer L.; Rice, Ian M.; Rice, Laura A.

2015-01-01

Ten full-time adolescent wheelchair users (ages 13–18) completed a total of three propulsion trials on carpet and tile surfaces, at a self-selected velocity, and on a concrete surface, at a controlled velocity. All trials were performed in their personal wheelchair with force and moment sensing wheels attached bilaterally. The first two trials on each surface were used as pre-intervention control trials. The third trial was performed after receiving training on proper propulsion technique. Peak resultant force, contact angle, stroke frequency, and velocity were recorded during all trials for primary analysis. Carpet and tile trials resulted in significant increases in contact angle and peak total force with decreased stroke frequency after training. During the velocity controlled trials on concrete, significant increases in contact angle occurred, as well as decreases in stroke frequency after training. Overall, the use of a training video and verbal feedback may help to improve short-term propulsion technique in adolescent wheelchair users and decrease the risk of developing upper limb pain and injury. PMID:26042217

Fabrication of a novel superhydrophobic and superoleophilic surface by one-step electrodeposition method for continuous oil/water separation

NASA Astrophysics Data System (ADS)

Xiang, Meisu; Jiang, Meihuizi; Zhang, Yanzong; Liu, Yan; Shen, Fei; Yang, Gang; He, Yan; Wang, Lilin; Zhang, Xiaohong; Deng, Shihuai

2018-03-01

A novel superhydrophobic and superoleophilic surface was fabricated by one-step electrodeposition on stainless steel meshes, and the durability and oil/water separation properties were assessed. Field emission scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fourier transform infrared spectroscopy (FT-IR) and optical contact angle measurements were used to characterize surface morphologies, chemical compositions, and wettabilities, respectively. The results indicated that the as-prepared mesh preformed excellent superhydrophobicity and superoleophilicity with a high water contact angle (WCA) of 162 ± 1° and oil contact angle of (OCA) 0°. Meanwhile, the as-prepared mesh also exhibited continuous separation capacity of many kinds of oil/water mixtures, and the separation efficiency for lubrication oil/water mixture was about 98.6%. In addition, after 10 separation cycles, the as-prepared mesh possessed the WCAs of 155 ± 2°, the OCAs of 0° and the separation efficiency of 97.8% for lubrication oil/water mixtures. The as-prepared mesh also retained superhydrophobic and superoleophilic properties after abrading, immersing in salt solutions and different pH solutions.

Ion adsorption-induced wetting transition in oil-water-mineral systems.

PubMed

Mugele, Frieder; Bera, Bijoyendra; Cavalli, Andrea; Siretanu, Igor; Maestro, Armando; Duits, Michel; Cohen-Stuart, Martien; van den Ende, Dirk; Stocker, Isabella; Collins, Ian

2015-05-27

The relative wettability of oil and water on solid surfaces is generally governed by a complex competition of molecular interaction forces acting in such three-phase systems. Herein, we experimentally demonstrate how the adsorption of in nature abundant divalent Ca(2+) cations to solid-liquid interfaces induces a macroscopic wetting transition from finite contact angles (≈ 10°) with to near-zero contact angles without divalent cations. We developed a quantitative model based on DLVO theory to demonstrate that this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for monovalent K(+) and Na(+) cations is driven by charge reversal of the solid-liquid interface. Small amounts of a polar hydrocarbon, stearic acid, added to the ambient decane synergistically enhance the effect and lead to water contact angles up to 70° in the presence of Ca(2+). Our results imply that it is the removal of divalent cations that makes reservoir rocks more hydrophilic, suggesting a generalizable strategy to control wettability and an explanation for the success of so-called low salinity water flooding, a recent enhanced oil recovery technology.

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.

Droplet sliding on inclined superhydrophobic surfaces: the effect of anisotropic contact line

NASA Astrophysics Data System (ADS)

Jiang, Youhua; Cao, Lile; Guo, Zongqi; Choi, Chang-Hwan

2017-11-01

Although the effects of solid structures on droplet retention on superhydrophobic surfaces have been studied extensively, the investigation has been restricted to the sessile droplets on horizontal surfaces where the contact line motions are axisymmetric or isotropic (either advancing or receding). In the droplet retention on inclined surfaces, the contact line motions are asymmetric or anisotropic; the advancing and receding motions coexist. In this study, we investigate the correlation between the droplet boundary pinning and the surface morphology on inclined superhydrophobic surfaces. The evolution of the droplet contact angle and width show contrary behaviors between pillar- and pore-structured surfaces due to the distinctive microscopic contact line motions. Therefore, the visualizations of the contact line motions at different locations of the boundary on inclined superhydrophobic surfaces are performed and the averaged contact line density of the boundary is quantified. The result shows that the droplet retentive force monotonously increase with the increase in contact line density, regardless of the surface morphological types, dimensions, or the direction of contact line motion (advancing, receding, or both). The result indicates that the droplet retentive force on superhydrophobic surfaces is mainly determined by the contact line density, regardless of the isotropy of the contact line.

Deformation of Surface Nanobubbles Induced by Substrate Hydrophobicity.

PubMed

Wei, Jiachen; Zhang, Xianren; Song, Fan

2016-12-13

Recent experimental measurements have shown that there exists a population of nanobubbles with different curvature radii, whereas both computer simulations and theoretical analysis indicated that the curvature radii of different nanobubbles should be the same at a given supersaturation. To resolve such inconsistency, we perform molecular dynamics simulations on surface nanobubbles that are stabilized by heterogeneous substrates either in the geometrical heterogeneity model (GHM) or in the chemical heterogeneity model (CHM) and propose that the inconsistency could be ascribed to the substrate-induced nanobubble deformation. We find that, as expected from theory and computer simulation, for either the GHM or the CHM, there exists a universal upper limit of contact angle for the nanobubbles, which is determined by the degree of supersaturation alone. By analyzing the evolution of the shape of nanobubbles as a function of substrate hydrophobicity that is controlled here by the liquid-solid interaction, two different origins of nanobubble deformation are identified. For substrates in the GHM, where the contact line is pinned by surface roughness, variation in the liquid-solid interaction changes only the location of the contact line and the measured contact angle, without causing a change in the nanobubble curvature. For substrates in the CHM, however, the liquid-solid interaction exerted by the bottom substrate can deform the vapor-liquid interface, resulting in variations in both the curvature of the vapor-liquid interface and the contact angle.

Surface properties of functional polymer systems

NASA Astrophysics Data System (ADS)

Wong, Derek

Polymer surface modification typically involves blending with other polymers or chemical modification of the parent polymer. Such strategies inevitably result in polymer systems that are spatially and chemically heterogeneous, and which exhibit the phenomenon of surface segregation. This work investigates the effects of chain architecture on the surface segregation behavior of such functionally modified polymers using a series of end- and center-fluorinated poly(D,L-lactide). Surface segregation of the fluorinated functional groups was observed in both chain architectures via AMPS and water contact angle. Higher surface segregation was noted for functional groups located at the chain end as opposed to those in the middle of the chain. A self-consistent mean-field lattice theory was used to model the composition depth profiles of functional groups and excellent agreement was found between the model predictions and the experimental AMPS data in both chain architectures. Polymer properties are also in general dependent on both time and temperature, and exhibit a range of relaxation times in response to environmental stimuli. This behavior arises from the characteristic frequencies of molecular motions of the polymer chain and the interrelationship between time and temperature has been widely established for polymer bulk properties. There is evidence that surface properties also respond in a manner that is time and temperature dependent and that this dependence may not be the same as that observed for bulk properties. AMPS and water contact angle experiments were used to investigate the surface reorganization behavior of functional groups using a series of anionically synthesized end-fluorinated and end-carboxylated poly(styrene). It was found that both types of functional end-groups reorganized upon a change in the polarity of the surface environment in order to minimize the surface free energy. ADXPS and contact angle results suggest that the reorganization depth was confined to the top 2--3 nm of the surface. Contact angle results showed also that the reorganization process proceeded as a function of (time) 1/2, indicating that it is likely diffusion controlled. The magnitudes of the activation energies determined from the experimental data according to the Arhenius equation, suggest that the process is possibly correlated with known bulk beta and gamma relaxations in the polymer.

Characterization and reactivity of organic monolayers on gold and platinum surfaces

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

Wu, Chien-Ching

1995-12-06

Purpose is to understand how the mobilization, dielectric, orientation, composition, coverage, and structure of self-assembled organic monolayers on metal surfaces affects the surface reactivities and properties of these films in order to facilitate the construction of desired films. Two model systems were used: tiols at Au and aromatic acids at Pt. Surface analysis methods, including contact angle, electrochemistry, ellipsometry, infrared reflection absorption spectroscopy (IRRAS), and x-ray photospectroscopy, were used to study the self-assembled organic monolayers on Au and Pt. IRRAS, contact angle, and electrochemistry were used to determine the surface pK a of phenylcarboxylic acids and pyridylcarboxylic acids monolayers onmore » Pt. These techniques were also used to determine the orientation of polymethylene chain axis and the carboxylic follow the structural evolution of the chains and end group of the thiolate monolayers during formation. IRRAS was also used to assess the carboxylic acid group in terms of its possible existence as the non-hydrogen-bonded species, the hydrogen-bonded dimeric group, and the hydrogen-bonded polymeric group. These different forms of the end group were also followed vs coverage, as well as the reactivity vs solution pH. IRRAS and contact angle were used to calculate the rate constant of the esterification of carboxylic acid-terminated monolayers on Au.« less

Enhanced super-hydrophobic and switching behavior of ZnO nanostructured surfaces prepared by simple solution--immersion successive ionic layer adsorption and reaction process.

PubMed

Suresh Kumar, P; Sundaramurthy, J; Mangalaraj, D; Nataraj, D; Rajarathnam, D; Srinivasan, M P

2011-11-01

A simple and cost-effective successive ionic layer adsorption and reaction (SILAR) method was adopted to fabricate hydrophobic ZnO nanostructured surfaces on transparent indium-tin oxide (ITO), glass and polyethylene terephthalate (PET) substrates. ZnO films deposited on different substrates show hierarchical structures like spindle, flower and spherical shape with diameters ranging from 30 to 300 nm. The photo-induced switching behaviors of ZnO film surfaces between hydrophobic and hydrophilic states were examined by water contact angle and X-ray photoelectron spectroscopy (XPS) analysis. ZnO nanostructured films had contact angles of ~140° and 160°±2 on glass and PET substrates, respectively, exhibiting hydrophobic behavior without any surface modification or treatment. Upon exposure to ultraviolet (UV) illumination, the films showed hydrophilic behavior (contact angle: 15°±2), which upon low thermal stimuli revert back to its original hydrophobic nature. Such reversible and repeatable switching behaviors were observed upon cyclical exposure to ultraviolet radiation. These biomimetic ZnO surfaces exhibit good anti-reflective properties with lower reflectance of 9% for PET substrates. Thus, the present work is significant in terms of its potential application in switching devices, solar coatings and self-cleaning smart windows. Copyright © 2011 Elsevier Inc. All rights reserved.

Diagnostics of hydrogen plasma with in situ optical emission and silicon probes

NASA Astrophysics Data System (ADS)

Lee, Szetsen; Chung, Yi-Jie

2005-11-01

In this work, an approach has been adopted to explore plasma properties by combining an in situ optical emission technique with a contact angle measurement. Hydrogen plasma was generated with a radio-frequency power source. The plasma parameters such as number densities and temperatures were derived from the optical emission spectroscopic data. Small silicon chips were placed at various positions inside a discharge tube as probes for the plasma conditions. The hydrogen-plasma-treated silicon chip surfaces were characterized with the contact angle measurement method. The change of wettability on the silicon surface was observed with various plasma treatment times. The spectroscopic information about the plasma is correlated with the results of the surface characterization. It is found that the rate of the increasing hydrophilicity is sensitive to the amount of helium added and the location in the discharge tube. A simple model describing the relation between the surface coverage area of water droplet and the variation of contact angle has been established. We have proposed plasma excitation and reaction mechanisms for the observed correlation between plasma temperatures and the wettability of the silicon surface. It shows that small silicon chips can serve as "litmus tests" for the plasma conditions without introducing too much perturbation.

Stable superhydrophilic coating on superhydrophobic porous media by functionalized nanoparticles

NASA Astrophysics Data System (ADS)

Khazaei, Masoud; Taghi Sadeghi, Mohammad; Sadat Hosseini, Marzieh

2018-01-01

In this study, the hydrophilicity property of TiO2 nano-coating was improved by zinc acetate-assisted sol-gel method. The stable superhydrophilic coating was fabricated on a superhydrophobic mineral rock surface. The wettability of surface before and after coating was characterized by contact angle measurements. The n-heptane and water droplet contact angle was 0° and 168° respectively, so the untreated rock was superhydrophobic. After nano-treatment, the n-heptane and water contact angle changed to 172° and 0° respectively, so the superhydrophilic coating was formed on the superhydrophobic surface. The thermal, mechanical and salinity stability of the fabricated coatings was investigated. The coatings had high thermal and salinity stability; they also had moderate mechanical stability that was evaluated by abrasion test. The morphology and composition of synthesized nanoparticles were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and x-ray diffraction (XRD) analyses. Characterization of the coated surfaces was conducted by SEM and XRD analyses. Applications of these nano-coatings include surfaces where cleanliness is paramount such as in hospitals as well as the protection of public monuments and building facades from weathering. Novel industrial application includes wettability alteration of oil wet carbonate rock for enhanced oil recovery.

Evaporation of liquid droplets on solid substrates. II. Periodic substrates with moving contact lines

NASA Astrophysics Data System (ADS)

Amini, Amirhossein; Homsy, G. M.

2017-04-01

Experiments on evaporating droplets on structured surfaces have shown that the contact line does not move with constant speed, but rather in a steplike "stick-slip" fashion. As a first step in understanding such behavior, we study the evaporation of a two-dimensional volatile liquid droplet on a nonplanar heated solid substrate with a moving contact line and fixed contact angle. The model for the flat case is adapted to include curved substrates, numerical solutions are achieved for various periodic and quasiperiodic substrate profiles, and the dynamics of the contact line and the apparent contact angle are studied. In contrast with our results for a flat substrate, for which the contact line recedes in a nearly constant speed, we observe that the contact line speed and position show significant time variation and that the contact line moves in an approximate steplike fashion on relatively steep substrates. For the simplest case of a periodic substrate, we find that the apparent contact angle is periodic in time. For doubly periodic substrates, we find that the apparent contact angle is periodic and that the problem exhibits a phase-locking behavior. For multimode quasiperiodic substrates, we find the contact line behavior to be temporally complex and not only limited to a stick-slip motion. In all cases, we find that the overall evaporation is increased relative to the flat substrate.

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.

Comparison of the effect of plasma treatment and gamma ray irradiation on PS-Cu nanocomposite films surface

NASA Astrophysics Data System (ADS)

Farag, O. F.

2018-06-01

Polystyrene-copper (PS-Cu) nanocomposite films were treated with DC N2 plasma and gamma rays irradiations. The plasma treatment of PS-Cu film surface was carried out at different treatment times, gas pressure 0.4 Torr and the applied power 3.5 W. On the other hand, the treatment with gamma rays irradiation were carried out at irradiation doses 10, 30 and 50 kGy. The induced changes in surface properties of PS-Cu films were investigated with UV-viss spectroscopy, scanning electron microscopy (SEM) and FTIR spectroscopy techniques. In addition, the wettability property, surface free energy, spreading coefficient and surface roughness of the treated samples were studied by measuring the contact angle. The UV-viss spectroscopy analysis revealed that the optical band gap decreases with increasing the treatment time and the irradiation dose for plasma and gamma treatments, respectively. SEM observations showed that the particle size of copper particles was increased with increasing the treatment time and the irradiation dose, but gamma treatment changes the copper particles size from nano scale to micro scale. The contact angle measurements showing that the wettability property, surface free energy, spreading coefficient and surface roughness of the treated PS-Cu samples were increased remarkably with increasing the treatment time and the irradiation dose for plasma and gamma treatments, respectively. The contact angle, surface free energy, spreading coefficient and surface roughness of the treated PS-Cu samples are more influenced by plasma treatment than gamma treatment.

Fabrication of anti-adhesion surfaces on aluminium substrates of rubber plastic moulds using electrolysis plasma treatment

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

Meng, Jianbing, E-mail: jianbingmeng@126.com; Dong, Xiaojuan; Wei, Xiuting

An anti-adhesion surface with a water contact angle of 167° was fabricated on aluminium samples of rubber plastic moulds by electrolysis plasma treatment using mixed electrolytes of C{sub 6}H{sub 5}O{sub 7}(NH{sub 4}){sub 3} and Na{sub 2}SO{sub 4}, followed by fluorination. To optimise the fabrication conditions, several important processing parameters such as the discharge voltage, discharge time, concentrations of supporting electrolyte and stearic acid ethanol solution were examined systematically. Using scanning electron microscopy (SEM) to analyse surfaces morphology, micrometer scale pits, and protrusions were found on the surface, with numerous nanometer mastoids contained in the protrusions. These binary micro/nano-scale structures, whichmore » are similar to the micro-structures of soil-burrowing animals, play a critical role in achieving low adhesion properties. Otherwise, the anti-adhesion behaviours of the resulting samples were analysed by the atomic force microscope (AFM), Fourier-transform infrared spectrophotometer (FTIR), electrons probe micro-analyzer (EPMA), optical contact angle meter, digital Vickers microhardness (Hv) tester, and electronic universal testing. The results show that the electrolysis plasma treatment does not require complex processing parameters, using a simple device, and is an environment-friendly and effective method. Under the optimised conditions, the contact angle (CA) for the modified anti-adhesion surface is up to 167°, the sliding angle (SA) is less than 2°, roughness of the sample surface is only 0.409μm. Moreover, the adhesion force and H{sub v} are 0. 9KN and 385, respectively.« less

Droplet spreading and capillary imbibition in a porous medium: A coupled IB-VOF method based numerical study

NASA Astrophysics Data System (ADS)

Das, Saurish; Patel, H. V.; Milacic, E.; Deen, N. G.; Kuipers, J. A. M.

2018-01-01

We investigate the dynamics of a liquid droplet in contact with a surface of a porous structure by means of the pore-scale level, fully resolved numerical simulations. The geometrical details of the solid porous matrix are resolved by a sharp interface immersed boundary method on a Cartesian computational grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid method. The numerical simulations are performed considering a model porous structure that is approximated by a 3D cubical scaffold with cylindrical struts. The effect of the porosity and the equilibrium contact angle (between the gas-liquid interface and the solid struts) on the spreading behavior, liquid imbibition, and apparent contact angle (between the gas-liquid interface and the porous base) are studied. We also perform several simulations for droplet spreading on a flat surface as a reference case. Gas-liquid systems of the Laplace number, La = 45 and La = 144 × 103 are considered neglecting the effect of gravity. We report the time exponent (n) and pre-factor (C) of the power law describing the evolution of the spreading diameter (S = Ctn) for different equilibrium contact angles and porosity. Our simulations reveal that the apparent or macroscopic contact angle varies linearly with the equilibrium contact angle and increases with porosity. Not necessarily for all the wetting porous structures, a continuous capillary drainage occurs, and we find that the rate of the capillary drainage very much depends on the fluid inertia. At La = 144 × 103, numerically we capture the capillary wave induced pinch-off and daughter droplet ejection. We observe that on the porous structure the pinch-off is weak compared to that on a flat plate.

Intensify dodecylamine adsorption on magnesite and dolomite surfaces by monohydric alcohols

NASA Astrophysics Data System (ADS)

Zhang, Hao; Liu, Wengang; Han, Cong; Wei, Dezhou

2018-06-01

The flotation of magnesite and dolomite were investigated with the presence of single dodecylamine (DDA) and combined mixtures of DDA and monohydric alcohols, respectively. The adsorption behavior of DDA, butanol, hexanol and octanol on the surface of the two minerals were shown by molecular dynamics simulation, and the results were corresponding with the analysis of zeta potential, measurements of the contact angle and adsorption. Flotation results indicated that part of DDA could be replaced by the three alcohols (butanol, hexanol, octanol) to get better flotation results. Molecular dynamics simulation and the results of zeta potential and contact angle measurements indicated that adsorption of DDA on mineral surfaces could be strengthened by monohydric alcohols.

Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

NASA Technical Reports Server (NTRS)

Beger, Lauren; Roberts, Lily; deGroh, Kim; Banks, Bruce

2007-01-01

In the low Earth orbit (LEO) space environment, spacecraft surfaces can be altered during atomic oxygen exposure through oxidation and erosion. There can be terrestrial benefits of such interactions, such as the modification of hydrophobic or hydrophilic properties of polymers due to chemical modification and texturing. Such modification of the surface may be useful for biomedical applications. For example, atomic oxygen texturing may increase the hydrophilicity of polymers, such as chlorotrifluoroethylene (Aclar), thus allowing increased adhesion and spreading of cells on textured Petri dishes. The purpose of this study was to determine the effect of atomic oxygen exposure on the hydrophilicity of nine different polymers. To determine whether hydrophilicity remains static after atomic oxygen exposure or changes with exposure, the contact angles between the polymer and a water droplet placed on the polymer s surface were measured. The polymers were exposed to atomic oxygen in a radio frequency (RF) plasma asher. Atomic oxygen plasma treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Significant decreases in the water contact angle occurred with atomic oxygen exposure. Fluorinated polymers were found to be less sensitive to changes in hydrophilicity for equivalent atomic oxygen exposures, and two of the fluorinated polymers became more hydrophobic. The majority of change in water contact angle of the non-fluorinated polymers was found to occur with very low fluence exposures, indicating potential cell culturing benefit with short treatment time.

Effect of contact angle hysteresis on moving liquid film integrity

NASA Technical Reports Server (NTRS)

Simon, F. F.; Hsu, Y. Y.

1972-01-01

A study was made of the formation and breakdown of a water film moving over solid surfaces (teflon, lucite, stainless steel, and copper). The flow rate associated with film formation was found to be higher than the flow rate at which film breakdown occurred. The difference in the flow rates for film formation and film breakdown was attributed to contact angle hysteresis. Analysis and experiment, which are in good agreement, indicated that film formation and film breakdown are functions of the advancing and receding angles, respectively.

Effect of contact angle hysteresis on moving liquid film integrity.

NASA Technical Reports Server (NTRS)

Simon, F. F.; Hsu, Y. Y.

1972-01-01

A study was made of the formation and breakdown of a water film moving over solid surfaces (teflon, lucite, stainless steel, and copper). The flow rate associated with film formation was found to be higher than the flow rate at which film breakdown occurred. The difference in the flow rates for film formation and film breakdown was attributed to contact angle hysteresis. Analysis and experiment, which are in good agreement, indicated that film formation and film breakdown are functions of the advancing and receding angles, respectively.

Control of laser-ablated aluminum surface wettability to superhydrophobic or superhydrophilic through simple heat treatment or water boiling post-processing

NASA Astrophysics Data System (ADS)

Ngo, Chi-Vinh; Chun, Doo-Man

2018-03-01

Recently, controlling the wettability of a metallic surface so that it is either superhydrophobic or superhydrophilic has become important for many applications. However, conventional techniques require long fabrication times or involve toxic chemicals. Herein, through a combination of pulse laser ablation and simple post-processing, the surface of aluminum was controlled to either superhydrophobic or superhydrophilic in a short time of only a few hours. In this study, grid patterns were first fabricated on aluminum using a nanosecond pulsed laser, and then additional post-processing without any chemicals was used. Under heat treatment, the surface became superhydrophobic with a contact angle (CA) greater than 150° and a sliding angle (SA) lower than 10°. Conversely, when immersed in boiling water, the surface became superhydrophilic with a low contact angle. The mechanism for wettability change was also explained. The surfaces, obtained in a short time with environmentally friendly fabrication and without the use of toxic chemicals, could potentially be applied in various industry and manufacturing applications such as self-cleaning, anti-icing, and biomedical devices.

Experiments on the contact angle of n-propanol on differently prepared silver substrates at various temperatures and implications for the properties of silver nanoparticles

NASA Astrophysics Data System (ADS)

Pinterich, T.; Winkler, P. M.; Vrtala, A. E.; Wagner, P. E.

2011-08-01

In this paper we present the results of contact angle measurements between n-propanol and silver substrates in the temperature range from -10 °C to 30 °C. The interest in a potential temperature dependence of contact angles originates from recent experiments by S. Schobesberger et al. (Schobesberger S., Strange temperature dependence observed for heterogeneous nucleation of n-propanol vapor on NaCl particles. Master's thesis, University of Vienna, 2008; Schobesberger S. et al., Experiments on the temperature dependence of heterogeneous nucleation on NaCl and Ag particles. In preparation.) investigating the temperature dependence for heterogeneous nucleation of n-propanol vapour on NaCl and on silver particles. We determined dynamic advancing θ a and receding θ r angles on variously prepared silver probes. The Dynamic Wilhelmy method (Wilhelmy L., Über die Abhängigkeit der Capillaritäts-Constanten des Alkohols von Substanz und Gestalt des benetzten festen Körpers. Ann. Phys. Chem., 199:177-217, 1863) was applied using a Krüss K12 Tensiometer, with a refrigerated double-walled glass top. With respect to its potential influence on heterogeneous nucleation mainly the advancing angle is of interest. The uniform probe geometry required was achieved by accurate cutting and by multiple polishing stages up to the accomplishment of a 0.04 μm grain size. The original probes consist of 925 sterling silver including a 7.5% copper content. Additional coating with silver pro Analysi (p.A.) was applied making use of pure silver powder evaporation process via Physical Vapour Deposition (PVD). Results show that a surface contamination by copper cannot be neglected for the specification of contact angles. It turned out that additional PVD coatings not only change the values of θa but also their temperature dependence. With increasing the number of coatings of a plate the contact angle decreases and its temperature dependence inverts. Since the contact angle hysteresis θhyst. obtained for the variously often coated probes remained practically constant possible changes in surface roughness with increasing number of PVD layers could be excluded.

On accurate determination of contact angle

NASA Technical Reports Server (NTRS)

Concus, P.; Finn, R.

1992-01-01

Methods are proposed that exploit a microgravity environment to obtain highly accurate measurement of contact angle. These methods, which are based on our earlier mathematical results, do not require detailed measurement of a liquid free-surface, as they incorporate discontinuous or nearly-discontinuous behavior of the liquid bulk in certain container geometries. Physical testing is planned in the forthcoming IML-2 space flight and in related preparatory ground-based experiments.

Development of accurate potentials to explore the structure of water on 2D materials

NASA Astrophysics Data System (ADS)

Bejagam, Karteek; Singh, Samrendra; Deshmukh, Sanket; Deshmkuh Group Team; Samrendra Group Collaboration

Water play an important role in many biological and non-biological process. Thus structure of water at various interfaces and under confinement has always been the topic of immense interest. 2-D materials have shown great potential in surface coating applications and nanofluidic devices. However, the exact atomic level understanding of the wettability of single layer of these 2-D materials is still lacking mainly due to lack of experimental techniques and computational methodologies including accurate force-field potentials and algorithms to measure the contact angle of water. In the present study, we have developed a new algorithm to measure the accurate contact angle between water and 2-D materials. The algorithm is based on fitting the best sphere to the shape of the droplet. This novel spherical fitting method accounts for every individual molecule of the droplet, rather than those at the surface only. We employ this method of contact angle measurements to develop the accurate non-bonded potentials between water and 2-D materials including graphene and boron nitride (BN) to reproduce the experimentally observed contact angle of water on these 2-D materials. Different water models such as SPC, SPC/Fw, and TIP3P were used to study the structure of water at the interfaces.

An evaluation of complementary approaches to elucidate fundamental interfacial phenomena driving adhesion of energetic materials

DOE PAGES

Hoss, Darby J.; Knepper, Robert; Hotchkiss, Peter J.; ...

2016-03-23

In this study, cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamakermore » constants and surface energy components of the materials. The cohesive Hamaker constants range from 85 zJ to 135 zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle > Lifshitz > IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings.« less

Study of the Relationship between Boundary Slip and Nanobubbles on a Smooth Hydrophobic Surface.

PubMed

Li, Dayong; Jing, Dalei; Pan, Yunlu; Bhushan, Bharat; Zhao, Xuezeng

2016-11-01

Surface nanobubbles, which are nanoscopic or microscopic gaseous domains forming at the solid/liquid interface, have a strong impact on the interface by changing the two-phase contact to a three-phase contact. Therefore, they are believed to affect the boundary condition and liquid flow. However, there are still disputes in the theoretical studies as to whether the nanobubbles can increase the slip length effectively. Furthermore, there are still no direct experimental studies to support either side. Therefore, an intensive study on the effective slip length for flows over bare surfaces with nanobubbles is essential for establishing the relation between nanobubbles and slip length. Here, we study the effect of nanobubbles on the slippage experimentally and theoretically. Our experimental results reveal an increase from 8 to 512 nm in slip length by increasing the surface coverage of nanobubbles from 1.7 to 50.8% and by decreasing the contact angle of nanobubbles from 42.8 to 16.6°. This is in good agreement with theoretical results. Our results indicate that nanobubbles could always act as a lubricant and significantly increase the slip length. The surface coverage, height, and contact angle are key factors for nanobubbles to reduce wall friction.

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.

Effects of hysteresis of static contact angle (HSCA) and boundary slip on the hydrodynamics of water striders

NASA Astrophysics Data System (ADS)

Zheng, J.; Wang, B. S.; Chen, W. Q.; Han, X. Y.; Li, C. F.; Zhang, J. Z.; Yu, K. P.

2017-02-01

It is known that contact lines keep relatively still on solids until static contact angles exceed an interval of hysteresis of static contact angle (HSCA), and contact angles keep changing as contact lines relatively slide on the solid. Here, the effects of HSCA and boundary slip were first distinguished on the micro-curvature force (MCF) on the seta. Hence, the total MCF is partitioned into static and dynamic MCFs correspondingly. The static MCF was found proportional to the HSCA and related with the asymmetry of the micro-meniscus near the seta. The dynamic MCF, exerting on the relatively sliding contact line, is aroused by the boundary slip. Based on the Blake-Haynes mechanism, the dynamic MCF was proved important for water walking insects with legs slower than the minimum wave speed 23 cm\\cdot s^{-1}. As insects brush the water by laterally swinging legs backwards, setae on the front side of the leg are pulled and the ones on the back side are pushed to cooperatively propel bodies forward. If they pierce the water surface by vertically swinging legs downwards, setae on the upside of the legs are pulled, and the ones on the downside are pushed to cooperatively obtain a jumping force. Based on the dependency between the slip length and shear rate, the dynamic MCF was found correlated with the leg speed U, as F˜ C1U+C2 U^{2+ɛ}, where C1 and C2 are determined by the dimple depth. Discrete points on this curve could give fitted relations as F˜ Ub (Suter et al., J. Exp. Biol. 200, 2523-2538, 1997). Finally, the axial torque on the inclined and partially submerged seta was found determined by the surface tension, contact angle, HSCA, seta width, and tilt angle. The torque direction coincides with the orientation of the spiral grooves of the seta, which encourages us to surmise it is a mechanical incentive for the formation of the spiral morphology of the setae of water striders.

Wetting of a Charged Surface of Glassy Carbon by Molten Alkali-Metal Chlorides

NASA Astrophysics Data System (ADS)

Stepanov, V. P.

2018-03-01

Values of the contact angle of wetting of a surface of glassy carbon by molten chlorides of lithium, sodium, potassium, and cesium are measured by the meniscus weight method to determine the common factors of wettability of solid surfaces by ionic melts upon a change in the salt phase composition and a jump in electric potential. It is found that with a potential shift in the positive direction the shape of the curve of the contact angle's dependence on the potential varies upon substitution of one salt by another: the angle of wetting shrinks monotonously in lithium chloride but remains constant in molten cesium chloride. This phenomenon is explained by the hypothesis that the nature of the halide anion adsorption on the positively charged surface of an electrode is chemical and not electrostatic. It is shown that the adsorption process is accompanied by charge transfer through the interface, with covalent bonding between the adsorbent and adsorbate.

Controllable stearic acid crystal induced high hydrophobicity on cellulose film surface.

PubMed

He, Meng; Xu, Min; Zhang, Lina

2013-02-01

A novel, highly hydrophobic cellulose composite film (RCS) with biodegradability was fabricated via solvent-vaporized controllable crystallization of stearic acid in the porous structure of cellulose films (RC). The interface structure and properties of the composite films were investigated with wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), FT-IR, solid-state (13)C NMR, water uptake, tensile testing, water contact angle, and biodegradation tests. The results indicated that the RCS films exhibited high hydrophobicity (water contact angle achieved to 145°), better mechanical properties in the humid state and lower water uptake ratio than RC. Interestingly, the stearic acid crystallization was induced by the pore wall of the cellulose matrix to form a micronano binary structure, resulting in a rough surface. The rough surface with a hierarchical structure containing micronanospace on the RCS film surface could trap abundant air, leading to the high hydrophobicity. Moreover, the RCS films were flexible, biodegradable, and low-cost, showing potential applications in biodegradable water-proof packaging.

Reversible superhydrophobic-superhydrophilic transition of ZnO nanorod/epoxy composite films.

PubMed

Liu, Yan; Lin, Ziyin; Lin, Wei; Moon, Kyoung Sik; Wong, C P

2012-08-01

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.

Surface properties of HMX crystal

NASA Technical Reports Server (NTRS)

Yee, R. Y.; Adicoff, A.; Dibble, E. J.

1980-01-01

The surface properties of Beta-HMX crystals were studied. The surface energies of three principal crystal faces were obtained by measuring contact angles with several reference liquids. The surface energies and polarity of the three crystal faces are found to be different.

Wetting and interfacial properties of water nanodroplets in contact with graphene and monolayer boron-nitride sheets.

PubMed

Li, Hui; Zeng, Xiao Cheng

2012-03-27

Born-Oppenheim quantum molecular dynamics (QMD) simulations are performed to investigate wetting, diffusive, and interfacial properties of water nanodroplets in contact with a graphene sheet or a monolayer boron-nitride (BN) sheet. Contact angles of the water nanodroplets on the two sheets are computed for the first time using QMD simulations. Structural and dynamic properties of the water droplets near the graphene or BN sheet are also studied to gain insights into the interfacial interaction between the water droplet and the substrate. QMD simulation results are compared with those from previous classic MD simulations and with the experimental measurements. The QMD simulations show that the graphene sheet yields a contact angle of 87°, while the monolayer BN sheet gives rise to a contact angle of 86°. Hence, like graphene, the monolayer BN sheet is also weakly hydrophobic, even though the BN bonds entail a large local dipole moment. QMD simulations also show that the interfacial water can induce net positive charges on the contacting surface of the graphene and monolayer BN sheets, and such charge induction may affect electronic structure of the contacting graphene in view that graphene is a semimetal. Contact angles of nanodroplets of water in a supercooled state on the graphene are also computed. It is found that under the supercooled condition, water nanodroplets exhibit an appreciably larger contact angle than under the ambient condition. © 2012 American Chemical Society

Durable anti-fogging effect and adhesion improvement on polymer surfaces

NASA Astrophysics Data System (ADS)

Moser, E. M.; Gilliéron, D.; Henrion, G.

2010-01-01

The hydrophobic properties of polymeric surfaces may cause fogging in transparent packaging and poor adhesion to printing colours and coatings. Novel plasma processes for durable functionalization of polypropylene and polyethylene terephthalate substrates were developed and analysed using optical emission spectroscopy. A worm-like nano pattern was created on the polypropylene surface prior to the deposition of thin polar plasma polymerised layers. For both substrates, highly polar surfaces exhibiting a surface tension of up to 69 mN/m and a water contact angle of about 10° were produced - providing the anti-fogging effect. The deposition of thin plasma polymerised layers protects the increased surface areas and enables to tailoring the surface energy of the substrate in a wide range. Wetting characteristics were determined by dynamic contact angle measurements. Investigations of the chemical composition of several layers using X-ray photoelectron spectroscopy and FT-infrared spectroscopy were correlated with functional testing. The surface topography was investigated using atomic force microscopy. The weldability and peeling-off characteristics of the plasma treated polymer films could be adjusted by varying the process parameters. Global and specific migration analyses were undertaken in order to ensure the manufacturing of plasma treated polymer surfaces for direct food contact purposes.

Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading.

PubMed

Chen, Bo; Pernodet, Nadine; Rafailovich, Miriam H; Bakhtina, Asya; Gross, Richard A

2008-12-02

A series of epoxy-activated polymer films composed of poly(glycidyl methacrylate/butyl methacrylate/hydroxyethyl methacrylate) were prepared. Variation in comonomer composition allowed exploration of relationships between surface wettability and Candida antartica lipase B (CALB) binding to surfaces. By changing solvents and polymer concentrations, suitable conditions were developed for preparation by spin-coating of uniform thin films. Film roughness determined by AFM after incubation in PBS buffer for 2 days was less than 1 nm. The occurrence of single CALB molecules and CALB aggregates at surfaces was determined by AFM imaging and measurements of volume. Absolute numbers of protein monomers and multimers at surfaces were used to determine values of CALB specific activity. Increased film wettability, as the water contact angle of films increased from 420 to 550, resulted in a decreased total number of immobilized CALB molecules. With further increases in the water contact angle of films from 55 degrees to 63 degrees, there was an increased tendency of CALB molecules to form aggregates on surfaces. On all flat surfaces, two height populations, differing by more than 30%, were observed from height distribution curves. They are attributed to changes in protein conformation and/or orientation caused by protein-surface and protein-protein interactions. The fraction of molecules in these populations changed as a function of film water contact angle. The enzyme activity of immobilized films was determined by measuring CALB-catalyzed hydrolysis of p-nitrophenyl butyrate. Total enzyme specific activity decreased by decreasing film hydrophobicity.

Control of melt-crystal interface shape during sapphire crystal growth by heat exchanger method

NASA Astrophysics Data System (ADS)

Wu, Ming; Liu, Lijun; Ma, Wencheng

2017-09-01

We numerically investigate the melt-crystal interface shape during the early stage of the solidification process when the crystal diameter increases. The contact angle between the melt-crystal interface and the crucible bottom wall is found obtuse during this stage, which is unfavorable for the crystal quality. We found that the obtuse contact angle is caused by the thermal resistance difference between the sapphire crystal and melt as well as the insufficient cooling effect of the crucible bottom. Two approaches are proposed to suppress the obtuse contact angle. The first approach is to increase the emissivity of the outer surface of crucible bottom. The second approach is to install a heat shield near the crucible bottom. The reduction of the emissivity of the heat shield is also favorable for the suppression of the obtuse contact angle. Compared with the increase of the emissivity of the crucible bottom, the installation of a heat shield is a more effective approach to prevent the appearance of an obtuse contact angle for the sake of reliability since a molybdenum heat shield can be reused and will not induce other impurities.

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.

Wetting of crystalline polymer surfaces: A molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Fan, Cun Feng; Caǧin, Tahir

1995-11-01

Molecular dynamics has been used to study the wetting of model polymer surfaces, the crystal surfaces of polyethylene (PE), poly(tetrafluoroethylene) (PTFE), and poly(ethylene terephthalate) (PET) by water and methylene iodide. In the simulation a liquid droplet is placed on a model surface and constant temperature, rigid body molecular dynamics is carried out while the model surface is kept fixed. A generally defined microscopic contact angle between a liquid droplet and a solid surface is quantitatively calculated from the volume of the droplet and the interfacial area between the droplet and the surface. The simulation results agree with the trend in experimental data for both water and methylene iodide. The shape of the droplets on the surface is analyzed and no obvious anisotropy of the droplets is seen in the surface plane, even though the crystal surfaces are highly oriented. The surface free energies of the model polymer surfaces are estimated from their contact angles with the two different liquid droplets.

Water retention of repellent and subcritical repellent soils: New insights from model and experimental investigations

NASA Astrophysics Data System (ADS)

Czachor, H.; Doerr, S. H.; Lichner, L.

2010-01-01

SummarySoil organic matter can modify the surface properties of the soil mineral phase by changing the surface tension of the mineral surfaces. This modifies the soil's solid-water contact angle, which in turn would be expected to affect its water retention curve (SWRC). Here we model the impact of differences in the soil pore-water contact angle on capillarity in non-cylindrical pores by accounting for their complex pore geometry. Key outcomes from the model include that (i) available methods for measuring the Young's wetting angle on soil samples are insufficient in representing the wetting angle in the soil pore space, (ii) the wetting branch of water retention curves is strongly affected by the soil pore-water contact angle, as manifest in the wetting behavior of water repellent soils, (iii) effects for the drying branch are minimal, indicating that both wettable and water repellent soils should behave similarly, and (vi) water retention is a feature not of only wettable soils, but also soils that are in a water repellent state. These results are tested experimentally by determining drying and wetting branches for (a) 'model soil' (quartz sands with four hydrophobization levels) and (b) five field soil samples with contrasting wettability, which were used with and without the removal of the soil organic matter. The experimental results support the theoretical predictions and indicate that small changes in wetting angle can cause switches between wettable and water repellent soil behavior. This may explain the common observation that relatively small changes in soil water content can cause substantial changes in soil wettability.

Plant surfaces with cuticular folds are slippery for beetles

PubMed Central

Prüm, Bettina; Seidel, Robin; Bohn, Holger Florian; Speck, Thomas

2012-01-01

Plant surfaces covered with three-dimensional (3D) waxes are known to strongly reduce insect adhesion, leading to slippery surfaces. Besides 3D epicuticular waxes, cuticular folds are a common microstructure found on plant surfaces, which have not been quantitatively investigated with regard to their influence on insect adhesion. We performed traction experiments with Colorado potato beetles on five plant surfaces with cuticular folds of different magnitude. For comparison, we also tested (i) smooth plant surfaces and (ii) plant surfaces possessing 3D epicuticular waxes. Traction forces on surfaces with medium cuticular folds, of about 0.5 µm in both height and thickness and a spacing of 0.5–1.5 µm, were reduced by an average of 88 per cent in comparison to smooth plant surfaces. Traction forces were reduced by the same order of magnitude as on plant surfaces covered with 3D epicuticular waxes. For surface characterization, we performed static contact angle measurements, which proved a strong effect of cuticular folds also on surface wettability. Surfaces possessing cuticular folds of greater magnitude showed higher contact angles up to superhydrophobicity. We hypothesize that cuticular folds reduce insect adhesion mainly due to a critical roughness, reducing the real contact area between the surface and the insect's adhesive devices. PMID:21642366

Understanding deviations in lithographic patterns near interfaces: Characterization of bottom anti-reflective coatings (BARC) and the BARC resist interface

NASA Astrophysics Data System (ADS)

Lenhart, Joseph L.; Fischer, Daniel; Sambasivan, Sharadha; Lin, Eric K.; Wu, Wen-Li; Guerrero, Douglas J.; Wang, Yubao; Puligadda, Rama

2007-02-01

Interactions between a bottom anti-reflective coating (BARC) and a photoresist can critically impact lithographic patterns. For example, a lithographic pattern can shrink or spread near a BARC interface, a process called undercutting or footing respectively, due to incompatibility between the two materials. Experiments were conducted on two industrial BARC coatings in an effort to determine the impact of BARC surface chemistry on the footing and undercutting phenomena. The BARC coatings were characterized by near edge X-ray absorption fine structure (NEXAFS), contact angle measurements, and neutron and X-ray reflectivity. Contact angle measurement using a variety of fluids showed that the fluid contact angles were independent of the type of BARC coating or the BARC processing temperature. NEXAFS measurements showed that the surface chemistry of each BARC was also independent of the processing temperature. These results suggest that acid-base interactions at the BARC-resist interface are not the cause of the footing-undercutting phenomena encountered in lithographic patterns.

Tunable Physical Properties of Ethylcellulose/Gelatin Composite Nanofibers by Electrospinning.

PubMed

Liu, Yuyu; Deng, Lingli; Zhang, Cen; Feng, Fengqin; Zhang, Hui

2018-02-28

In this work, the ethylcellulose/gelatin blends at various weight ratios in water/ethanol/acetic acid solution were electrospun to fabricate nanofibers with tunable physical properties. The solution compatibility was predicted based on Hansen solubility parameters and evaluated by rheological measurements. The physical properties were characterized by scanning electron microscopy, porosity, differential scanning calorimetry, thermogravimetry, Fourier transform infrared spectroscopy, and water contact angle. Results showed that the entangled structures among ethylcellulose and gelatin chains through hydrogen bonds gave rise to a fine morphology of the composite fibers with improved thermal stability. The fibers with higher gelatin ratio (75%), possessed hydrophilic surface (water contact angle of 53.5°), and adequate water uptake ability (1234.14%), while the fibers with higher ethylcellulose proportion (75%) tended to be highly water stable with a hydrophobic surface (water contact angle of 129.7°). This work suggested that the composite ethylcellulose/gelatin nanofibers with tunable physical properties have potentials as materials for bioactive encapsulation, food packaging, and filtration applications.

Dopant controlled photoinduced hydrophilicity and photocatalytic activity of SnO2 thin films

NASA Astrophysics Data System (ADS)

Talinungsang; Dhar Purkayastha, Debarun; Krishna, M. Ghanashyam

2018-07-01

The influence of Fe and Ni (1 wt.%) doping on the wettability and photocatalytic activity of sol-gel derived SnO2 films is reported. X-ray diffraction studies revealed the presence of tetragonal phase for both pure and doped SnO2 thin films. The crystallite size was of the order of 8 nm indicating the nanocrystalline nature of the films. The pure SnO2 films which were hydrophilic with a contact angle of 11.8° showed increase in contact angle with doping (38.7° for Fe and 48.6° for Ni). This is accompanied by decrease in surface energy and root mean square roughness, with doping of SnO2 film. In order to further increase the water contact angle, the film surfaces were modified using a layer of stearic acid. As a consequence, the water contact angles increased to 108°, 110° and 111° for the pure, Fe and Ni doped SnO2 films respectively, rendering them hydrophobic. Significantly, the unmodified surfaces that did not exhibit any change under UV irradiation showed photoinduced hydrophilicity on modification with stearic acid. There was a red-shift in the optical band gap of SnO2 films from 3.8 to 3.5 eV with doping, indicating the possibility of dopant controlled photocatalytic activity. This was confirmed by observing the photocatalytic degradation of an aqueous solution of methylene blue under UV irradiation. There was, indeed, significant improvement in the photocatalytic efficiency of the metal doped SnO2 thin film in comparison to undoped film. The current work, thus, demonstrates a simple method to chemically engineer the wettability and photocatalytic activity of SnO2 thin film surfaces.

Effect of Hydrofluoric Acid Concentration on Resin Adhesion to a Feldspathic Ceramic.

PubMed

Venturini, Andressa Borin; Prochnow, Catina; Rambo, Dagma; Gundel, Andre; Valandro, Luiz Felipe

2015-08-01

To evaluate the effect of different concentrations of hydrofluoric acid (HF) on the contact angle and the resin bond strength durability to feldspathic ceramic. To evaluate the contact angles of distilled water on etched feldspathic ceramic, 25 specimens (12×10×2.4 mm) of VitaBlocks Mark II were used, divided into 5 groups (n=5): one unconditioned control (UC) group with no ceramic surface treatment, and 4 other groups that were etched for 60 s with different concentrations of HF: 1% (HF1), 3% (HF3), 5% (HF5) and 10% (HF10). The bond testing utilized 40 ceramic blocks (12×10×4 mm) that were fabricated and subjected to the same surface treatments as previously mentioned (excluding the control). The etched surfaces were silanized and resin cement was applied. After 24 h, the blocks were sectioned to produce bar specimens that were divided into two groups, non-aged (immediate testing) and aged (storage for 230 days+12,000 thermocycles at 5°C and 55°C), and subjected to microtensile testing (μTBS). Micromorphogical analysis of the treated surfaces was also performed (atomic force and scanning electron microscopy). One-way ANOVA and Tukey's tests were applied for data analysis. UC had the highest contact angle (61.4°), whereas HF10 showed the lowest contact angle (17.5°). In non-aged conditions, different acids promoted statistically similar bond strengths (14.2 to 15.7 MPa) (p>0.05); in terms of bond durability, only the bond strength of the HF1 group presented a statistically significant decrease comparing before and after aging (14.5 to 10.2 MPa). When etched with 3%, 5%, or 10% hydrofluoric acid, the ceramic tested showed stable resin adhesion after long-term aging.

An investigation into a micro-sized droplet impinging on a surface with sharp wettability contrast

NASA Astrophysics Data System (ADS)

Lim, C. Y.; Lam, Y. C.

2014-10-01

An experimental investigation was conducted into a micro-sized droplet jetted onto a surface with sharp wettability contrast. The dynamics of micro-sized droplet impingement on a sharp wettability contrast surface, which is critical in inkjet printing technology, has not been investigated in the literature. Hydrophilic lines with line widths ranging from 27 to 53 µm, and contact angle ranging from 17° to 77°, were patterned on a hydrophobic surface with a contact angle of 107°. Water droplets with a diameter of 81 µm were impinged at various offset distances from the centre of the hydrophilic line. The evolution of the droplet upon impingement can be divided into three distinct phases, namely the kinematic phase, the translating phase where the droplet moves towards the centre of the hydrophilic line, and the conforming phase where the droplet spreads along the line. The key parameters affecting the conformability of the droplet to the hydrophilic line pattern are the ratio of the line width to the initial droplet diameter and the contact angle of the hydrophilic line. The droplet will only conform completely to the hydrophilic pattern if the line width is not overly small relative to the droplet and the contact angle of the hydrophilic line is sufficiently low. The impact offset distance does not affect the final shape and final location of the droplet, as long as part of the droplet touches the hydrophilic line upon impingement. This process has a significant impact on inkjet printing technology as high accuracy of inkjet droplet deposition and shape control can be achieved through wettability patterning.

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.

Engineering a nanostructured "super surface" with superhydrophobic and superkilling properties.

PubMed

Hasan, Jafar; Raj, Shammy; Yadav, Lavendra; Chatterjee, Kaushik

2015-05-12

We present a nanostructured "super surface" fabricated using a simple recipe based on deep reactive ion etching of a silicon wafer. The topography of the surface is inspired by the surface topographical features of dragonfly wings. The super surface is comprised of nanopillars 4 μm in height and 220 nm in diameter with random inter-pillar spacing. The surface exhibited superhydrophobicity with a static water contact angle of 154.0° and contact angle hysteresis of 8.3°. Bacterial studies revealed the bactericidal property of the surface against both gram negative ( Escherichia coli ) and gram positive ( Staphylococcus aureus ) strains through mechanical rupture of the cells by the sharp nanopillars. The cell viability on these nanostructured surfaces was nearly six-fold lower than on the unmodified silicon wafer. The nanostructured surface also killed mammalian cells (mouse osteoblasts) through mechanical rupture of the cell membrane. Thus, such nanostructured super surfaces could find applications for designing self-cleaning and anti-bacterial surfaces in diverse applications such as microfluidics, surgical instruments, pipelines and food packaging.

Stick-Jump (SJ) Evaporation of Strongly Pinned Nanoliter Volume Sessile Water Droplets on Quick Drying, Micropatterned Surfaces.

PubMed

Debuisson, Damien; Merlen, Alain; Senez, Vincent; Arscott, Steve

2016-03-22

We present an experimental study of stick-jump (SJ) evaporation of strongly pinned nanoliter volume sessile water droplets drying on micropatterned surfaces. The evaporation is studied on surfaces composed of photolithographically micropatterned negative photoresist (SU-8). The micropatterning of the SU-8 enables circular, smooth, trough-like features to be formed which causes a very strong pinning of the three phase (liquid-vapor-solid) contact line of an evaporating droplet. This is ideal for studying SJ evaporation as it contains sequential constant contact radius (CCR) evaporation phases during droplet evaporation. The evaporation was studied in nonconfined conditions, and forced convection was not used. Micropatterned concentric circles were defined having an initial radius of 1000 μm decreasing by a spacing ranging from 500 to 50 μm. The droplet evaporates, successively pinning and depinning from circle to circle. For each pinning radius, the droplet contact angle and volume are observed to decrease quasi-linearly with time. The experimental average evaporation rates were found to decrease with decreasing pining radii. In contrast, the experimental average evaporation flux is found to increase with decreasing droplet radii. The data also demonstrate the influence of the initial contact angle on evaporation rate and flux. The data indicate that the total evaporation time of a droplet depends on the specific micropattern spacing and that the total evaporation time on micropatterned surfaces is always less than on flat, homogeneous surfaces. Although the surface patterning is observed to have little effect on the average droplet flux-indicating that the underlying evaporation physics is not significantly changed by the patterning-the total evaporation time is considerably modified by patterning, up to a factor or almost 2 compared to evaporation on a flat, homogeneous surface. The closely spaced concentric circle pinning maintains a large droplet radius and small contact angle from jump to jump; the result is a large evaporation rate leading to faster evaporation.

Large area optical mapping of surface contact angle.

PubMed

Dutra, Guilherme; Canning, John; Padden, Whayne; Martelli, Cicero; Dligatch, Svetlana

2017-09-04

Top-down contact angle measurements have been validated and confirmed to be as good if not more reliable than side-based measurements. A range of samples, including industrially relevant materials for roofing and printing, has been compared. Using the top-down approach, mapping in both 1-D and 2-D has been demonstrated. The method was applied to study the change in contact angle as a function of change in silver (Ag) nanoparticle size controlled by thermal evaporation. Large area mapping reveals good uniformity for commercial Aspen paper coated with black laser printer ink. A demonstration of the forensic and chemical analysis potential in 2-D is shown by uncovering the hidden CsF initials made with mineral oil on the coated Aspen paper. The method promises to revolutionize nanoscale characterization and industrial monitoring as well as chemical analyses by allowing rapid contact angle measurements over large areas or large numbers of samples in ways and times that have not been possible before.

Facile Fabrication and Characterization of a PDMS-Derived Candle Soot Coated Stable Biocompatible Superhydrophobic and Superhemophobic Surface.

PubMed

Iqbal, R; Majhy, B; Sen, A K

2017-09-13

We report a simple, inexpensive, rapid, and one-step method for the fabrication of a stable and biocompatible superhydrophobic and superhemophobic surface. The proposed surface comprises candle soot particles embedded in a mixture of PDMS+n-hexane serving as the base material. The mechanism responsible for the superhydrophobic behavior of the surface is explained, and the surface is characterized based on its morphology and elemental composition, wetting properties, mechanical and chemical stability, and biocompatibility. The effect of %n-hexane in PDMS, the thickness of the PDMS+n-hexane layer (in terms of spin coating speed) and sooting time on the wetting property of the surface is studied. The proposed surface exhibits nanoscale surface asperities (average roughness of 187 nm), chemical compositions of soot particles, very high water and blood repellency along with excellent mechanical and chemical stability and excellent biocompatibility against blood sample and biological cells. The water contact angle and roll-off angle is measured as 160° ± 1° and 2°, respectively, and the blood contact angle is found to be 154° ± 1°, which indicates that the surface is superhydrophobic and superhemophobic. The proposed superhydrophobic and superhemophobic surface offers significantly improved (>40%) cell viability as compared to glass and PDMS surfaces.

Impinging Water Droplets on Inclined Glass Surfaces

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

Armijo, Kenneth Miguel; Lance, Blake; Ho, Clifford K.

Multiphase computational models and tests of falling water droplets on inclined glass surfaces were developed to investigate the physics of impingement and potential of these droplets to self-clean glass surfaces for photovoltaic modules and heliostats. A multiphase volume-of-fluid model was developed in ANSYS Fluent to simulate the impinging droplets. The simulations considered different droplet sizes (1 mm and 3 mm), tilt angles (0°, 10°, and 45°), droplet velocities (1 m/s and 3 m/s), and wetting characteristics (wetting=47° contact angle and non-wetting = 93° contact angle). Results showed that the spread factor (maximum droplet diameter during impact divided by the initialmore » droplet diameter) decreased with increasing inclination angle due to the reduced normal force on the surface. The hydrophilic surface yielded greater spread factors than the hydrophobic surface in all cases. With regard to impact forces, the greater surface tilt angles yielded lower normal forces, but higher shear forces. Experiments showed that the experimentally observed spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) was significantly larger than the simulated spread factor. Observed spread factors were on the order of 5 - 6 for droplet velocities of ~3 m/s, whereas the simulated spread factors were on the order of 2. Droplets were observed to be mobile following impact only for the cases with 45° tilt angle, which matched the simulations. An interesting phenomenon that was observed was that shortly after being released from the nozzle, the water droplet oscillated (like a trampoline) due to the "snapback" caused by the surface tension of the water droplet being released from the nozzle. This oscillation impacted the velocity immediately after the release. Future work should evaluate the impact of parameters such as tilt angle and surface wettability on the impact of particle/soiling uptake and removal to investigate ways that photovoltaic modules and heliostats can be designed to maximize self-cleaning.« less

Surface analysis of selected hydrophobic materials

NASA Astrophysics Data System (ADS)

Wisniewska, Sylwia Katarzyna

This dissertation contains a series of studies on hydrophobic surfaces by various surface sensitive techniques such as contact angle measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Hydrophobic surfaces have been classified as mineral surfaces, organic synthetic surfaces, or natural biological surfaces. As a model hydrophobic mineral surface, elemental sulfur has been selected. The sulfur surface has been characterized for selected allotropic forms of sulfur such as rhombic, monoclinic, plastic, and cyclohexasulfur. Additionally, dextrin adsorption at the sulfur surface was measured. The structure of a dextrin molecule showing hydrophobic sites has been presented to support the proposed hydrophobic bonding nature of dextrin adsorption at the sulfur surface. As a model organic hydrophobic surface, primary fatty amines such as dodecylamine, hexadecylamine, and octadecylamine were chosen. An increase of hydrophobicity, significant changes of infrared bands, and surface topographical changes with time were observed for each amine. Based on the results it was concluded that hydrocarbon chain rearrangement associated with recrystallization took place at the surface during contact with air. A barley straw surface was selected as a model of biological hydrophobic surfaces. The differences in the contact angles for various straw surfaces were explained by the presence of a wax layer. SEM images confirmed the heterogeneity and complexity of the wax crystal structure. AFM measurements provided additional structural details including a measure of surface roughness. Additionally, straw degradation as a result of conditioning in an aqueous environment was studied. Significant contact angle changes were observed as soon as one day after conditioning. FTIR studies showed a gradual wax layer removal due to straw surface decomposition. SEM and AFM images revealed topographical changes and biological life development as part of the straw degradation process. Three different classes of hydrophobic surfaces have been studied, and in each case important surface chemistry issues have been identified that influence the hydrophobic state. Many of the studies are unique to the particular system, but common phenomena that influence the hydrophobic state of all of these surfaces include time dependence due to crystallization and chemical degradation (oxidation, hydration, biological activity).

Influence of surfactants in forced dynamic dewetting.

PubMed

Henrich, Franziska; Fell, Daniela; Truszkowska, Dorota; Weirich, Marcel; Anyfantakis, Manos; Nguyen, Thi-Huong; Wagner, Manfred; Auernhammer, Günter K; Butt, Hans-Jürgen

2016-09-20

In this work we show that the forced dynamic dewetting of surfactant solutions depends sensitively on the surfactant concentration. To measure this effect, a hydrophobic rotating cylinder was horizontally half immersed in aqueous surfactant solutions. Dynamic contact angles were measured optically by extrapolating the contour of the meniscus to the contact line. Anionic (sodium 1-decanesulfonate, S-1DeS), cationic (cetyl trimethylammonium bromide, CTAB) and nonionic surfactants (C 4 E 1 , C 8 E 3 and C 12 E 5 ) with critical micelle concentrations (CMCs) spanning four orders of magnitude were used. The receding contact angle in water decreased with increasing velocity. This decrease was strongly enhanced when adding surfactant, even at surfactant concentrations of 10% of the critical micelle concentration. Plots of the receding contact angle-versus-velocity almost superimpose when being plotted at the same relative concentration (concentration/CMC). Thus the rescaled concentration is the dominating property for dynamic dewetting. The charge of the surfactants did not play a role, thus excluding electrostatic effects. The change in contact angle can be interpreted by local surface tension gradients, i.e. Marangoni stresses, close to the three-phase contact line. The decrease of dynamic contact angles with velocity follows two regimes. Despite the existence of Marangoni stresses close to the contact line, for a dewetting velocity above 1-10 mm s -1 the hydrodynamic theory is able to describe the experimental results for all surfactant concentrations. At slower velocities an additional steep decrease of the contact angle with velocity was observed. Particle tracking velocimetry showed that the flow profiles do not differ with and without surfactant on a scales >100 μm.

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.

Super Water-Repellent Fractal Surfaces of a Photochromic Diarylethene Induced by UV Light

NASA Astrophysics Data System (ADS)

Izumi, Norikazu; Minami, Takayuki; Mayama, Hiroyuki; Takata, Atsushi; Nakamura, Shinichiro; Yokojima, Satoshi; Tsujii, Kaoru; Uchida, Kingo

2008-09-01

Photochromic diarylethene forms super water-repellent surfaces upon irradiation with UV light. Microfibril-like crystals grow on the solid diarylethene surface after UV irradiation, and the contact angle of water on the surface becomes larger with increasing surface roughness with time. The fractal analysis was made by the box-counting method for the rough surfaces. There are three regions in the roughness size having the fractal dimension of ca. 2.4 (size of roughness smaller than 5 µm), of ca. 2.2 (size of roughness between 5-40 µm), and of ca. 2.0 (size of roughness larger than 40 µm). The fractal dimension of ca. 2.4 was due to the fibril-like structures generated gradually by UV irradiation on diarylethene surfaces accompanied with an increase in the contact angle. The surface structure with larger fractal dimension mainly contributes to realizing the super water-repellency of the diarylethene surfaces. This mechanism of spontaneous formation of fractal surfaces is similar to that for triglyceride and alkylketene dimer waxes.

The Hydrophobicity and Adhesion of Heterogeneous Surfaces of Dual Nanometer and Micron Scale Structures

DTIC Science & Technology

2011-04-11

scale post geometry. superhydrophobic , surface modification, adhesion, contact angle, Cassie, Wenzel, PDMS, CYTOP, Teflon AF, roll-off angle U U U U SAR...width > 1, the micro-scale features dominated the wetting state regardless of the nano-scale post geometry., KEYWORDS superhydrophobic , surface... superhydrophobicity can be routinely found in nature. Fo~ example, many plant leaves1.2, bird feathers3, insect wings and insect legs4 take advantage of

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.

Effect of electrolyte on surface free energy components of feldspar minerals using thin-layer wicking method.

PubMed

Karagüzel, C; Can, M F; Sönmez, E; Celik, M S

2005-05-01

Application of the thin-layer wicking (TLW) technique on powdered minerals is useful for characterizing their surfaces. Albite (Na-feldspar) and orthoclase (K-feldspar) are feldspar minerals which are frequently found in the same matrix. Despite similarities in their physicochemical properties, separation of these minerals from each other by flotation is generally possible in the presence of monovalent salts such as NaCl. Both albite and orthoclase exhibit the same microflotation properties and rather close electrokinetic profiles in the absence of salt. In this study, contact angles of albite and orthoclase determined by the TLW technique yielded close values in the absence and presence of amine collector. While the calculated surface energies and their components determined using contact angle data reveal that the energy terms remain farther apart in the absence of the collector, the differences narrow down at collector concentrations where full flotation recoveries are obtained. However, the effect of addition of NaCl on contact angles and surface free energy components at constant amine concentration indicates that albite is significantly affected by salt addition, whereas orthoclase remains marginally affected. This interesting finding is explained on the basis of ion-exchange properties, the stability of the interface, flotation data, and zeta potential data in the presence of NaCl.

Superhydrophobic polymeric films with hierarchical structures produced by nanoimprint (NIL) and plasma roughening

NASA Astrophysics Data System (ADS)

Durret, Jérôme; Szkutnik, Pierre-David; Frolet, Nathalie; Labau, Sebastien; Gourgon, Cécile

2018-07-01

The structuration of various polymeric films has been studied to create superhydrophobic surfaces. Nanoimprint lithography and/or plasma etching processes with CF4/Ar have been used on FEP, PMMA and PET polymer films. On the one hand, the effect of the CF4/Ar gases, the input power and the plasma treatment duration have been investigated in terms of etching and fluorination degree, and XPS analyses are precisely discussed. On the other hand, wettability performances were characterized. Relationships between the contact angle, the contact angle hysteresis and the surface structures have been investigated. The wetting behaviors and the transition between the Wenzel and the Cassie-Baxter states was discussed as a function of the roughness. We have prepared each studied polymer films in transparent and flexible superhydrophobic surfaces whose contact angle are ∼160° and hysteresis are ∼2°. A short plasma treatment time (10 s) is sufficient to obtain a superhydrophobic behavior on FEP and PMMA. Results indicate that hierarchical structures allow a more stable superhydrophobic state regarding inhomogeneities. Moreover, the use of plasma etching is suggested to overcome some limitations of the NIL in the case of structures with a high aspect ratio. Finally, a quick and large surface fabrication method for superhydrophobic films is detailed.

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

Surface free energy analysis of oil palm empty fruit bunches fiber reinforced biocomposites

NASA Astrophysics Data System (ADS)

Suryadi, G. S.; Nikmatin, S.; Sudaryanto; Irmansyah; Sukaryo, S. G.

2017-05-01

Study of the size effect of natural fiber from oil palm empty fruit bunches (OPEFB) as filler, onto the contact angle and surface free energy of fiber reinforced biocomposites has been done. The OPEFB fibers were prepared by mechanical milling and sieving to obtain various sizes of fiber (long-fiber, medium-fiber, short-fiber, and microparticle). The biocomposites has been produced by extrusion using single-screw extruder with EFB fiber as filler, recycled Acrylonitrile Butadiene Styrene (ABS) polymer as matrix, and primary antioxidant, acid scavanger, and coupling agent as additives. The obtained biocomposites in form of granular, were made into test piece by injection molding method. Contact angles of water, methanol, and hexane on the surface of biocomposites at room temperature were measured using Phoenix 300 Contact Angle Analyzer. The surface free energy (SFE) and their components were calculated using three previous known methods (Girifalco-Good-Fowkes-Young (GGFY), Owens-Wendt, and van Oss-Chaudhury-Good (vOCG)). The results showed that total SFE of Recycled ABS as control was about 24.38 mJ/m2, and SFE of biocomposites was lower than control, decreased with decreasing of EFB fiber size as biocomposites filler. The statistical analysis proved that there are no statistically significant differences in the value of the SFE calculated with the three different methods.

Dancing droplets: Contact angle, drag, and confinement

NASA Astrophysics Data System (ADS)

Benusiglio, Adrien; Cira, Nate; Prakash, Manu

2015-11-01

When deposited on a clean glass slide, a mixture of water and propylene glycol forms a droplet of given contact angle, when both pure liquids spread. (Cira, Benusiglio, Prakash: Nature, 2015). The droplet is stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow from the border to the apex of the droplets. The apparent contact angle of the droplets depends on both their composition and the external humidity as captured by simple models. These droplets present remarkable properties such as lack of a large pinning force. We discuss the drag on these droplets as a function of various parameters. We show theoretical and experimental results of how various confinement geometries change the vapor gradient and the dynamics of droplet attraction.

Influence of Surface Properties and Impact Conditions on Adhesion of Insect Residues

NASA Technical Reports Server (NTRS)

Wohl, Christopher J.; Smith, Joseph G.; Connell, John W.; Siochi, Emilie J.; Doss, Jereme R.; Shanahan, Michelle H.; Penner, Ronald K.

2015-01-01

Insect residues can cause premature transition to turbulent flow on laminar flow airfoils. Engineered surfaces that mitigate the adhesion of insect residues provide, therefore, a route to more efficient aerodynamics and reduced fuel burn rates. Areal coverage and heights of residues depend not only on surface properties, but also on impact conditions. We report high speed photography of fruit fly impacts at different angles of inclination on a rigid aluminum surface, optical microscopy and profilometry, and contact angle goniometry to support the design of engineered surfaces. For the polyurethane and epoxy coatings studied, some of which exhibited superhydrophobicity, it was determined that impact angle and surface compositions play critical roles in the efficacy of these surfaces to reduce insect residue adhesion.

Durable polymer-aerogel based superhydrophobic coatings, a composite material

DOEpatents

Kissel, David J; Brinker, Charles Jeffrey

2014-03-04

Provided are polymer-aerogel composite coatings, devices and articles including polymer-aerogel composite coatings, and methods for preparing the polymer-aerogel composite. The exemplary article can include a surface, wherein the surface includes at least one region and a polymer-aerogel composite coating disposed over the at least one region, wherein the polymer-aerogel composite coating has a water contact angle of at least about 140.degree. and a contact angle hysteresis of less than about 1.degree.. The polymer-aerogel composite coating can include a polymer and an ultra high water content catalyzed polysilicate aerogel, the polysilicate aerogel including a three dimensional network of silica particles having surface functional groups derivatized with a silylating agent and a plurality of pores.

Durable polymer-aerogel based superhydrophobic coatings: a composite material

DOEpatents

Kissel, David J.; Brinker, Charles Jeffrey

2016-02-02

Provided are polymer-aerogel composite coatings, devices and articles including polymer-aerogel composite coatings, and methods for preparing the polymer-aerogel composite. The exemplary article can include a surface, wherein the surface includes at least one region and a polymer-aerogel composite coating disposed over the at least one region, wherein the polymer-aerogel composite coating has a water contact angle of at least about 140.degree. and a contact angle hysteresis of less than about 1.degree.. The polymer-aerogel composite coating can include a polymer and an ultra high water content catalyzed polysilicate aerogel, the polysilicate aerogel including a three dimensional network of silica particles having surface functional groups derivatized with a silylating agent and a plurality of pores.

The effect of aluminium nanocoating and water pH value on the wettability behavior of an aluminium surface

NASA Astrophysics Data System (ADS)

Ali, Naser; Teixeira, Joao A.; Addali, Abdulmajid; Al-Zubi, Feras; Shaban, Ehab; Behbehani, Ismail

2018-06-01

Experimental investigation was performed to highlight the influence of ionic bounding and surface roughness effects on the surface wettability. Nanocoating technique via e-beam physical vapor deposition process was used to fabricate aluminium (Al) film of 50, 100, and 150 nm on the surface of an Al substrate. Microstructures of the samples before and after deposition were observed using an atomic force microscopy. A goniometer device was later on used to examine the influence of surface topography on deionised water of pH 4, 7 and 9 droplets at a temperature ranging from 10 °C to 60 °C through their contact angles with the substrate surface, for both coated and uncoated samples. It was found that, although the coated layer has reduced the mean surface roughness of the sample from 10.7 nm to 4.23 nm, by filling part of the microstructure gaps with Al nanoparticles, the wettability is believed to be effected by the ionic bounds between the surface and the free anions in the fluid. As the deionised water of pH 4, and 9 gave an increase in the average contact angles with the increase of the coated layer thickness. On the other hand, the deionised water of pH 7 has showed a negative relation with the film thickness, where the contact angle reduced as the thickness of the coated layer was increased. The results from the aforementioned approach had showed that nanocoating can endorse the hydrophobicity (unwitting) nature of the surface when associated with free ions hosted by the liquid.

Mechanical stability, corrosion resistance of superhydrophobic steel and repairable durability of its slippery surface.

PubMed

Gao, Xiaoyu; Guo, Zhiguang

2018-02-15

A simple way of chemical etching with H 2 SO 4 and H 2 O 2 was employed to prepare a superhydrophobic steel surface with a water contact angle of 163.5° and a sliding angle of about 0°, in addition to modification with 1H,1H,2H,2H-perfluoroalkyltriethoxysilane (FAS-13). On the basis of perfluropolyethers (PFPE) infusion, a slippery liquid-infused porous surface (SLIPS) was fabricated that had a water contact angle of 115.6° and a sliding angle of 2.27°. The prepared sample can still maintain superhydrophobicity after moving 100 cm on 1000 # sandpaper under 100 g loading via an abrasion test, while its corrosion resistance was exhibited via more positive corrosion potentials (E corr ) and lower corrosion current densities (I corr ) in electrochemical corrosion tests with various solutions. Even if superhydrophobic and slippery properties were lost in the process of long-time soaking in salt solution, the superhydrophobic steel could regain its ability and slippery surfaces also exhibited the repairable durability through retreatment. Such stable, corrosion resistant and superhydrophobic bearing steel and repairable slippery surface have potential for application in practical production and life. Copyright © 2017 Elsevier Inc. All rights reserved.

Influence of aramid fiber moisture regain during atmospheric plasma treatment on aging of treatment effects on surface wettability and bonding strength to epoxy

NASA Astrophysics Data System (ADS)

Ren, Yu; Wang, Chunxia; Qiu, Yiping

2007-09-01

One of the main differences between a low-pressure plasma treatment and an atmospheric pressure plasma treatment is that in atmosphere, the substrate material may absorb significant amount of water which may potentially influence the plasma treatment effects. This paper investigates how the moisture absorbed by aramid fibers during the atmospheric pressure plasma treatment influences the aging behavior of the modified surfaces. Kevlar 49 fibers with different moisture regains (MR) (0.5, 3.5 and 5.5%, respectively) are treated with atmospheric pressure plasma jet (APPJ) with helium as the carrier gas and oxygen as the treatment gas. Surface wettability and chemical compositions, and interfacial shear strengths (IFSS) to epoxy for the aramid fibers in all groups are determined using water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and micro-bond pull out tests, respectively. Immediately after the plasma treatment, the treated fibers have substantially lower water contact angles, higher surface oxygen and nitrogen contents, and larger IFSS to epoxy than those of the control group. At the end of 30 day aging period, the fibers treated with 5.5% moisture regain had a lower water contact angle and more polar groups on the fiber surface, leading to 75% improvement of IFSS over the control fibers, while those for the 0.5 and 3.5% moisture regain groups were only 30%.

Boundary slip and wetting properties of interfaces: correlation of the contact angle with the slip length.

PubMed

Voronov, Roman S; Papavassiliou, Dimitrios V; Lee, Lloyd L

2006-05-28

Correlations between contact angle, a measure of the wetting of surfaces, and slip length are developed using nonequilibrium molecular dynamics for a Lennard-Jones fluid in Couette flow between graphitelike hexagonal-lattice walls. The fluid-wall interaction is varied by modulating the interfacial energy parameter epsilonr=epsilonsfepsilonff and the size parameter sigmar=sigmasfsigmaff, (s=solid, f=fluid) to achieve hydrophobicity (solvophobicity) or hydrophilicity (solvophilicity). The effects of surface chemistry, as well as the effects of temperature and shear rate on the slip length are determined. The contact angle increases from 25 degrees to 147 degrees on highly hydrophobic surfaces (as epsilonr decreases from 0.5 to 0.1), as expected. The slip length is functionally dependent on the affinity strength parameters epsilonr and sigmar: increasing logarithmically with decreasing surface energy epsilonr (i.e., more hydrophobic), while decreasing with power law with decreasing size sigmar. The mechanism for the latter is different from the energetic case. While weak wall forces (small epsilonr) produce hydrophobicity, larger sigmar smoothes out the surface roughness. Both tend to increase the slip. The slip length grows rapidly with a high shear rate, as wall velocity increases three decades from 100 to 10(5) ms. We demonstrate that fluid-solid interfaces with low epsilonr and high sigmar should be chosen to increase slip and are prime candidates for drag reduction.

Facile fabrication of uniform hierarchical structured (UHS) nanocomposite surface with high water repellency and self-cleaning properties

NASA Astrophysics Data System (ADS)

Bagheri, H.; Aliofkhazraei, M.; Forooshani, H. Mojiri; Rouhaghdam, A. Sabour

2018-04-01

In the present study, two-stage process for the fabrication of superhydrophobic Ni-Cu-TiO2 nanocomposite coatings on the copper substrate has been introduced. Surface modification was performed on the electrodeposited coatings by myristic acid-ethanol solution to achieve superhydrophobicity. Additionally, in order to further study the roughness effect, instead of addition of copper ions in electrodeposition bath, three substrates were roughened by electrochemical etching method. Water repellency properties were studied through measurement of static and dynamic contact angles, and performing bouncing test, self-cleaning and water-jet evaluation. The samples were electrodeposited in various current densities, and the highest corrosion resistance and water repellency properties were obtained for the sample which was electrodeposited in two consecutive steps and modified by a fatty acid called myristic acid (which significantly reduces surface energy of the coating). The highest water contact angle (161°) and the lowest contact angle hysteresis (3°) were obtained for the sample which was coated by 10 mA/cm2 (144 min) and 20 mA/cm2 (18 min), respectively. Since this approach does not require any sophisticated equipment and materials, it shows promising future in the fabrication of superhydrophobic coatings.

Wear-resistant and electromagnetic absorbing behaviors of oleic acid post-modified ferrite-filled epoxy resin composite coating

NASA Astrophysics Data System (ADS)

Wang, Wenjie; Zang, Chongguang; Jiao, Qingjie

2015-03-01

The post-modified Mn-Zn ferrite was prepared by grafting oleic acid on the surface of Mn-Zn ferrite to inhibit magnetic nanoparticle aggregation. Fourier Transform Infrared (FT-IR) spectroscopy was used to characterize the particle surfaces. The friction and electromagnetic absorbing properties of a thin coating fabricated by dispersing ferrite into epoxy resin (EP) were investigated. The roughness of the coating and water contact angle were measured using the VEECO and water contact angle meter. Friction tests were conducted using a stainless-steel bearing ball and a Rockwell diamond tip, respectively. The complex permittivity and complex permeability of the composite coating were studied in the low frequency (10 MHz-1.5 GHz). Surface modified ferrites are found to improve magnetic particles dispersion in EP resulting in significant compatibility between inorganic and organic materials. Results also indicate that modified ferrite/EP coatings have a lower roughness average value and higher water contact angle than original ferrite/EP coatings. The enhanced tribological properties of the modified ferrite/EP coatings can be seen from the increased coefficient value. The composite coatings with modified ferrite are observed to exhibit better reflection loss compared with the coatings with original ferrite.

A Course in Colloid and Surface Science.

ERIC Educational Resources Information Center

Scamehorn, John F.

1984-01-01

Describes a course for chemical engineers, chemists, and petroleum engineers that focuses on colloid and surface science. Major topic areas in the course include capillarity, surface thermodynamics, adsorption contact angle, micelle formation, solubilization in micelles, emulsions, foams, and applications. (JN)

Preparation of MTMS based transparent superhydrophobic silica films by sol-gel method.

PubMed

Venkateswara Rao, A; Latthe, Sanjay S; Nadargi, Digambar Y; Hirashima, H; Ganesan, V

2009-04-15

Superhydrophobic surfaces with water contact angle higher than 150 degrees generated a lot of interest both in academia and in industry because of the self-cleaning properties. Optically transparent superhydrophobic silica films were synthesized at room temperature (27 degrees C) using sol-gel process by a simple dip coating technique. The molar ratio of MTMS:MeOH:H(2)O (5 M NH(4)OH) was kept constant at 1:10.56:4.16, respectively. Emphasis is given to the effect of the surface modifying agents on the hydrophobic behavior of the films. Methyl groups were introduced in the silica film by post-synthesis grafting from two solutions using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents in hexane solvent, individually. The percentage of silylating agents and silylation period was varied from 2.5 to 7.5% and 1 to 3 h, respectively. The TMCS modified films exhibited a very high water contact angle (166+/-2 degrees) in comparison to the HMDZ (138+/-2 degrees) modified films, indicating the water repellent behavior of the surface. When the TMCS and HMDZ modified films were heated at temperatures higher than 350 degrees C and 335 degrees C, respectively, the films became superhydrophilic; the contact angle for water on the films was smaller than 5 degrees. Further, the humidity study was carried out at a relative humidity of 85% at 30 degrees C temperature over 30 days. The films have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), % optical transmission, humidity tests and contact angle (CA) measurements.

Dynamic Roughness Ratio-Based Framework for Modeling Mixed Mode of Droplet Evaporation.

PubMed

Gunjan, Madhu Ranjan; Raj, Rishi

2017-07-18

The spatiotemporal evolution of an evaporating sessile droplet and its effect on lifetime is crucial to various disciplines of science and technology. Although experimental investigations suggest three distinct modes through which a droplet evaporates, namely, the constant contact radius (CCR), the constant contact angle (CCA), and the mixed, only the CCR and the CCA modes have been modeled reasonably. Here we use experiments with water droplets on flat and micropillared silicon substrates to characterize the mixed mode. We visualize that a perfect CCA mode after the initial CCR mode is an idealization on a flat silicon substrate, and the receding contact line undergoes intermittent but recurring pinning (CCR mode) as it encounters fresh contaminants on the surface. The resulting increase in roughness lowers the contact angle of the droplet during these intermittent CCR modes until the next depinning event, followed by the CCA mode of evaporation. The airborne contaminants in our experiments are mostly loosely adhered to the surface and travel along with the receding contact line. The resulting gradual increase in the apparent roughness and hence the extent of CCR mode over CCA mode forces appreciable decrease in the contact angle observed during the mixed mode of evaporation. Unlike loosely adhered airborne contaminants on flat samples, micropillars act as fixed roughness features. The apparent roughness fluctuates about the mean value as the contact line recedes between pillars. Evaporation on these surfaces exhibits stick-jump motion with a short-duration mixed mode toward the end when the droplet size becomes comparable to the pillar spacing. We incorporate this dynamic roughness into a classical evaporation model to accurately predict the droplet evolution throughout the three modes, for both flat and micropillared silicon surfaces. We believe that this framework can also be extended to model the evaporation of nanofluids and the coffee-ring effect, among others.

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.

Deformation of an Elastic Substrate Due to a Resting Sessile Droplet

NASA Astrophysics Data System (ADS)

Bardall, Aaron; Daniels, Karen; Shearer, Michael

2017-11-01

On a sufficiently soft substrate, a resting fluid droplet will cause significant deformation of the substrate. This deformation is driven by a combination of capillary forces at the contact line and the fluid pressure at the solid surface. These forces are balanced at the surface by the solid traction stress induced by the substrate deformation. Young's Law, which predicts the equilibrium contact angle of the droplet, also indicates an a priori radial force balance for rigid substrates, but not necessarily for soft substrates which deform under loading. It remains an open question whether the contact line transmits a non-zero force tangent to the substrate surface in addition to the conventional normal force. This talk will present a model for the static deformation of the substrate that includes a non-zero tangential contact line force as well as general interfacial energy conditions governing the angle of a two-dimensional droplet. We discuss extensions of this model to non-symmetric droplets and their effect on the static configuration of the droplet/substrate system. NSF #DMS-1517291.

Novel method for controllable fabrication of a superhydrophobic CuO surface on AZ91D magnesium alloy.

PubMed

She, Zuxin; Li, Qing; Wang, Zhongwei; Li, Longqin; Chen, Funan; Zhou, Juncen

2012-08-01

A novel method for controllable fabrication of a superhydrophobic CuO surface on AZ91D magnesium alloy is reported in this paper. Hierarchical structure composed of micro/nano-featherlike CuO was obtained by electrodeposition of Cu-Zn alloy coating and subsequently an electrochemical anodic treatment in alkaline solution. After modification with lauric acid, the surface became hydrophobicity/superhydrophobicity. The formation of featherlike CuO structures was controllable by varying the coating composition. By applying SEM, ICP-AES, and water contact angle analysis, the effects of coating composition on the surface morphology and hydrophobicity of the as-prepared surfaces were detailedly studied. The results indicated that at the optimal condition, the surface showed a good superhydrophobicity with a water contact angle as high as 155.5 ± 1.3° and a sliding angle as low as about 3°. Possible growth mechanism of featherlike CuO hierarchical structure was discussed. Additionally, the anticorrosion effect of the superhydrophobic surface was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The interface model for anticorrosion mechanism of superhydrophobic surface in corrosive medium was proposed. Besides, the mechanical stability test indicated that the resulting superhydrophobic surfaces have good mechanical stability.

EMIIM Wetting Properties & Their Effect on Electrospray Thruster Design

DTIC Science & Technology

2012-03-01

tension and contact or “wetting" angle formed when a liquid droplet comes in contact with a solid surface. Ideally this angle is a function of the...3 3 Picture of a Taylor cone formed at AFRL, note bubbles present. . . . . . . 3 4 Titanium electrode grids in use at AFRL...cone formed using an internally wetted emitter and the ionic liquid BMI-BG4 is shown in Figure 3.[7] Emitters are precisely aligned with openings

Oil/water/rock wettability: Influencing factors and implications for low salinity water flooding in carbonate reservoirs

DOE PAGES

Chen, Yongqiang; Xie, Quan; Sari, Ahmad; ...

2017-11-21

Wettability of the oil/brine/rock system is an essential petro-physical parameter which governs subsurface multiphase flow behaviour and the distribution of fluids, thus directly affecting oil recovery. Recent studies [1–3] show that manipulation of injected brine composition can enhance oil recovery by shifting wettability from oil-wet to water-wet. However, what factor(s) control system wettability has not been completely elucidated due to incomplete understanding of the geochemical system. To isolate and identify the key factors at play we used in this paper SO 4 2—free solutions to examine the effect of salinity (formation brine/FB, 10 times diluted formation brine/10 dFB, and 100more » times diluted formation brine/100 dFB) on the contact angle of oil droplets at the surface of calcite. We then compared contact angle results with predictions of surface complexation by low salinity water using PHREEQC software. We demonstrate that the conventional dilution approach likely triggers an oil-wet system at low pH, which may explain why the low salinity water EOR-effect is not always observed by injecting low salinity water in carbonated reservoirs. pH plays a fundamental role in the surface chemistry of oil/brine interfaces, and wettability. Our contact angle results show that formation brine triggered a strong water-wet system (35°) at pH 2.55, yet 100 times diluted formation brine led to a strongly oil-wet system (contact angle = 175°) at pH 5.68. Surface complexation modelling correctly predicted the wettability trend with salinity; the bond product sum ([>CaOH 2 +][–COO -] + [>CO 3 -][–NH +] + [>CO 3 -][–COOCa +]) increased with decreasing salinity. Finally, at pH < 6 dilution likely makes the calcite surface oil-wet, particularly for crude oils with high base number. Yet, dilution probably causes water wetness at pH > 7 for crude oils with high acid number.« less

Oil/water/rock wettability: Influencing factors and implications for low salinity water flooding in carbonate reservoirs

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

Chen, Yongqiang; Xie, Quan; Sari, Ahmad

Wettability of the oil/brine/rock system is an essential petro-physical parameter which governs subsurface multiphase flow behaviour and the distribution of fluids, thus directly affecting oil recovery. Recent studies [1–3] show that manipulation of injected brine composition can enhance oil recovery by shifting wettability from oil-wet to water-wet. However, what factor(s) control system wettability has not been completely elucidated due to incomplete understanding of the geochemical system. To isolate and identify the key factors at play we used in this paper SO 4 2—free solutions to examine the effect of salinity (formation brine/FB, 10 times diluted formation brine/10 dFB, and 100more » times diluted formation brine/100 dFB) on the contact angle of oil droplets at the surface of calcite. We then compared contact angle results with predictions of surface complexation by low salinity water using PHREEQC software. We demonstrate that the conventional dilution approach likely triggers an oil-wet system at low pH, which may explain why the low salinity water EOR-effect is not always observed by injecting low salinity water in carbonated reservoirs. pH plays a fundamental role in the surface chemistry of oil/brine interfaces, and wettability. Our contact angle results show that formation brine triggered a strong water-wet system (35°) at pH 2.55, yet 100 times diluted formation brine led to a strongly oil-wet system (contact angle = 175°) at pH 5.68. Surface complexation modelling correctly predicted the wettability trend with salinity; the bond product sum ([>CaOH 2 +][–COO -] + [>CO 3 -][–NH +] + [>CO 3 -][–COOCa +]) increased with decreasing salinity. Finally, at pH < 6 dilution likely makes the calcite surface oil-wet, particularly for crude oils with high base number. Yet, dilution probably causes water wetness at pH > 7 for crude oils with high acid number.« less

Contact sheet recording with a self-acting negative air bearing

NASA Technical Reports Server (NTRS)

Muftu , Sinan (Inventor); Hinteregger, Hans F (Inventor)

2000-01-01

A flat head and a tape transport arrangement impart a wrap angle to the tape at the upstream corner of the head. The wrap angle, corner sharpness and tape stiffness are sufficient to cause a moving tape to form a hollow bump at the upstream corner, thereby creating a hollow into which entrained air can expand, causing a subambient pressure within and downstream of the bump. This pressure keeps the tape in contact with the head. It is created without the need for a groove or complex pressure relief slot(s). No contact pressure arises at the signal exchange site due to media wrap. The highest contact pressures are developed at a wrapped upstream corner. For a tape drive, traveling in both forward and reverse, the wrap can be at both the upstream and downstream (which is the reverse upstream) corners. Heads that are not flat can also be used, if the wrap angle relative to a main surface is sufficient and not too large. The wrapped head can also be used with rotating media, such as disks (floppy and hard) and rotating heads, such as helical wound heads for video recording. Multiple flat tape bearing surfaces can be separated by grooves and/or angles. Each flat can carry heads along one or more gap lines. Multiple adjacent narrow tracks can thus be written for extreme high track density recording.

The contact mechanics and occurrence of edge loading in modular metal-on-polyethylene total hip replacement during daily activities.

PubMed

Hua, Xijin; Li, Junyan; Jin, Zhongmin; Fisher, John

2016-06-01

The occurrence of edge loading in hip joint replacement has been associated with many factors such as prosthetic design, component malposition and activities of daily living. The present study aimed to quantify the occurrence of edge loading/contact at the articulating surface and to evaluate the effect of cup angles and edge loading on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR) during different daily activities. A three-dimensional finite element model was developed based on a modular MoP bearing system. Different cup inclination and anteversion angles were modelled and six daily activities were considered. The results showed that edge loading was predicted during normal walking, ascending and descending stairs activities under steep cup inclination conditions (≥55°) while no edge loading was observed during standing up, sitting down and knee bending activities. The duration of edge loading increased with increased cup inclination angles and was affected by the cup anteversion angles. Edge loading caused elevated contact pressure at the articulating surface and substantially increased equivalent plastic strain of the polyethylene liner. The present study suggested that correct positioning the component to avoid edge loading that may occur during daily activities is important for MoP THR in clinical practice. Copyright © 2016. Published by Elsevier Ltd.

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.

Rice- and butterfly-wing effect inspired self-cleaning and low drag micro/nanopatterned surfaces in water, oil, and air flow.

PubMed

Bixler, Gregory D; Bhushan, Bharat

2014-01-07

In search of new solutions to complex challenges, researchers are turning to living nature for inspiration. For example, special surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we study four microstructured surfaces inspired by rice leaves and fabricated with photolithography techniques. We also present a method of creating such surfaces using a hot embossing procedure for scaled-up manufacturing. Fluid drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of sample geometrical dimensions. Conceptual modeling provides design guidance when developing novel low drag, self-cleaning, and potentially antifouling surfaces for medical, marine, and industrial applications.

Superhydrophobic and icephobic surfaces prepared by RF-sputtered polytetrafluoroethylene coatings

NASA Astrophysics Data System (ADS)

Jafari, R.; Menini, R.; Farzaneh, M.

2010-12-01

A superhydrophobic and icephobic surface were investigated on aluminum alloy substrate. Anodizing was used first to create a micro-nanostructured aluminum oxide underlayer on the alloy substrate. In a second step, the rough surface was coated with RF-sputtered polytetrafluoroethylene (PTFE or Teflon ®). Scanning electron microscopy images showed a " bird's nest"-like structure on the anodized surface. The RF-sputtered PTFE coating exhibited a high static contact angle of ˜165° with a very low contact angle hysteresis of ˜3°. X-ray photoelectron spectroscopy (XPS) results showed high quantities of CF 3 and CF 2 groups, which are responsible for the hydrophobic behavior of the coatings. The performance of this superhydrophobic film was studied under atmospheric icing conditions. These results showed that on superhydrophobic surfaces ice-adhesion strength was 3.5 times lower than on the polished aluminum substrate.

Rice- and butterfly-wing effect inspired self-cleaning and low drag micro/nanopatterned surfaces in water, oil, and air flow

NASA Astrophysics Data System (ADS)

Bixler, Gregory D.; Bhushan, Bharat

2013-12-01

In search of new solutions to complex challenges, researchers are turning to living nature for inspiration. For example, special surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we study four microstructured surfaces inspired by rice leaves and fabricated with photolithography techniques. We also present a method of creating such surfaces using a hot embossing procedure for scaled-up manufacturing. Fluid drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of sample geometrical dimensions. Conceptual modeling provides design guidance when developing novel low drag, self-cleaning, and potentially antifouling surfaces for medical, marine, and industrial applications.

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.

Improvement in surface hydrophilicity and resistance to deformation of natural leather through O2/H2O low-temperature plasma treatment

NASA Astrophysics Data System (ADS)

You, Xuewei; Gou, Li; Tong, Xingye

2016-01-01

The natural leather was modified through O2/H2O low-temperature plasma treatment. Surface morphology was characterized by scanning electron microscopy (SEM) and the results showed that the pores on the leather surface became deeper and larger with enhanced permeability of water and vapor. XPS and FTIR-ATR was performed to determine the chemical composition of natural leather surface. Oxygen-containing groups were successfully grafted onto the surface of natural leather and oxygen content increased with longer treatment time. After O2/H2O plasma treatment, initial water contact angle was about 21° and water contact angles were not beyond 55° after being stored for 3 days. Furthermore, the tensile test indicated that the resistance to deformation had a prominent transform without sacrificing the tensile strength.

Fabrication of hydrophobic compressed oil palm trunk surface by sol-gel process

NASA Astrophysics Data System (ADS)

Muzakir, Syafiqah; Salim, Nurjannah; Huda Abu Bakar, Nurul; Roslan, Rasidi; Sin, Lim Wan; Hashim, Rokiah

2018-04-01

Improvement of the robustness of hydrophobic surfaces is crucial to achieving commercial applications of these surfaces in such various areas as self-cleaning, water repellency and corrosion resistance. Compressed oil palm trunk (OPT) panel is one of potential product which can be used as panelling and indoor furniture application. By adding hydrophobic properties to compressed oil palm trunk panel might increase the application of compressed oil palm trunk especially for outdoor application. In this study, fabrication is using the sol-gel technique. Sol-gel was prepared by adding ethanol with Hexadecyl Trimethyl Ammonium Bromide (CTAB) solution with Tetraethyl Orthosilicate (TEOS) with surface modification of chlorotrimethylsilane (CTMS). The surface with hydrophobic coating was undergone surface analysis with contact angle machine with the aid of software SCA 20 and the determined of the morphology of surface with scanning electron microscope (SEM). The produced compressed oil palm trunk surfaces exhibited promising hydrophobic properties with a contact angle of 104° and the relatively better mechanical robustness.

Copoly(Imide Siloxane) Abhesive Materials with Varied Siloxane Oligomer Length

NASA Technical Reports Server (NTRS)

Wohl, Christopher J.; Atkins, Brad M.; Belcher, Marcus A.; Connell, John W.

2010-01-01

Incorporation of PDMS moieties into a polyimide matrix lowered the surface energy resulting in enhanced adhesive interactions. Polyimide siloxane materials were generated using amine-terminated PDMS oligomers of different lengths to study changes in surface migration behavior, phase segregation, mechanical, thermal, and optical properties. These materials were characterized using contact angle goniometry, tensile testing, and differential scanning calorimetry. The surface migration behavior of the PDMS component depended upon the siloxane molecular weight as indicated by distinct relationships between PDMS chain length and advancing water contact angles. Similar correlations were observed for percent elongation values obtained from tensile testing, while the addition of PDMS reduced the modulus. High fidelity topographical modification via laser ablation patterning further reduced the polyimide siloxane surface energy. Initial particulate adhesion testing experiments demonstrated that polyimide siloxane materials exhibited greater abhesive interactions relative to their respective homopolyimides.

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.

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.

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

Icephobicity and the effect of water condensation on the superhydrophobic low-density polyethylene surface

NASA Astrophysics Data System (ADS)

Yuan, Zhiqing; Wang, Menglei; Huang, Juan; Wang, Xian; Bin, Jiping; Peng, Chaoyi; Xing, Suli; Xiao, Jiayu; Zeng, Jingcheng; Xiao, Ximei; Fu, Xin; Gong, Huifang; Zhao, Dejian; Chen, Hong

2015-06-01

A superhydrophobic surface was obtained on a low-density polyethylene (LDPE) substrate using a facile method. The water contact angle and the sliding angle of the superhydrophobic LDPE surface were 155 ± 2° and 4°, respectively. The ice shear stress of the superhydrophobic LDPE surface was 2.08 times smaller than that of the flat LDPE surface. The superhydrophobic surface still showed excellent icephobicity and superhydrophobicity after undergoing a circulatory icing/deicing procedure five times. In addition, water condensation and its effect on the icephobicity of the as-prepared superhydrophobic surface were also studied.

Influence of hydrophobic surface treatment toward performance of air filter

NASA Astrophysics Data System (ADS)

Shahfiq Zulkifli, Nazrul; Zaini Yunos, Muhamad; Ahmad, Azlinnorazia; Harun, Zawati; Akhair, Siti Hajar Mohd; Adibah Raja Ahmad, Raja; Hafeez Azhar, Faiz; Rashid, Abdul Qaiyyum Abd; Ismail, Al Emran

2017-08-01

This study investigated the performance of hydrophobic surface treatment by using silica aerogel powder via spray coating techniques. Hydrophobic properties were determined by measuring the level of the contact angle. Meanwhile, performance was evaluated in term of the hydrogen gas flow and humidity rejection. The results are shown by contact angle that the microstructure filter, especially in the upper layer and sub-layer has been changed. The results also show an increase of hydrophobicity due to the increased quantity of silica aerogel powder. Results also showed that the absorption and rejection filter performance filter has increased after the addition of silica aerogel powder. The results showed that with the addition of 5 grams of powder of silica aerogel have the highest result of wetting angle 134.11°. The highest humidity rejection found with 5 grams of powder of silica aerogel.

Scaling analysis and SE simulation of the tilted cylinder-interface capillary interaction

NASA Astrophysics Data System (ADS)

Gao, S. Q.; Zhang, X. Y.; Zhou, Y. H.

2018-06-01

The capillary interaction induced by a tilted cylinder and interface is the basic configuration of many complex systems, such as micro-pillar arrays clustering, super-hydrophobicity of hairy surface, water-walking insects, and fiber aggregation. We systematically analyzed the scaling laws of tilt angle, contact angle, and cylinder radius on the contact line shape by SE simulation and experiment. The following in-depth analysis of the characteristic parameters (shift, stretch and distortion) of the deformed contact lines reveals the self-similar shape of contact line. Then a general capillary force scaling law is proposed to incredibly grasp all the simulated and experimental data by a quite straightforward ellipse approximation approach.

Fabrication and condensation characteristics of metallic superhydrophobic surface with hierarchical micro-nano structures

NASA Astrophysics Data System (ADS)

Chu, Fuqiang; Wu, Xiaomin

2016-05-01

Metallic superhydrophobic surfaces have various applications in aerospace, refrigeration and other engineering fields due to their excellent water repellent characteristics. This study considers a simple but widely applicable fabrication method using a two simultaneous chemical reactions method to prepare the acid-salt mixed solutions to process the metal surfaces with surface deposition and surface etching to construct hierarchical micro-nano structures on the surface and then modify the surface with low surface-energy materials. Al-based and Cu-based superhydrophobic surfaces were fabricated using this method. The Al-based superhydrophobic surface had a water contact angle of 164° with hierarchical micro-nano structures similar to the lotus leaves. The Cu-based surface had a water contact angle of 157° with moss-like hierarchical micro-nano structures. Droplet condensation experiments were also performed on these two superhydrophobic surfaces to investigate their condensation characteristics. The results show that the Al-based superhydrophobic surface has lower droplet density, higher droplet jumping probability, slower droplet growth rate and lower surface coverage due to the more structured hierarchical structures.

Surface Modification by Atmospheric Pressure Plasma for Improved Bonding

NASA Astrophysics Data System (ADS)

Williams, Thomas Scott

An atmospheric pressure plasma source operating at temperatures below 150?C and fed with 1.0-3.0 volume% oxygen in helium was used to activate the surfaces of the native oxide on silicon, carbon-fiber reinforced epoxy composite, stainless steel type 410, and aluminum alloy 2024. Helium and oxygen were passed through the plasma source, whereby ionization occurred and ˜10 16 cm-3 oxygen atoms, ˜1015 cm -3 ozone molecules and ˜1016 cm-3 metastable oxygen molecules (O21Deltag) were generated. The plasma afterglow was directed onto the substrate material located 4 mm downstream. Surface properties of the plasma treated materials have been investigated using water contact angle (WCA), atomic force microscopy (AFM), infrared spectroscopy (IR), and x-ray photoelectron spectroscopy (XPS). The work presented herein establishes atmospheric-pressure plasma as a surface preparation technique that is well suited for surface activation and enhanced adhesive bond strength in a variety of materials. Atmospheric plasma activation presents an environmentally friendly alternative to wet chemical and abrasive methods of surface preparation. Attenuated total internal reflection infrared spectroscopy was used to study the aging mechanism of the native oxide on silicon. During storage at ambient conditions, the water contact angle of a clean surface increased from <5° to 40° over a period of 12 hours. When stored under a nitrogen purge, the water contact angle of a clean surface increased from <5° to 30° over a period of 40-60 hours. The change in contact angle resulted from the adsorption of nonanal onto the exposed surface hydroxyl groups. The rate of adsorption of nonanal under a nitrogen purged atmosphere ranged from 0.378+/-0.011 hr-1 to 0.182+/-0.008 hr -1 molecules/(cm2•s), decreasing as the fraction of hydrogen-bonded hydroxyl groups increased from 49% to 96% on the SiO 2 surface. The adsorption of the organic contaminant could be suppressed indefinitely by storing the silicon wafers in the presence of activated carbon or in a freezer at -22°C. The enhancement of adhesive bond strength and durability for carbon-fiber reinforced epoxy composite, stainless steel type 410, and aluminum alloy 2024 was demonstrated with the atmospheric pressure helium-oxygen plasma. All surfaces studied were converted from a hydrophobic state with a water contact angle of 65° to 80° into a hydrophilic state with a water contact angle between 20° and 40° within 5 seconds of plasma exposure. X-ray photoelectron spectroscopy confirmed that the carbon atoms on the carbon-fiber/epoxy composite were oxidized, yielding 17 atom% carboxylic acid groups, 10% ketones or aldehydes and 9% alcohols. Analysis of stainless steel and aluminum by XPS illustrate oxidation of the metal surface and an increase in the concentration of hydroxyl groups in the oxide film. Following plasma activation, the total hydroxyl species concentration on stainless steel increased from 31% to 57%, while aluminum exhibited an increase from 4% to 16% hydroxyl species. Plasma activation of the surface led to an increase in bond strength of the different surfaces by up to 150% when using Cytec FM300 and FM300-2 epoxy adhesives. Wedge crack extension tests following plasma activation revealed cohesive failure percentages of 97% for carbon-fiber/epoxy composite bonded to stainless steel, and 96% for aluminum bonded to itself. The bond strength and durability of the substrates correlated with changes in the specific surface chemistry, not the wetting angle or the morphological properties of the material. This suggests that enhanced chemical bonding at the interface was responsible for the improvement in mechanical properties following plasma activation. The surface preparation of polymers and composites using atmospheric pressure plasmas is a promising technique for replacing traditional methods of surface preparation by sanding, grit blasting or peel ply. After oxygen plasma activation and joining the materials together with epoxy, one observes 100% cohesive failure within the cured film adhesive. Depending on the material, the lap shear strength can be increased several fold over that achieved by either solvent wiping or abrasion. The trends in adhesion with plasma exposure time do not correlate well with surface wetting or roughness; instead they correlate with the fraction of the polymer surface sites that are converted into carboxylic acid groups.

Caustics and Caustic-Interference in Measurements of Contact Angle and Flow Visualization Through Laser Shadowgraphy

NASA Technical Reports Server (NTRS)

Chao, David F.; Zhang, Neng-Li

2002-01-01

As one of the basic elements of the shadowgraphy optical system, the image of the far field from the droplet implicates plentiful information on the droplet profile. An analysis of caustics by wave theory shows that a droplet with a cylindrically symmetric Gaussian-hill-type profile produces a circular directional caustic in far field, which arises from the singularities (inflection line on the surface). The sessile liquid droplets, which profiles are restricted by surface tension, usually have a 'protruding foot' where the surface inflects. Simple geometrical optics indicates that the circular caustic stemming from the surface inflection at the protruding-foot takes the shape of the outmost ring on the image of the far field. It is the diameter of the outmost ring that is used as one of the key parameters in the measurements of contact angle through the laser shadowgraphic method. Different surface characteristics of the droplets produce different type of caustics, and therefore, the shape of the caustics can be used to determine the surface property of the sessile droplets. The present paper describes the measurement method of contact angIe using the circular caustics and the estimation of the protruding-foot height through the caustic interference.

Hydrophobic Surface Modification of Silk Fabric Using Plasma-Polymerized Hmdso

NASA Astrophysics Data System (ADS)

Rani, K. Vinisha; Chandwani, Nisha; Kikani, Purvi; Nema, S. K.; Sarma, Arun Kumar; Sarma, Bornali

In this work, we study the hydrophobic properties of silk fabrics by deposition of plasma-polymerized (pp) hexamethyldisiloxane (HMDSO) using low-pressure plasma-enhanced chemical vapor deposition. Recently, hydrophobic properties are under active research in textile industry. The effects of coating time and power on the HMDSO-coated silk fabrics are investigated. Water contact angle of pp-HMDSO-coated silk fabric surface is measured as a function of power and coating time. Fabric surface shows an enhancement in hydrophobicity after coating. Attenuated total reflectance-Fourier transform infrared spectroscopy reveals the surface chemistry, and scanning electron microscopy shows the surface morphology of the uncoated and HMDSO-coated fabrics, respectively. In the case of uncoated fabric, water droplet absorbs swiftly, whereas in the case of HMDSO-coated fabric, water droplet remains on the fabric surface with a maximum contact angle of 140∘. The HMDSO-deposited silk surface is found to be durable after detergent washing. Common stains such as ink, tea, milk, turmeric and orange juice are tested on the surface of both fabrics. In HMDSO-coated fabrics, all the stains are bedded like ball droplet. In order to study the self-cleaning property, the fabric is tilted to 45∘ angle; stain droplets easily roll off from the fabric.

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.

Fabrication of high wettability gradient on copper substrate

NASA Astrophysics Data System (ADS)

Huang, Ding-Jun; Leu, Tzong-Shyng

2013-09-01

Copper is one of the most widely used materials in condensation heat transfer. Recently there has been great interest in improving the condensation heat transfer efficiency through copper surface modification. In this study, we describe the fabrication processes of how copper surfaces were modified to be superhydrophilic (CA ≤ 10°) and superhydrophobic (CA > 150°) by means of H2O2 immersion and fluorination with Teflon. The wettability gradient of copper surfaces with contact angles (CA) changing from superhydrophilic to superhydrophobic are also demonstrated. Unlike previous studies on gradient surfaces in which the wettability gradient is controlled either non-precisely or entirely uncontrolled, in this study, the contact angles along wettability gradient copper surfaces vary with a precisely designed gradient. It is demonstrated that a high wettability gradient copper surface can be successfully fabricated using photolithography to define the area ratios between superhydrophilic and superhydrophobic patterns within a short distance. The fabricated wettability gradient of copper surfaces is expected to be able to enhance the condensation heat transfer efficiency.

Topography and surface energy dependent calcium phosphate formation on Sol-Gel derived TiO2 coatings.

PubMed

Järn, Mikael; Areva, Sami; Pore, Viljami; Peltonen, Jouko; Linden, Mika

2006-09-12

Heterogeneous nucleation and growth of calcium phosphate (CaP) on sol-gel derived TiO(2) coatings was investigated in terms of surface topography and surface energy. The topography of the coatings was derived from AFM measurements, while the surface energy was determined with contact angle measurements. The degree of precipitation was examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The precipitation of CaP was found to be dependent on both topography and surface energy. A high roughness value when combining the RMS roughness parameter S(q) with the number of local maxima per unit area parameter S(ds) enhances CaP formation. The hydrophilicity of the coating was also found to be of importance for CaP formation. We suggest that the water contact angle, which is a direct measure of the hydrophilicity of the surface, may be used to evaluate the surface energy dependent precipitation kinetics rather than using the often applied Lewis base parameter.

Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer

PubMed Central

Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.

2013-01-01

Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer. PMID:23759735

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.

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.

Dynamics of water droplets detached from porous surfaces of relevance to PEM fuel cells.

PubMed

Theodorakakos, A; Ous, T; Gavaises, M; Nouri, J M; Nikolopoulos, N; Yanagihara, H

2006-08-15

The detachment of liquid droplets from porous material surfaces used with proton exchange membrane (PEM) fuel cells under the influence of a cross-flowing air is investigated computationally and experimentally. CCD images taken on a purpose-built transparent fuel cell have revealed that the water produced within the PEM is forming droplets on the surface of the gas-diffusion layer. These droplets are swept away if the velocity of the flowing air is above a critical value for a given droplet size. Static and dynamic contact angle measurements for three different carbon gas-diffusion layer materials obtained inside a transparent air-channel test model have been used as input to the numerical model; the latter is based on a Navier-Stokes equations flow solver incorporating the volume of fluid (VOF) two-phase flow methodology. Variable contact angle values around the gas-liquid-solid contact-line as well as their dynamic change during the droplet shape deformation process, have allowed estimation of the adhesion force between the liquid droplet and the solid surface and successful prediction of the separation line at which droplets loose their contact from the solid surface under the influence of the air stream flowing around them. Parametric studies highlight the relevant importance of various factors affecting the detachment of the liquid droplets from the solid surface.

Spray-coating of superhydrophobic aluminum alloys with enhanced mechanical robustness.

PubMed

Zhang, Youfa; Ge, Dengteng; Yang, Shu

2014-06-01

A superhydrophobic aluminum alloy was prepared by one-step spray coating of an alcohol solution consisting of hydrophobic silica nanoparticles (15-40 nm) and methyl silicate precursor on etched aluminum alloy with pitted morphology. The as-sprayed metal surface showed a water contact angle of 155° and a roll-off angle of 4°. The coating was subjected to repeated mechanical tests, including high-pressure water jetting, sand particles impacting, and sandpaper shear abrasion. It remained superhydrophobic with a roll-off angle <10° up to three cycles of water jetting (25 kPa for 10 min) and sand particle impinging. After five cycles, the roll-off angle increased, but no more than 19° while the water contact angle remained greater than 150°. The superhydrophobic state was also maintained after three cycles of sandpaper abrasion. It was found that the micro-protrusion structures on the etched aluminum alloy played an important role to enhance the coating mechanical robustness, where the nanoparticles could grab on the rough surface, specifically in the groove structures, in comparison with the smooth glass substrates spray coated with the same materials. Further, we showed that the superhydrophobicity could be restored by spray a new cycle of the nanocomposite solution on the damaged surface. Copyright © 2014 Elsevier Inc. All rights reserved.

Preparation of anticoagulant PyC biomaterials with super-hydrophobic surface.

PubMed

Ze, Wang; Wen-Sheng, Tan; Ye-Xia; Ming, Zhang; Xiao-Ping, Li; Jian-Guo, Qiu; Xiao-Hong, Yang

2018-01-01

Pyrolytic carbon (PyC) is a kind of biomaterial which is chemically inert and has excellent biocompatibility. In order to obtain a super-hydrophobic PyC surface to improve anticoagulation and inhibit thrombus, this study prepares grating pair structure, microhole array structure, helix structure on PyC surface by nanoseconds laser etching. Rod-like ZnO film and ball-like ZnO film are prepared on the PyC surface by the hydrothermal method; polyvinyl pyrrolidone (PVP) nanofiber film and PVP/TiO 2 complex nanofiber film are prepared on the PyC surface by the electrospinning method; the PyC surface is silanized. Finally, surface microstructure and surface energy are characterized by scanning electron microscopy and contact angle meter (OCA20, German DataPhysics Co.). The periodical microstructures are formed respectively by nanoseconds laser etching. The surface roughness is increased by the hydrothermal and electrospinning method. Through infiltration experiment on rough and smooth PyC surfaces, rough PyC surface with microstructure is super-hydrophobic and has greater than 150° contact angle, which decreases blood flow resistance and inhibits thrombus.

A coating of silane modified silica nanoparticles on PET substrate film for inkjet printing

NASA Astrophysics Data System (ADS)

Wu, J.; Liu, L.; Jiang, B.; Hu, Z.; Wang, X. Q.; Huang, Y. D.; Lin, D. R.; Zhang, Q. H.

2012-04-01

The paper aims to design nanoporous coatings for inkjet printing and study its microstructure influence on the ink absorption. In the present work, two inkjet materials were prepared: one with unmodified nano-SiO2 (S_1), the other with silica coupling agent modified nano-SiO2 (S_2). The surface characteristic changing after modification was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM). Wetting with contact angles was determined by the dynamic contact angle analysis test (DCAT). Through measurements, the dispersion of modified nano-SiO2 particles in the coating was superior to the dispersion of unmodified nano-SiO2 particles, surface roughness value (Ra) of S_1 was significantly higher than that of S_2, dynamic contact angle of S_2 is smaller than that of S_1 and ink droplet absorption in S_2 was much faster than in S_1. These results also reveal that the modification method is effective and offers a potential way to fabricate inkjet material with the advantages of microstructure and ink absorption over traditional methods.

Investigation of antibacterial and wettability behaviours of plasma-modified PMMA films for application in ophthalmology

NASA Astrophysics Data System (ADS)

Rezaei, Fatemeh; Abbasi-Firouzjah, Marzieh; Shokri, Babak

2014-02-01

The main objective of this research is the experimental investigation of the surface properties of polymethyl methacrylate (PMMA) such as wettability and the roughness effect on Escherichia coli (gram negative) cell adhesion. Radio frequency (RF; 13.56 MHz) oxygen plasma was used to enhance the antibacterial and wettability properties of this polymer for biomedical applications, especially ophthalmology. The surface was activated by O2 plasma to produce hydrophilic functional groups. Samples were treated with various RF powers from 10 to 80 W and different gas flow rates from 20 to 120 sccm. Optical emission spectroscopy was used to monitor the plasma process. The modified surface hydrophilicity, morphology and transparency characteristics were studied by water contact angle measurements, atomic force microscopy and UV-vis spectroscopy, respectively. Based on the contact angle measurements of three liquids, surface free energy variations were investigated. Moreover, the antibacterial properties were evaluated utilizing the method of plate counting of Escherichia coli. Also, in order to investigate stability of the plasma treatment, an ageing study was carried out by water contact angle measurements repeated in the days after the treatment. For biomedical applications, especially eye lenses, highly efficient antibacterial surfaces with appropriate hydrophilicity and transparency are of great importance. In this study, it is shown that the plasma process is a reliable and convenient method to achieve these purposes. A significant alteration in the hydrophilicity of a pristine PMMA surface was observed after treatment. Also, our results indicated that the plasma-modified PMMAs exhibit appropriate antibacterial performance. Moreover, surface hydrophilicity and surface charge have more influence on bacterial adhesion rate than surface roughness. UV-vis analysis results do not show a considerable difference for transparency of samples after plasma treatment.

Motion of Liquid Droplets on a Superhydrophobic Oleophobic Surface (Postprint)

DTIC Science & Technology

2010-08-01

prediction , NyCo multifilament plain woven fabric can be superhydro- phobic and oleophobic once the fabric is treated with an LSTM . Figure 4 shows water and...to predict the wetting behavior of superhydrophobic and oleophobic materials. Using chemical and geometrical modifications, a superhydrophobic...oleophobic surface was prepared. Good agreement between the predicted and measured contact angles and roll-off angles were obtained. The effect of the

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.

Bonding Strength Properties of Adhesively-Timber Joint with Thixotropic and Room Temperature Cured Epoxy Based Adhesive Reinforced with Nano- and Micro-particles

NASA Astrophysics Data System (ADS)

Ahmad, Z.; Ansell, M. P.; Smedley, D.

2011-02-01

This research work is concerned with in situ bonded-in timber connection using pultruded rod; where the manufacturing of such joint requires adhesive which can produce thick glue-lines and does not allow any use of pressure and heat. Four types of thixotropic (for ease application) and room temperature cured epoxy based were used namely CB10TSS (regarded as standards adhesive), Nanopox (modification of CB10TSS with addition of nanosilica), Albipox (modification of CB10TSS with addition of liquid rubber) and Timberset (an epoxy-based adhesive with addition of micro-size ceramic particles). The quality of the adhesive bonds was accessed using block shear test in accordance with ASTM D905. The bond strength depends on how good the adhesive wet the timber surface. Therefore the viscosity and contact angle was also measured. The nano- and microfiller additions increased the bond strength significantly. The viscosity correlates well with contact angle measurements where lower viscosities are associated with lower contact angles. However contact angle contradicts with measured strength and wettability.

Microfabrication of polymeric surfaces with extreme wettability using hot embossing

NASA Astrophysics Data System (ADS)

Falah Toosi, Salma; Moradi, Sona; Ebrahimi, Marzieh; Hatzikiriakos, Savvas G.

2016-08-01

Hot embossing was utilized to imprint topographical metallic patterns on the surfaces of thermoplastic polymers in order to create superhydrophobic and superoleophobic polymeric surfaces. The stainless steel (SS) micro/nano structured templates were fabricated using femtosecond laser ablation. The SS laser ablated templates were employed to imprint micron/submicron periodic structures onto the surface of high density polyethylene (HDPE), polylactic acid (PLA), and medical PVC at temperatures slightly above their melting points and pressures in the range of 3-12 MPa. Results have shown that the water contact angle (CA) of imprinted polymers increased to above 160° in the case of PLA and HDPE, while their water contact angle hysteresis (CAH) were significantly below 10°. In the case of medical-PVC, imprinting produced morphologies with high CA and high CAH (petal effect) due to the adhesion forces developed at the interface between the hydrophilic plasticizer of medical-PVC (TOTM) and water droplets. It is also noted that the re-entrant superoleophobic patterns created on HDPE through imprinting closely resemble the patterns found on the surface of filefish skin that is densely angled microfiber arrays. This bioinspired surface is highly capable of repelling both polar (water) and non-polar liquids of low surface tension and meets the superoleophobicity criteria.

Synthesis and Characterization of Superhydrophobic, Self-cleaning NIR-reflective Silica Nanoparticles

NASA Astrophysics Data System (ADS)

Sriramulu, Deepa; Reed, Ella Louise; Annamalai, Meenakshi; Venkatesan, Thirumalai Venky; Valiyaveettil, Suresh

2016-11-01

Multifunctional coatings offer many advantages towards protecting various surfaces. Here we apply aggregation induced segregation of perylene diimide (PDI) to control the surface morphology and properties of silica nanoparticles. Differentially functionalized PDI was incorporated on the surface of silica nanoparticles through Si-O-Si bonds. The absorption and emission spectra of the resultant functionalised nanoparticles showed monomeric or excimeric peaks based on the amounts of perylene molecules present on the surface of silica nanoparticles. Contact angle measurements on thin films prepared from nanoparticles showed that unfunctionalised nanoparticles were superhydrophilic with a contact angle (CA) of 0°, whereas perylene functionalised silica particles were hydrophobic (CA > 130°) and nanoparticles functionalised with PDI and trimethoxy(octadecyl)silane (TMODS) in an equimolar ratio were superhydrophobic with static CA > 150° and sliding angle (SA) < 10°. In addition, the near infrared (NIR) reflectance properties of PDI incorporated silica nanoparticles can be used to protect various heat sensitive substrates. The concept developed in this paper offers a unique combination of super hydrophobicity, interesting optical properties and NIR reflectance in nanosilica, which could be used for interesting applications such as surface coatings with self-cleaning and NIR reflection properties.

Surface modification of paper on a continuous atmospheric-pressure-plasma system

NASA Astrophysics Data System (ADS)

Cruz-Barba, Luis Emilio

Plasma technologies for the continuous modification of materials in atmospheric-pressure-plasma conditions were used to evaluate the surface modification of paper under different plasma conditions. The generation of hydrophobic layers was used to characterize the efficiency of the originally designed system for future application in the paper industry. Generation of hydrophobic layers was carried out by deposition of thin layers from fluorine containing gases, as well as cross-linking of pre-deposited thin layers of hydrophobic materials, such as fluoropolymers and silicones, in a continuous system plasma reactor (CSPR). Physical and chemical characterization of these layers was carried out by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), contact angle goniometry, and water absorption evaluations. Pure gaseous CF4 and a CF4/CH4 mixture were used to deposit fluorinated layers, rendering paper surfaces with low to moderate relative surface atomic contents of fluorine (2.5 to 16.3%). Morphological characterization revealed that the deposition consists of small clusters of fluorinated species scattered on the surface. Contact angle evaluations (50°--70°) indicated a reduction in the water affinity of the paper. Thin layers of fluoropolymer pre-deposited on paper surfaces were cross-linked in the presence of CF4, CF4/CH4, and NH 3 plasmas. All of the gases proved to be effective for the cross-linking under different conditions. These cross-linked layers were determined to maintain the original polymer structure, consisting mainly of CF2-CF 2 and small quantities of CFx. Surface characterization by AFM indicated lower roughness values compared to the untreated additive-free paper (45.1 vs 67.1 nm). Paper samples treated by this approach showed a highly hydrophobic character with up to 160° contact angles, and water absorption was reduced by as much as 61.6%. Silicone layers were cross-linked in the presence of argon and oxygen plasmas. Characterization of the silicone-coated paper indicated, as in the case of fluoropolymers, the retention of the original chemical structure. Surface roughness values (AFM) were in the range of 11.8 to 18.2 nm, evidence of a very smooth surface. High hydrophobicity levels were reached, as shown by contact angles of up to 126°, and water absorption showed a maximum reduction of 76.8%.

Hydrophobization of epoxy nanocomposite surface with 1H,1H,2H,2H-perfluorooctyltrichlorosilane for superhydrophobic properties

NASA Astrophysics Data System (ADS)

Psarski, Maciej; Marczak, Jacek; Celichowski, Grzegorz; Sobieraj, Grzegorz B.; Gumowski, Konrad; Zhou, Feng; Liu, Weimin

2012-10-01

Nature inspires the design of synthetic materials with superhydrophobic properties, which can be used for applications ranging from self-cleaning surfaces to microfluidic devices. Their water repellent properties are due to hierarchical (micrometer- and nanometre-scale) surface morphological structures, either made of hydrophobic substances or hydrophobized by appropriate surface treatment. In this work, the efficiency of two surface treatment procedures, with a hydrophobic fluoropolymer, synthesized and deposited from 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS) is investigated. The procedures involved reactions from the gas and liquid phases of the PFOTS/hexane solutions. The hierarchical structure is created in an epoxy nanocomposite surface, by filling the resin with alumina nanoparticles and micron-sized glass beads and subsequent sandblasting with corundum microparticles. The chemical structure of the deposited fluoropolymer was examined using XPS spectroscopy. The topography of the modified surfaces was characterized using scanning electron microscopy (SEM), and atomic force microscopy (AFM). The hydrophobic properties of the modified surfaces were investigated by water contact and sliding angles measurements. The surfaces exhibited water contact angles of above 150° for both modification procedures, however only the gas phase modification provided the non-sticking behaviour of water droplets (sliding angle of 3°). The discrepancy is attributed to extra surface roughness provided by the latter procedure.

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

A new water retention and hydraulic conductivity model accounting for contact angle

NASA Astrophysics Data System (ADS)

Diamantopoulos, Efstathios; Durner, Wolfgang

2013-04-01

The description of soil water transport in the unsaturated zone requires the knowledge of the soil hydraulic properties, i.e. the water retention and the hydraulic conductivity function. A great amount of parameterizations for this can be found in the literature, the majority of which represent the complex pore space of soils as a bundle of cylindrical capillary tubes of various sizes. The assumption of zero contact angles between water and surface of the grains is also made. However, these assumptions limit the predictive capabilities of these models, leading often to enormous errors in the prediction of water dynamics in soils. We present a pore scale analysis for equilibrium liquid configurations (retention) in angular pores taking the effect of contact angle into account. Furthermore, we propose an alternative derivation of the hydraulic conductivity function, again as a function of the contact angle, assuming flow perpendicular to pore cross sections. Finally, we upscale our model from the pore to the sample scale by assuming a gamma statistical distribution of the pore sizes. Closed form expressions are derived for both sample water retention and conductivity functions. The new model was tested against experimental data from multistep inflow/outflow (MSI/MSO) experiments for a sandy material. They were conducted using ethanol and water as the wetting liquid. Ethanol was assumed to form a zero contact angle with the soil grains. The proposed model described both imbibition and drainage of water and ethanol very well. Lastly, the consideration of the contact angle allowed the description of the observed hysteresis.

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.

Picosecond laser micro/nano surface texturing of nickel for superhydrophobicity

NASA Astrophysics Data System (ADS)

Wang, X. C.; Wang, B.; Xie, H.; Zheng, H. Y.; Lam, Y. C.

2018-03-01

A single step direct picosecond laser texturing process was demonstrated to be able to obtain a superhydrophobic surface on a nickel substrate, a key material for mold fabrication in the manufacture of various devices, including polymeric microfluidic devices. A two-scale hierarchical surface structure of regular 2D array micro-bumps with nano-ripples was produced on a nickel surface. The laser textured surface initially showed superhydrophilicity with almost complete wetting of the structured surface just after laser treatment, then quickly changed to nearly superhydrophobic with a water contact angle (WCA) of 140° in less than 1 d, and finally became superhydrophobic with a WCA of more than 150° and a contact angle hysteresis (CAH) of less than 5°. The mechanism involved in the process is discussed in terms of surface morphology and surface chemistry. The ultra-fast laser induced NiO catalytic effect was thought to play a key role in modifying the surface chemistry so as to lower the surface energy. The developed process has the potential to improve the performance of nickel mold in the fabrication of microfluidic devices.

Superhydrophobic ceramic coating: Fabrication by solution precursor plasma spray and investigation of wetting behavior.

PubMed

Xu, Pengyun; Coyle, Thomas W; Pershin, Larry; Mostaghimi, Javad

2018-08-01

Superhydrophobic surfaces are often created by fabricating suitable surface structures from low-surface-energy organic materials using processes that are not suitable for large-scale fabrication. Rare earth oxides (REO) exhibit hydrophobic behavior that is unusual among oxides. Solution precursor plasma spray (SPPS) deposition is a rapid, one-step process that can produce ceramic coatings with fine scale columnar structures. Manipulation of the structure of REO coatings through variation in deposition conditions may allow the wetting behavior to be controlled. Yb 2 O 3 coatings were fabricated via SPPS. Coating structure was investigated by scanning electron microscopy, digital optical microscopy, and x-ray diffraction. The static water contact angle and roll-off angle were measured, and the dynamic impact of water droplets on the coating surface recorded. Superhydrophobic behavior was observed; the best coating exhibited a water contact angle of ∼163°, a roll-off angle of ∼6°, and complete droplet rebound behavior. All coatings were crystalline Yb 2 O 3 , with a nano-scale roughness superimposed on a micron-scale columnar structure. The wetting behaviors of coatings deposited at different standoff distances were correlated with the coating microstructures and surface topographies. The self-cleaning, water flushing and water jetting tests were conducted and further demonstrated the excellent and durable hydrophobicity of the coatings. Copyright © 2018 Elsevier Inc. All rights reserved.

Bioinspired, roughness-induced, water and oil super-philic and super-phobic coatings prepared by adaptable layer-by-layer technique

PubMed Central

Brown, Philip S.; Bhushan, Bharat

2015-01-01

Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, anti-icing, self-cleaning, anti-smudge, and oil-water separation applications. Many previous bioinspired surfaces are of limited use due to a lack of mechanical durability. Here, a layer-by-layer technique is utilized to create coatings with four combinations of water and oil repellency and affinity. An adapted layer-by-layer approach is tailored to yield specific surface properties, resulting in a durable, functional coating. This technique provides necessary flexibility to improve substrate adhesion combined with desirable surface chemistry. Polyelectrolyte binder, SiO2 nanoparticles, and silane or fluorosurfactant layers are deposited, combining surface roughness and necessary chemistry to result in four different coatings: superhydrophilic/superoleophilic, superhydrophobic/superoleophilic, superhydrophobic/superoleophobic, and superhydrophilic/superoleophobic. The superoleophobic coatings display hexadecane contact angles >150° with tilt angles <5°, whilst the superhydrophobic coatings display water contact angles >160° with tilt angles <2°. One coating combines both oleophobic and hydrophobic properties, whilst others mix and match oil and water repellency and affinity. Coating durability was examined through the use of micro/macrowear experiments. These coatings display transparency acceptable for some applications. Fabrication via this novel combination of techniques results in durable, functional coatings displaying improved performance compared to existing work where either durability or functionality is compromised. PMID:26353971

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°.

Hydrometer calibration by hydrostatic weighing with automated liquid surface positioning

NASA Astrophysics Data System (ADS)

Aguilera, Jesus; Wright, John D.; Bean, Vern E.

2008-01-01

We describe an automated apparatus for calibrating hydrometers by hydrostatic weighing (Cuckow's method) in tridecane, a liquid of known, stable density, and with a relatively low surface tension and contact angle against glass. The apparatus uses a laser light sheet and a laser power meter to position the tridecane surface at the hydrometer scale mark to be calibrated with an uncertainty of 0.08 mm. The calibration results have an expanded uncertainty (with a coverage factor of 2) of 100 parts in 106 or less of the liquid density. We validated the apparatus by comparisons using water, toluene, tridecane and trichloroethylene, and found agreement within 40 parts in 106 or less. The new calibration method is consistent with earlier, manual calibrations performed by NIST. When customers use calibrated hydrometers, they may encounter uncertainties of 370 parts in 106 or larger due to surface tension, contact angle and temperature effects.

A New Green Ionic Liquid-Based Corrosion Inhibitor for Steel in Acidic Environments.

PubMed

Atta, Ayman M; El-Mahdy, Gamal A; Al-Lohedan, Hamad A; Ezzat, Abdel Rahman O

2015-06-17

This work examines the use of new hydrophobic ionic liquid derivatives, namely octadecylammonium tosylate (ODA-TS) and oleylammonium tosylate (OA-TS) for corrosion protection of steel in 1 M hydrochloric acid solution. Their chemical structures were determined from NMR analyses. The surface activity characteristics of the prepared ODA-TS and OA-TS were evaluated from conductance, surface tension and contact angle measurements. The data indicate the presence of a double bond in the chemical structure of OA-TS modified its surface activity parameters. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements, scanning electron microscope (SEM), Energy dispersive X-rays (EDX) analysis and contact angle measurements were utilized to investigate the corrosion protection performance of ODA-TS and OA-TS on steel in acidic solution. The OA-TS and ODA-TS compounds showed good protection performance in acidic chloride solution due to formation of an inhibitive film on the steel surface.

Influence of short chain organic acids and bases on the wetting properties and surface energy of submicrometer ceramic powders.

PubMed

Neirinck, Bram; Soccol, Dimitri; Fransaer, Jan; Van der Biest, Omer; Vleugels, Jef

2010-08-15

The effect of short chained organic acids and bases on the surface energy and wetting properties of submicrometer alumina powder was assessed. The surface chemistry of treated powders was determined by means of Diffuse Reflectance Infrared Fourier Transform spectroscopy and compared to untreated powder. The wetting of powders was measured using a modified Washburn method, based on the use of precompacted powder samples. The geometric factor needed to calculate the contact angle was derived from measurements of the porous properties of the powder compacts. Contact angle measurements with several probe liquids before and after modification allowed a theoretical estimation of the surface energy based on the surface tension component theory. Trends in the surface energy components were linked to observations in infrared spectra. The results showed that the hydrophobic character of the precompacted powder depends on both the chain length and polar group of the modifying agent. Copyright 2010 Elsevier Inc. All rights reserved.

Hydrophobic durability characteristics of butterfly wing surface after freezing cycles towards the design of nature inspired anti-icing surfaces

PubMed Central

Choy, Kwang-Leong

2018-01-01

The hydrophobicity and anti-icing performance of the surfaces of some artificial hydrophobic coatings degraded after several icing and de-icing cycles. In this paper, the frost formation on the surfaces of butterfly wings from ten different species was observed, and the contact angles were measured after 0 to 6 frosting/defrosting cycles. The results show that no obvious changes in contact angle for the butterfly wing specimens were not obvious during the frosting/defrosting process. Further, the conclusion was inferred that the topography of the butterfly wing surface forms a special space structure which has a larger space inside that can accommodate more frozen droplets; this behavior prevents destruction of the structure. The findings of this study may provide a basis and new concepts for the design of novel industrially important surfaces to inhibit frost/ice growth, such as durable anti-icing coatings, which may decrease or prevent the socio-economic loss. PMID:29385390

Hydrophobic durability characteristics of butterfly wing surface after freezing cycles towards the design of nature inspired anti-icing surfaces.

PubMed

Chen, Tingkun; Cong, Qian; Qi, Yingchun; Jin, Jingfu; Choy, Kwang-Leong

2018-01-01

The hydrophobicity and anti-icing performance of the surfaces of some artificial hydrophobic coatings degraded after several icing and de-icing cycles. In this paper, the frost formation on the surfaces of butterfly wings from ten different species was observed, and the contact angles were measured after 0 to 6 frosting/defrosting cycles. The results show that no obvious changes in contact angle for the butterfly wing specimens were not obvious during the frosting/defrosting process. Further, the conclusion was inferred that the topography of the butterfly wing surface forms a special space structure which has a larger space inside that can accommodate more frozen droplets; this behavior prevents destruction of the structure. The findings of this study may provide a basis and new concepts for the design of novel industrially important surfaces to inhibit frost/ice growth, such as durable anti-icing coatings, which may decrease or prevent the socio-economic loss.

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).

Interaction of thrombocytes with poly(ether imide): The influence of processing.

PubMed

Braune, S; Lange, M; Richau, K; Lützow, K; Weigel, T; Jung, F; Lendlein, A

2010-01-01

The processing of polymers for blood contacting devices can have a major influence on surface properties. In this study, we fabricated poly(ether imide) (PEI) membranes and films to investigate the effects of the processing on physicochemical surface properties by atomic force microscopy (AFM), scanning electron microscopy, contact angle as well as zeta potential measurements. A static platelet adhesion test was performed to analyze the thrombogenicity of both devices. While contact angle measurements showed similar levels of hydrophobicity and zeta potential values were equivalent, mean surface roughness as well as surface energies in the dispersive part were found to be increased for the PEI membrane. The static platelet adhesion test showed a significantly decreased number of adherent platelets per surface area on the PEI film (178.98 ± 102.70/45000 μm2) compared to the PEI membrane (504 ± 314.27/45000μm2) and, consequently, revealed evidence for higher thrombogenicity of the PEI membrane. This study shows that processing can have a significant effect on platelet adhesion to biomaterials, even though, molar weight was identical. Thrombogenicity of polymer-based cardiovascular devices, therefore, have to be evaluated at the final product level, following the entire processing procedure.

Effect of collector molecular structure on the wettability of gold for froth flotation

NASA Astrophysics Data System (ADS)

Moncayo-Riascos, Ivan; Hoyos, Bibian A.

2017-10-01

Molecular dynamics simulations were conducted to evaluate the alteration of the hydrophilic state of gold surfaces caused by the adsorption of collectors with different molecular structures, using the contact angle of water droplets as an evaluation parameter. Four collectors were evaluated: SDS (with twelve hydrogenated carbon atoms), PAX (with five hydrogenated carbon atoms), DTP (with two branched aliphatic chains) and MBT (with an aromatic ring). The contact angle was evaluated for coatings of a monolayer (ML) and for surface densities of 2.89 μmol/m2 for each collector. For a ML, the hydrophobic effect generated by the aromatic ring of the MBT collector is comparable with the effect of the non-polar short chain of the PAX collector. The increase in hydrophobicity for the gold surfaces achieved by collectors with aliphatic chains is because the water-collector interaction energy is significantly higher (repulsive) than the water-gold interactions (attractive). The lowest increase in hydrophobicity was achieved with the MBT collector, since the carbon-water interaction energy of the aromatic ring is stronger than the interaction with the carbon atoms in the aliphatic chains. The calculated contact angles of the water droplets deviated less than 4% with respect to the experimental values.

Assessing Ink Transfer Performance of Gravure-Offset Fine-Line Circuitry Printing

NASA Astrophysics Data System (ADS)

Cheng, Hsien-Chie; Chen, You-Wei; Chen, Wen-Hwa; Lu, Su-Tsai; Lin, Shih-Ming

2018-03-01

In this study, the printing mechanism and performance of gravure-offset fine-line circuitry printing technology are investigated in terms of key printing parameters through experimental and theoretical analyses. First, the contact angles of the ink deposited on different substrates, blankets, and gravure metal plates are experimentally determined; moreover, their temperature and solvent content dependences are analyzed. Next, the ink solvent absorption and evaporation behaviors of the blankets at different temperatures, times, and numbers of printing repetitions are characterized by conducting experiments. In addition, while printing repeatedly, the surface characteristics of the blankets, such as the contact angle, vary with the amount of absorbed ink solvent, further affecting the ink transfer performance (ratio) and printing quality. Accordingly, the surface effect of the blanket due to ink solvent absorption on the ink contact angle is analyzed. Furthermore, the amount of ink transferred from the gravure plate to the blanket in the "off process" and from the blanket to the substrate in the "set process" is evaluated by conducting a simplified plate-to-plate experiment. The influences of loading rate (printing velocity), temperature, and solvent content on the ink transfer performance are addressed. Finally, the ink transfer mechanism is theoretically analyzed for different solvent contents using Surface Evolver. The calculation results are compared with those of the experiment.

The Significance of Interfacial Water Structure in Soluble Salt Flotation Systems.

PubMed

Hancer, M.; Celik, M. S.; Miller, J. D.

2001-03-01

Flotation of soluble salts with dodecyl amine hydrochloride (DAH) and sodium dodecyl sulfate (SDS) collectors has demonstrated that the interfacial water structure and hydration states of soluble salt surfaces together with the precipitation tendency of the corresponding collector salts are of considerable importance in explaining their flotation behavior. In particular, the high concentration of ions in these soluble salt brines and their hydration appear to modify the bulk and interfacial structure of water as revealed by contact angle measurements and this effect is shown to be an important feature in the flotation chemistry of soluble salt minerals including alkali halide and alkali oxyanion salts. Depending on characteristic chemical features (salt type), the salt can serve either as a structure maker, in which intermolecular hydrogen bonding between water molecules is facilitated, or as a structure breaker, in which intermolecular hydrogen bonding between water molecules is disrupted. For structure making salts the brine completely wets the salt surface and no contact angle can be measured. For structure breaking salts the brine does not completely wet the salt surface and a finite contact angle is measured. In this regard it has been found that soluble salt flotation either with the cationic DAH or anionic SDS collector is possible only if the salt is a structure breaker. Copyright 2001 Academic Press.

Tailoring the optical and hydrophobic property of zinc oxide nanorod by coating with amorphous graphene

NASA Astrophysics Data System (ADS)

Pahari, D.; Das, N. S.; Das, B.; Chattopadhyay, K. K.; Banerjee, D.

2016-09-01

Zinc oxide (ZnO) nanorods were synthesized at room temperature on potassium permanganate activated silicon and glass substrate by simple chemical method using zinc acetate as precursor. To modify the surface energy of the as prepared ZnO thin films the samples were coated with amorphous graphene (a-G) synthesized by un-zipping of chemically synthesized amorphous carbon nanotubes (a-CNTs). All the pure and coated samples were characterized by x-ray diffraction, field emission scanning electron microscope, Raman spectroscopy, and Fourier transformed infrared spectroscopy. The roughness analysis of the as prepared samples was done by atomic force microscopic analysis. The detail optical properties of all the samples were studied with the help of a UV-Visible spectrophotometer. The surface energy of the as prepared pure and coated samples was calculated by measuring the contact angle of two different liquids. It is seen that the water repellence of ZnO nanorods got increased after they are being coated with a-Gs. Also even after UV irradiation the contact angle remain same unlike the case for the uncoated sample where the contact angle gets decreased significantly after UV irradiation. Existing Cassie-Wenzel model has been employed along with the Owen's approach to determine the different components of surface energy.

Fabrication and characterization of superhydrophobic copper fiber sintered felt with a 3D space network structure and their oil-water separation

NASA Astrophysics Data System (ADS)

Hu, Jinyi; Yuan, Wei; Chen, Wenjun; Xu, Xiaotian; Tang, Yong

2016-12-01

This study reports the fabrication of a novel stable superhydrophobic and superoleophylic porous metal material on a copper fiber sintered felt (CFSF) substrate via a simple solution-immersion method. Oxidation and modification times are two important factors related to the level of hydrophobicity; oxidation for 1 h and modification for 24 h are appropriate to build a superhydrophobic CFSF surface with a water contact angle of 152.83° and a kerosene contact angle of 0°. The stability and high temperature resistance of superhydrophobic CFSF were studied. A novel device was designed to measure the water repellent ability of the treated CFSF. The results indicated that the water repellent ability of superhydrophobic CFSF was almost constant after 40 cycles of sanding. Both the water contact angle and the microstructure of the modified CFSF surface remained nearly unchanged after experiencing ultrasonic vibration for 1 min. The modified CFSF surface maintains super hydrophobicity after being treated at 180 °C for 1 h. The separation efficiencies for different types of oils and organic solvents (kerosene, chloroform, n-hexane and gasoline) are more than 96%. The modified CFSF retains a high robustness of separation efficiency even after it is recycled for the separation of kerosene and water for more than 10 times.

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.

Three-dimensional simulation of rivulet and film flows over an inclined plate: Effects of solvent properties and contact angle

DOE PAGES

Singh, Rajesh K.; Galvin, Janine E.; Sun, Xin

2015-12-10

We numerically investigated the film flow down an inclined plate using the volume of fluid (VOF) method. The flow simulations have been systematically carried out for a wide range of parameters, such as inlet size, inclination angle, contact angle, flow rates and solvent properties (viscosity and surface tension). Based on the simulation results, scaling theory is proposed for both interfacial area and for film thickness in terms of the Kapitza number (Ka).The Kapitza number is advantageous because it depends only on solvent properties. The Kapitza number decreases with increased solvent viscosity and is fixed for a given fluid. Here, tomore » investigate the effects of solvent properties on interfacial area a small inlet cross-section was used. The interfacial area decreases with increased value of Ka. The time to reach pseudo-steady state of rivulet is also observed to increase with decreasing Ka. For a fixed flow rate, the inlet cross-section has marginal effect on the interfacial area; however, the developed width of the rivulet remains unchanged. In addition to inlet size, flow rate and solvent properties, the impact of contact angle on film thickness and interfacial area was also investigated. The contact angle has negligible effect for a fully wetted plate, but it significantly affects the interfacial area of the rivulet. Finally, a scaling theory for interfacial area in terms of the contact angle and Ka is presented.« less

Capillary Pressure of a Liquid Between Uniform Spheres Arranged in a Square-Packed Layer

NASA Technical Reports Server (NTRS)

Alexader, J. Iwan D.; Slobozhanin, Lev A.; Collicott, Steven H.

2004-01-01

The capillary pressure in the pores defined by equidimensional close-packed spheres is analyzed numerically. In the absence of gravity the menisci shapes are constructed using Surface Evolver code. This permits calculation the free surface mean curvature and hence the capillary pressure. The dependences of capillary pressure on the liquid volume constructed here for a set of contact angles allow one to determine the evolution of basic capillary characteristics under quasi-static infiltration and drainage. The maximum pressure difference between liquid and gas required for a meniscus passing through a pore is calculated and compared with that for hexagonal packing and with approximate solution given by Mason and Morrow [l]. The lower and upper critical liquid volumes that determine the stability limits for the equilibrium capillary liquid in contact with square packed array of spheres are tabulated for a set of contact angles.