On some relations between advancing, receding and Young's contact angles.
Chibowski, Emil
2007-05-31
Problems of experimental determination and theoretical verification of equilibrium contact angles are discussed basing on the literature data. A relationship between the advancing and receding contact angles versus the equilibrium contact angle is described and then verified using the literature contact angles determined on paraffin wax and polypropylene. Using the proposed relationship and experimentally determined equilibrium contact angles, obtained by plotting the advancing and receding contact angles versus the contact angle hysteresis or by applying vibration of the system liquid drop/solid surface, it is found that the same value of the surface free energy for paraffin wax is calculated from the contact angles of water and ethylene glycol. However, in the case of polypropylene some inconsistency appears between the equilibrium contact angles of the probe liquid used and the calculated surface free energy. More experimental data of the equilibrium contact angle are needed to verify further the relationship.
Lam, C N C; Wu, R; Li, D; Hair, M L; Neumann, A W
2002-02-25
Two types of experiments were used to study the behavior of both advancing and receding contact angles, namely the dynamic one-cycle contact angle (DOCA) and the dynamic cycling contact angle (DCCA) experiments. For the preliminary study, DOCA measurements of different liquids on different solids were performed using an automated axisymmetric drop shape analysis-profile (ADSA-P). From these experimental results, four patterns of receding contact angle were observed: (1) time-dependent receding contact angle; (2) constant receding contact angle; (3) 'stick/slip'; (4) no receding contact angle. For the purpose of illustration, results from four different solid surfaces are shown. These solids are: FC-732-coated surface; poly(methyl methacrylate/n-butyl methacrylate) [P(MMA/nBMA)]; poly(lactic acid) (DL-PLA); and poly(lactic/glycolic acid) 50/50 (DL-PLGA 50/50). Since most of the surfaces in our studies exhibit time dependence in the receding contact angle, a more extended study was conducted using only FC-732-coated surfaces to better understand the possible causes of decreasing receding contact angle and contact angle hysteresis. Contact angle measurements of 21 liquids from two homologous series (i.e. n-alkanes and 1-alcohols) and octamethylcyclotetrasiloxane (OCMTS) on FC-732-coated surfaces were performed. It is apparent that the contact angle hysteresis decreases with the chain length of the liquid. It was found that the receding contact angle equals the advancing angle when the alkane molecules are infinitely large. These results strongly suggest that the chain length and size of the liquid molecule could contribute to contact angle hysteresis phenomena. Furthermore, DCCA measurements of six liquids from the two homologous series on FC-732-coated surfaces were performed. With these experimental results, one can construe that the time dependence of contact angle hysteresis on relatively smooth and homogeneous surfaces is mainly caused by liquid retention
Anomalous contact angle hysteresis of a captive bubble: advancing contact line pinning.
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.
A modified captive bubble method for determining advancing and receding contact angles
NASA Astrophysics Data System (ADS)
Xue, Jian; Shi, Pan; Zhu, Lin; Ding, Jianfu; Chen, Qingmin; Wang, Qingjun
2014-03-01
In this work, a modification to the captive bubble method was proposed to test the advancing and receding contact angle. This modification is done by adding a pressure chamber with a pressure control system to the original experimental system equipped with an optical angle mater equipped with a high speed CCD camera, a temperature control system and a computer. A series of samples with highly hydrophilic, hydrophilic, hydrophobic and superhydrophobic surfaces were prepared. The advancing and receding contact angles of these samples with highly hydrophilic, hydrophilic, and hydrophobic surfaces through the new methods was comparable to the result tested by the traditional sessile drop method. It is proved that this method overcomes the limitation of the traditional captive bubble method and the modified captive bubble method allows a smaller error from the test. However, due to the nature of the captive bubble technique, this method is also only suitable for testing the surface with advancing or receding contact angle below 130°.
Contact angle hysteresis explained.
Gao, Lichao; McCarthy, Thomas J
2006-07-04
A view of contact angle hysteresis from the perspectives of the three-phase contact line and of the kinetics of contact line motion is given. Arguments are made that advancing and receding are discrete events that have different activation energies. That hysteresis can be quantified as an activation energy by the changes in interfacial area is argued. That this is an appropriate way of viewing hysteresis is demonstrated with examples.
Equilibrium contact angle or the most-stable contact angle?
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.
Hysteresis during contact angles measurement.
Diaz, M Elena; Fuentes, Javier; Cerro, Ramon L; Savage, Michael D
2010-03-15
A theory, based on the presence of an adsorbed film in the vicinity of the triple contact line, provides a molecular interpretation of intrinsic hysteresis during the measurement of static contact angles. Static contact angles are measured by placing a sessile drop on top of a flat solid surface. If the solid surface has not been previously in contact with a vapor phase saturated with the molecules of the liquid phase, the solid surface is free of adsorbed liquid molecules. In the absence of an adsorbed film, molecular forces configure an advancing contact angle larger than the static contact angle. After some time, due to an evaporation/adsorption process, the interface of the drop coexists with an adsorbed film of liquid molecules as part of the equilibrium configuration, denoted as the static contact angle. This equilibrium configuration is metastable because the droplet has a larger vapor pressure than the surrounding flat film. As the drop evaporates, the vapor/liquid interface contracts and the apparent contact line moves towards the center of the drop. During this process, the film left behind is thicker than the adsorbed film and molecular attraction results in a receding contact angle, smaller than the equilibrium contact angle.
Apparent dynamic contact angle of an advancing gas--liquid meniscus
Kalliadasis, S.; Chang, H. )
1994-01-01
The steady motion of an advancing meniscus in a gas-filled capillary tube involves a delicate balance of capillary, viscous, and intermolecular forces. The limit of small capillary numbers Ca (dimensionless speeds) is analyzed here with a matched asymptotic analysis that links the outer capillary region to the precursor film in front of the meniscus through a lubricating film. The meniscus shape in the outer region is constructed and the apparent dynamic contact angle [Theta] that the meniscus forms with the solid surface is derived as a function of the capillary number, the capillary radius, and the Hamaker's constant for intermolecular forces, under conditions of weak gas--solid interaction, which lead to fast spreading of the precursor film and weak intermolecular forces relative to viscous forces within the lubricating film. The dependence on intermolecular forces is very weak and the contact angle expression has a tight upper bound tan [Theta]=7.48 Ca[sup 1/3] for thick films, which is independent of the Hamaker constant. This upper bound is in very good agreement with existing experimental data for wetting fluids in any capillary and for partially wetting fluids in a prewetted capillary. Significant correction to the Ca[sup 1/3] dependence occurs only at very low Ca, where the intermolecular forces become more important and tan [Theta] diverges slightly from the above asymptotic behavior toward lower values.
Dynamic contact angle measurements on superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Kim, Jeong-Hyun; Kavehpour, H. Pirouz; Rothstein, Jonathan P.
2015-03-01
In this paper, the dynamic advancing and receding contact angles of a series of aqueous solutions were measured on a number of hydrophobic and superhydrophobic surfaces using a modified Wilhelmy plate technique. Superhydrophobic surfaces are hydrophobic surfaces with micron or nanometer sized surface roughness. These surfaces have very large static advancing contact angles and little static contact angle hysteresis. In this study, the dynamic advancing and dynamic receding contact angles on superhydrophobic surfaces were measured as a function of plate velocity and capillary number. The dynamic contact angles measured on a smooth hydrophobic Teflon surface were found to obey the scaling with capillary number predicted by the Cox-Voinov-Tanner law, θD3 ∝ Ca. The response of the dynamic contact angle on the superhydrophobic surfaces, however, did not follow the same scaling law. The advancing contact angle was found to remain constant at θA = 160∘, independent of capillary number. The dynamic receding contact angle measurements on superhydrophobic surfaces were found to decrease with increasing capillary number; however, the presence of slip on the superhydrophobic surface was found to result in a shift in the onset of dynamic contact angle variation to larger capillary numbers. In addition, a much weaker dependence of the dynamic contact angle on capillary number was observed for some of the superhydrophobic surfaces tested.
Contact angle hysteresis of microbead suspensions.
Waghmare, Prashant R; Mitra, Sushanta K
2010-11-16
Microbead suspensions are often used in microfluidic devices for transporting biomolecules. An experimental investigation on the wettability of microbead suspension is presented in this study. The variation in the surface tension and the equilibrium contact angle with the change in the volume fraction of the microbead is presented here. The surface tension of the microbead suspension is measured with the pendant drop technique, whereas the dynamic contact angle measurements, i.e., advancing and receding contact angles, are measured with the sessile drop technique. An equilibrium contact angle of a suspension with particular volume fraction is determined by computing an average over the measured advancing and receding contact angles. It is observed that the surface tension and the equilibrium contact angle determined from advancing and receding contact angles vary with the magnitude of the microbeads volume fraction in the suspension. A decrease in the surface tension with an increase in the volume fraction of the microbead suspension is observed. The advancement and the recession in contact line for dynamic contact angle measurements are achieved with the motorized dosing mechanism. For microbead suspensions, the advancement of the contact line is faster as compared to the recession of the contact line for the same flow rate. The presence of microbeads assists in the advancement and the recession of the contact line of the suspension. A decrease in the equilibrium contact angles with an increase in the microbead suspension volume fraction is observed. Inclusion of microbeads in the suspension increases the wetting capability for the considered combination of the microbead suspension and substrate. Finally, empirical correlations for the surface tension and the contact angle of the suspension as a function of microbead volume fraction are proposed. Such correlations can readily be used to develop mechanistic models for the capillary transport of microbead
Contact angle measurements under thermodynamic equilibrium conditions.
Lages, Carol; Méndez, Eduardo
2007-08-01
The precise control of the ambient humidity during contact angle measurements is needed to obtain stable and valid data. For a such purpose, a simple low-cost device was designed, and several modified surfaces relevant to biosensor design were studied. Static contact angle values for these surfaces are lower than advancing contact angles published for ambient conditions, indicating that thermodynamic equilibrium conditions are needed to avoid drop evaporation during the measurements.
Dynamic contact angle analysis of silicone hydrogel contact lenses.
Read, Michael Leonard; Morgan, Philip Bruce; Kelly, Jeremiah Michael; Maldonado-Codina, Carole
2011-07-01
Contact angle measurements are used to infer the clinical wetting characteristics of contact lenses. Such characterization has become more commonplace since the introduction of silicone hydrogel contact lens materials, which have been associated with reduced in vivo wetting due to the inclusion of siloxane-containing components. Using consistent methodology and a single investigator, advancing and receding contact angles were measured for 11 commercially available silicone hydrogel contact lens types with a dynamic captive bubble technique employing customized, fully automated image analysis. Advancing contact angles were found to range between 20° and 72° with the lenses falling into six statistically discrete groupings. Receding contact angles fell within a narrower range, between 17° and 22°, with the lenses segregated into three groups. The relationship between these laboratory measurements and the clinical performance of the lenses requires further investigation.
Contact angle measurement on rough surfaces.
Meiron, Tammar S; Marmur, Abraham; Saguy, I Sam
2004-06-15
A new method for the measurement of apparent contact angles at the global energy minimum on real surfaces has been developed. The method consists of vibrating the surface, taking top-view pictures of the drop, monitoring the drop roundness, and calculating the contact angle from the drop diameter and weight. The use of the new method has been demonstrated for various rough surfaces, all having the same surface chemistry. In order to establish the optimal vibration conditions, the proper ranges for the system parameters (i.e., drop volume, vibration time, frequency of vibration, and amplitude of vibration) were determined. The reliability of the method has been demonstrated by the fact that the ideal contact angles of all surfaces, as calculated from the Wenzel equation using the measured apparent contact angles, came out to be practically identical. This ideal contact angle has been compared with three methods of calculation from values of advancing and receding contact angles.
Reliable measurement of the receding contact angle.
Korhonen, Juuso T; Huhtamäki, Tommi; Ikkala, Olli; Ras, Robin H A
2013-03-26
Surface wettability is usually evaluated by the contact angle between the perimeter of a water drop and the surface. However, this single measurement is not enough for proper characterization, and the so-called advancing and receding contact angles also need to be measured. Measuring the receding contact angle can be challenging, especially for extremely hydrophobic surfaces. We demonstrate a reliable procedure by using the common needle-in-the-sessile-drop method. Generally, the contact line movement needs to be followed, and true receding movement has to be distinguished from "pseudo-movement" occurring before the receding angle is reached. Depending on the contact angle hysteresis, the initial size of the drop may need to be surprisingly large to achieve a reliable result. Although our motivation for this work was the characterization of superhydrophobic surfaces, we also show that this method works universally ranging from hydrophilic to superhydrophobic surfaces.
Contact angle hysteresis on fluoropolymer surfaces.
Tavana, H; Jehnichen, D; Grundke, K; Hair, M L; Neumann, A W
2007-10-31
Contact angle hysteresis of liquids with different molecular and geometrical properties on high quality films of four fluoropolymers was studied. A number of different causes are identified for hysteresis. With n-alkanes as probe liquids, contact angle hysteresis is found to be strongly related to the configuration of polymer chains. The largest hysteresis is obtained with amorphous polymers whereas the smallest hysteresis occurs for polymers with ordered molecular chains. This is explained in terms of sorption of liquid by the solid and penetration of liquid into the polymer film. Correlation of contact angle hysteresis with the size of n-alkane molecules supports this conclusion. On the films of two amorphous fluoropolymers with different molecular configurations, contact angle hysteresis of one and the same liquid with "bulky" molecules is shown to be quite different. On the surfaces of Teflon AF 1600, with stiff molecular chains, the receding angles of the probe liquids are independent of contact time between solid and liquid and similar hysteresis is obtained for all the liquids. Retention of liquid molecules on the solid surface is proposed as the most likely cause of hysteresis in these systems. On the other hand, with EGC-1700 films that consist of flexible chains, the receding angles are strongly time-dependent and the hysteresis is large. Contact angle hysteresis increases even further when liquids with strong dipolar intermolecular forces are used. In this case, major reorganization of EGC-1700 chains due to contact with the test liquids is suggested as the cause. The effect of rate of motion of the three-phase line on the advancing and receding contact angles, and therefore contact angle hysteresis, is investigated. For low viscous liquids, contact angles are independent of the drop front velocity up to approximately 10 mm/min. This agrees with the results of an earlier study that showed that the rate-dependence of the contact angles is an issue only
Contact angle hysteresis, adhesion, and marine biofouling.
Schmidt, Donald L; Brady, Robert F; Lam, Karen; Schmidt, Dale C; Chaudhury, Manoj K
2004-03-30
Adhesive and marine biofouling release properties of coatings containing surface-oriented perfluoroalkyl groups were investigated. These coatings were prepared by cross-linking a copolymer of 1H,1H,2H,2H-heptadecafluorodecyl acrylate and acrylic acid with a copolymer of poly(2-isopropenyl-2-oxazoline) and methyl methacrylate at different molar ratios. The relationships between contact angle, contact angle hysteresis, adhesion, and marine biofouling were studied. Adhesion was determined by peel tests using pressure-sensitive adhesives. The chemical nature of the surfaces was studied by using X-ray photoelectron spectroscopy. Resistance to marine biofouling of an optimized coating was studied by immersion in seawater and compared to previous, less optimized coatings. The adhesive release properties of the coatings did not correlate well with the surface energies of the coatings estimated from the static and advancing contact angles nor with the amount of fluorine present on the surface. The adhesive properties of the surfaces, however, show a correlation with water receding contact angles and contact angle hysteresis (or wetting hysteresis) resulting from surface penetration and surface reconstruction. Coatings having the best release properties had both the highest cross-link density and the lowest contact angle hysteresis. An optimized coating exhibited unprecedented resistance to marine biofouling. Water contact angle hysteresis appears to correlate with marine biofouling resistance.
Contact angle hysteresis on superhydrophobic stripes.
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.
Contact angle and contact angle hysteresis measurements using the capillary bridge technique.
Restagno, Frédéric; Poulard, Christophe; Cohen, Céline; Vagharchakian, Laurianne; Léger, Liliane
2009-09-15
A new experimental technique is proposed to easily measure both advancing and receding contact angles of a liquid on a solid surface, with unprecedented accuracy. The technique is based on the analysis of the evolution of a capillary bridge formed between a liquid bath and a solid surface (which needs to be spherical) when the distance between the surface and the liquid bath is slowly varied. The feasibility of the technique is demonstrated using a low-energy perfluorinated surface with two different test liquids (water and hexadecane). A detailed description of both experimental procedures and computational modeling are given, allowing one to determine contact angle values. It is shown that the origin of the high accuracy of this technique relies on the fact that the contact angles are automatically averaged over the whole periphery of the contact. This method appears to be particularly adapted to the characterization of surfaces with very low contact angle hysteresis.
Statistical analysis of Contact Angle Hysteresis
NASA Astrophysics Data System (ADS)
Janardan, Nachiketa; Panchagnula, Mahesh
2015-11-01
We present the results of a new statistical approach to determining Contact Angle Hysteresis (CAH) by studying the nature of the triple line. A statistical distribution of local contact angles on a random three-dimensional drop is used as the basis for this approach. Drops with randomly shaped triple lines but of fixed volumes were deposited on a substrate and their triple line shapes were extracted by imaging. Using a solution developed by Prabhala et al. (Langmuir, 2010), the complete three dimensional shape of the sessile drop was generated. A distribution of the local contact angles for several such drops but of the same liquid-substrate pairs is generated. This distribution is a result of several microscopic advancing and receding processes along the triple line. This distribution is used to yield an approximation of the CAH associated with the substrate. This is then compared with measurements of CAH by means of a liquid infusion-withdrawal experiment. Static measurements are shown to be sufficient to measure quasistatic contact angle hysteresis of a substrate. The approach also points towards the relationship between microscopic triple line contortions and CAH.
Constitutive modeling of contact angle hysteresis.
Vedantam, Srikanth; Panchagnula, Mahesh V
2008-05-15
We introduce a phase field model of wetting of surfaces by sessile drops. The theory uses a two-dimensional non-conserved phase field variable to parametrize the Gibbs free energy of the three-dimensional system. Contact line tension and contact angle hysteresis arise from the gradient term in the free energy and the kinetic coefficient respectively. A significant advantage of this approach is in the constitutive specification of hysteresis. The advancing and receding angles of a surface, the liquid-vapor interfacial energy and three-phase line tension are the only required constitutive inputs to the model. We first simulate hysteresis on a smooth chemically homogeneous surface using this theory. Next we show that it is possible to study heterogeneous surfaces whose component surfaces are themselves hysteretic. We use this theory to examine the wetting of a surface containing a circular heterogeneous island. The contact angle for this case is found to be determined solely by the material properties at the contact line in accord with recent experimental data.
Dynamic contact angle cycling homogenizes heterogeneous surfaces.
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.
Hennig, A; Eichhorn, K-J; Staudinger, U; Sahre, K; Rogalli, M; Stamm, M; Neumann, A W; Grundke, K
2004-08-03
The phenomenon of contact angle hysteresis was studied on smooth films of polyimide, a polymer type used in the microelectronic industry, by dynamic cycling contact angle measurements based on axisymmetric drop shape analysis-profile in combination with variable angle spectroscopic ellipsometry (VASE). It was found that both advancing and receding contact angles became smaller with increasing the number of cycles and are, therefore, not a property of the dry solid alone. The changes of the wetting behavior during these dynamic cycling contact angle measurements are attributed mainly to swelling and/or liquid retention. To reveal the water-induced changes of the polymer film, the polyimide surface was studied before and after the contact with a water droplet by VASE. Both the experimental ellipsometric spectrum for Delta and that for Psi as well as the corresponding simulations show characteristic shifts due to the contact with water. The so-called effective medium approximation was applied to recover information about the thickness and effective optical constants of the polymer layer from the ellipsometrically measured values of Delta and Psi. On the basis of these results, the swelling and retention behavior of the polyimide films in contact with water droplets were discussed.
As-placed contact angles for sessile drops.
Tadmor, Rafael; Yadav, Preeti S
2008-01-01
As-placed contact angle is the contact angle a drop adapts as a result of its placement on a surface. As expected, the as-placed contact angle, thetaAP, of a sessile drop on a horizontal surface decreases with the drop size due to the increase in hydrostatic pressure. We present a theoretical prediction for thetaAP which shows that it is a unique function of the advancing contact angle, thetaA, drop size, and material properties (surface tensions and densities). We test our prediction with published and new data. The theory agrees with the experiments. From the relation of the as-placed contact angle to drop size the thermodynamic equilibrium contact angle is also calculated.
Can dynamic contact angle be measured using molecular modeling?
Malani, Ateeque; Raghavanpillai, Anilkumar; Wysong, Ernest B; Rutledge, Gregory C
2012-11-02
A method is presented for determining the dynamic contact angle at the three-phase contact between a solid, a liquid, and a vapor under an applied force, using molecular simulation. The method is demonstrated using a Lennard-Jones fluid in contact with a cylindrical shell of the fcc Lennard-Jones solid. Advancing and receding contact angles and the contact angle hysteresis are reported for the first time by this approach. The increase in force required to wet fully an array of solid cylinders (robustness) with decreasing separation distance between cylinders is evaluated. The dynamic contact angle is characterized by partial slipping of the three phase contact line when a force is applied.
Apparent contact angle and contact angle hysteresis on liquid infused surfaces
NASA Astrophysics Data System (ADS)
Semprebon, Ciro; McHale, Glen; Kusumaatmaja, Halim
We theoretically investigate the apparent contact angle and contact angle hysteresis of a droplet placed on a liquid infused surface. We show that the apparent contact angle is not uniquely defined by material parameters, but also has a strong dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the contact angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict contact angle hysteresis on liquid infused surfaces generated by the pinning of the contact lines by the surface corrugations. Our analytical expressions for both the apparent contact angle and contact angle hysteresis can be interpreted as `weighted sums' between the contact angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.
Apparent contact angle and contact angle hysteresis on liquid infused surfaces.
Semprebon, Ciro; McHale, Glen; Kusumaatmaja, Halim
2016-12-21
We theoretically investigate the apparent contact angle and contact angle hysteresis of a droplet placed on a liquid infused surface. We show that the apparent contact angle is not uniquely defined by material parameters, but also has a dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the contact angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict contact angle hysteresis on liquid infused surfaces generated by the pinning of the contact lines by the surface corrugations. Our analytical expressions for both the apparent contact angle and contact angle hysteresis can be interpreted as 'weighted sums' between the contact angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.
Nanodrop contact angles from molecular dynamics simulations
NASA Astrophysics Data System (ADS)
Ravipati, Srikanth; Aymard, Benjamin; Yatsyshin, Petr; Galindo, Amparo; Kalliadasis, Serafim
2016-11-01
The contact angle between three phases being in thermodynamic equilibrium is highly sensitive to the nature of the intermolecular forces as well as to various fluctuation effects. Determining the Young contact angle of a sessile drop sitting on a substrate from molecular dynamics (MD) simulations is a highly non-trivial task. Most commonly employed methods for finding droplet contact angles from MD simulation data either require large numbers of particles or are system-dependent. We propose a systematic geometry based methodology for extracting the contact angle from simulated sessile droplets by analysing an appropriately coarse-grained density field. To demonstrate the method, we consider Lennard-Jones (LJ) and SPC/E water nanodroplets of different sizes sitting on planar LJ walls. Our results are in good agreement with Young contact angle values computed employing test-area perturbation method.
Contact angle and local wetting at contact line.
Li, Ri; Shan, Yanguang
2012-11-06
This theoretical study was motivated by recent experiments and theoretical work that had suggested the dependence of the static contact angle on the local wetting at the triple-phase contact line. We revisit this topic because the static contact angle as a local wetting parameter is still not widely understood and clearly known. To further clarify the relationship of the static contact angle with wetting, two approaches are applied to derive a general equation for the static contact angle of a droplet on a composite surface composed of heterogeneous components. A global approach based on the free surface energy of a thermodynamic system containing the droplet and solid surface shows the static contact angle as a function of local surface chemistry and local wetting state at the contact line. A local approach, in which only local forces acting on the contact line are considered, results in the same equation. The fact that the local approach agrees with the global approach further demonstrates the static contact angle as a local wetting parameter. Additionally, the study also suggests that the wetting described by the Wenzel and Cassie equations is also the local wetting of the contact line rather than the global wetting of the droplet.
Modeling contact angle hysteresis on chemically patterned and superhydrophobic surfaces.
Kusumaatmaja, H; Yeomans, J M
2007-05-22
We investigate contact angle hysteresis on chemically patterned and superhydrophobic surfaces, as the drop volume is quasistatically increased and decreased. We consider both two (cylindrical drops) and three (spherical drops) dimensions using analytical and numerical approaches to minimize the free energy of the drop. In two dimensions, we find, in agreement with other authors, a slip, jump, stick motion of the contact line. In three dimensions, this behavior persists, but the position and magnitude of the contact line jumps are sensitive to the details of the surface patterning. In two dimensions, we identify analytically the advancing and receding contact angles on the different surfaces, and we use numerical insights to argue that these provide bounds for the three-dimensional cases. We present explicit simulations to show that a simple average over the disorder is not sufficient to predict the details of the contact angle hysteresis and to support an explanation for the low contact angle hysteresis of suspended drops on superhydrophobic surfaces.
Pressure dependence of the contact angle.
Wu, Jiyu; Farouk, T; Ward, C A
2007-06-07
When a liquid and its vapor contact a smooth, homogeneous surface, Gibbsian thermodynamics indicates that the contact angle depends on the pressure at the three-phase line of an isothermal system. When a recently proposed adsorption isotherm for a solid-vapor interface is combined with the equilibrium conditions and the system is assumed to be in a cylinder where the liquid-vapor interface can be approximated as spherical, the contact-angle-pressure relation can be made explicit. It indicates that a range of contact angles can be observed on a smooth homogeneous surface by changing the pressure at the three-phase line, but it also indicates that the adsorption at the solid-liquid interface is negative, and leads to the prediction that the contact angle increases with pressure. The predicted dependence of the contact angle on pressure is investigated experimentally in a system that has an independent mechanism for determining when thermodynamic equilibrium is reached. The predictions are in agreement with the measurements. The results provide a possible explanation for contact angle hysteresis.
Contact line and contact angle dynamics in superhydrophobic channels.
Zhang, Junfeng; Kwok, Daniel Y
2006-05-23
The dynamics of the wetting and movement of a three-phase contact line confined between two superhydrophobic surfaces were studied using a mean-field free-energy lattice Boltzmann model. Principle features of superhydrophobic surfaces, such as trapped vapor/air between rough microstructures, high contact angles, reduced contact angle hysteresis, and low resistance to fluid flow, were all observed. Movement of the three-phase contact line over a well-patterned superhydrophobic surface displays a periodic stick-jump-slip behavior, while the dynamic contact angle changes accordingly from maximum to minimum. Two regimes were found for the flow velocity as a function of surface roughness and can be related directly to the balance between driving force and flow resistance. This work provides a better understanding of dynamic wetting and fluid flow behaviors over superhydrophobic surfaces and hence could be useful in related applications.
Measuring static and dynamic contact angles using a liquid needle
NASA Astrophysics Data System (ADS)
Sanedrin, Raymond; Jin, Ming; Frese, Daniel; Scheithauer, Carsten; Willers, Thomas
2016-11-01
The optical determination of static and advancing contact angle is made on drops applied or extended, respectively, onto a substrate through the use of thin solid needles. Although this method has been used extensively, this method of dosing can be time consuming, cumbersome and if not meticulously performed can lead to erroneous contact angle results. Herein, we present an alternative way of applying drops onto substrates using a small liquid jet, which is produced by a liquid pressure dosing system acting as a "liquid needle." A comparative static contact angle study on 14 different surfaces with two different liquids were performed utilizing two different ways of dosing: the conventional solid and a novel liquid needle based technique. We found, for all but one sample, that the obtained results were highly comparable. Observed differences can be explained by the characteristics of either way of dosing. In addition, we used the liquid pressure based dosing system for optical advancing contact angle measurement on two different samples. The liquid needle based method facilitates the expansion of a drop from 0.1 to 22 μL within less than 1.2 seconds, which provided constant contact angle versus drop base diameter curves. The obtained results were highly comparable with dynamic Wilhelmy contact angle measurements.
Modeling liquid bridge between surfaces with contact angle hysteresis.
Chen, H; Amirfazli, A; Tang, T
2013-03-12
This paper presents the behaviors of a liquid bridge when being compressed and stretched in a quasi-static fashion between two solid surfaces that have contact angle hysteresis (CAH). A theoretical model is developed to obtain the profiles of the liquid bridge given a specific separation between the surfaces. Different from previous models, both contact lines in the upper and lower surfaces were allowed to move when the contact angles reach their advancing or receding values. When the contact angles are between their advancing and receding values, the contact lines are pinned while the contact angles adjust to accommodate the changes in separation. Effects of CAH on both asymmetric and symmetric liquid bridges were analyzed. The model was shown to be able to correctly predict the behavior of the liquid bridge during a quasi-static compression/stretching loading cycle in experiments. Because of CAH, the liquid bridge can have two different profiles at the same separation during one loading and unloading cycle, and more profiles can be obtained during multiple cycles. The maximum adhesion force generated by the liquid bridge is found to be influenced by the CAH of surfaces. CAH also leads to energy cost during a loading cycle of the liquid bridge. In addition, the minimum separation between the two solid surfaces is shown to affect how the contact radii and angles change on the two surfaces as the liquid bridge is stretched.
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.
Methodology for high accuracy contact angle measurement.
Kalantarian, A; David, R; Neumann, A W
2009-12-15
A new version of axisymmetric drop shape analysis (ADSA) called ADSA-NA (ADSA-no apex) was developed for measuring interfacial properties for drop configurations without an apex. ADSA-NA facilitates contact angle measurements on drops with a capillary protruding into the drop. Thus a much simpler experimental setup, not involving formation of a complete drop from below through a hole in the test surface, may be used. The contact angles of long-chained alkanes on a commercial fluoropolymer, Teflon AF 1600, were measured using the new method. A new numerical scheme was incorporated into the image processing to improve the location of the contact points of the liquid meniscus with the solid substrate to subpixel resolution. The images acquired in the experiments were also analyzed by a different drop shape technique called theoretical image fitting analysis-axisymmetric interfaces (TIFA-AI). The results were compared with literature values obtained by means of the standard ADSA for sessile drops with the apex. Comparison of the results from ADSA-NA with those from TIFA-AI and ADSA reveals that, with different numerical strategies and experimental setups, contact angles can be measured with an accuracy of less than 0.2 degrees. Contact angles and surface tensions measured from drops with no apex, i.e., by means of ADSA-NA and TIFA-AI, were considerably less scattered than those from complete drops with apex. ADSA-NA was also used to explore sources of improvement in contact angle resolution. It was found that using an accurate value of surface tension as an input enhances the accuracy of contact angle measurements.
Line Tension Measurements through Drop Size Dependence of Contact Angle.
Amirfazli; Kwok; Gaydos; Neumann
1998-09-01
Experiments with different organic liquids have been conducted to study the drop size dependence of the contact angles on a self-assembled monolayer (SAM) surface of 1-octadecanethiol (HS(CH2)17CH3) on gold. Low-rate dynamic advancing contact angles were measured for sessile drops in vapor-saturated air using Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The experiments were performed using a minimum of eight separately prepared SAM surfaces for each liquid. Although a degree of scatter in the measured contact angles existed, the general trend observed for each run was that the contact angles decreased as the radius of the three-phase line for the sessile drop increased from approximately 1 to 5 mm. To obtain a better view of the overall trend, the contact angles from all of the individual runs for each liquid were averaged at corresponding radii. Subsequently, the averaged results from these experiments were interpreted using the modified Young equation. It was found that the drop size dependence of contact angles was due to a positive line tension. The line tension values are of the order of 1 µJ/m with a trend toward larger values for higher liquid surface tensions. Copyright 1998 Academic Press.
Probing with a laser sheet the contact angle distribution along a contact line.
Rio, E; Daerr, A; Limat, L
2004-01-01
An optical method for probing contact angle distribution along contact lines of any shape using a laser sheet is proposed. This method is applied to a dry patch formed inside a film flowing along an inclined plane, both liquid and solid being transparent. Falling normally to the plane, a laser sheet cuts the contact line and is moved along this line. Distortions of the sheet trace observed on a screen put below the plane allow us to extract the contact angle distribution and the local line inclination along the line. Our results show that the contact angle around a dry patch is nearly constant and equal to the static advancing angle, at least when the evolution of its shape is followed for increasing flow rates. This supports a model of dry patch shape recently proposed by Podgorski and co-workers. Preliminary results obtained for decreasing flow are also qualitatively observed.
Contact angle hysteresis at the nanometer scale.
Delmas, Mathieu; Monthioux, Marc; Ondarçuhu, Thierry
2011-04-01
Using atomic force microscopy with nonconventional carbon tips, the pinning of a liquid contact line on individual nanometric defects was studied. This mechanism is responsible for the occurrence of the contact angle hysteresis. The presence of weak defects which do not contribute to the hysteresis is evidenced for the first time. The dissipated energy associated with strong defects is also measured down to values in the range of kT, which correspond to defect sizes in the order of 1 nm.
Thermodynamic modeling of contact angles on rough, heterogeneous surfaces.
Long, J; Hyder, M N; Huang, R Y M; Chen, P
2005-12-30
Theoretical modelling for contact angle hysteresis carried out to date has been mostly limited to several idealized surface configurations, either rough or heterogeneous surfaces. This paper presents a preliminary study on the thermodynamics of contact angles on rough and heterogeneous surfaces by employing the principle of minimum free energy and the concept of liquid front. Based on a two-dimensional regular model surface, a set of relations were obtained, which correlate advancing, receding and system equilibrium contact angles to surface topography, roughness and heterogeneity. It was found that system equilibrium contact angles (theta(ES)) can be expressed as a function of surface roughness factor (delta) and the Cassie contact angle (theta(C)): costheta(ES) = deltacostheta(C). This expression can be reduced to the classical Wenzel equation.: theta(ES) = theta(W) for rough but homogeneous surfaces, and the classical Cassie equation theta(ES) = theta(C) for heterogeneous but smooth surfaces. A non-dimensional parameter called surface feature factor (omega) was proposed to classify surfaces into three categories (types): roughness-dominated, heterogeneity-dominated and mixed-rough-heterogeneous. The prediction of advancing and receding contact angles of a surface is dependent on which category the surface belongs to. The thermodynamic analysis of contact angle hysteresis was further extended from the regular model surface to irregular surfaces; consistent results were obtained. The current model not only agrees well with the models previously studied by other researchers for idealized surfaces, but also explores more possibilities to explain the reported experimental results/observations that most existing theories could not explain.
Contact Angle Changes Induced by Immunocomplex Formation†
Kim, Jong-Hoon; Shen, Amy Q.; Lee, Kyong-Hoon; Cangelosi, Gerard A.; Chung, Jae-Hyun
2014-01-01
Immunoassays analyzing interactions between antigens and antibodies can be affected by capillary action together with binding affinity. This paper studies contact-angle changes of bacterial suspensions on antibody immobilized surfaces. The capillary action and the dried pattern of the cell suspensions are analyzed and correlated with specific- and nonspecific bindings between bacteria and antibodies. PMID:24482797
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.
Drop impact on soft surfaces: beyond the static contact angles.
Rioboo, Romain; Voué, Michel; Adão, Helena; Conti, Joséphine; Vaillant, Alexandre; Seveno, David; De Coninck, Joël
2010-04-06
The wettability of cross-linked poly(dimethylsiloxane) elastomer films and of octadecyltrichlorosilane self-assembled monolayers with water has been measured and compared using various methods. Contact angle hysteresis values were compared with values reported in the literature. A new method to characterize advancing, receding contact angles, and hysteresis using drop impact have been tested and compared with usual methods. It has been found that for the rigid surfaces the drop impact method is comparable with other methods but that for elastomer surfaces the hysteresis is function of the drop impact velocity which influences the extent of the deformation of the soft surface at the triple line.
Krasovitski, Boris; Marmur, Abraham
2005-04-26
The limiting inclination angle (slip angle), for which a two-dimensional water drop may be at equilibrium on a chemically heterogeneous surface, is exactly calculated for a variety of cases. The main conclusion is that, in the cases studied, the contact angles at the upper and lower contact line do not always simultaneously equal the receding and advancing contact angles, respectively. On a hydrophobic surface, the lowest contact angle (at the upper contact line) tends to be approximately equal to the receding contact angle, while the highest contact angle (at the lower contact line) may be much lower than the advancing contact angle. For hydrophilic surfaces, the opposite is true. These conclusions imply that the hysteresis range cannot in general be measured by analyzing the shape of a drop on an inclined plane. Also, the limiting inclination angle cannot in general be calculated from the classical equation based only on the advancing and receding contact angles.
Surface free energy of a solid from contact angle hysteresis.
Chibowski, Emil
2003-04-25
Nature of contact angle hysteresis is discussed basing on the literature data (Colloids Surf. A 189 (2001) 265) of dynamic advancing and receding contact angles of n-alkanes and n-alcohols on a very smooth surface of 1,1,2,-trichloro-1,2,2,-trifluoroethane (FC-732) film deposited on a silicon plate. The authors considered the liquid absorption and/or retention (swelling) processes responsible for the observed hysteresis. In this paper hysteresis is considered to be due to the liquid film left behind the drop during retreating of its contact line. Using the contact angle hysteresis an approach is suggested for evaluation of the solid surface free energy. Molecular spacing and the film structure are discussed to explain the difference in n-alkanes and n-alcohols behaviour as well as to explain the difference between dispersion free energy gamma(s)(d) and total surface free energy gamma(s)(tot) of FC-732, as determined from the advancing contact angles and the hysteresis, respectively.
Picoliter water contact angle measurement on polymers.
Taylor, Michael; Urquhart, Andrew J; Zelzer, Mischa; Davies, Martyn C; Alexander, Morgan R
2007-06-19
Water contact angle measurement is the most common method for determining a material's wettability, and the sessile drop approach is the most frequently used. However, the method is generally limited to macroscopic measurements because the base diameter of the droplet is usually greater than 1 mm. Here we report for the first time on a dosing system to dispense smaller individual droplets with control of the position and investigate whether water contact angles determined from picoliter volume water droplets are comparable with those obtained from the conventional microliter volume water droplets. This investigation was conducted on a group of commonly used polymers. To demonstrate the higher spatial resolution of wettability that can be achieved using picoliter volume water droplets, the wettability of a radial plasma polymer gradient was mapped using a 250 microm interval grid.
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.
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.
Tool Indicates Contact Angles In Bearing Raceways
NASA Technical Reports Server (NTRS)
Akian, Richard A.; Butner, Myles F.
1995-01-01
Tool devised for use in measuring contact angles between balls and races in previously operated ball bearings. Used on both inner and outer raceways of bearings having cross-sectional widths between approximately 0.5 and 2.0 in. Consists of integral protractor mounted in vertical plane on bracket equipped with leveling screws and circular level indicator. Protractor includes rotatable indicator needle and set of disks of various sizes to fit various raceway curvatures.
Contact angle hysteresis and pinning at periodic defects in statics.
Iliev, Stanimir; Pesheva, Nina; Nikolayev, Vadim S
2014-07-01
This article deals with the theoretical prediction of the wetting hysteresis on nonideal solid surfaces in terms of the surface heterogeneity parameters. The spatially periodical chemical heterogeneity is considered. We propose precise definitions for both the advancing and the receding contact angles for the Wilhelmy plate geometry. It is well known that in such a system, a multitude of metastable states of the liquid meniscus occurs for each different relative position of the defect pattern on the plate with respect to the liquid level. As usual, the static advancing and receding angles are assumed to be a consequence of the preceding contact line motion in the respective direction. It is shown how to select the appropriate states among all metastable states. Their selection is discussed. The proposed definitions are applicable to both the static and the dynamic contact angles on heterogeneous surfaces. The static advancing and receding angles are calculated for two examples of periodic heterogeneity patterns with sharp borders: the horizontal alternating stripes of a different wettability (studied analytically) and the doubly periodic pattern of circular defects on a homogeneous base (studied numerically). The wetting hysteresis is determined as a function of the defect density and the spatial period. A comparison with the existing results is carried out.
Contact angle hysteresis and pinning at periodic defects in statics
NASA Astrophysics Data System (ADS)
Iliev, Stanimir; Pesheva, Nina; Nikolayev, Vadim S.
2014-07-01
This article deals with the theoretical prediction of the wetting hysteresis on nonideal solid surfaces in terms of the surface heterogeneity parameters. The spatially periodical chemical heterogeneity is considered. We propose precise definitions for both the advancing and the receding contact angles for the Wilhelmy plate geometry. It is well known that in such a system, a multitude of metastable states of the liquid meniscus occurs for each different relative position of the defect pattern on the plate with respect to the liquid level. As usual, the static advancing and receding angles are assumed to be a consequence of the preceding contact line motion in the respective direction. It is shown how to select the appropriate states among all metastable states. Their selection is discussed. The proposed definitions are applicable to both the static and the dynamic contact angles on heterogeneous surfaces. The static advancing and receding angles are calculated for two examples of periodic heterogeneity patterns with sharp borders: the horizontal alternating stripes of a different wettability (studied analytically) and the doubly periodic pattern of circular defects on a homogeneous base (studied numerically). The wetting hysteresis is determined as a function of the defect density and the spatial period. A comparison with the existing results is carried out.
Hong, Seung Do; Ha, Man Yeong; Balachandar, S
2009-11-01
The present study investigates the variation of static contact angle of a water droplet in equilibrium with a solid surface in the absence of a body force and the dynamic contact angles of water droplet moving on a solid surface for different characteristic energies using the molecular dynamics simulation. With increasing characteristic energy, the static contact angle in equilibrium with a solid surface in the absence of a body force decreases because the hydrophobic surface changes its characteristics to the hydrophilic surface. In order to consider the effect of moving water droplet on the dynamic contact angles, we apply the constant acceleration to an individual oxygen and hydrogen atom. In the presence of a body force, the water droplet changes its shape with larger advancing contact angle than the receding angle. The dynamic contact angles are compared with the static contact angle in order to see the effect of the presence of a body force.
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.
Modeling contact angle hysteresis of a liquid droplet sitting on a cosine wave-like pattern surface.
Promraksa, Arwut; Chen, Li-Jen
2012-10-15
A liquid droplet sitting on a hydrophobic surface with a cosine wave-like square-array pattern in the Wenzel state is simulated by using the Surface Evolver to determine the contact angle. For a fixed drop volume, multiple metastable states are obtained at two different surface roughnesses. Unusual and non-circular shape of the three-phase contact line of a liquid droplet sitting on the model surface is observed due to corrugation and distortion of the contact line by structure of the roughness. The contact angle varies along the contact line for each metastable state. The maximum and minimum contact angles among the multiple metastable states at a fixed viewing angle correspond to the advancing and the receding contact angles, respectively. It is interesting to observe that the advancing/receding contact angles (and contact angle hysteresis) are a function of viewing angle. In addition, the receding (or advancing) contact angles at different viewing angles are determined at different metastable states. The contact angle of minimum energy among the multiple metastable states is defined as the most stable (equilibrium) contact angle. The Wenzel model is not able to describe the contact angle along the three-phase contact line. The contact angle hysteresis at different drop volumes is determined. The number of the metastable states increases with increasing drop volume. Drop volume effect on the contact angles is also discussed.
On the role of energy barriers in determining contact angle hysteresis.
Long, J; Chen, P
2006-11-30
The thermodynamic model of contact angles on rough, heterogeneous surfaces developed by Long et al. [J. Long, M.N. Hyder, R.Y.M. Huang and P. Chen, Adv. Colloid Interface Sci. 118 (2005) 173] was employed to study the role of energy barriers in determining contact angle hysteresis. Major energy barriers corresponding to metastable states and minor energy barriers corresponding to secondary metastable states were defined. Distributions of major and/or minor energy barriers as a function of apparent contact angle for various surfaces were obtained. The reproducibility of contact angle measurement, the effect of vibrational energy on contact angle hysteresis and the "stick-slip" phenomenon were discussed. Quantitative relations between contact angles and vibrational energy were obtained. It was found that receding contact angles are normally poorly reproducible for hydrophilic surfaces, but for extremely hydrophobic surfaces, advancing contact angles may have a poor reproducibility. When the vibrational energy available to a system increases, the measured advancing contact angle will decrease while the receding angle will increase until both reach a common value: the system equilibrium angle. This finding not only agrees well with the experimental observations in system equilibrium contact angle measurements, but also lays a theoretical foundation for such measurements. A small vibrational energy may result in a "stick-slip" phenomenon.
Measuring contact angles inside of capillary tubes with a tensiometer.
Extrand, C W; Moon, Sung In
2014-10-01
We describe a new tensiometry method that allows for determination of wetting inside small diameter tubes or hollow fibers, where the maximum force from the ultimate rise height of liquid is used to estimate advancing contact angles. The technique was first validated with transparent tubes of glass, poly(carbonate) (PC) and poly(tetrafluoroethylene) (PTFE) using four liquids: isopropanol, silicone oil, ethylene glycol and water. Advancing contact angles measured with the tensiometer agreed well with those estimated from final rise height. As this tensiometry technique does not require a view of the liquid, it can be used to measure the wettability inside opaque tubes. We demonstrated this with poly(ether ether ketone) (PEEK) tubes.
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.
Long, Christopher J; Schumacher, James F; Brennan, Anthony B
2009-11-17
Translationally symmetric topographies can be designed to induce anisotropy of static and dynamic contact angles. The validity of ignoring directionality of topography in contact angle characterization was evaluated using microscale patterned topographies. Seven patterned topographies comprising elongated discontinuous microfeatures oriented along parallel paths and one topography comprising ridges were fabricated in a poly(dimethyl siloxane) elastomer (PDMSe). The static contact angle, advancing contact angle, receding contact angle, contact angle hysteresis, and slip angle were measured using water on each surface at three in-plane perspectives, with respect to the feature orientation. Static and dynamic contact angle anisotropies were investigated on the topographies to evaluate the effect of discontinuities along the feature lengths on the anisotropy that has been shown on channels or ridges in previous reports. Discontinuous feature topographies exhibited a statistically significant anisotropy of 2 degrees-6 degrees between the perpendicular and parallel directions, with respect to the static and dynamic contact angles. The ridges topography exhibited much larger 5 degrees-42 degrees anisotropy in the contact angles. The discontinuities along the feature lengths greatly reduced, but did not eliminate, the anisotropies compared to the ridges. This evidence of contact angle anisotropy indicates a need to identify the orientation of topography, in relation to contact angle measurements. It also implies a need to consider directionality in the design of microfluidic devices and self-cleaning surfaces.
A Hydrodynamic Model of Dynamic Contact Angle Hysteresis.
contact angle hysteresis is developed in terms of the interaction of capillary, viscous, and...used to obtain the equations which describe the contact angle region and thereby to define the dynamic contact angle . The analysis is limited to...velocity dependence of the receding contact angle and of the thickness of the deposited film of the receding interface of a wetting liquid are determined as functions of the capillary, viscous, and disjoining forces.
Facile manipulation of receding contact angles of a substrate by roughening and fluorination
NASA Astrophysics Data System (ADS)
Li, Yueh-Feng; Wu, Cyuan-Jhang; Sheng, Yu-Jane; Tsao, Heng-Kwong
2015-11-01
Contact angle hysteresis plays a paramount role in anti-smudge surfaces. In this study, surface roughness is systematically altered on some polymeric substrates such as polystyrene and poly(methyl methacrylate) by roughening and its effect on contact angle hysteresis is investigated via measuring advancing and receding contact angles of water. The wettability on these substrates is also modified by vapor-phase deposition of perfluorooctyltrichlorosilane, while the surface morphology is kept the same. As surface roughness is increased, the advancing contact angle grows but three types of the receding contact angle (θr) behavior have been identified: (i) monotonic reduction of θr, (ii) monotonic enhancement of θr, and (iii) presence of a minimum of θr. A plausible mechanism based on the stability of air pockets is proposed to explain our experimental findings. The manipulation of receding contact angles can be achieved based on our findings.
Diminution of contact angle hysteresis under the influence of an oscillating force.
Manor, Ofer
2014-06-17
We suggest a simple quantitative model for the diminution of contact angle hysteresis under the influence of an oscillatory force invoked by thermal fluctuations, substrate vibrations, acoustic waves, or oscillating electric fields. Employing force balance rather than the usual description of contact angle hysteresis in terms of Gibbs energy, we highlight that a wetting system, such as a sessile drop or a bubble adhered to a solid substrate, appears at long times to be partially or fully independent of contact angle hysteresis and thus independent of static friction forces, as a result of contact line pinning. We verify this theory by studying several well-known experimental observations such as the approach of an arbitrary contact angle toward the Young contact angle and the apparent decrease (or increase) in an advancing (or a receding) contact angle under the influence of an external oscillating force.
Estimation of Intrinsic Contact Angle of Various Liquids on PTFE by Utilizing Ultrasonic Vibration
NASA Astrophysics Data System (ADS)
Urai, Takuya; Kamai, Masayoshi; Fujii, Hidetoshi
2016-08-01
The contact angle measured using the sessile drop method is typically an advancing contact angle, which is often used for the evaluation of wettability. However, the precise measurement of the contact angle on rough substrates has been required for developing various industrial processes. In this study, a new measuring method by achieving the minimum total free energy by ultrasonic vibration (USV) was developed. The new method has been demonstrated for different rough surfaces, droplet volumes, and wettability conditions. The advancing contact angle significantly decreased when the USV is applied, but it immediately increased after stopping the USV. In order to capture the droplet behavior at the beginning and end of the USV, a high-speed camera was used. The contact angle was apparently a receding contact angle after stopping the ultrasonic vibration. Accordingly, the intrinsic contact angle was estimated using the values of the advancing contact angles obtained before applying the ultrasonic vibration and the receding contact angles obtained after stopping the ultrasonic vibration.
Contact-angle of water drop on a sloped water repellent soil
NASA Astrophysics Data System (ADS)
Arye, Gilboa; Bachmann, Jörg
2015-04-01
Soil water repellency is a well-known phenomenon worldwide and currently well documented in the scientific literature. Most methods used to characterize the magnitude and/or persistency of soil water repellency is directly or indirectly related to the initial advancing contact angle at the solid-liquid-vapor interface. These methods are commonly involved by placing a water (or solution) drops on horizontal surface of water repellent soil (WRS)particles attached to a plane surface. Under natural conditions, however, a soil surface layer is mostly sloped due to micro and/or macro topography. Therefore, the formation of advancing contact angle (downhill) and receding contact angle (uphill) should be considered, rather than a unique value of the contact angle. The difference between the advancing and receding contact angle values is defined as the contact angle hysteresis, commonly attributed to surface roughness and/or chemical heterogeneities. For a given tilt angle, a water drop exceeding a critical volume will slide downhill. Alternatively, for a given drop volume, a critical sliding angle can be defined. Measurements of advancing, receding and sliding angles on sloped WRS is indispensable for our understanding on water adhesion due to hysteresis and may provide critical values for predicting the initiation of water runoff in sloped landscapes on the micro and macro scales of WRS. Accordingly, the main objective of this study was to measure the advancing and receding contact angles on a sloped WRS as a function of: i) water drop volume, ii) particle size distribution and iii) surface slope. The measurements of contact angles on sloped WRS were taken with an advanced goniometer microscope (OCA20, DataPhysics) with external tilting device and SCA20 software for analyzing contact angles highly resolved with respect to time and spatial scales. The results obtained will be presented and the rolling-drop-criteria will be discussed.
Investigation of drop dynamic contact angle on copper surface
NASA Astrophysics Data System (ADS)
Orlova, Evgenija; Feoktistov, Dmitriy; Kuznetsov, Geniy
2015-01-01
This paper presents experimental results of the studying the effect of surface roughness, microstructure and flow rate on the dynamic contact angle at spreading of distilled non deaerate water drop on a solid horizontal substrates. Copper substrates with different roughness have been investigated. For each substrate static contact angles depending on volume flow rate have been obtained using shadow system. Increasing the volume flow rate resulted in an increase of the static contact angle. It was found that with increasing surface roughness dynamic contact angle arises. Also difference in formation of the equilibrium contact angle at low and high rates of drop growth has been detected.
Contact angle hysteresis on textured surfaces with nanowire clusters.
Liao, Ying-Chih; Chiang, Cheng-Kun; Lu, Yen-Wen
2013-04-01
Nanowire arrays with various agglomeration patterns were synthesized by adjusting the solvent evaporation rates. Nanowires with 200 nm diameter and 2-25 microm in length were fabricated from an anodic aluminum oxide (AAO) porous template. Various drying treatments were applied to develop nanostructured surfaces with topological differences. Due to surface tension forces, copper nanowires after thermal and evaporative drying treatments agglomerated into clusters, while supercritical drying technique provided excellent bundled-free and vertically-standing nanowire arrays. Although all dried surfaces exhibited hydrophobic nature, the contact angle hysteresis, or the difference between advancing and receding angles, was found to be larger on those surfaces with bundled nanowire clusters. To explain the difference, the wetted solid fraction on each surface was calculated using the Cassie-Baxter model to show that the hysteresis was contributed by liquid/solid contact area on the textured surfaces.
Understanding contact angle hysteresis on an ambient solid surface.
Wang, Yong Jian; Guo, Shuo; Chen, Hsuan-Yi; Tong, Penger
2016-05-01
We report a systematic study of contact angle hysteresis (CAH) with direct measurement of the capillary force acting on a contact line formed on the surface of a long glass fiber intersecting a liquid-air interface. The glass fiber of diameter 1-2μm and length 100-200μm is glued onto the front end of a rectangular cantilever beam, which is used for atomic force microscopy. From the measured hysteresis loop of the capillary force for 28 different liquids with varying surface tensions and contact angles, we find a universal behavior of the unbalanced capillary force in the advancing and receding directions and the spring constant of a stretched meniscus by the glass fiber. Measurements of the capillary force and its fluctuations suggest that CAH on an ambient solid surface is caused primarily by two types of coexisting and spatially intertwined defects with opposite natures. The contact line is primarily pinned by the relatively nonwetting (repulsive) defects in the advancing direction and by the relatively wetting (attractive) defects in the receding direction. Based on the experimental observations, we propose a "composite model" of CAH and relevant scaling laws, which explain the basic features of the measured hysteresis force loops.
Understanding contact angle hysteresis on an ambient solid surface
NASA Astrophysics Data System (ADS)
Wang, Yong Jian; Guo, Shuo; Chen, Hsuan-Yi; Tong, Penger
2016-05-01
We report a systematic study of contact angle hysteresis (CAH) with direct measurement of the capillary force acting on a contact line formed on the surface of a long glass fiber intersecting a liquid-air interface. The glass fiber of diameter 1 -2 μ m and length 100 -200 μ m is glued onto the front end of a rectangular cantilever beam, which is used for atomic force microscopy. From the measured hysteresis loop of the capillary force for 28 different liquids with varying surface tensions and contact angles, we find a universal behavior of the unbalanced capillary force in the advancing and receding directions and the spring constant of a stretched meniscus by the glass fiber. Measurements of the capillary force and its fluctuations suggest that CAH on an ambient solid surface is caused primarily by two types of coexisting and spatially intertwined defects with opposite natures. The contact line is primarily pinned by the relatively nonwetting (repulsive) defects in the advancing direction and by the relatively wetting (attractive) defects in the receding direction. Based on the experimental observations, we propose a "composite model" of CAH and relevant scaling laws, which explain the basic features of the measured hysteresis force loops.
Apparent contact angle of an evaporating drop
NASA Astrophysics Data System (ADS)
Morris, S. J. S.
2012-11-01
In experiments by Poulard et al. (2005), a sessile drop of perfectly wetting liquid evaporates from a non-heated substrate into an under-saturated mixture of vapour with an inert gas; evaporation is limited by vapour diffusion. The system exhibits an apparent contact angle θ that is a flow property. Under certain conditions, the apparent contact line was stationary relative to the substrate; we predict θ for this case. Observed values of θ are small, allowing lubrication analysis of the liquid film. The liquid and vapour flows are coupled through conditions holding at the phase interface; in particular, vapour partial pressure there is related to the local value of liquid pressure through the Kelvin condition. Because the droplet is shallow, the interfacial conditions can be transferred to the solid-liquid interface at y = 0 . We show that the dimensionless partial pressure p (x , y) and the film thickness h (x) are determined by solving ∇2 p = 0 for y > 0 subject to a matching condition at infinity, and the conditions - p = L hxx +h-3 and (h3px) x + 3py = 0 at y = 0 . The parameter L controls the ratio of Laplace to disjoining pressure. We analyse this b.v.p. for the experimentally-relevant case L --> 0 .
Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis.
Hozumi, Atsushi; McCarthy, Thomas J
2010-02-16
Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis for probe liquids were prepared by chemical vapor deposition (CVD) of bis((tridecafluoro-1,1,2,2,-tetrahydrooctyl)-dimethylsiloxy)methylsilane (CF(3)(CF(2))(5)CH(2)CH(2)Si(CH(3))(2)O)(2)SiCH(3)H, (R(F)Si(Me)(2)O)(2)SiMeH). Oxidized aluminum surfaces were prepared by photooxidation/cleaning of sputter-coated aluminum on silicon wafers (Si/Al(Al(2)(O(3)))) using oxygen plasma. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that this facile CVD method produces a monolayer with a thickness of 1.1 nm on the Si/Al(Al(2)(O(3))) surface without a discernible change in surface morphology. After monolayer deposition, the hydrophilic Si/Al(Al(2)(O(3))) surface became both hydrophobic and oleophobic and exhibited essentially no contact angle hysteresis for water and n-hexadecane (advancing/receding contact angles (theta(A)/theta(R)) = 110 degrees/109 degrees and 52 degrees/50 degrees, respectively). Droplets move very easily on this surface and roll off of slightly tilted surfaces, independently of the contact angle (which is a practical definition of ultralyophobic). A conventional fluoroalkylsilane monolayer was also prepared from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (CF(3)(CF(2))(7)CH(2)CH(2)Si(OCH(3))(3), R(F)Si(OMe)(3)) for comparison. The theta(A)/theta(R) values for water and n-hexadecane are 121 degrees/106 degrees and 76 degrees/71 degrees, respectively. The larger hysteresis values indicate the "pinning" of probe liquids, even though advancing contact angles are larger than those of the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers. The (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers have excellent hydrolytic stability in water. We propose that the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers are flexible and liquidlike and that drops in contact with these surfaces experience very low energy barriers between metastable states, leading to the
NASA Astrophysics Data System (ADS)
Erbil, H. Yildirim
2014-12-01
A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, wetting has been studied using contact angles of drops on solids for more than 200 years, the question remains unanswered: Is wetting of a rough and chemically heterogeneous surface controlled by the interactions within the solid/liquid contact area beneath the droplet or only at the three-phase contact line? After the publications of Pease in 1945, Extrand in 1997, 2003 and Gao and McCarthy in 2007 and 2009, it was proposed that advancing, receding contact angles, and contact angle hysteresis of rough and chemically heterogeneous surfaces are determined by interactions of the liquid and the solid at the three-phase contact line alone and the interfacial area within the contact perimeter is irrelevant. As a consequence of this statement, the well-known Wenzel (1934) and Cassie (1945) equations which were derived using the contact area approach are proposed to be invalid and should be abandoned. A hot debate started in the field of surface science after 2007, between the three-phase contact line and interfacial contact area approach defenders. This paper presents a review of the published articles on contact angles and summarizes the views of the both sides. After presenting a brief history of the contact angles and their measurement methods, we discussed the basic contact angle theory and applications of contact angles on the characterization of flat, rough and micropatterned superhydrophobic surfaces. The weak and strong sides of both three-phase contact line and contact area approaches were discussed in detail and some practical conclusions were drawn.
Kuchin, I; Starov, V
2015-05-19
A theory of contact angle hysteresis of liquid droplets on smooth, homogeneous solid substrates is developed in terms of the shape of the disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all contact angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium contact angle θ ≠ θe, correspond to the state of slow "microscopic" advancing or receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This "microscopic" motion almost abruptly becomes fast "macroscopic" advancing or receding motion after the contact angle reaches the critical values θa or θr, correspondingly. The values of the static receding, θr, and static advancing, θa, contact angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown now that (i) both advancing and receding contact angles of a droplet on a on smooth, homogeneous solid substrate can be calculated based on shape of disjoining/conjoining pressure isotherm, and (ii) both advancing and receding contact angles depend on the drop volume and are not unique characteristics of the liquid-solid system. The latter is different from advancing/receding contact angles in thin capillaries. It is shown also that the receding contact angle is much closer to the equilibrium contact angle than the advancing contact angle. The latter conclusion is unexpected and is in a contradiction with the commonly accepted view that the advancing contact angle can be taken as the first approximation for the equilibrium contact angle. The dependency of hysteresis contact angles on the drop volume has a direct experimental confirmation.
Dynamic contact angles and hysteresis under electrowetting-on-dielectric.
Nelson, Wyatt C; Sen, Prosenjit; Kim, Chang-Jin C J
2011-08-16
By designing and implementing a new experimental method, we have measured the dynamic advancing and receding contact angles and the resulting hysteresis of droplets under electrowetting-on-dielectric (EWOD). Measurements were obtained over wide ranges of applied EWOD voltages, or electrowetting numbers (0 ≤ Ew ≤ 0.9), and droplet sliding speeds, or capillary numbers (1.4 × 10(-5) ≤ Ca ≤ 6.9 × 10(-3)). If Ew or Ca is low, dynamic contact angle hysteresis is not affected much by the EWOD voltage or the sliding speed; that is, the hysteresis increases by less than 50% with a 2 order-of-magnitude increase in sliding speed when Ca < 10(-3). If both Ew and Ca are high, however, the hysteresis increases with either the EWOD voltage or the sliding speed. Stick-slip oscillations were observed at Ew > 0.4. Data are interpreted with simplified hydrodynamic (Cox-Voinov) and molecular-kinetic theory (MKT) models; the Cox-Voinov model captures the trend of the data, but it yields unreasonable fitting parameters. MKT fitting parameters associated with the advancing contact line are reasonable, but a lack of symmetry indicates that a more intricate model is required.
Applicability of Washburn capillary rise for determining contact angles of powders/porous materials.
Kirdponpattara, Suchata; Phisalaphong, Muenduen; Newby, Bi-min Zhang
2013-05-01
The Washburn capillary rise (WCR) technique has been widely utilized for determining contact angles of powders or porous materials; however, there are concerns regarding powder size and powder packing, especially for materials that exhibit large contact angle hysteresis. In this paper, some of these concerns were addressed. Due to the large water contact angle hysteresis on flat nylon 6/6 films, these films were ground into powders of different sizes and then used as model packing materials. The powders were packed in glass tubes to result in various packing structures that affected the penetration (i.e. advancing) rate of the test liquids. While all advancing contact angles obtained from WCR were found to be overestimated, more reasonable values were resulted when relatively large powders (e.g. 500-2000 μm) were used to pack the tubes. With larger powders, the packing contained bigger voids and consequently lead to slower penetration rates of the liquids, hence a relatively smaller advancing contact angle. The smaller advancing contact angle obtained from the slower advancing rate was also observed by using the sessile drop method. To verify the applicability of using large powders (500-2000 μm) for contact angle determination by using WCR, the advancing water contact angles of a bacterial cellulose/alginate composite sponge (BCA) with and without UV/ozone treatment were measured. The results showed that by using relatively large powders, WCR could be applied to obtain a reasonable advancing contact angle and assess the wettability change of complex porous materials.
UPPER LIMITS FOR THE CONTACT ANGLES OF LIQUIDS ON SOLIDS
Earlier systematic studies of the angle of contact (theta) exhibited by drops of liquid on plane solid surfaces of low surface energy have made data...available on equilibrium contact angles. These data were obtained under well- controlled and comparable experimental conditions for many liquids on...From the parameters defining this straight line, estimates can be made of the limiting contact angles for each liquid.
THE EFFECT OF LIQUID STRUCTURE ON CONTACT ANGLE HYSTERESIS
Contact angle hysteresis was measured for a variety of liquids on condensed monolayers of 17-(perfluoroheptyl)-heptadecanoic acid adsorbed on...into the porous monolayer. However, contact angle hysteresis was negligible when the average diameter of the liquid molecules was larger than the...monolayers by contact angle hysteresis measurements on a series of liquids having gradations in molecular volume. The results of this investigation
Contact-angle hysteresis on super-hydrophobic surfaces.
McHale, G; Shirtcliffe, N J; Newton, M I
2004-11-09
The relationship between perturbations to contact angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium contact angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high contact angle and the droplet completely contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high contact angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of contact-angle amplification or attenuation and distinguishes between the increases in contact angles due to roughening or texturing surfaces and perturbations to the resulting contact angles. The theory is applied to predicting contact-angle hysteresis on rough surfaces from the hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.
Contact angle distribution of particles at fluid interfaces.
Snoeyink, Craig; Barman, Sourav; Christopher, Gordon F
2015-01-27
Recent measurements have implied a distribution of interfacially adsorbed particles' contact angles; however, it has been impossible to measure statistically significant numbers for these contact angles noninvasively in situ. Using a new microscopy method that allows nanometer-scale resolution of particle's 3D positions on an interface, we have measured the contact angles for thousands of latex particles at an oil/water interface. Furthermore, these measurements are dynamic, allowing the observation of the particle contact angle with high temporal resolution, resulting in hundreds of thousands of individual contact angle measurements. The contact angle has been found to fit a normal distribution with a standard deviation of 19.3°, which is much larger than previously recorded. Furthermore, the technique used allows the effect of measurement error, constrained interfacial diffusion, and particle property variation on the contact angle distribution to be individually evaluated. Because of the ability to measure the contact angle noninvasively, the results provide previously unobtainable, unique data on the dynamics and distribution of the adsorbed particles' contact angle.
Drop trapping in axisymmetric constrictions with arbitrary contact angle
NASA Astrophysics Data System (ADS)
Ratcliffe, Thomas; Davis, Robert H.
2012-06-01
The differential Young-Laplace equations are solved numerically with an iterative solution using the method of steepest descent to determine the shape of a drop trapped under gravity in an axisymmetric ring constriction. Prior work for non-wetting drops with a contact angle of π is extended to arbitrary values of the contact angle at the three-phase contact lines. The critical Bond number, representing a dimensionless ratio of gravitational and interfacial forces, and separating static trapping at lower Bond numbers from dynamic squeezing at higher Bond numbers, decreases with decreasing contact angle, indicating that drop squeezing occurs more easily at smaller contact angle. Indeed, a critical contact angle, which depends only on the drop-to-hole and ring-cross-section-to-hole size ratios, is found, below which all drops squeeze through the hole.
Drop rebound after impact: the role of the receding contact angle.
Antonini, C; Villa, F; Bernagozzi, I; Amirfazli, A; Marengo, M
2013-12-31
Data from the literature suggest that the rebound of a drop from a surface can be achieved when the wettability is low, i.e., when contact angles, measured at the triple line (solid-liquid-air), are high. However, no clear criterion exists to predict when a drop will rebound from a surface and which is the key wetting parameter to govern drop rebound (e.g., the "equilibrium" contact angle, θeq, the advancing and the receding contact angles, θA and θR, respectively, the contact angle hysteresis, Δθ, or any combination of these parameters). To clarify the conditions for drop rebound, we conducted experimental tests on different dry solid surfaces with variable wettability, from hydrophobic to superhydrophobic surfaces, with advancing contact angles 108° < θA < 169° and receding contact angles 89° < θR < 161°. It was found that the receding contact angle is the key wetting parameter that influences drop rebound, along with surface hydrophobicity: for the investigated impact conditions (drop diameter 2.4 < D0 < 2.6 mm, impact speed 0.8 < V < 4.1 m/s, Weber number 25 < We < 585), rebound was observed only on surfaces with receding contact angles higher than 100°. Also, the drop rebound time decreased by increasing the receding contact angle. It was also shown that in general care must be taken when using statically defined wetting parameters (such as advancing and receding contact angles) to predict the dynamic behavior of a liquid on a solid surface because the dynamics of the phenomenon may affect surface wetting close to the impact point (e.g., as a result of the transition from the Cassie-Baxter to Wenzel state in the case of the so-called superhydrophobic surfaces) and thus affect the drop rebound.
A robust polynomial fitting approach for contact angle measurements.
Atefi, Ehsan; Mann, J Adin; Tavana, Hossein
2013-05-14
Polynomial fitting to drop profile offers an alternative to well-established drop shape techniques for contact angle measurements from sessile drops without a need for liquid physical properties. Here, we evaluate the accuracy of contact angles resulting from fitting polynomials of various orders to drop profiles in a Cartesian coordinate system, over a wide range of contact angles. We develop a differentiator mask to automatically find a range of required number of pixels from a drop profile over which a stable contact angle is obtained. The polynomial order that results in the longest stable regime and returns the lowest standard error and the highest correlation coefficient is selected to determine drop contact angles. We find that, unlike previous reports, a single polynomial order cannot be used to accurately estimate a wide range of contact angles and that a larger order polynomial is needed for drops with larger contact angles. Our method returns contact angles with an accuracy of <0.4° for solid-liquid systems with θ < ~60°. This compares well with the axisymmetric drop shape analysis-profile (ADSA-P) methodology results. Above about 60°, we observe significant deviations from ADSA-P results, most likely because a polynomial cannot trace the profile of drops with close-to-vertical and vertical segments. To overcome this limitation, we implement a new polynomial fitting scheme by transforming drop profiles into polar coordinate system. This eliminates the well-known problem with high curvature drops and enables estimating contact angles in a wide range with a fourth-order polynomial. We show that this approach returns dynamic contact angles with less than 0.7° error as compared to ADSA-P, for the solid-liquid systems tested. This new approach is a powerful alternative to drop shape techniques for estimating contact angles of drops regardless of drop symmetry and without a need for liquid properties.
ON THE CONTACT-ANGLES OF SMALL DROPLETS,
a liquid film which becomes unstable within a certain interval of thickness, droplets which have a certain finite contact - angle and a thin stable film...of liquid which may exceed monomolecular dimensions. It is assumed that the magnitude of the contact - angle for any given solid surface and liquid
Comparing contact angle measurements and surface tension assessments of solid surfaces.
Cwikel, Dory; Zhao, Qi; Liu, Chen; Su, Xueju; Marmur, Abraham
2010-10-05
Four types of contact angles (receding, most stable, advancing, and "static") were measured by two independent laboratories for a large number of solid surfaces, spanning a large range of surface tensions. It is shown that the most stable contact angle, which is theoretically required for calculating the Young contact angle, is a practical, useful tool for wettability characterization of solid surfaces. In addition, it is shown that the experimentally measured most stable contact angle may not always be approximated by an average angle calculated from the advancing and receding contact angles. The "static" CA is shown in many cases to be very different from the most stable one. The measured contact angles were used for calculating the surface tensions of the solid samples by five methods. Meaningful differences exist among the surface tensions calculated using four previously known methods (Owens-Wendt, Wu, acid-base, and equation of state). A recently developed, Gibbsian-based correlation between interfacial tensions and individual surface tensions was used to calculate the surface tensions of the solid surfaces from the most stable contact angle of water. This calculation yielded in most cases higher values than calculated with the other four methods. On the basis of some low surface energy samples, the higher values appear to be justified.
Contact angle hysteresis of cylindrical drops on chemically heterogeneous striped surfaces.
Iwamatsu, Masao
2006-05-15
Contact angle hysteresis of a macroscopic droplet on a heterogeneous but flat substrate is studied using the interface displacement model. First, the apparent contact angle of a droplet on a heterogeneous surface under the condition of constant volume is considered. By assuming a cylindrical liquid-vapor surface (meniscus) and minimizing the total free energy, we derive an equation for the apparent contact angle, which is similar but different from the well-known Cassie's law. Next, using this modified Cassie's law as a guide to predict the behavior of a droplet on a heterogeneous striped surface, we examine several scenarios of contact angle hysteresis using a periodically striped surface model. By changing the volume of the droplet, we predict a sudden jump of the droplet edge, and a continuous change of the apparent contact angle at the edge of two stripes. Our results suggest that as drop volume is increased (advancing contact lines), the predominant drop configuration observed is the one whose contact angle is large; whereas, decreasing drop volume from a large value (receding contact lines) yields drop configuration that predominantly exhibit the smaller contact angle.
Marmur, Abraham
2008-07-15
The possibility of making high-contact-angle, rough surfaces from low-contact-angle materials has recently been suggested and demonstrated. A thermodynamic analysis of this possibility in terms of feasibility and stability is presented. It turns out that only roughness topographies that conform to a feasibility condition which is developed in the present paper can support this phenomenon. Even under conditions that support the phenomenon, the high-contact-angle state may not be stable, and transition from the heterogeneous (Cassie-Baxter) wetting regime to the homogeneous (Wenzel) regime with a lower contact angle may occur. In addition, it is suggested to use the general terms hygrophilic and hygrophobic (based on the Greek prefix hygro- that means liquid) to describe low- and high-contact-angle surfaces, respectively.
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.
Wetting properties of AFM probes by means of contact angle measurement
NASA Astrophysics Data System (ADS)
Tao, Zhenhua; Bhushan, Bharat
2006-09-01
An atomic force microscopy (AFM) based technique was developed to measure the wetting properties of probe tips. By advancing and receding the AFM tip across the water surface, the meniscus force between the tip and the liquid was measured at the tip-water separation. The water contact angle was determined from the meniscus force. The obtained contact angle results were compared with that by the sessile drop method. It was found that the AFM based technique provided higher contact angle values than the sessile drop method. The mechanisms responsible for the difference are discussed.
Measuring the Contact Angle of Individual Colloidal Particles.
Preuss; Butt
1998-12-15
The aim of this study was to measure the contact angles of individual colloidal spheres ( solidus in circle 4.4 µm) and compare it to contact angles obtained on similarly prepared planar surfaces. For this purpose the particles were attached to atomic force microscope cantilevers. Then the force between the particle in aqueous medium and an air bubble was measured versus the distance. From the resulting force curves we obtained contact angles and detachment forces of single particles. Contact angles of gold coated silica particles were adjusted between 20 degrees and 100 degrees by self-assembling monolayers from different mixtures of undecanethiols and omega-hydroxy undecanethiols from solution. In parallel, contact angles on flat gold surfaces prepared in the same way were determined by the sessile drop method. A systematic difference between contact angles measured with particles and on planar surfaces was observed. Results are discussed in terms of line tension of the three-phase contact line. In addition, detachment forces were measured. Detachment forces were slightly higher than predicted from flotation theory. This might be caused by a pinning of the three phase contact line. Copyright 1998 Academic Press.
Unified model for contact angle hysteresis on heterogeneous and superhydrophobic surfaces.
Raj, Rishi; Enright, Ryan; Zhu, Yangying; Adera, Solomon; Wang, Evelyn N
2012-11-13
Understanding the complexities associated with contact line dynamics on chemically heterogeneous and superhydrophobic surfaces is important for a wide variety of engineering problems. Despite significant efforts to capture the behavior of a droplet on these surfaces over the past few decades, modeling of the complex dynamics at the three-phase contact line is needed. In this work, we demonstrate that contact line distortion on heterogeneous and superhydrophobic surfaces is the key aspect that needs to be accounted for in the dynamic droplet models. Contact line distortions were visualized and modeled using a thermodynamic approach to develop a unified model for contact angle hysteresis on chemically heterogeneous and superhydrophobic surfaces. On a surface comprised of discrete wetting defects on an interconnected less wetting area, the advancing contact angle was determined to be independent of the defects, while the relative fraction of the distorted contact line with respect to the baseline surface was shown to govern the receding contact angle. This behavior reversed when the relative wettability of the discrete defects and interconnected area was inverted. The developed model showed good agreement with the experimental advancing and receding contact angles, both at low and high solid fractions. The thermodynamic model was further extended to demonstrate its capability to capture droplet shape evolution during liquid addition and removal in our experiments and those in literature. This study offers new insight extending the fundamental understanding of solid-liquid interactions required for design of advanced functional coatings for microfluidics, biological, manufacturing, and heat transfer applications.
Measurement of critical contact angle in a microgravity space experiment
Concus, P.; Finn, R.; Weislogel, M.
1999-06-01
Mathematical theory predicts that small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. This phenomenon was investigated in the Interface Configuration Experiment on board the NASA USML-2 Space Shuttle flight. The experiment's double proboscis containers were designed to strike a balance between conflicting requirements of sizable volume of liquid shift (for ease of observation) and abruptness of the shift (for accurate determination of critical contact angle). The experimental results support the classical concept of macroscopic contact angle and demonstrate the role of hysteresis in impeding orientation toward equilibrium.
Measurement of Critical Contact Angle in a Microgravity Space Experiment
NASA Technical Reports Server (NTRS)
Concus, P.; Finn, R.; Weislogel, M.
1998-01-01
Mathematical theory predicts that small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. This phenomenon was investigated in the Interface Configuration Experiment on board the USMT,2 Space Shuttle flight. The experiment's "double proboscis" containers were designed to strike a balance between conflicting requirements of sizable volume of liquid shift (for ease of observation) and abruptness of the shift (for accurate determination of critical contact angle). The experimental results support the classical concept of macroscopic contact angle and demonstrate the role of hysteresis in impeding orientation toward equilibrium.
Measurement of Critical Contact Angle in a Microgravity Space Experiment
NASA Technical Reports Server (NTRS)
Concus, P.; Finn, R.; Weislogel, M.
1998-01-01
Mathematical theory predicts that small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. This phenomenon was investigated in the Interface Configuration Experiment on board the USML-2 Space Shuttle flight. The experiment's "double proboscis" containers were designed to strike a balance between conflicting requirements of sizable volume of liquid shift (for ease of observation) and abruptness of the shift (for accurate determination of critical contact angle). The experimental results support the classical concept of macroscopic contact angle and demonstrate the role of hysteresis in impeding orientation toward equilibrium.
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.
Capillary rise with velocity-dependent dynamic contact angle.
Popescu, M N; Ralston, J; Sedev, R
2008-11-04
The classic description of the rate of capillary rise given by the Washburn equation, which assumes that the contact angle preserves the equilibrium value at all times, has been recently questioned in the light of the known experimental dependence of the dynamic contact angle on the velocity of the contact line. For a number of such proposed functions of velocity for the dynamic contact angle, we analyze the resulting dependences of the contact angle and of the time of rise, respectively, on the height of the capillary rise. By applying our results to the particular cases of a high-viscosity silicone oil and water, respectively, in a glass capillary, we show that, in general, strong similarities arise between the various approaches and the classic theory in what concerns the time dependence of the capillary rise, which explains the lack of consistent experimental evidence for deviations in the rate of capillary rise from the Washburn equation. However, for a strong dependency of the contact angle on the velocity in the range of small velocities, as in the case of water on glass, one of the models predicts significant deviations even for the time dependence of the capillary rise. Moreover, our results show that the time or height dependence of the contact angle during the capillary rise can clearly discriminate between the various models.
The impact of contact angle on the biocompatibility of biomaterials.
Menzies, Kara L; Jones, Lyndon
2010-06-01
Biomaterials may be defined as artificial materials that can mimic, store, or come into close contact with living biological cells or fluids and are becoming increasingly popular in the medical, biomedical, optometric, dental, and pharmaceutical industries. Within the ophthalmic industry, the best example of a biomaterial is a contact lens, which is worn by approximately 125 million people worldwide. For biomaterials to be biocompatible, they cannot illicit any type of unfavorable response when exposed to the tissue they contact. A characteristic that significantly influences this response is that related to surface wettability, which is often determined by measuring the contact angle of the material. This article reviews the impact of contact angle on the biocompatibility of tissue engineering substrates, blood-contacting devices, dental implants, intraocular lenses, and contact lens materials.
Aerial wetting contact angle measurement using confocal microscopy
NASA Astrophysics Data System (ADS)
Chesna, Jacob W.; Wiedmaier, Bob F.; Wang, Jinlin; Samara, Ayman; Leach, Richard K.; Her, Tsing-Hua; Smith, Stuart T.
2016-12-01
A method is presented in which the wetting contact angle of a sessile drop is acquired aerially using confocal techniques to measure the radius and the height of a droplet deposited on a planar surface. The repeatability of this method is typically less than 0.25°, and often less than 0.1°, for droplet diameters less than 1 mm. To evaluate accuracy of this method, an instrument uncertainty budget is developed, which predicts a combined uncertainty of 0.91° for a 1 mm diameter water droplet with a contact angle of 110°. For droplets having diameters less than 1 mm and contact angles between 15° and 160°, these droplets approach spherical shape and their contact angles can be computed analytically with less than 1% error. For larger droplets, gravitational deformation needs to be considered.
Contact angle hysteresis on regular pillar-like hydrophobic surfaces.
Yeh, Kuan-Yu; Chen, Li-Jen; Chang, Jeng-Yang
2008-01-01
A series of pillar-like patterned silicon wafers with different pillar sizes and spacing are fabricated by photolithography and further modified by a self-assembled fluorosilanated monolayer. The dynamic contact angles of water on these surfaces are carefully measured and found to be consistent with the theoretical predictions of the Cassie model and the Wenzel model. When a water drop is at the Wenzel state, its contact angle hysteresis increases along with an increase in the surface roughness. While the surface roughness is further raised beyond its transition roughness (from the Wenzel state to the Cassie state), the contact angle hysteresis (or receding contact angle) discontinuously drops (or jumps) to a lower (or higher) value. When a water drop is at the Cassie state, its contact angle hysteresis strongly depends on the solid fraction and has nothing to do with the surface roughness. Even for a superhydrophobic surface, the contact angle hysteresis may still exhibit a value as high as 41 degrees for the solid fraction of 0.563.
Contact angle of sessile drops in Lennard-Jones systems.
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.
Hierarchically structured superoleophobic surfaces with ultralow contact angle hysteresis.
Kota, Arun K; Li, Yongxin; Mabry, Joseph M; Tuteja, Anish
2012-11-14
Hierarchically structured, superoleophobic surfaces are demonstrated that display one of the lowest contact angle hysteresis values ever reported - even with extremely low-surface-tension liquids such as n-heptane. Consequently, these surfaces allow, for the first time, even ≈2 μL n-heptane droplets to bounce and roll-off at tilt angles. ≤ 2°.
A refractive tilting-plate technique for measurement of dynamic contact angles.
Smedley, Gregory T; Coles, Donald E
2005-06-01
The contact angle is a critical parameter in liquid interface dynamics ranging from liquid spreading on a solid surface on earth to liquid motion in partially filled containers in space. A refractive tilting-plate technique employing a scanning laser beam is developed to conduct an experimental study of a moving contact line, with the intention of making accurate measurements of the contact angle. The technique shows promise as an accurate and potentially fully automated means to determine the velocity dependence of the contact angle at the intersection of the interface between two transparent fluids with a transparent solid surface. Ray tracing calculations are included to reinforce the measurement concept. The principal experiments were conducted at speeds ranging from 0.05 to 1.00 mm/s, both advancing and receding, using an immiscible liquid pair (nonane/formamide) in contact with glass. The contact angle was found to depend for practical purposes only on the sign of the velocity and not on its magnitude for the range of velocities studied. Other observations revealed a bimodal behavior of the contact line that depends on which liquid first contacts the glass, with resulting drift in the dynamic contact angle with time.
Solute concentration-dependent contact angle hysteresis and evaporation stains.
Li, Yueh-Feng; Sheng, Yu-Jane; Tsao, Heng-Kwong
2014-07-08
The presence of nonvolatile solutes in a liquid drop on a solid surface can affect the wetting properties. Depending on the surface-activity of the solutes, the extent of contact angle hysteresis (CAH) can vary with their concentration and the pattern of the evaporation stain is altered accordingly. In this work, four types of concentration-dependent CAH and evaporation stains are identified for a water drop containing polymeric additives on polycarbonate. For polymers without surface-activity such as dextran, advancing and receding contact angles (θa and θr) are independent of solute concentrations, and a concentrated stain is observed in the vicinity of the drop center after complete evaporation. For polymers with weak surface-activity such as poly(ethylene glycol) (PEG), both θa and θr are decreased by solute addition, and the stain pattern varies with increasing PEG concentration, including a concentrated stain and a mountain-like island. For polymers with intermediate surface-activity such as sodium polystyrenesulfonate (NaPSS), θa descends slightly, but θr decreases significantly after the addition of a substantial amount of NaPSS, and a ring-like stain pattern is observed. Moreover, the size of the ring stain can be controlled by NaPSS concentration. For polymers with strong surface-activity such as poly(vinylpyrrolidone) (PVP), θa remains essentially a constant, but θr is significantly lowered after the addition of a small amount of PVP, and the typical ring-like stain is seen.
Equilibrium contact angles of liquid droplets on ideal rough solids.
Kang, Hie Chan; Jacobi, Anthony M
2011-12-20
This work proposes a theoretical model for predicting the apparent equilibrium contact angle of a liquid on an ideal rough surface that is homogeneous and has a negligible body force, line tension, or contact angle hysteresis between solid and liquid. The model is derived from the conservation equations and the free-energy minimization theory for the changes of state of liquid droplets. The work of adhesion is expressed as the contact angles in the wetting process of the liquid droplets. Equilibrium contact angles of liquid droplets for rough surfaces are expressed as functions of the area ratios for the solid, liquid, and surrounding gas and the roughness ratio and wetting ratio of the liquid on the solid for the partially and fully wet states. It is found that the ideal critical angle for accentuating the contact angles by the surface roughness is 48°. The present model is compared with existing experimental data and the classical Wenzel and Cassie-Baxter models and agrees with most of the experimental data for various surfaces and liquids better than does the Wenzel model and accounts for trends that the Wenzel model cannot explain.
Dynamic contact angles in oil-aqueous polymer solutions.
Al-Shareef, Amer; Neogi, P; Bai, Baojun
2017-01-25
Polymer flooding is an important process in enhanced oil recovery. The displacement front is unstable when low viscosity brine displaces the heavy crude oil in the reservoir. Water-soluble polymers are added to the brine to increase its viscosity which stabilizes the displacement process. To analyze the displacement process at the micro-level, we have investigated the dynamic contact angles in silicone oil-polymer (polyethylene oxide) solution and for the first time. The dynamic contact angle is the apparent contact angle at the three-phase contact line which governs the capillary pressure, and thus is important for the displacement process. The data show no obvious signs of either shear thinning or elastic behavior, although for some systems with highest elastic effects some unexplained effects on dynamic contact angles are observed that correlate with elastic effects. Overall, dynamic contact angles are explained well using existing models for two Newtonian fluids, when the zero shear viscosity is used for the polymer solution.
Constraints on Contact Angles for Multiple Phases in Thermodynamic Equilibrium.
Blunt, Martin J.
2001-07-01
For three or more fluid phases in thermodynamic equilibrium and in contact with a solid surface, the Young equation can be used to find relations between the contact angles for different pairs of fluids. For an n-fluid-phase system, n(n-1)/2 contact angles can be defined, but there are (n-1)(n-2)/2 constraints between them, leaving only n-1 independent values of the contact angle. These constraints are very powerful in limiting and determining possible types of wetting behavior. The consequences are discussed for three- and four-phase flow. They have important applications for the understanding of gas injection processes in petroleum reservoirs. Copyright 2001 Academic Press.
How pinning and contact angle hysteresis govern quasi-static liquid drop transfer.
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.
Gokhale, Shripad J; Plawsky, Joel L; Wayner, Peter C
2003-03-15
Image-analyzing interferometry is used to measure the apparent contact angle and the curvature of a drop and a meniscus during condensation and evaporation processes in a constrained vapor bubble (CVB) cell. The apparent contact angle is found to be a function of the interfacial mass flux. The interfacial velocity for the drop during condensation and evaporation is a function of the apparent contact angle and the rate of change of radius of curvature. The dependence of velocity on the apparent contact angle is consistent with Tanner's scaling equation. The results support the hypothesis that evaporation/condensation is an important factor in contact line motion. The main purpose of this article is to present the experimental technique and the data. The equilibrium contact angle for the drop is found experimentally to be higher than that for the corner meniscus. The contact angle is a function of the stress field in the fluid. The equilibrium contact angle is related to the thickness of the thin adsorbed film in the microscopic region and depends on the characteristics of the microscopic region. The excess interfacial free energy and temperature jump were used to calculate the equilibrium thickness of the thin adsorbed film in the microscopic region.
Repulsion-based model for contact angle saturation in electrowetting.
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 angle of a nanodrop on a nanorough solid surface.
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.
Fabrication of zero contact angle ultra-super hydrophilic surfaces.
Jothi Prakash, C G; Clement Raj, C; Prasanth, R
2017-06-15
Zero contact angle surfaces have been created with the combined effect of nanostructure and UV illumination. The contact angle of titanium surface has been optimized to 3.25°±1°. with nanotubular structures through electrochemical surface modification. The porosity and surface energy of tubular TiO2 layer play critical role over the surface wettability and the hydrophilicity of the surface. The surface free energy has been enhanced from 23.72mJ/m(2) (bare titanium surface) to 87.11mJ/m(2) (nanotubular surface). Similar surface with TiO2 nanoparticles coating shows superhydrophilicity with contact angle up to 5.63°±0.95°. This implies liquid imbibition and surface curvature play a crucial role in surface hydrophilicity. The contact angle has been further reduced to 0°±0.86° by illuminating the surface with UV radiation. Results shows that by tuning the nanotube morphology, highly porous surfaces can be fabricated to reduce contact angle and enhance wettability. This study provides an insight into the inter-relationship between surface structural factors and ultra-superhydrophilic surfaces which can help to optimize thermal hydraulic and self cleaning surfaces.
Contact angle measurements at the colemanite and realgar surfaces
NASA Astrophysics Data System (ADS)
Koca, Sabiha; Savas, Mehmet
2004-03-01
Colemanite is one of the most important boron minerals and covers an important part of Turkey's boron mineral deposits. The friable nature of the colemanite tends to produce a large amount of fines. Flotation appears to be a promising technique to recover colemanite from such fines. During flotation process, selectivity problem arises between colemanite and associated gangue minerals such as realgar. There is a close relationship between floatability of minerals and contact angle. Therefore, surface hydrophobicity of colemanite and realgar minerals were investigated by receding contact angle measurements in the absence and presence of flotation reagents. The water contact angle values at the colemanite surface remained almost unchanged at 32-35° in the solutions of potassium amyl xanthate (KAX), potassium ethyl xanthate (KEX) and petroleum sulphanate (R825) while another petroleum sulphanate (R840), sodium oleate and tallow amine (Armac-T) affected hydrophobicity of colemanite, and the contact angle values increased up to 47°. The contact angle values of 62, 63, 45, 46, 39, and 43° at the realgar surface were obtained in the solutions of KAX, KEX, sodium oleate, R825, R840 and Armac-T, respectively.
Repulsion-based model for contact angle saturation in electrowetting
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
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.
Magnetically induced decrease in droplet contact angle on nanostructured surfaces.
Zhou, Qian; Ristenpart, William D; Stroeve, Pieter
2011-10-04
We report a magnetic technique for altering the apparent contact angle of aqueous droplets deposited on a nanostructured surface. Polymeric tubes with embedded superparamagnetic magnetite (Fe(3)O(4)) nanoparticles were prepared via layer-by-layer deposition in the 800 nm diameter pores of polycarbonate track-etched (PCTE) membranes. Etching away the original membrane yields a superparamagnetic film composed of mostly vertical tubes attached to a rigid substrate. We demonstrate that the apparent contact angle of pure water droplets deposited on the nanostructured film is highly sensitive to the ante situm strength of an applied magnetic field, decreasing linearly from 117 ± 1.3° at no applied field to 105 ± 0.4° at an applied field of approximately 500 G. Importantly, this decrease in contact angle did not require an inordinately strong magnetic field: a 15° decrease in contact angle was observed even with a standard alnico bar magnet. We interpret the observed contact angle behavior in terms of magnetically induced conformation changes in the film nanostructure, and we discuss the implications for reversibly switching substrates from hydrophilic to hydrophobic via externally tunable magnetic fields.
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.
The Dependence of the Apparent Contact Angles on Gravity.
Sakai; Fujii
1999-02-01
We have studied theoretically the effect of gravity on the rough solid-liquid interface and have shown that its tension is enhanced by gravity when gas is adsorbed at it. As a result, the apparent contact angle on rough surfaces, which has been considered not to be influenced by gravity so far, can be raised by gravity. The calculated dependence of contact angles on gravity under the ordinary conditions of the sessile drop method is large enough to detect by experiment. The observed asymmetrical deviations from Wenzel's contact angle caused by the gas adsorption at the solid-liquid interface and by the liquid adsorption at the solid-gas interface are explained in terms of this gravitational effect. Copyright 1999 Academic Press.
Brandon; Wachs; Marmur
1997-07-01
A public domain software package is employed in the quasi-steady-state simulation of contact angle hysteresis. Three-dimensional sessile drops in equilibrium with a model chemically heterogeneous smooth solid surface are considered; evolving drop shapes, as a function of incremental changes in their volume, are investigated. Results are presented for a model system in which the intrinsic contact angle is assumed to vary along the surface in a periodic manner. Throughout the simulation, calculated contact angles show reasonable agreement with the local intrinsic contact angle values, and the computed drop shapes are found to be constant mean curvature surfaces. Significant hysteresis in the liquid-fluid interface curvature and average contact angle is found; a complete hysteresis loop is simulated. Advancing and receding contact angles exhibit the "stick-slip" behavior observed in experiments as well as in previous 2-D simulations.
Wang, Lijuan; Liang, Jinsheng; Di, Xingfu; Tang, Qingguo
2014-05-01
The cleanability of easy-to-clean ceramic glazes doped with nanometer far-infrared materials was compared with that of some high-quality household ceramic glazes from the market. The cleanability was evaluated by the contact angle measurement using a sessile drop method with a Dataphysics OCA-30 contact angle analyzer. The results showed that the difference of contact angles of water on the glazes before soiling and after cleaning could be used as a parameter for evaluating the cleanability of the glazes. The relationship between cleanability and surface properties, such as surface free energy and surface topography, was investigated. The surface free energy of the samples and their components were calculated using van Oss acid-base approach. By measuring advancing and receding contact angles, the contact angle hysteresis of the ceramic glazes due to the surface topography was investigated. It was shown that the cleanability of ceramic glazes containing nanometer far-infrared materials (NFIM) is better than that of household ceramic glazes from market, due to a higher ratio of electron-acceptor parameter to electron-donor parameter, which led to the effect of water hydration as well as better hydrophilic property and increased smoothness. The contact angle measurement not only accurately evaluates the cleanability of the ceramic glazes, but also has a contribution to the study of cleanability theory. Moreover, this method is simple, convenient and less sample-consumption.
Contact angles in the pseudopotential lattice Boltzmann modeling of wetting.
Li, Qing; Luo, K H; Kang, Q J; Chen, Q
2014-11-01
In this paper we investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio ρ_{L}/ρ_{V}=500. The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994)10.1103/PhysRevE.49.2941] is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions, the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles θ<90^{∘}, however, it is unable to reproduce static contact angles close to 180^{∘}. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles θ>90^{∘} as compared with the two other types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
Contact angles in the pseudopotential lattice Boltzmann modeling of wetting
NASA Astrophysics Data System (ADS)
Li, Qing; Luo, K. H.; Kang, Q. J.; Chen, Q.
2014-11-01
In this paper we investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio ρL/ρV=500 . The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994), 10.1103/PhysRevE.49.2941] is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions, the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles θ <90∘ , however, it is unable to reproduce static contact angles close to 180∘. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles θ >90∘ as compared with the two other types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
Droplet compression and relaxation by a superhydrophobic surface: contact angle hysteresis.
Hong, Siang-Jie; Chou, Tung-He; Chan, Seong Heng; Sheng, Yu-Jane; Tsao, Heng-Kwong
2012-04-03
In this article, the contact angle hysteresis (CAH) of acrylic glass is experimentally and theoretically studied through the compression-relaxation process of droplets by using a superhydrophobic surface with negligible CAH effect. In contrast to the existing technique in which the volume of the droplet changes during the measurement of CAH, this procedure is carried out at a constant volume of the droplet. By observing the base diameter (BD) and the contact angle (CA) of the droplet during the compression-relaxation process, the wetting behavior of the droplet can be divided into two regimes, the contact line withdrawal and the contact line pinning regimes, depending on the gap thickness (H) at the end of the compression process. During the compression process, both regimes possess similar droplet behavior; the contact line will move outward and the BD will expand while the CA remains at the advancing angle. During the relaxation process, the two regimes are significantly different. In the contact line withdrawal regime, the contact line will withdraw with the CA remaining at the receding angle. In the contact line pinning regime, however, the contact line will be pinned at the final position and the CA will decline to a certain value higher than the receding angle. Furthermore, the advancing pinning behavior can also be realized through a successive compression-relaxation process. On the basis of the liquid-induced defects model, Surface Evolver simulations are performed to reproduce the behavior of the droplet during the compression-relaxation process; both contact line withdrawal and pinning regimes can also be identified. The results of the experiment and simulation agree with each other very well.
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.
Static contact angle in lattice Boltzmann models of immiscible fluids.
Latva-Kokko, M; Rothman, Daniel H
2005-10-01
We study numerically the capillary rise between two horizontal plates and in a rectangular tube, using a lattice Boltzmann (LB) method. We derive an equation for the static fluid-solid contact angle as a function of the wetting tendency of the walls and test its validity. We show that the generalized Laplace law with two independent radii of curvature is followed in capillary rise in rectangular tubes. Our method removes the history dependence of the fluid-solid contact angle that had been present in earlier LB schemes.
Dynamic Contact Angle at the Nanoscale: A Unified View.
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.
Origin of dynamic contact angle at the nanoscale
NASA Astrophysics Data System (ADS)
Lukyanov, Alex; Likhtman, Alexei
2016-11-01
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, which is demonstrated using large-scale molecular dynamics simulations of bead-spring model fluids. It has been shown 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 force with high accuracy to understand its nature and its characteristic physical parameters. 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 first formulated by Thompson & Troian on the basis of molecular dynamics simulations of Lennard-Jones liquids. 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. Deceased.
Effect of surface texturing on superoleophobicity, contact angle hysteresis, and "robustness".
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
Bourassa, S; Benjamin, W J
1989-08-01
Functional wettability of daily wear rigid gas permeable (RGP) contact lenses worn by 16 human subjects was monitored over a 4-month period during which wettability was also assessed with an equilibrium sessile-drop contact angle method in vivo. In all, 2,128 lens surface break-up time (LBUT) and in vivo contact angle data points were accumulated. Six hundred thirty-one associated graded evaluations of lens surface deposition and patient discomfort were also recorded. The four factors (LBUT, contact angle, deposition, and discomfort) were found to be correlated to each other, their paired values having statistically significant correlation coefficients. Contact angles were of predictive value for extremes of functional wettability, based on criterion of 20 degrees equivalent to an LBUT of 5 seconds. We confirm that surface deposition and subject discomfort are related to RGP lens wettability on the eye. In addition, the in vivo contact angle is perhaps the first contact angle measurement to be correlated with functional RGP wettability.
A review of factors that affect contact angle and implications for flotation practice.
Chau, T T; Bruckard, W J; Koh, P T L; Nguyen, A V
2009-09-30
. Other advanced techniques and measures complementary to contact angle will be essential to establish the link between research and practice in flotation.
Contact Angle Measurements Using a Simplified Experimental Setup
ERIC Educational Resources Information Center
Lamour, Guillaume; Hamraoui, Ahmed; Buvailo, Andrii; Xing, Yangjun; Keuleyan, Sean; Prakash, Vivek; Eftekhari-Bafrooei, Ali; Borguet, Eric
2010-01-01
A basic and affordable experimental apparatus is described that measures the static contact angle of a liquid drop in contact with a solid. The image of the drop is made with a simple digital camera by taking a picture that is magnified by an optical lens. The profile of the drop is then processed with ImageJ free software. The ImageJ contact…
Slovin, Mitchell R; Shirts, Michael R
2015-07-28
We quantify some of the effects of patterned nanoscale surface texture on static contact angles, dynamic contact angles, and dynamic contact angle hysteresis using molecular dynamics simulations of a moving Lennard-Jones droplet in contact with a solid surface. We observe static contact angles that change with the introduction of surface texture in a manner consistent with theoretical and experimental expectations. However, we find that the introduction of nanoscale surface texture at the length scale of 5-10 times the fluid particle size does not affect dynamic contact angle hysteresis even though it changes both the advancing and receding contact angles significantly. This result differs significantly from microscale experimental results where dynamic contact angle hysteresis decreases with the addition of surface texture due to an increase in the receding contact angle. Instead, we find that molecular-kinetic theory, previously applied only to nonpatterned surfaces, accurately describes dynamic contact angle and dynamic contact angle hysteresis behavior as a function of terminal fluid velocity. Therefore, at length scales of tens of nanometers, the kinetic phenomena such as contact line pinning observed at larger scales become insignificant in comparison to the effects of molecular fluctuations for moving droplets, even though the static properties are essentially scale-invariant. These findings may have implications for the design of highly hierarchical structures with particular wetting properties. We also find that quantitatively determining the trends observed in this article requires the careful selection of system and analysis parameters in order to achieve sufficient accuracy and precision in calculated contact angles. Therefore, we provide a detailed description of our two-surface, circular-fit approach to calculating static and dynamic contact angles on surfaces with nanoscale texturing.
Contact-angle hysteresis on periodic microtextured surfaces: Strongly corrugated liquid interfaces.
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.
Contact-angle hysteresis on periodic microtextured surfaces: Strongly corrugated liquid interfaces
NASA Astrophysics Data System (ADS)
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), 10.1021/la303070s] in the case of block depinning is theoretically substantiated through the capillary force, acting on the solid plate at the meniscus contact line.
Statistical contact angle analyses; "slow moving" drops on a horizontal silicon-oxide surface.
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.
Slip-stick wetting and large contact angle hysteresis on wrinkled surfaces.
Bukowsky, Colton; Torres, Jessica M; Vogt, Bryan D
2011-02-15
Wetting on a corrugated surface that is formed via wrinkling of a hard skin layer formed by UV oxidation (UVO) of a poly(dimethylsiloxane) (PDMS) slab is studied using advancing and receding water contact angle measurements. The amplitude of the wrinkled pattern can be tuned through the pre-strain of the PDMS prior to surface oxidation. These valleys and peaks in the surface topography lead to anisotropic wetting by water droplets. As the droplet advances, the fluid is free to move along the direction parallel to the wrinkles, but the droplet moving orthogonal to the wrinkles encounters energy barriers due to the topography and slip-stick behavior is observed. As the wrinkle amplitude increases, anisotropy in the sessile droplet increases between parallel and perpendicular directions. For the drops receding perpendicular to the wrinkles formed at high strains, the contact angle tends to decrease steadily towards zero as the drop volume decreases, which can result in apparent hysteresis in the contact angle of over 100°. The wrinkled surfaces can exhibit high sessile and advancing contact angles (>115°), but the receding angle in these cases is generally vanishing as the drop is removed. This effect results in micrometer sized drops remaining in the grooves for these highly wrinkled surfaces, while the flat analogous UVO-treated PDMS shows complete removal of all macroscopic water drops under similar conditions. These wetting characteristics should be considered if these wrinkled surfaces are to be utilized in or as microfluidic devices.
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.
Read, Michael L; Morgan, Philip B; Maldonado-Codina, Carole
2009-11-01
This work sought to undertake a comprehensive investigation of the measurement errors associated with contact angle assessment of curved hydrogel contact lens surfaces. The contact angle coefficient of repeatability (COR) associated with three measurement conditions (image analysis COR, intralens COR, and interlens COR) was determined by measuring the contact angles (using both sessile drop and captive bubble methods) for three silicone hydrogel lenses (senofilcon A, balafilcon A, lotrafilcon A) and one conventional hydrogel lens (etafilcon A). Image analysis COR values were about 2 degrees , whereas intralens COR values (95% confidence intervals) ranged from 4.0 degrees (3.3 degrees , 4.7 degrees ) (lotrafilcon A, captive bubble) to 10.2 degrees (8.4 degrees , 12.1 degrees ) (senofilcon A, sessile drop). Interlens COR values ranged from 4.5 degrees (3.7 degrees , 5.2 degrees ) (lotrafilcon A, captive bubble) to 16.5 degrees (13.6 degrees , 19.4 degrees ) (senofilcon A, sessile drop). Measurement error associated with image analysis was shown to be small as an absolute measure, although proportionally more significant for lenses with low contact angle. Sessile drop contact angles were typically less repeatable than captive bubble contact angles. For sessile drop measures, repeatability was poorer with the silicone hydrogel lenses when compared with the conventional hydrogel lens; this phenomenon was not observed for the captive bubble method, suggesting that methodological factors related to the sessile drop technique (such as surface dehydration and blotting) may play a role in the increased variability of contact angle measurements observed with silicone hydrogel contact lenses.
Dynamic contact angle of water-based titanium oxide nanofluid.
Radiom, Milad; Yang, Chun; Chan, Weng Kong
2013-06-11
This paper presents an investigation into spreading dynamics and dynamic contact angle of TiO2-deionized water nanofluids. Two mechanisms of energy dissipation, (1) contact line friction and (2) wedge film viscosity, govern the dynamics of contact line motion. The primary stage of spreading has the contact line friction as the dominant dissipative mechanism. At the secondary stage of spreading, the wedge film viscosity is the dominant dissipative mechanism. A theoretical model based on combination of molecular kinetic theory and hydrodynamic theory which incorporates non-Newtonian viscosity of solutions is used. The model agreement with experimental data is reasonable. Complex interparticle interactions, local pinning of the contact line, and variations in solid-liquid interfacial tension are attributed to errors.
Dynamic contact angle of water-based titanium oxide nanofluid
2013-01-01
This paper presents an investigation into spreading dynamics and dynamic contact angle of TiO2-deionized water nanofluids. Two mechanisms of energy dissipation, (1) contact line friction and (2) wedge film viscosity, govern the dynamics of contact line motion. The primary stage of spreading has the contact line friction as the dominant dissipative mechanism. At the secondary stage of spreading, the wedge film viscosity is the dominant dissipative mechanism. A theoretical model based on combination of molecular kinetic theory and hydrodynamic theory which incorporates non-Newtonian viscosity of solutions is used. The model agreement with experimental data is reasonable. Complex interparticle interactions, local pinning of the contact line, and variations in solid–liquid interfacial tension are attributed to errors. PMID:23759071
Drop shape visualization and contact angle measurement on curved surfaces.
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.
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…
Effects of temperature and conditioning on contact lens wetting angles.
Knick, P D; Huff, J W
1991-07-01
Because wettability is not always examined under standard conditions, we investigated the temperature dependence of saline wettability on unconditioned and conditioned polymethylmethacrylate (PMMA), cellulose acetate butyrate (CAB), and three silicone acrylate lens materials. Sessile drop contact angles were measured in a humidity chamber at 23 degrees C and 34 degrees C using laser-assisted contact angle goniometry. In separate experiments, saline-stored and preconditioned lenses were examined either with or without rinsing. Sessile drop contact angles at 34 degrees C were within 2 degrees to 5 degrees of the room temperature values for both conditioned and unconditioned lenses, demonstrating a negligible temperature dependence. At both temperatures, the conditioned PMMA, CAB, silafocon A, and pasifocon C lenses wet slightly better, by 1 degree to 12 degrees, than unconditioned lenses. However, this increase was only significant with PMMA and silafocon A (P less than 0.05) and reversed when the preconditioned lenses were rinsed repeatedly in saline and reexamined. The results suggest that for these materials: 1) in vitro saline contact angles do not approach those seen on the eye, and this discrepancy can not be explained by temperature or conditioning; and 2) conditioning does not increase material wettability but merely forms a temporary hydrophilic interface that is more wettable than the lens material.
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
Contact angles of wetting and water stability of soil structure
NASA Astrophysics Data System (ADS)
Kholodov, V. A.; Yaroslavtseva, N. V.; Yashin, M. A.; Frid, A. S.; Lazarev, V. I.; Tyugai, Z. N.; Milanovskiy, E. Yu.
2015-06-01
From the soddy-podzolic soils and typical chernozems of different texture and land use, dry 3-1 mm aggregates were isolated and sieved in water. As a result, water-stable aggregates and water-unstable particles composing dry 3-1 mm aggregates were obtained. These preparations were ground, and contact angles of wetting were determined by the static sessile drop method. The angles varied from 11° to 85°. In most cases, the values of the angles for the water-stable aggregates significantly exceeded those for the water-unstable components. In terms of carbon content in structural units, there was no correlation between these parameters. When analyzing the soil varieties separately, the significant positive correlation between the carbon content and contact angle of aggregates was revealed only for the loamy-clayey typical chernozem. Based on the multivariate analysis of variance, the value of contact wetting angle was shown to be determined by the structural units belonging to water-stable or water-unstable components of macroaggregates and by the land use type. In addition, along with these parameters, the texture has an indirect effect.
Hilpert, Markus
2009-09-01
In a recent paper, we generalized Washburn's analytical solution for capillary flow in a horizontally oriented tube by accounting for a dynamic contact angle. In this paper, we derive solutions for flow in inclined tubes that account for gravity. We again consider two general models for dynamic contact angle: the uncompensated Young force on the contact line depends on the capillary number in the form of (1) a power law with exponent beta, or (2) a polynomial. A dimensional analysis shows that, aside from the parameters for the model for the uncompensated Young force, the problem is defined through four nondimensional parameters: (1) the advancing equilibrium contact angle, (2) the initial contact angle, (3) a Bond number, and (4) nondimensional liquid pressure at the tube inlet relative to the constant gas pressure. For both contact angle models, we derive analytical solutions for the travel time of the gas-liquid interface as a function of interface velocity. The interface position as a function of travel time can be obtained through numerical integration. For the power law and beta=1 (an approximation of Cox's model for dynamic contact angle), we obtain an analytical solution for travel time as a function of interface position, as Washburn did for constant contact angle. Four different flow scenarios may occur: the interface moves (1) upward and approaches the height of capillary rise, (2) downward with the steady-state velocity, (3) downward while approaching the steady-state velocity from an initially higher velocity, or (4) downward while approaching the steady-state velocity from an initially smaller velocity.
Inkjet printing of precisely defined features using contact-angle hysteresis.
Soltman, Dan; Smith, Ben; Morris, S J S; Subramanian, Vivek
2013-06-15
Motivated by the process of inkjet printing of electronics, we study experimentally and theoretically the processes limiting the printing of sharply defined, equilibrium corners. Using a non-volatile ionic liquid, we inkjet print squares with rounded corners on a substrate of roughened, display-grade glass. We show experimentally that with increasing roughness, corner radius decreases, allowing more precisely defined features to be printed. To interpret these results in terms of contact-angle hysteresis (difference between the advancing and retreating contact angles θA and θR), we implement the following model with the Surface Evolver program. With drop volume fixed, we minimize drop surface energy subject to a prescribed contact line. We identify θA and θR as the minimum and maximum contact angles around the drop perimeter. We find that with decreasing corner fidelity, contact-angle hysteresis also decreases. We are thus able to infer θR from the corner radius of printed features. We conclude that increasing contact-angle hysteresis allows the printing of more precisely defined features.
Measurement of Capillary Radius and Contact Angle within Porous Media.
Ravi, Saitej; Dharmarajan, Ramanathan; Moghaddam, Saeed
2015-12-01
The pore radius (i.e., capillary radius) and contact angle determine the capillary pressure generated in a porous medium. The most common method to determine these two parameters is through measurement of the capillary pressure generated by a reference liquid (i.e., a liquid with near-zero contact angle) and a test liquid. The rate of rise technique, commonly used to determine the capillary pressure, results in significant uncertainties. In this study, we utilize a recently developed technique for independently measuring the capillary pressure and permeability to determine the equivalent minimum capillary radii and contact angle of water within micropillar wick structures. In this method, the experimentally measured dryout threshold of a wick structure at different wicking lengths is fit to Darcy's law to extract the maximum capillary pressure generated by the test liquid. The equivalent minimum capillary radii of different wick geometries are determined by measuring the maximum capillary pressures generated using n-hexane as the working fluid. It is found that the equivalent minimum capillary radius is dependent on the diameter of pillars and the spacing between pillars. The equivalent capillary radii of micropillar wicks determined using the new method are found to be up to 7 times greater than the current geometry-based first-order estimates. The contact angle subtended by water at the walls of the micropillars is determined by measuring the capillary pressure generated by water within the arrays and the measured capillary radii for the different geometries. This mean contact angle of water is determined to be 54.7°.
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.
Stadler, H; Mondon, M; Ziegler, C
2003-01-01
Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film.
Dynamic contact angle of a liquid spreading on a heated plate
Ripple, D.
1999-06-01
An equation determining the steady-state profile of a liquid meniscus advancing or receding across a heated plate is derived. The effects of liquid evaporation, intermolecular interaction with the plate, and thermocapillarity are included. Numerical and analytical estimates of the dynamic contact angle are calculated for water and the refrigerant 1,1,1,2 tetrafluoroethane. The dynamic contact angle depends primarily on three dimensionless parameters: one proportional to the velocity of the interface, one proportional to the rate of evaporation from the surface, and one proportional to the thermal coefficient of the liquid-vapor surface tension.
Eccentricity effect of micropatterned surface on contact angle.
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.
Effect of contact angle hysteresis on the measurement of capillary forces.
De Souza, E J; Gao, L; McCarthy, T J; Arzt, E; Crosby, A J
2008-02-19
We conduct experimental investigations of macroscopic capillary forces between two flat rigid substrates characterized by their advancing and receding contact angles with water. Our results exhibit excellent agreement with theoretical predictions obtained by the numerical solution of the capillary equation. On the basis of this comparison, we use the measurements of the capillary force to investigate the phenomenon of contact angle hysteresis. We present examples of force measurements for surfaces that display low, moderate, and high contact angle hysteresis and compare results for a larger variety of substrates. Finally, we show that for the case of water, the role of viscosity is insignificant within the range of force and velocity measured in the present work.
Non-Contact Ultrasonic Characterization of Angled Surface Defects
NASA Astrophysics Data System (ADS)
Edwards, R. S.; Dutton, B.; Rosli, M. H.; Clough, A. R.
2011-06-01
Surface ultrasonic waves have been shown to have many uses in non-destructive testing, in particular for gauging the depth of surface defects. Much of the previous work has assumed that these defects are oriented normal to the surface. However, this is not always the case; for example, rolling contact fatigue in rails propagates at an angle of around 25° to the surface, and this angle may affect the characterisation. We present results using non-contact ultrasonic methods to generate and detect ultrasound on samples with a range of defect angles, and compare these with finite element method (FEM) models. We use both electromagnetic acoustic transducers (EMATs) and laser ultrasound. The depth calibration when measuring ultrasound transmission is considered, and what affect the angle of a defect has. Several other methods of characterising crack depth and angle are also discussed, including the arrival times of reflected and mode-converted waves, the delay in the transmission of the high-frequency Rayleigh wave, and the enhancement of the signal at the defect in both the in-plane and out-of-plane components.
Scheme for contact angle and its hysteresis in a multiphase lattice Boltzmann method.
Wang, Lei; Huang, Hai-bo; Lu, Xi-Yun
2013-01-01
In this paper, a scheme for specifying contact angle and its hysteresis is incorporated into a multiphase lattice Boltzmann method. The scheme is validated through investigations of the dynamic behaviors of a droplet sliding along two kinds of walls: a smooth (ideal) wall and a rough or chemically inhomogeneous (nonideal) wall. For an ideal wall, the wettability of solid substrates is able to be prescribed. For a nonideal wall, arbitrary contact angle hysteresis can be obtained through adjusting advancing and receding angles. Significantly different phenomena can be recovered for the two kinds of walls. For instance, a droplet on an inclined ideal wall under gravity is impossible to stay stationary. However, the droplet on a nonideal wall may be pinned due to contact angle hysteresis. The steady interface shapes of the droplet on an inclined nonideal wall under gravity or in a shear flow quantitatively agree well with the previous numerical studies. Besides, the complex motion of a droplet creeping like an inchworm could be simulated. The scheme is found suitable for the study of contact line problems with and without contact angle hysteresis.
Effect of electric fields on contact angle and surface tension of drops.
Bateni, A; Laughton, S; Tavana, H; Susnar, S S; Amirfazli, A; Neumann, A W
2005-03-01
Contact angles of sessile drops were experimentally investigated in the electric field. The experimental setup was designed such that the electric field was applied to all three interfaces. The advanced Automated Polynomial Fitting (APF) methodology was employed to measure contact angles with high accuracy. The significance of the observations and trends was examined by conducting statistical tests of hypothesis. It was found that contact angles of polar liquids such as alcohols increase in the electric field. However, no significant trend was observed for nonpolar liquids such as alkanes. The change in the contact angle was found to be stronger for liquids with longer molecules. It was shown that the polarity of the electric field is not an underlying factor in the observed trends. Using the equation of state for interfacial tensions, the observed shift in contact angles was translated into a corresponding change in surface tension of the liquids. The results suggest that the surface tension of alcohols increases by one to two percent (depending on the size of molecules) when an electric field of the order of magnitude of 10(6) V/m is applied.
The effect of contact angle hysteresis on droplet coalescence and mixing.
Nilsson, Michael A; Rothstein, Jonathan P
2011-11-15
In this work, droplet coalescence and the subsequent mixing in superhydrophobic surfaces is studied over a range of impact velocities and impact angles. Sanded Teflon surfaces are used as a novel two-dimensional microfluidics platform. These superhydrophobic surfaces exhibit a constant advancing contact angle of θ(A)=150° over a broad range of contact angle hysteresis. As a result, the effect of contact angle hysteresis on droplet coalescence and mixing can be studied. Based on the observed characteristics of coalescence, three different regimes of coalescence are identified as a function of both Weber number and impact angle. These regimes include oscillation dominated, rotation dominated, and mixed dynamics. It is shown that within Weber number ranges achievable in this experiment, hysteresis greatly reduces the deformation of the droplet coalescence process and the subsequent mixing. In head-on collisions, higher hysteresis is found to decrease the frequency at which the resulting dr oscillates. In the case of glancing collisions, where the resulting droplet is found to rotate, higher hysteresis increases the rate of rotation although the overall angular momentum is found to be independent of contact angle hysteresis.
Study of contact angle hysteresis using the Cellular Potts Model.
Mortazavi, Vahid; D'Souza, Roshan M; Nosonovsky, Michael
2013-02-28
We use the Cellular Potts Model (CPM) to study the contact angle (CA) hysteresis in multiphase (solid-liquid-vapour) systems. We simulate a droplet over the tilted patterned surface, and a bubble placed under the surface immersed in liquid. The difference between bubbles and droplets was discussed through their CA hysteresis. Dependency of CA hysteresis on the surface structure and other parameters was also investigated. This analysis allows decoupling of the 1D (pinning of the triple line) and 2D (adhesion hysteresis in the contact area) effects and provides new insight into the nature of CA hysteresis.
Gunshot residue patterns on skin in angled contact and near contact gunshot wounds.
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.
Simulations of contact angle induced pearling for sliding drops
NASA Astrophysics Data System (ADS)
McCue, Scott; Mayo, Lisa; Moroney, Timothy
2015-11-01
Droplets sliding down an incline can develop a corner or a cusp at their rear, or undergo a pearling transition whereby the tail breaks up into a number of smaller satellite droplets. These phenomena have been of interest since the experimental work of. It appears that the experimental investigation of this problem is limited due to the inherent difficulty of minimising contact angle hysteresis, whereby physical or chemical heterogeneities of the substrate cause pinning and distortion of the droplet. By applying a lubrication model with a disjoining pressure term, we investigate these flows numerically in order to further shed light on how certain conditions (such as contact angle) affect the corner-cusp-pearling transition. We acknowledge support from the ARC Linkage Project LP100200476.
Lightweight autoclavable wide-angle contact lens for vitreous surgery.
Chalam, K V; Gupta, Shailesh K; Agarwal, Swati
2007-01-01
The authors describe an autoclavable, self-stabilizing, lightweight wide-angle contact lens for vitrectomy. The lens has two optical pieces with perforated plastic casing to sustain a high temperature (150 degrees C) for autoclaving. The lens has a 106 degrees static and 127 degrees dynamic field of view. The footplates and reduced weight (2.4 grams) due to the plastic casing allow self-stabilization of the lens. The open lens design.with high temperature resistant plastic prevents fogging during autoclaving and surgery. The autoclavable, self-stabilizing, lightweight wide-angle contact lens allows visualization of the peripheral retina during surgery and faster sterilization by autoclaving between surgeries without the disadvantage of lens fogging.
Brugnara, Marco; Della Volpe, Claudio; Penati, Amabile; Siboni, Stefano; Poli, Tommaso; Toniolo, Lucia
2003-11-01
The control of the protective efficacy obtained on the stone by treatments with polymers is commonly performed through the measure of the static contact angle as it is described by the norm UNI 10921. However this approach does not allow an easy interpretation of the results, because of the porosity and of the heterogeneity of the stone surface, which represent an obstacle to the analysis. Moreover the commonest interpretation of this technique can often bring to important errors. The measure of the static contact angle substantially corresponds to the measure of the so-called "advancing" contact angle and it allows only to verify if on the surface a hydrophobic material is present; unfortunately it cannot determine if the stone is effectively protected. Vice versa, both, the measure of the "true" equilibrium contact angle obtained through a new technique called VIECA, and the measure of the receding contact angle give more coherent parameters which better correlate with the data of absorption of water by capillarity. The equilibrium contact angle corresponds to an "average" description of the surface, the receding angle corresponds, by excess, to the condition of maximum penetration of the liquid by capillarity. From the knowledge of the equilibrium angle of the protective polymer and from the measure of the advancing and receding angles of the protected stone, it is certainly possible to determine what is the minimum polymer quantity to obtain an almost homogeneous stone protection.
Contact angle hysteresis on randomly rough surfaces: a computational study.
David, Robert; Neumann, A Wilhelm
2013-04-09
Wetting is important in many applications, and the solid surfaces being wet invariably feature some amount of surface roughness. A free energy-based computational simulation is used to study the effect of roughness on wetting and especially contact angle hysteresis. On randomly rough, self-affine surfaces, it is found that hysteresis depends primarily on the value of the Wenzel roughness parameter r, increasing in proportion with r - 1. Micrometer-level roughness causes hysteresis of a few degrees.
What is the contact angle of water on graphene?
Taherian, Fereshte; Marcon, Valentina; van der Vegt, Nico F A; Leroy, Frédéric
2013-02-05
Although experimental and theoretical studies have addressed the question of the wetting properties of graphene, the actual value of the contact angle of water on an isolated graphene monolayer remains unknown. While recent experimental literature indicates that the contact angle of water on graphite is in the range 90-95°, it has been suggested that the contact angle on graphene may either be as high as 127° or moderately enhanced in comparison with graphite. With the support of classical molecular dynamics simulations using empirical force-fields, we develop an argumentation to show that the value of 127° is an unrealistic estimate and that a value of the order of 95-100° should be expected. Our study establishes a connection between the variation of the work of adhesion of water on graphene-based surfaces and the interaction potential between individual water molecules and these surfaces. We show that a variation of the contact angle from 90° on graphite to 127° on graphene would imply that both of the first two carbon layers of graphite contribute approximately the same interaction energy with water. Such a situation is incompatible with the short-range nature of the interaction between water and this substrate. We also show that the interaction potential energy between water and the graphene-based substrates is the main contribution to the work of adhesion of water with a relative magnitude that is independent of the number of graphene layers. We introduce the idea that the remaining contribution is entropic in nature and is connected to the fluctuations in the water-substrate interaction energy.
Dynamic contact angle and three-phase contact line of water drop on copper surface
NASA Astrophysics Data System (ADS)
Orlova, E. G.; Feoktistov, D. V.; Batishcheva, K. A.
2015-10-01
Nowadays there is a lack of experimental data describing the physical process of drop spreading on a solid metal surface for developing wetting and spreading theory. The experimental data obtained by using the high speed video-recording will allow to identify unknown previously spreading modes as well as the change of the dynamic contact angle and the three-phase contact line. The purpose of the work is to determine the effect of the drop growth rate and the copper substrate surface roughness on the dynamic contact angle and the three-phase contact line speed at distilled water drop spreading. Shadow and Schlieren methods are used to obtain experimental data. Three drop spreading modes on the rough surfaces were identified. Time dependences of the dynamic contact angle and contact line speed were obtained. Experimental results can be used for assessing the validity of the developed mathematical models of wetting and spreading processes in the field of micro- and nanoelectronics, ink jet printing, thin-film coatings, spray cooling, and optoelectronics.
NASA Astrophysics Data System (ADS)
Pendota, Premchand
Many physical phenomena and industrial applications involve multiphase fluid flows and hence it is of high importance to be able to simulate various aspects of these flows accurately. The Dynamic Contact Angles (DCA) and the contact lines at the wall boundaries are a couple of such important aspects. In the past few decades, many mathematical models were developed for predicting the contact angles of the inter-face with the wall boundary under various flow conditions. These models are used to incorporate the physics of DCA and contact line motion in numerical simulations using various interface capturing/tracking techniques. In the current thesis, a simple approach to incorporate the static and dynamic contact angle boundary conditions using the level set method is developed and implemented in multiphase CFD codes, LIT (Level set Interface Tracking) (Herrmann (2008)) and NGA (flow solver) (Desjardins et al (2008)). Various DCA models and associated boundary conditions are reviewed. In addition, numerical aspects such as the occurrence of a stress singularity at the contact lines and grid convergence of macroscopic interface shape are dealt with in the context of the level set approach.
Wetting angles of rigid contact lens plastics: the effect of contact lens wear.
Poster, M G; Gelfer, D M; Fernandez, N M
1986-06-01
Several adapted rigid contact lens wearers were given duplicates of their present lenses made in different plastics. They were required to wear each material on each eye for a period of four hours. Both the average wetting angle and its range of values for each material was compiled. All lenses tended to give similar average wetting angles but ranges of angles for the PMMA/siloxanyl materials were greater than that for PMMA and GP IITM. Both values should be utilized when evaluating the wettability of a specific material.
Bormashenko, Edward; Bormashenko, Yelena; Whyman, Gene; Pogreb, Roman; Musin, Albina; Jager, Rachel; Barkay, Zahava
2008-04-15
The effect of contact angle hysteresis (CAH) was studied on various polymer substrates with traditional and new experimental techniques. The new experimental technique presented in the article is based on the slow deformation of the droplet, thus CAH is studied under the constant volume of the drop in contrast to existing techniques when the volume of the drop is changed under the measurement. The energy of hysteresis was calculated in the framework of the improved Extrand approach. The advancing contact angle established with a new technique is in a good agreement with that measured with the needle-syringe method. The receding angles measured with three experimental techniques demonstrated a very significant discrepancy. The force pinning the triple line responsible for hysteresis was calculated.
Characterizing the microscopic physics near moving contact lines using dynamic contact angle data.
Ramé, E; Garoff, S; Willson, K R
2004-09-01
Directly probing the fluid flow and liquid-vapor interface shape in the microscopic immediate vicinity of the moving contact line can only be accomplished in very specific and isolated cases. Yet this physics is critical to macroscopic dynamic wetting. Here we examine the microscopic (or inner) physics of spreading silicone fluids using data of macroscopic dynamic contact angle versus Capillary number Ca=U mu/sigma. This dynamic contact angle is precisely defined so that it can be related back to the microscopic behavior through detailed theory. Our results indicate that the parameters describing the inner region have a detectable dependence on spreading velocity when this velocity exceeds a critical value. This dependence is not scaled (i.e., the data are not collapsed) by Ca, which suggests that an additional time scale must be present in the model of the inner region.
Contact angle hysteresis generated by strong dilute defects.
Reyssat, Mathilde; Quéré, David
2009-03-26
Water on solid decorated with hydrophobic defects (such as micropillars) often stays at the top of the defects in a so-called fakir state, which explains the superhydrophobicity observed in such case, provided that the density of defects is small enough. Here we show that this situation provides an ideal frame for studying the contact angle hysteresis; the phase below the liquid is "perfect" and slippery (it is air), contrasting with pillars' tops whose edges form strong pining sites for the contact line. This model system thus allows us to study the hysteresis as a function of the density of defects and to compare it to the classical theory by Joanny and de Gennes, which is based on very similar hypothesis.
Surface tension and contact angles: Molecular origins and associated microstructure
NASA Technical Reports Server (NTRS)
Davis, H. T.
1982-01-01
Gradient theory converts the molecular theory of inhomogeneous fluid into nonlinear boundary value problems for density and stress distributions in fluid interfaces, contact line regions, nuclei and microdroplets, and other fluid microstructures. The relationship between the basic patterns of fluid phase behavior and the occurrence and stability of fluid microstructures was clearly established by the theory. All the inputs of the theory have molecular expressions which are computable from simple models. On another level, the theory becomes a phenomenological framework in which the equation of state of homogeneous fluid and sets of influence parameters of inhomogeneous fluids are the inputs and the structures, stress tensions and contact angles of menisci are the outputs. These outputs, which find applications in the science and technology of drops and bubbles, are discussed.
Contact angle of a hemispherical bubble: an analytical approach.
Teixeira, M A C; Teixeira, P I C
2009-10-01
We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace's equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity.
Contact angles of surfactant solutions on heterogeneous surfaces.
Milne, A J B; Elliott, J A W; Amirfazli, A
2015-02-28
Using Gibbs' adsorption equation and a literature isotherm, a new general model to predict the contact angle of surfactant solutions on (smooth or rough) chemically heterogeneous surfaces is constructed based on the Cassie equation. The model allows for adsorption at the liquid-vapor, solid-liquid, and solid-vapor interfaces. Solid-vapor adsorption is allowed in order to model the autophobic effect on hydrophilic surfaces. Using representative values for the coefficients which describe adsorption at each interface, model predictions for contact angles as a function of f parameters (area fractions) and surfactant concentration are made for heterogeneous surfaces made up of different materials. On smooth surfaces, the f parameters serve as weighting factors determining how to combine the effects of surfactant adsorption on each material to predict the behavior on the heterogeneous surface. Due to the non-linear nature of the model, the inclusion of a small amount of hydrophobic material has a greater effect on a predominantly hydrophilic material than vice versa, explaining the result seen in literature that a small amount of hydrophobic contamination (such as oil) significantly increases contact angle on a hydrophilic surface. The fact that even a small amount of heterogeneity can greatly change experimental results could lead to incorrect experimental conclusions about surfactant adsorption if a surface were wrongly assumed to be homogeneous. Model predictions rapidly become more complex as the number of differently wettable materials present on the surface increases. Also, an approximately equal weighting of different materials generally leads to more complex behaviors compared to heterogeneous surfaces composed largely of a single material. Rough heterogeneous surfaces follow previous results for surfactant wetting of rough homogeneous surfaces, leading to an amplification/attenuation of surfactant effects for penetrated/unpenetrated wetting, and further
Contact angle dependence of the resonant properties of sessile drops
NASA Astrophysics Data System (ADS)
Sharp, James
2012-02-01
A simple optical deflection technique was used to monitor the vibrations of microlitre sessile drops of glycerol/water mixtures with glycerol compositions ranging from 0% to 75%. A photodiode was used to detect time dependent variations in the intensity of laser light reflected from the droplets. The intensity variations were Fourier transformed to obtain information about the resonant properties of the drops (frequency and width of the resonance). These experiments were performed on a range of different substrates where the contact angle formed by the droplets varied between 38±2^o and 160±4^o. The measured resonant frequency values were found to be in agreement with a recently developed theory of vibrations which considers standing wave states along the profile length of the droplet. The widths of the resonances were also compared with theories which predict the influence of substrate effects, surface contamination effects and bulk viscous effects on the damping of capillary waves at the free surface of the droplets. These experiments indicate that the dominant source of damping in sessile liquid droplet is due to bulk viscous effects but that for small contact angles damping due to the droplet/substrate interaction becomes more important.
Capillary Contact Angle in a Completely Wet Groove
NASA Astrophysics Data System (ADS)
Parry, A. O.; Malijevský, A.; Rascón, C.
2014-10-01
We consider the phase equilibria of a fluid confined in a deep capillary groove of width L with identical side walls and a bottom made of a different material. All walls are completely wet by the liquid. Using density functional theory and interfacial models, we show that the meniscus separating liquid and gas phases at two phase capillary coexistence meets the bottom capped end of the groove at a capillary contact angle θcap(L) which depends on the difference between the Hamaker constants. If the bottom wall has a weaker wall-fluid attraction than the side walls, then θcap>0 even though all the isolated walls are themselves completely wet. This alters the capillary condensation transition which is now first order; this would be continuous in a capped capillary made wholly of either type of material. We show that the capillary contact angle θcap(L) vanishes in two limits, corresponding to different capillary wetting transitions. These occur as the width (i) becomes macroscopically large, and (ii) is reduced to a microscopic value determined by the difference in Hamaker constants. This second wetting transition is characterized by large scale fluctuations and essential critical singularities arising from marginal interfacial interactions.
Hydrophilic property by contact angle change of ion implanted polycarbonate.
Lee, Chan Young; Kil, Jae Keun
2008-02-01
In this study, ion implantation was performed onto a polymer, polycarbonate (PC), in order to investigate surface hydrophilic property through contact angle measurement. PC was irradiated with N, Ar, and Xe ions at the irradiation energy of 20-50 keV and the dose range of 5x10(15), 1x10(16), 7x10(16) ions/cm(2). The contact angle of water was estimated by means of the sessile drop method and was reduced with increasing fluence and ion mass but increased with increasing implanted energy. The changes of chemical and structural properties are discussed in view of Furier transform infrared and x-ray photoelectron spectroscopy, which shows increasing C-O bonding and C-C bonding. The surface roughness examined by atomic force microscopy measurement changed smoothly from 3.59 to 2.22 A as the fluence increased. It is concluded that the change in wettability may be caused by surface carbonization and oxidation as well as surface roughness.
Hydrophilic property by contact angle change of ion implanted polycarbonatea)
NASA Astrophysics Data System (ADS)
Lee, Chan Young; Kil, Jae Keun
2008-02-01
In this study, ion implantation was performed onto a polymer, polycarbonate (PC), in order to investigate surface hydrophilic property through contact angle measurement. PC was irradiated with N, Ar, and Xe ions at the irradiation energy of 20-50keV and the dose range of 5×1015, 1×1016, 7×1016ions/cm2. The contact angle of water was estimated by means of the sessile drop method and was reduced with increasing fluence and ion mass but increased with increasing implanted energy. The changes of chemical and structural properties are discussed in view of Furier transform infrared and x-ray photoelectron spectroscopy, which shows increasing C O bonding and C C bonding. The surface roughness examined by atomic force microscopy measurement changed smoothly from 3.59to2.22Å as the fluence increased. It is concluded that the change in wettability may be caused by surface carbonization and oxidation as well as surface roughness.
Capillary contact angle in a completely wet groove.
Parry, A O; Malijevský, A; Rascón, C
2014-10-03
We consider the phase equilibria of a fluid confined in a deep capillary groove of width L with identical side walls and a bottom made of a different material. All walls are completely wet by the liquid. Using density functional theory and interfacial models, we show that the meniscus separating liquid and gas phases at two phase capillary coexistence meets the bottom capped end of the groove at a capillary contact angle θ(cap)(L) which depends on the difference between the Hamaker constants. If the bottom wall has a weaker wall-fluid attraction than the side walls, then θ(cap) > 0 even though all the isolated walls are themselves completely wet. This alters the capillary condensation transition which is now first order; this would be continuous in a capped capillary made wholly of either type of material. We show that the capillary contact angle θ(cap)(L) vanishes in two limits, corresponding to different capillary wetting transitions. These occur as the width (i) becomes macroscopically large, and (ii) is reduced to a microscopic value determined by the difference in Hamaker constants. This second wetting transition is characterized by large scale fluctuations and essential critical singularities arising from marginal interfacial interactions.
Effect of flow field and geometry on the dynamic contact angle.
Lukyanov, A V; Shikhmurzaev, Y D
2007-05-01
A number of recent experiments suggest that, at a given wetting speed, the dynamic contact angle formed by an advancing liquid-gas interface with a solid substrate depends on the flow field and geometry near the moving contact line. In the present work, this effect is investigated in the framework of an earlier developed theory that was based on the fact that dynamic wetting is, by its very name, a process of formation of a new liquid-solid interface (newly "wetted" solid surface) and hence should be considered not as a singular problem but as a particular case from a general class of flows with forming or/and disappearing interfaces. The results demonstrate that, in the flow configuration of curtain coating, where a liquid sheet ("curtain") impinges onto a moving solid substrate, the actual dynamic contact angle indeed depends not only on the wetting speed and material constants of the contacting media, as in the so-called slip models, but also on the inlet velocity of the curtain, its height, and the angle between the falling curtain and the solid surface. In other words, for the same wetting speed the dynamic contact angle can be varied by manipulating the flow field and geometry near the moving contact line. The obtained results have important experimental implications: given that the dynamic contact angle is determined by the values of the surface tensions at the contact line and hence depends on the distributions of the surface parameters along the interfaces, which can be influenced by the flow field, one can use the overall flow conditions and the contact angle as a macroscopic multiparametric signal-response pair that probes the dynamics of the liquid-solid interface. This approach would allow one to investigate experimentally such properties of the interface as, for example, its equation of state and the rheological properties involved in the interface's response to an external torque, and would help to measure its parameters, such as the coefficient of
Advanced high efficiency wraparound contact solar cell
NASA Technical Reports Server (NTRS)
Scott-Monck, J. A.; Uno, F. M.; Thornhill, J. W.
1977-01-01
A significant advancement in the development of thin high efficiency wraparound contact silicon solar cells has been made by coupling space and terrestrial processing procedures. Although this new method for fabricating cells has not been completely reduced to practice, some of the initial cells have delivered over 20 mW/sq cm when tested at 25 C under AMO intensity. This approach not only yields high efficiency devices, but shows promise of allowing complete freedom of choice in both the location and size of the wraparound contact pad area
Advanced high efficiency wraparound contact solar cell
NASA Technical Reports Server (NTRS)
Scott-Monck, J. A.; Uno, F. M.; Thornhill, J. W.
1977-01-01
A significant advancement in the development of thin high efficiency wraparound contact silicon solar cells has been made by coupling space and terrestrial processing procedures. Although this new method for fabricating cells has not been completely reduced to practice, some of the initial cells have delivered over 20 mW/sq cm when tested at 25 C under AMO intensity. This approach not only yields high efficiency devices, but shows promise of allowing complete freedom of choice in both the location and size of the wraparound contact pad area.
In Situ Local Contact Angle Measurement in a CO2-Brine-Sand System Using Microfocused X-ray CT.
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, CO2 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 CO2-brine-sand system under various conditions. The effects of ionic strength, CO2 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 CO2 (gCO2) turns into supercritical CO2 (scCO2). Contact angle hysteresis also occurred between drainage and imbibition procedures, and the hysteresis was more significant under gCO2 condition.
The effect of contact angle hysteresis on droplet motion and collisions on superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Nilsson, Michael; Rothstein, Jonathan
2010-11-01
The effect of varying the contact angle hysteresis of a superhydrophobic surface on the characteristics and dynamics of water droplet motion and their subsequent collision are investigated using a high-speed camera. The surfaces are created by imparting random roughness to Teflon through sanding. With this technique, it is possible to create surfaces with similar advancing contact angles near 150 degrees, but with varying contact angle hysteresis. This talk will focus on a number of interesting experimental observations pertaining to drop dynamics along a surface with uniform hysteresis, drop motion along surfaces with transition zones from one hysteresis to another, and the collision of droplets on surfaces of uniform hysteresis. For single drop studies, gravity is used as the driving force, while the collision studies use pressurized air to propel one drop into the other. For the case of droplet collision, the effect of hysteresis, Weber number, and impact number on the maximum deformation of the drops, and the post-collision dynamics will be discussed. For the single droplet measurements, the resistance to motion will be characterized as well as the transition from rolling to sliding as a function of drop size, inclination angle, and hysteresis. Additionally, we will quantify the effect of surface transitions on the resulting motion, mixing, and deflection of the drops.
Comparison of contact angle hysteresis of different probe liquids on the same solid surface.
Chibowski, Emil; Jurak, Malgorzata
2013-02-01
Advancing and receding contact angles of water, formamide and diiodomethane were measured on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on three different solid supports-glass, mica and poly(methyl methacrylate). Up to five statistical monolayers were deposited on the surfaces by spreading DPPC solution. It was found that even on five statistical DPPC monolayers, the hysteresis of a given liquid depends on the kind of solid support. Also on the same solid support the contact angle hysteresis is different for each probe liquid used. The AFM images show that the heights of roughness of the DPPC films cannot be the primary cause of the observed hysteresis because the heights are too small to cause the observed hystereses. It is believed that the hysteresis is due to the liquid film present right behind the three-phase solid surface/liquid drop/gas (vapour) contact line and the presence of Derjaguin pressure. The value of contact angle hysteresis depends on both the solid surface and liquid properties as well as on intermolecular interactions between them.
Lattice boltzmann study on the contact angle and contact line dynamics of liquid-vapor interfaces.
Zhang, Junfeng; Kwok, Daniel Y
2004-09-14
The moving contact line problem of liquid-vapor interfaces was studied using a mean-field free-energy lattice Boltzmann method recently proposed [Phys. Rev. E 2004, 69, 032602]. We have examined the static and dynamic interfacial behaviors by means of the bubble and capillary wave tests and found that both the Laplace equation of capillarity and the dispersion relation were satisfied. Dynamic contact angles followed the general trend of contact line velocity observed experimentally and can be described by Blake's theory. The velocity fields near the interface were also obtained and are in good agreement with fluid mechanics and molecular dynamics studies. Our simulations demonstrated that incorporating interfacial effects into the lattice Boltzmann model can be a valuable and powerful alternative in interfacial studies.
Porous media characterization by the two-liquid method: effect of dynamic contact angle and inertia.
Lavi, Becky; Marmur, Abraham; Bachmann, Joerg
2008-03-04
The validity of using the Lucas-Washburn (LW) equation for porous media characterization by the two-liquid capillary penetration method was tested numerically and experimentally. A cylindrical capillary of known radius and contact angle was used as a model system for the tests. It was found that using the LW equation (i.e., ignoring inertia and dynamic contact angle effects) may lead to very erroneous assessment of the capillary radius and the equilibrium contact angle, for a relatively wide range of capillary radii and equilibrium contact angles. A correct assessment requires the application of a penetration kinetics equation that considers inertia and the dynamic contact angle.
Effect of contact angle on the orientation, stability, and assembly of dense floating cubes.
Daniello, Robert; Khan, Kashan; Donnell, Michael; Rothstein, Jonathan P
2014-02-01
In this paper, the effect of contact angle, density, and size on the orientation, stability, and assembly of floating cubes was investigated. All the cubes tested were more dense than water. Floatation occurred as a result of capillary stresses induced by deformation of the air-water interface. The advancing contact angle of the bare acrylic cubes was measured to be 85°. The contact angle of the cubes was increased by painting the cubes with a commercially available superhydrophobic paint to reach an advancing contact angle of 150°. Depending on their size, density, and contact angle, the cubes were observed to float in one of three primary orientations: edge up, vertex up, and face up. An experimental apparatus was built such that the sum of the gravitational force, buoyancy force, and capillary forces could be measured using a force transducer as a function of cube position as it was lowered through the air-water interface. Measurements showed that the maximum capillary forces were always experienced for the face up orientation. However, when floatation was possible in the vertex up orientation, it was found to be the most stable cube orientation because it had the lowest center of gravity. A series of theoretical predictions were performed for the cubes floating in each of the three primary orientations to calculate the net force on the cube. The theoretical predictions were found to match the experimental measurements well. A cube stability diagram of cube orientation as a function of cube contact angle and size was prepared from the predictions of theory and found to match the experimental observations quite well. The assembly of cubes floating face up and vertex up were also studied for assemblies of two, three, and many cubes. Cubes floating face up were found to assemble face-to-face and form regular square lattice patterns with no free interface between cubes. Cubes floating vertex up were found to assemble in a variety of different arrangements
Water slippage versus contact angle: a quasiuniversal relationship.
Huang, David M; Sendner, Christian; Horinek, Dominik; Netz, Roland R; Bocquet, Lydéric
2008-11-28
Using molecular dynamics simulations of an atomistic water model, we study the interfacial hydrodynamic slippage of water at various hydrophobic surfaces, both organic (silane monolayers) and inorganic (diamondlike and Lennard-Jones models). The measured slip lengths range from nanometers to tens of nanometers. Slip lengths on different surfaces are found to collapse nearly onto a single curve as a function of the static contact angle characterizing the surface wettability, thereby suggesting a quasiuniversal relationship. This dependence is rationalized on the basis of a simple scaling description of the fluid-solid friction at the microscopic level. The link between slippage and water depletion at hydrophobic surfaces is clarified. These results shed light on the controversy over experimental measurements of the slip length at smooth hydrophobic surfaces.
Choi, Wonjae; Tuteja, Anish; Mabry, Joseph M; Cohen, Robert E; McKinley, Gareth H
2009-11-01
The Cassie-Baxter model is widely used to predict the apparent contact angles obtained on composite (solid-liquid-air) superhydrophobic interfaces. However, the validity of this model has been repeatedly challenged by various research groups because of its inherent inability to predict contact angle hysteresis. In our recent work, we have developed robust omniphobic surfaces which repel a wide range of liquids. An interesting corollary of constructing such surfaces is that it becomes possible to directly image the solid-liquid-air triple-phase contact line on a composite interface, using an electron microscope with non-volatile organic liquids or curable polymers. Here, we fabricate a range of model superoleophobic surfaces with controlled surface topography in order to correlate the details of the local texture with the experimentally observed apparent contact angles. Based on these experiments, in conjunction with numerical simulations, we modify the classical Cassie-Baxter relation to include a local differential texture parameter which enables us to quantitatively predict the apparent advancing and receding contact angles, as well as contact angle hysteresis. This quantitative prediction also allows us to provide an a priori estimation of roll-off angles for a given textured substrate. Using this understanding we design model substrates that display extremely small or extremely large roll-off angles, as well as surfaces that demonstrate direction-dependent wettability, through a systematic control of surface topography and connectivity.
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.
Ultrasonic estimation of the contact angle of a sessile droplet
Quintero, R.; Simonetti, F.
2014-02-18
Radiation of energy by large amplitude leaky Rayleigh waves is regarded as one of the key physical mechanisms regulating the actuation and manipulation of droplets in surface acoustic wave (SAW) microfluidic devices. The interaction between a SAW and a droplet is highly complex and is presently the subject of extensive research. This paper investigates the existence of an additional interaction mechanism based on the propagation of quasi-Stoneley waves inside sessile droplets deposited on a solid substrate. In contrast with the leaky Rayleigh wave, the energy of the Stoneley wave is confined within a thin fluid layer in contact with the substrate. The hypothesis is confirmed by three-dimensional finite element simulations and ultrasonic scattering experiments measuring the reflection of Rayleigh waves from droplets of different diameters. Moreover, real-time monitoring of the droplet evaporation process reveals a clear correlation between the droplet contact angle and the spectral information of the reflected Rayleigh signal, thus paving the way for ultrasonic measurements of surface tension.
Chaudhuri, Rajib Ghosh; Paria, Santanu
2009-09-15
This study presents the experimental results on dynamic contact angles of pure surfactants and surfactants with electrolyte solutions on PTFE (Teflon) surface. Dynamic advancing (theta(A)) and receding (theta(R)) contact angles measurements by the Wilhelmy plate technique were carried out for aqueous solution of three different surfactants Triton X-100 (TX-100), sodium dodecylbenzene sulfonate (SDBS), and cetyltrimethylammonium bromide (CTAB). The same measurements in the presence of different electrolytes NaCl, Na(2)SO(4), and CaCl(2) for ionic surfactants (SDBS and CTAB) were also carried out to see the change in contact angle and wetting behavior. The presence of electrolytes changes the advancing contact angle as well as wetting properties of hydrophobic solid surface significantly even at very low surfactant concentration. Counter ion valency of the electrolyte is more important in reducing advancing contact angle on hydrophobic PTFE surface at very low concentration of ionic surfactants from CMC. Pure surfactants and ionic surfactants in the presence of electrolytes show a linear relationship between the adhesional tension and surface tension at air-water interface with different slope and intercept.
Chibowski, Emil J
2005-05-30
Using the literature data of the advancing and receding contact angles for water, diiodomethane and hexadecane measured on various hydrophobic silyl layers (mostly monolayers) produced on silicon wafers the apparent surface free energies gamma(s)(tot) were calculated by applying new model of the contact angle hysteresis interpretation. It was found that, for the same silyl layer, the calculated gamma(s)(tot) values to some degree depended on the probe liquid used. Therefore, thus calculated the surface free energies should be considered as apparent ones. Moreover, also the values of the dispersion component gamma(s)(d) of these layers depend on the probe liquid used, but to a less degree. This must be due to the strength of the force field originating from the probe liquid and the spacing between the interacting molecules. The relationships between gamma(s)(tot) and gamma(s)(d) are discussed on the basis of the equations derived. It may be postulated that applying proposed model of the contact angle hysteresis and calculating the apparent total surface free energies and the dispersion contributions better insight into wetting properties of the silyled silicon surface can be achieved.
Zhang, Bo; Wang, Jianjun; Liu, Zhiping; Zhang, Xianren
2014-01-01
The application of Cassie equation to microscopic droplets is recently under intense debate because the microdroplet dimension is often of the same order of magnitude as the characteristic size of substrate heterogeneities, and the mechanism to describe the contact angle of microdroplets is not clear. By representing real surfaces statistically as an ensemble of patterned surfaces with randomly or regularly distributed heterogeneities (patches), lattice Boltzmann simulations here show that the contact angle of microdroplets has a wide distribution, either continuous or discrete, depending on the patch size. The origin of multiple contact angles observed is ascribed to the contact line pinning effect induced by substrate heterogeneities. We demonstrate that the local feature of substrate structure near the contact line determines the range of contact angles that can be stabilized, while the certain contact angle observed is closely related to the contact line width. PMID:25059292
Apparent and Actual Dynamic Contact Angles in Confined Two-Phase Flows
NASA Astrophysics Data System (ADS)
Omori, Takeshi; Kajishima, Takeo
2016-11-01
To accurately predict the fluid flow with moving contact lines, it has a crucial importance to use a model for the dynamic contact angle which gives contact angles on the length scale corresponding to the spacial resolution of the fluid solver. The angle which a moving fluid interface forms to a solid surface deviates from an actual (microscopic) dynamic contact angle depending on the distance from the contact line and should be called an apparent (macroscopic) dynamic contact angle. They were, however, often undistinguished especially in the experimental works, on which a number of empirical correlations between a contact angle and a contact line velocity have been proposed. The present study is the first attempt to measure both apparent and actual contact angles from the identical data sets to discuss the difference and the relationship between these two contact angles of difference length scales. The study is conducted by means of numerical simulation, solving the Navier-Stokes equation and the Cahn-Hilliard equation under the generalized Navier boundary condition for the immiscible two-phase flow in channels. The present study also illustrates how the system size and the physical properties of the adjoining fluid affect the apparent and the actual dynamic contact angles. JSPS KAKENHI Grant No. 15K17974.
Motion of an isolated liquid plug inside a capillary tube: effect of contact angle hysteresis
NASA Astrophysics Data System (ADS)
Srinivasan, Vyas; Khandekar, Sameer; Bouamrane, Nathan; Lefevre, Frederic; Bonjour, Jocelyn
2015-01-01
Dynamics of a single, small and isolated partially wetting liquid plug (of known length L and wettability), placed at rest inside a long, dry, circular capillary tube ( D = 1.5 mm), and subsequently quasi-statically pushed from one end by applying air pressure, the other end being kept exposed to atmosphere, are reported. The air pressure first overcomes the `static' friction manifested by the three-phase contact line at the advancing and receding menisci, and then, the plug motion gets initiated, eventually leading to a terminal velocity (Ca ~ 2.8 × 10-5), when pressure force balances net frictional resistance due to viscous and surface forces. It is seen that, under steady motion, the curvature profiles of the advancing and receding menisci of liquid plug, respectively, remain the same, independent of the plug length. Steady-state pressure drop is dominated by the contribution due to contact angle hysteresis, which is also independent of the plug length. Increasing the system wettability drastically decreased the contact angle hysteresis and the associated net pressure drop.
Dynamic contact angle in rim instability of dewetting holes.
Choi, Sung-Hwan; Newby, Bi-min Zhang
2006-02-07
The effects of dynamic contact angle (thetad), between a substrate and the melt of a dewetting polymer thin film, on the evolution of rim instabilities of dewetting holes were reported. Various thetad's were achieved by covering SiOx surfaces with different coverage of octadecyltrichlorosilane. On each surface, the morphology of the dewetting holes was examined in detail as the hole grew to a certain size. Rim instabilities, in terms of undulations in both r and z directions, became more pronounced as thetad increased, under which condition, narrower and higher rims were also observed. Experimentally, atomic force microscopic scans of the rim were used to obtain the rim profile, which was predicted using thetad. The predicted rim profile was used, in combination with the analysis of Rayleigh instability of a cylindrical fluid, to interpret the rim instability. The model captures the basic trend of the rim instability dependency on thetad. The study demonstrates the importance of the substrate properties on the rim instability and the destabilization of polymer thin films during hole growth.
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
A method to measure internal contact angle in opaque systems by magnetic resonance imaging.
Zhu, Weiqin; Tian, Ye; Gao, Xuefeng; Jiang, Lei
2013-07-23
Internal contact angle is an important parameter for internal wettability characterization. However, due to the limitation of optical imaging, methods available for contact angle measurement are only suitable for transparent or open systems. For most of the practical situations that require contact angle measurement in opaque or enclosed systems, the traditional methods are not effective. Based upon the requirement, a method suitable for contact angle measurement in nontransparent systems is developed by employing MRI technology. In the Article, the method is demonstrated by measuring internal contact angles in opaque cylindrical tubes. It proves that the method also shows great feasibility in transparent situations and opaque capillary systems. By using the method, contact angle in opaque systems could be measured successfully, which is significant in understanding the wetting behaviors in nontransparent systems and calculating interfacial parameters in enclosed systems.
Heshmati, Mohammad; Piri, Mohammad
2014-12-02
An extensive experimental study of the kinetics of capillary rise in borosilicate glass tubes of different sizes and cross-sectional shapes using various fluid systems and tube tilt angles is presented. The investigation is focused on the direct measurement of dynamic contact angle and its variation with the velocity of the moving meniscus (or capillary number) in capillary rise experiments. We investigated this relationship for different invading fluid densities, viscosities, and surface tensions. For circular tubes, the measured dynamic contact angles were used to obtain rise-versus-time values that agree more closely with their experimental counterparts (also reported in this study) than those predicted by Washburn equation using a fixed value of contact angle. We study the predictive capabilities of four empirical correlations available in the literature for velocity-dependence of dynamic contact angle by comparing their predicted trends against our measured values. We also present measurements of rise in noncircular capillary tubes where rapid advancement of arc menisci in the corners ahead of main terminal meniscus impacts the dynamics of rise. Using the extensive set of experimental data generated in this study, a new general empirical trend is presented for variation of normalized rise with dynamic contact angle that can be used in, for instance, dynamic pore-scale models of flow in porous media to predict multiphase flow behavior.
Effect of moisture equilibration time and medium on contact angles of bacterial spores.
Eschlbeck, Elisabeth; Kulozik, Ulrich
2017-04-01
Contact angle measurement of microorganisms is often described in literature, either to investigate their hydrophobic characteristic or the adhesion behavior of cells. However, in some key aspects the preparation methods differ. Thus, it is difficult to compare results and to choose a procedure for repetition of measurements. The aim of this paper is to point out some critical points during microorganism film preparation that can alter the resulting contact angles. Depending on the moisturizing medium and equilibration time, contact angles differ significantly.
Geysers advanced direct contact condenser research
Henderson, J.; Bahning, T.; Bharathan, D.
1997-12-31
The first geothermal application of the Advanced Direct Contact Condenser (ADCC) technology developed by the National Renewable Energy Laboratory (NREL) is now operational and is being tested at The Geysers Power Plant Unit 11. This major research effort is being supported through the combined efforts of NREL, The Department of Energy (DOE), and Pacific Gas and Electric (PG&E). NREL and PG&E have entered into a Cooperative Research And Development Agreement (CRADA) for a project to improve the direct-contact condenser performance at The Geysers Power Plant. This project is the first geothermal adaptation of an advanced condenser design developed for the Ocean Thermal Energy Conversion (OTEC) systems. PG&E expects this technology to improve power plant performance and to help extend the life of the steam field by using steam more efficiently. In accordance with the CRADA, no money is transferred between the contracting parties. In this case the Department of Energy is funding NREL for their efforts in this project and PG&E is contributing funds in kind. Successful application of this technology at The Geysers will provide a basis for NREL to continue to develop this technology for other geothermal and fossil power plant systems.
NASA Astrophysics Data System (ADS)
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), 10.1017/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
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
Technique to measure contact angle of micro/nanodroplets using atomic force microscopy
Jung, Yong Chae; Bhushan, Bharat
2008-07-15
Contact angle is the primary parameter that characterizes wetting; however, the measurement techniques have been limited to droplets with a diameter as low as about 50 {mu}m. The authors developed an atomic force microscopy-based technique to measure the contact angle of micro- and nanodroplets deposited using a modified nanoscale dispensing tip. The obtained contact angle results were compared with those of a macrodroplet (2.1 mm diameter). It was found that the contact angle on various surfaces decreases with decreasing the droplet size.
Kleingartner, Justin A; Srinivasan, Siddarth; Mabry, Joseph M; Cohen, Robert E; McKinley, Gareth H
2013-11-05
Goniometric techniques traditionally quantify two parameters, the advancing and receding contact angles, that are useful for characterizing the wetting properties of a solid surface; however, dynamic tensiometry, which measures changes in the net force on a surface during the repeated immersion and emersion of a solid into a probe liquid, can provide further insight into the wetting properties of a surface. We detail a framework for analyzing tensiometric results that allows for the determination of wetting hysteresis, wetting state transitions, and characteristic topographical length scales on textured, nonwetting surfaces, in addition to the more traditional measurement of apparent advancing and receding contact angles. Fluorodecyl POSS, a low-surface-energy material, was blended with commercially available poly(methyl methacrylate) (PMMA) and then dip- or spray-coated onto glass substrates. These surfaces were probed with a variety of liquids to illustrate the effects of probe liquid surface tension, solid surface chemistry, and surface texture on the apparent contact angles and wetting hysteresis of nonwetting surfaces. Woven meshes were then used as model structured substrates to add a second, larger length scale for the surface texture. When immersed into a probe liquid, these spray-coated mesh surfaces can form a metastable, solid-liquid-air interface on the largest length scale of surface texture. The increasing hydrostatic pressure associated with progressively greater immersion depths disrupts this metastable, composite interface and forces penetration of the probe liquid into the mesh structure. This transition is marked by a sudden change in the wetting hysteresis, which can be systematically probed using spray-coated, woven meshes of varying wire radius and spacing. We also show that dynamic tensiometry can accurately and quantitatively characterize topographical length scales that are present on microtextured surfaces.
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.
Dissolution-induced contact angle modification in dense nonaqueous phase liquid/water systems.
Mohammad, Orphius I; Kibbey, Tohren C G
2005-03-15
The contact angle between DNAPL, water, and aquifer material interfaces influences the spatial distribution of DNAPLs as they infiltrate into the aquifer, and may ultimately influence their remediation. The objective of this work was to evaluate the effects of dissolution on contact angle. Just as physically retracting a sessile drop reduces its contact angle with a surface, it was speculated that dissolution could cause contact angles to be reduced. Long-term dissolution experiments were conducted over the course of days to weeks, examining the dissolution of sessile drops of two DNAPLs, trichloroethylene (TCE) and tetrachloroethylene (PCE), in water and low concentration surfactant solutions, on glass surfaces. Experiments found that dissolution led to a continuous decrease of contact angle measured through the DNAPL drop, in most cases to near 0 degrees, far lower than angles achievable through measurements of receding contact angles for the same systems. Pinning of drop contact diameter was observed in most experiments. A model developed on the basis of the Bashforth-Adams equation to predict the effect of dissolution on contact angle for drops with a pinned contact diameter showed very good agreement with experimental observations.
NASA Astrophysics Data System (ADS)
Kamusewitz, H.; Possart, W.
The influence of the surface roughness of polypropylene on the contact angle hysteresis is investigated by means of ethylene glycol drops in order to estimate the true Young's equilibrium contact angle. A new relationship between the contact angle hysteresis and Wenzel's contact angle is derived. In addition, the determination of Wenzel's roughness factor by means of scanning force microscopy opens an alternative way to obtaining Young's equilibrium contact angle without any surface manipulation. The experimental results presented verify this new approach.
Wege, Hartmut Alexander; Aguilar, José Arturo; Rodríguez-Valverde, Miguel Angel; Toledano, Manuel; Osorio, Raquel; Cabrerizo-Vílchez, Miguel Angel
2003-07-01
A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other.
Ramé; Garoff
1996-01-15
We have studied shapes of dynamic fluid interfaces at distances contact line at capillary numbers (Ca) ranging from 10(-3) to 10(-1). Near the moving contact line where viscous deformation is important, an analysis valid to O(1) in Ca describes the shape of the fluid interface. Static capillarity should describe the interface shape far from the contact line. We have quantitatively determined the extent of the regions described by the analysis with viscous deformation and by a static shape as a function of Ca. We observe a third portion of the interface between the two regions cited above, which is not described by either the analysis with viscous deformation or a static shape. In this third region the interface shape is controlled by viscous and gravitational forces of comparable magnitude. We detect significant viscous deformation even far from the contact line at Ca approximately > 0.01. Our measured dynamic contact angle parameter extracted by fitting the analysis with viscous deformation to the shape near the moving contact line coincides with the contact angle of the static-like shape far from the contact line. We measure and explain the discrepancy between this dynamic contact angle parameter and the apparent contact angles based on meniscus or apex heights. Our observations of viscous effects at large distances from the contact line have implications for dynamic contact angle measurements in capillary tubes.
Investigation of the Dynamic Contact Angle Using a Direct Numerical Simulation Method.
Zhu, Guangpu; Yao, Jun; Zhang, Lei; Sun, Hai; Li, Aifen; Shams, Bilal
2016-11-15
A large amount of residual oil, which exists as isolated oil slugs, remains trapped in reservoirs after water flooding. Numerous numerical studies are performed to investigate the fundamental flow mechanism of oil slugs to improve flooding efficiency. Dynamic contact angle models are usually introduced to simulate an accurate contact angle and meniscus displacement of oil slugs under a high capillary number. Nevertheless, in the oil slug flow simulation process, it is unnecessary to introduce the dynamic contact angle model because of a negligible change in the meniscus displacement after using the dynamic contact angle model when the capillary number is small. Therefore, a critical capillary number should be introduced to judge whether the dynamic contact model should be incorporated into simulations. In this study, a direct numerical simulation method is employed to simulate the oil slug flow in a capillary tube at the pore scale. The position of the interface between water and the oil slug is determined using the phase-field method. The capacity and accuracy of the model are validated using a classical benchmark: a dynamic capillary filling process. Then, different dynamic contact angle models and the factors that affect the dynamic contact angle are analyzed. The meniscus displacements of oil slugs with a dynamic contact angle and a static contact angle (SCA) are obtained during simulations, and the relative error between them is calculated automatically. The relative error limit has been defined to be 5%, beyond which the dynamic contact angle model needs to be incorporated into the simulation to approach the realistic displacement. Thus, the desired critical capillary number can be determined. A three-dimensional universal chart of critical capillary number, which functions as static contact angle and viscosity ratio, is given to provide a guideline for oil slug simulation. Also, a fitting formula is presented for ease of use.
Ignition angle advancer for internal combustion engine
Yamazaki, T.
1986-08-19
This patent describes a throttle and spark advance control system for an internal combustion engine having a spark advance mechanism and a throttle valve comprising an operator controlled element, a throttle control lever supported for pivotal movement about an axis and directly connected to the operator controlled element for rotation under operator control. It also includes means for positively connecting the throttle control lever to the throttle valve for positioning the throttle valve in response to movement of the throttle control lever. A spark advance control lever supported for pivotal movement about an axis is included as well as motion transmitting means for operatively connecting the spark advance control lever to the throttle control lever for pivotal movement of the spark advance control lever about its axis in response to pivotal movement of the throttle control lever about its axis and the spark control lever to the spark advance mechanism for controlling the position of the spark advance mechanism in response to the position of the throttle control lever.
Comparison of different methods to measure contact angles of soil colloids.
Shang, Jianying; Flury, Markus; Harsh, James B; Zollars, Richard L
2008-12-15
We compared five different methods, static sessile drop, dynamic sessile drop, Wilhelmy plate, thin-layer wicking, and column wicking, to determine the contact angle of colloids typical for soils and sediments. The colloids (smectite, kaolinite, illite, goethite, hematite) were chosen to represent 1:1 and 2:1 layered aluminosilicate clays and sesquioxides, and were either obtained in pure form or synthesized in our laboratory. Colloids were deposited as thin films on glass slides, and then used for contact angle measurements using three different test liquids (water, formamide, diiodomethane). The colloidal films could be categorized into three types: (1) films without pores and with polar-liquid interactions (smectite), (2) films with pores and with polar-liquid interactions (kaolinite, illite, goethite), and (3) films without pores and no polar-liquid interactions (hematite). The static and dynamic sessile drop methods yielded the most consistent contact angles. For porous films, the contact angles decreased with time, and we consider the initial contact angle to be the most accurate. The differences in contact angles among the different methods were large and varied considerably: the most consistent contact angles were obtained for kaolinite with water, and illite with diiodomethane (contact angles were within 3 degrees); but mostly the differences ranged from 10 degrees to 40 degrees among the different methods. The thin-layer and column wicking methods were the least consistent methods.
Gerson, D F; Akit, J
1980-11-04
Partition coefficients in biphasic mixtures of poly(ethylene glycol) and Dextran are compared to cell surface energies obtained from contact angles of each liquid phase on cell layers. Linear relationships are observed between these two independent measurements for a variety of bacterial cells. The results demonstrate the importance of interfacial phenomena and contact angles in the phase-partition process.
Influence of contact angle on slow evaporation in two-dimensional porous media.
Chraïbi, H; Prat, M; Chapuis, O
2009-02-01
We study numerically the influence of contact angle on slow evaporation in two-dimensional model porous media. For sufficiently low contact angles, the drying pattern is fractal and can be predicted by a simple model combining the invasion percolation model with the computation of the diffusive transport in the gas phase. The overall drying time is minimum in this regime and is independent of contact angle over a large range of contact angles up to the beginning of a transition zone. As the contact angle increases in the transition region, the cooperative smoothing mechanisms of the interface become important and the width of the liquid gas interface fingers that form during the evaporation process increases. The mean overall drying time increases in the transition region up to an upper bound which is reached at a critical contact angle thetac. The increase in the drying time in the transition region is explained in relation with the diffusional screening phenomenon associated with the Laplace equation governing the vapor transport in the gas phase. Above thetac the drying pattern is characterized by a flat traveling front and the mean overall drying time becomes independent of the contact angle. Drying time fluctuations are studied and are found to be important below thetac, i.e., when the pattern is fractal. The fluctuations are of the same order of magnitude regardless of the value of contact angle in this range. The fluctuations are found to die out abruptly at thetac as the liquid gas interface becomes a flat front.
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.
Apparent-contact-angle model at partial wetting and evaporation: impact of surface forces.
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.
NASA Astrophysics Data System (ADS)
Liu, Yong-Ming; Chen, Rui-Qing; Wu, Zi-Qing; Zhu, Jing; Shi, Jian-Yu; Lu, Hui-Meng; Shang, Peng; Yin, Da-Chuan
2016-09-01
The contact angle is an important parameter that is essential for studying interfacial phenomena. The contact angle can be measured using commercially available instruments. However, these well-developed instruments may not function or may be unsuitable for use in some special environments. A simulated microgravity generated by a large gradient magnetic field is such an environment in which the current measurement instruments cannot be installed. To measure the contact angle in this environment, new tools must be designed and manufactured to be compatible with the size and physical environment. In this study, we report the development and construction of a new setup that was specifically designed for use in a strong magnetic field to measure the contact angle between a levitated droplet and a solid surface. The application of the setup in a large gradient magnetic field was tested, and the contact angles were readily measured.
Automated contact angle estimation for three-dimensional X-ray microtomography data
Klise, Katherine A.; Moriarty, Dylan; Yoon, Hongkyu; Karpyn, Zuleima
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 contact 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.
Mechanism of contact angle saturation and an energy-based model for electrowetting
NASA Astrophysics Data System (ADS)
Rui, Zhao; Zhong-Cheng, Liang
2016-06-01
Electrowetting, as a well-known approach to increasing droplet wettability on a solid surface by electrical bias, has broad applications. However, it is limited by contact angle saturation at large voltage. Although several debated hypotheses have been proposed to describe it, the physical origin of contact angle saturation still remains obscure. In this work, the physical factors responsible for the onset of contact angle saturation are explored, and the correlated theoretical models are established to characterize electrowetting behavior. Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25°, and validates that the contact angle saturation is not a result of device-related imperfection. Project supported by the Fund from the Research Center of Optical Communications Engineering & Technology, Jiangsu Province, China (Grant No. ZSF0402).
Indirect methods to measure wetting and contact angles on spherical convex and concave surfaces.
Extrand, C W; Moon, Sung In
2012-05-22
In this work, a method was developed for indirectly estimating contact angles of sessile liquid drops on convex and concave surfaces. Assuming that drops were sufficiently small that no gravitational distortion occurred, equations were derived to compute intrinsic contact angles from the radius of curvature of the solid surface, the volume of the liquid drop, and its contact diameter. These expressions were tested against experimental data for various liquids on polytetrafluoroethylene (PTFE) and polycarbonate (PC) in the form of flat surfaces, spheres, and concave cavities. Intrinsic contact angles estimated indirectly using dimensions and volumes generally agreed with the values measured directly from flat surfaces using the traditional tangent method.
Xu, Z N
2014-12-01
In this study, an error analysis is performed to study real water drop images and the corresponding numerically generated water drop profiles for three widely used static contact angle algorithms: the circle- and ellipse-fitting algorithms and the axisymmetric drop shape analysis-profile (ADSA-P) algorithm. The results demonstrate the accuracy of the numerically generated drop profiles based on the Laplace equation. A significant number of water drop profiles with different volumes, contact angles, and noise levels are generated, and the influences of the three factors on the accuracies of the three algorithms are systematically investigated. The results reveal that the above-mentioned three algorithms are complementary. In fact, the circle- and ellipse-fitting algorithms show low errors and are highly resistant to noise for water drops with small/medium volumes and contact angles, while for water drop with large volumes and contact angles just the ADSA-P algorithm can meet accuracy requirement. However, this algorithm introduces significant errors in the case of small volumes and contact angles because of its high sensitivity to noise. The critical water drop volumes of the circle- and ellipse-fitting algorithms corresponding to a certain contact angle error are obtained through a significant amount of computation. To improve the precision of the static contact angle measurement, a more accurate algorithm based on a combination of the three algorithms is proposed. Following a systematic investigation, the algorithm selection rule is described in detail, while maintaining the advantages of the three algorithms and overcoming their deficiencies. In general, static contact angles over the entire hydrophobicity range can be accurately evaluated using the proposed algorithm. The ease of erroneous judgment in static contact angle measurements is avoided. The proposed algorithm is validated by a static contact angle evaluation of real and numerically generated water drop
NASA Astrophysics Data System (ADS)
Xu, Z. N.
2014-12-01
In this study, an error analysis is performed to study real water drop images and the corresponding numerically generated water drop profiles for three widely used static contact angle algorithms: the circle- and ellipse-fitting algorithms and the axisymmetric drop shape analysis-profile (ADSA-P) algorithm. The results demonstrate the accuracy of the numerically generated drop profiles based on the Laplace equation. A significant number of water drop profiles with different volumes, contact angles, and noise levels are generated, and the influences of the three factors on the accuracies of the three algorithms are systematically investigated. The results reveal that the above-mentioned three algorithms are complementary. In fact, the circle- and ellipse-fitting algorithms show low errors and are highly resistant to noise for water drops with small/medium volumes and contact angles, while for water drop with large volumes and contact angles just the ADSA-P algorithm can meet accuracy requirement. However, this algorithm introduces significant errors in the case of small volumes and contact angles because of its high sensitivity to noise. The critical water drop volumes of the circle- and ellipse-fitting algorithms corresponding to a certain contact angle error are obtained through a significant amount of computation. To improve the precision of the static contact angle measurement, a more accurate algorithm based on a combination of the three algorithms is proposed. Following a systematic investigation, the algorithm selection rule is described in detail, while maintaining the advantages of the three algorithms and overcoming their deficiencies. In general, static contact angles over the entire hydrophobicity range can be accurately evaluated using the proposed algorithm. The ease of erroneous judgment in static contact angle measurements is avoided. The proposed algorithm is validated by a static contact angle evaluation of real and numerically generated water drop
Estimation of bearing contact angle in-situ by X-ray kinematography
NASA Technical Reports Server (NTRS)
Fowler, P. H.; Manders, F.
1982-01-01
The mounted, preloaded contact angle of the structural bearings in the assembled design mechanical assembly was measured. A modification of the Turns method is presented, based upon the clarity and definition of moving parts achieved with X-ray technique and cinematic display. Contact angle is estimated by counting the number of bearings passing a given point as a function of number of turns of the shaft. Ball and pitch diameter variations are discussed. Ball train and shaft angle uncertainties are also discussed.
Investigating How Contact Angle Effects the Interaction between Water and a Hydrophobic Surface
NASA Astrophysics Data System (ADS)
Poynor, Adele; Neidig, Caitlyn
2012-02-01
By definition hydrophobic substances hate water. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density region forms near the surface. Contact angle is a measure of how hydrophobic a surface is. We have employed an automated home-built Surface Plasmon Resonance (SPR) apparatus to investigate the effect of varying the contact angle on the depletion layer
Hydrophobic/superhydrophobic oxidized metal surfaces showing negligible contact angle hysteresis.
Hozumi, Atsushi; Cheng, Dalton F; Yagihashi, Makoto
2011-01-15
Dynamic wettability of oxidized metal (aluminum and titanium) surfaces could be tuned by chemical vapor deposition (CVD) of 1,3,5,7-tetramethylcyclotetrasiloxane (D(4)(H)). This facile CVD method produces not only monomeric layers but also particulate films by changing the CVD temperature, resulting in a marked difference in the final wetting properties. In the samples prepared at 80°C for ~3 days, D(4)(H) layers with thicknesses of ~0.5 nm were formed on the surfaces without discernible change in surface morphology, as evidenced by X-ray photoelectron spectroscopy and atomic force microscopy. After this D(4)(H) monomeric layer formation, the hydrophilic oxidized aluminum and titanium surfaces became hydrophobic (advancing/receding water contact angles (θ(A)/θ(R))=102-104°/99-102°) showing essentially negligible contact angle hysteresis. Performing CVD of D(4)(H) at 180°C for ~1 day produced opaque film with particulate morphologies with diameters in the range of 500 nm to 4 μm observed on the surfaces. This geometric morphology enhanced the surface hydrophobicity (θ(A)/θ(R)=163°/160-161°). Droplets on these negligible-hysteresis surfaces moved very easily without "pinning".
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.
Automated contact angle estimation for three-dimensional X-ray microtomography data
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
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.
Douillard; Médout-Marère
2000-03-15
The values of the contact angles of different liquids on the same solid are classically interpreted by theories assuming that the vapor adsorption is negligible on solids presenting contact angles. This implies that the solid may be defined by a certain tension, called "critical tension", which is not clearly thermodynamically defined. These assumptions are in disagreement with modern theories of vapor adsorption science. In this paper, it is shown that it is possible to understand the contact angle values using a rigorous derivation of the Young equation, which links the contact angle, the liquid-vapor surface tension of the drop, and the surface tension of the solid in equilibrium with its own vapor. Numerical approximations allow the contact angle variation to be predicted, without use of ad hoc definitions. It is then possible to link vapor adsorption results and contact angle experiments. It is also possible to deduce the surface tension of solids simply and to compute contact angles on powders without using the Washburn method. Copyright 2000 Academic Press.
Contact angle adjustment in equation-of-state-based pseudopotential model.
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.
Dahlgren, C; Sunqvist, T
1981-01-01
The correlation between the contact angle and degree of phagocytosis of different yeast particles has been investigated. To facilitate the estimation of the contact angle, we have tested the hypothesis that the shape of a small liquid drop put on a flat surface is that of a truncated sphere. By making this approximation it is possible to calculate the contact angle, i.e. the tangent to the drop in the 3-phase liquid/solid/air meeting point, by measuring the drop diameter. Known volumes of saline were put on different surfaces and the diameters of the drops were measured from above. Calculation of the contact angle with drops of different volumes, and comparison between expected and measured height of 10 microl drops, indicated that the assumption that the shape of a drop is that of a truncated sphere is valid. Monolayers of leukocytes was shown to give rise to a contact angle of 17.9 degrees. Particles with a lower contact angle than the phagocytic cells resisted phagocytosis, but opsonization of the particles with normal human serum rendered them susceptible to phagocytosis, conferring a higher contact angle than that of the phagocytic cells.
Simultaneous Soft Sensing of Tissue Contact Angle and Force for Millimeter-scale Medical Robots.
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.
Measuring contact angle and meniscus shape with a reflected laser beam.
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
Eibach, T. F.; Nguyen, H.; Butt, H. J.; Auernhammer, G. K.; Fell, D.
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. 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.
NASA Astrophysics Data System (ADS)
Liu, Yang; Zhao, Yue; Feng, Yue; Shen, Jiesheng; Liang, Xiaoyan; Huang, Jian; Min, Jiahua; Wang, Linjun; Shi, Weimin
2016-02-01
In this paper, oblique vacuum thermal evaporation and direct current (DC) magnetron sputtering technique are used to produce a novel back contact electrode (BCE) of CuInS2 solar cell. These novel back contact electrodes (BCEs) are based on a layered structure of Mo/Ag/Mo (MAM). The influence of vapor source incidence angle θ on optical-electrical properties of novel BCE is investigated by X-ray Diffraction (XRD), Surface Profiler, Atomic Force Microscope (AFM), UV-vis-IR Spectrometer, and Four-point Probe Method. According to the analysis of AFM images of BCEs, the variation tendencies of surface roughness and uniformity are closely related to the incidence angle θ. The surface roughness increases with the increase of incidence angle θ, but the uniformity becomes poor at same time. This phenomenon can be attributed to the variation of interlayer Ag films (the density and inclined angle of Ag nanorods). The results of four-point probe test show that the novel BCE deposited by vapor source incidence angle θ equal to 45° owns the lowest resistance value of 3.71 × 10-8 Ω m, which is probably due to a loose and multi-point contact interface between Ag layer and top layer (Mo2). The reflectance of novel BCEs deposited by incident angle less than 45° is higher than that of normal bi-layer Mo (Mo12) BCE. As a result, the efficiency of corresponding solar cell may be upgraded.
Effect of relative humidity on contact angle of inkjet-printed evaporating colloidal drops
NASA Astrophysics Data System (ADS)
Chhasatia, Viral; Joshi, Abhijit; Sun, Ying
2010-11-01
The deposition behavior of inkjet-printed aqueous colloidal drops onto glass and polymer (PEN and PET) substrates has been investigated by using fluorescence microscopy, a high-resolution CCD camera, and scanning electron microscopy. Real-time side-view images show that the contact angle of an evaporating colloidal drop is a function of the ambient humidity. The relative humidity also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively-driven flow inside the drop that drives the suspended particles towards the contact line. The difference between the contact line velocity and liquid velocity at the drop contact line induced by evaporation creates a larger contact angle compared to that of the case without evaporation. This increase in contact angle becomes more significant for a low ambient humidity. Results also show that the particle deposition area and pattern change with the ambient humidity.
Liu, Qian; Wang, Wanchun; Thoreson, Andrew R; Zhao, Chunfeng; Zhu, Weihong; Dou, Pengcheng
2017-02-01
Three dimensional finite element models of cam-type FAI with alpha angles of 60°, 70°, 80°, and 90° were created to investigate the cartilage contact mechanics in daily activities. Intra-articular cartilage contact pressures during routine daily activities were assessed and cross-compared with a normal control hip. Alpha angles and hip range of motion were found to have a combined influence on the cartilage contact mechanics in hips with cam-type FAI, thereby resulting in abnormally high pressures and driving the cartilage damage. In particular, alpha angles of 80° or greater contribute to substantial pressure increase under certain types of daily activities.
de Ruiter, Riëlle; Semprebon, Ciro; van Gorcum, Mathijs; Duits, Michèl H G; Brinkmann, Martin; Mugele, Frieder
2015-06-12
The equilibrium shape of a drop in contact with solid surfaces can undergo continuous or discontinuous transitions upon changes in either drop volume or surface energies. In many instances, such transitions involve the motion of the three-phase contact line and are thus sensitive to contact angle hysteresis. Using a combination of electrowetting-based experiments and numerical calculations, we demonstrate for a generic sphere-plate confinement geometry how contact angle hysteresis affects the mechanical stability of competing axisymmetric and nonaxisymmetric drop conformations and qualitatively changes the character of transitions between them.
Determination of the Surface Tension of Microporous Membranes Using Contact Angle Measurements
Tröger; Lunkwitz; Bürger
1997-10-15
In this paper, a new method of determining the surface tension of the solid material that a microporous membrane is made from is introduced. The method is based on the well known determination of the so-called contact angle that is formed on the solid/liquid/gaseous three phase line. A nonideal state of the solid phase leads to a deviation of the contact angle that can be observed experimentally from the equilibrium angle that arises from the thermodynamically state of lowest energy, as it must be used to calculate the solid surface tension via the Young equation. The deviation caused from the porous structure of the solid material will be taken into account in this work. Doing so, we derived an equation that connects the surface porosity, the measured contact angle, and the equilibrium contact angle. Using this equation, the measured and therefore deviated contact angles can be corrected for the porosity of the solid material, yielding the contact angle observable on a surface made from the same but nonporous material. The equation derived was tested on different microporous membranes made from expanded poly(tetrafluoroethylene). The surface porosity needed was determined using scanning electron microscopy followed by computerized image analysis. Copyright 1997 Academic Press. Copyright 1997Academic Press
Milne, A J B; Elliott, J A W; Zabeti, Parham; Zhou, Jiyan; Amirfazli, A
2011-09-28
Despite the practical need, no models exist to predict contact angles or wetting mode of surfactant solutions on rough hydrophobic or superhydrophobic surfaces. Using Gibbs' adsorption equation and a literature isotherm, a new model is constructed based on the Wenzel and Cassie equations. Experimental data for aqueous solutions of sodium dodecyl sulfate (SDS) contact angles on smooth Teflon surfaces are fit to estimate values for the adsorption coefficients in the model. Using these coefficients, model predictions for contact angles as a function of topological f (Cassie) and r (Wenzel) factors and SDS concentration are made for different intrinsic contact angles. The model is also used to design/tune surface responses. It is found that: (1) predictions compare favorably to data for SDS solutions on five superhydrophobic surfaces. Further, the model predictions can determine which wetting mode (Wenzel or Cassie) occurred in each experiment. The unpenetrated or partially penetrated Cassie mode was the most common, suggesting that surfactants inhibit the penetration of liquids into rough hydrophobic surfaces. (2) The Wenzel roughness factor, r, amplifies the effect of surfactant adsorption, leading to larger changes in contact angles and promoting total wetting. (3) The Cassie solid area fraction, f, attenuates the lowering of contact angles on rough surfaces. (4) The amplification/attenuation is understood to be due to increased/decreased solid-liquid contact-area.
Bonugli, L O; dos Santos, M V Puydinger; de Souza, E F; Teschke, O
2012-12-15
Apolar fibers wired into a mesh-like microstructure forming a coating with a contact angle larger than 160° and fabricated by polycyanoacrylate polymerization are described. Interconnected fibers with diameters measuring approximately 5 μm are formed by texturized linear or folded nanowires. The structure forming the deposited film occupies ~1.5% of the coating's top geometric area. This value agrees with the water/coating contact area given by the Cassie-Baxter contact-angle model (~1.5%). The spatial distribution of the surface in contact with water was determined by Raman spectral imaging (~1.5%) using the polycyanoacrylate lines and by scanning electron microscopy (~2.0%).
NASA Astrophysics Data System (ADS)
Baver, Christine E.; Parlange, J.-Yves; Stoof, Cathelijne R.; DiCarlo, David A.; Wallach, Rony; Durnford, Deanna S.; Steenhuis, Tammo S.
2014-06-01
Pore velocity-dependent dynamic contact angles provide a mechanism for explaining the formation of fingers/columns in porous media. To study those dynamic contact angles when gravity is present, rectangular capillary tubes were used to facilitate observation of the complete interface without geometric distortion. Results show that the Hoffman (1975) relationship between dynamic contact angle and water velocity applies to gravity-affected flow fields, and that it (when adjusted for nonzero static contact angles) can be used to model dynamic capillary pressures for unstable wettings fronts in porous media by assuming that (1) pressure at the wetting front is discontinuous, (2) the flow field behind the fingertip is highly heterogeneous, and (3) the front line advances one or a few pores at the time. We demonstrate the utility of the Hoffman relationship for porous media with a published infiltration experiment by calculating the capillary pressure successfully at the unstable wetting front as a function of the flux of water in the finger and the grain size diameter.
Contact angle hysteresis of non-flattened-top micro/nanostructures.
Moradi, Sona; Englezos, Peter; Hatzikiriakos, Savvas G
2014-03-25
A two-dimensional (2D) thermodynamic model is proposed to predict the contact angle (CA) and contact angle hysteresis (CAH) of different types of surface geometries, particularly those with asperities having nonflattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium contact angle (CA) and contact angle hysteresis (CAH). The effects of the geometrical details of two types of microstructures on maximizing the superhydrophobicity of the nanopatterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters that may lead to the lotus effect (high CA > 150° and low CAH < 10°) or petal effect (high CA > 150° and high CAH ≫ 10°).
Tatara, Shingo; Kuzumoto, Yasutaka; Kitamura, Masatoshi
2016-04-01
The water wettability of Au surfaces has been controlled using various benzenethiol derivatives including 4-methylbenzenethiol, pentafluorobenzenethiol, 4-flubrobenzenethiol, 4-methoxy-benzenethiol, 4-nitrobenzenethiol, and 4-hydroxybenzenethiol. The water contact angle of the Au surface modified with the benzenethiol derivative was found to vary in the wide range of 30.9° to 88.3°. The contact angle of the modified Au films annealed was also measured in order to investigate their thermal stability. The change in the contact angle indicated that the modified surface is stable at temperatures below about 400 K. Meanwhile, the activation energy of desorption from the modified surface was estimated from the change in the contact angle. The modified Au surface was also examined using X-ray photoelectron spectroscopy.
The effect of contact angle on triangular shape interrupted microchannel heat sinks performance
NASA Astrophysics Data System (ADS)
Mohd Azmi, Mohd Irwan; Chuan, Yeoh Chit; Tokit, Ernie Mat; Razali, Nadlene; Munir, Fudhail Abd; Azmi Nordin, Mohd Nur; Mat Nuri, Nur Rashid
2012-06-01
The effect of different contact angle on triangular shaped interrupted microchannel performance was studied by simulation using FLUENT software. The investigated effects were pressure drop and platinum film temperature. The flow in microchannel is laminar and single phase. Water was used as the working fluid and the interrupted microchannel is made of silicon. A thin platinum film plate was deposited to provide uniform heat flux. The geometry dimension of the heat sink is 30 mm in length, width of 7 mm and the thickness of 0.525 mm. The chosen contact angles that were investigated are 48.13°, 51.27° and 58.48°. From the simulation result, pressure drop and thermal dissipation is the highest for contact angle 58.48° and 48.13° respectively. Reducing the contact angle reduces the pressure drop and increases the thermal dissipation.
Grigoriev, D O; Krägel, J; Dutschk, V; Miller, R; Möhwald, H
2007-12-28
A novel and simple method for the determination of the contact angle of nano- and microparticles at the liquid/air interface is proposed. The principle is based on the consideration of differences between the pressure/area isotherms of a 2D single-component system of a surfactant and those of binary systems comprised of the same surfactant and the particles to be studied. The theoretical analysis of the contact-angle behavior in this system upon compression allows the prediction of direction of the particles' squeezing out of the surface layer and therefore the distinction between the particles with high contact angle (Theta(p) > 90 degrees) and low (Theta(p) < 90 degrees) hydrophobicity. The application of this method to microparticles of two different hydrophobicities demonstrates good agreement between the obtained contact angles and the corresponding degrees of hydrophobicity given by the particle provider.
Allen, Jeffrey S
2003-05-15
An analytical solution to the capillary equation of Young and Laplace is derived that allows determination of the static contact angle based on the volume of a sessile drop and the wetted area of the substrate. This solution does not require numerical integration to determine the drop profile and accounts for surface deformation due to gravitational effects. Calculation of the static contact angle by this method is remarkably simple and accurate when the contact angle is less than 30 degrees. A natural scaling arises in the solution, which provides indication of when a drop is small enough so as to neglect gravitational influences on the surface shape which, for small contact angles, is generally less than 1 microl. The technique described has the simplicity of the spherical cap approximation but remains accurate for any size of sessile drop.
The Interpretation of Dynamic Contact Angles Measured by the Wilhelmy Plate Method
Ramé
1997-01-01
We present an analysis for properly interpreting apparent dynamic contact angles measured using the Wilhelmy plate method at low capillary numbers, Ca. This analysis removes the ambiguity in current dynamic measurements which interpret data with the same formula as static measurements. We properly account for all forces, including viscous forces, acting on the plate as it moves into or out of a liquid bath. Our main result, valid at O(1) as Ca --> 0, relates the apparent dynamic contact angle to material-dependent, geometry-independent parameters necessary for describing dynamic wetting of a system. The special case of the apparent contact angle = pi/2 was solved to O(Ca). This O(Ca) solution can guide numerical work necessary for higher Ca's and arbitrary values of the apparent contact angle. These results make the Wilhelmy plate a viable method for determining material parameters for dynamic spreading.
Nonlocal hydrodynamic influence on the dynamic contact angle: slip models versus experiment.
Wilson, Mark C T; Summers, Jonathan L; Shikhmurzaev, Yulii D; Clarke, Andrew; Blake, Terence D
2006-04-01
Experiments reported by Blake [Phys. Fluids., 11, 1995 (1999)] suggest that the dynamic contact angle formed between the free surface of a liquid and a moving solid boundary at a fixed contact-line speed depends on the flow field and geometry near the moving contact line. We examine quantitatively whether or not it is possible to attribute this effect to the bending of the free surface due to hydrodynamic stresses acting upon it and hence interpret the results in terms of the so-called "apparent" contact angle. It is shown that this is not the case. Numerical analysis of the problem demonstrates that, at the spatial resolution reported in the experiments, the variations of the "apparent" contact angle (defined in two different ways) caused by variations in the flow field, at a fixed contact-line speed, are too small to account for the observed effect. The results clearly indicate that the actual (macroscopic) dynamic contact angle--i.e., the one used in fluid mechanics as a boundary condition for the equation determining the free surface shape--must be regarded as dependent not only on the contact-line speed but also on the flow field and geometry in the vicinity of the moving contact line.
Prediction of static contact angles on the basis of molecular forces and adsorption data.
Diaz, M Elena; Savage, Michael D; Cerro, Ramon L
2016-08-01
At a three-phase contact line, a liquid bulk phase is in contact with and coexists with a very thin layer of adsorbed molecules. This adsorbed film in the immediate vicinity of a liquid wedge modifies the balance of forces between the liquid and solid phases such that, when included in the balance of forces, a quantitative relationship emerges between the adsorbed film thickness and the static contact angle. This relationship permits the prediction of static contact angles from molecular forces and equilibrium adsorption data by means of quantities that are physically meaningful and measurable. For n-alkanes on polytetrafluoroethylene, for which there are experimental data available on adsorption and contact angles, our computations show remarkable agreement with the data. The results obtained are an improvement on previously published calculations-particularly for alkanes with a low number of carbon atoms, for which adsorption is significant.
Prediction of static contact angles on the basis of molecular forces and adsorption data
NASA Astrophysics Data System (ADS)
Diaz, M. Elena; Savage, Michael D.; Cerro, Ramon L.
2016-08-01
At a three-phase contact line, a liquid bulk phase is in contact with and coexists with a very thin layer of adsorbed molecules. This adsorbed film in the immediate vicinity of a liquid wedge modifies the balance of forces between the liquid and solid phases such that, when included in the balance of forces, a quantitative relationship emerges between the adsorbed film thickness and the static contact angle. This relationship permits the prediction of static contact angles from molecular forces and equilibrium adsorption data by means of quantities that are physically meaningful and measurable. For n-alkanes on polytetrafluoroethylene, for which there are experimental data available on adsorption and contact angles, our computations show remarkable agreement with the data. The results obtained are an improvement on previously published calculations—particularly for alkanes with a low number of carbon atoms, for which adsorption is significant.
Chow, Keat Theng; Chan, Lai Wah; Heng, Paul W S
2008-08-01
This study reports the characterization of spreadability of nonaqueous ethylcellulose (EC) gel matrices intended for topical drug delivery using a newly developed method based on dynamic contact angle. EC solutions were prepared using three grades of EC and propylene glycol dicaprylate/dicaprate. Dynamic contact angles of sessile drops of EC solutions on silicone elastomer were measured using a dynamic contact angle analyzer equipped with axisymmetric drop shape analysis-profile. Roughness of silicone elastomer, viscosity of EC solutions and compressibility of semisolid EC gels were determined by the atomic force microscope, cone-and-plate rheometer and tensile tester, respectively. The silicone elastomer employed as a substrate was demonstrated to have similar hydrophilic/lipophilic properties as the human skin. Spreadability of EC solutions was dependent on EC concentration, polymeric chain length and polydispersity. EC gel spreadability was governed by viscosity and the extent of gel-substrate interaction. From the apparent contact angle values, most EC gel formulations tested were found to be moderately spreadable. Linear correlation observed between spreading parameter and compressibility of EC gel verified the applicability of dynamic contact angle to characterize EC gel spreadability. Thus, the feasibility of employing dynamic contact angle as an alternative technique to measure gel spreadability was demonstrated. The spreadability demonstrated by EC gel would facilitate application on the skin indicating its potential usefulness as a topical dosage form.
Contact Angle Measurement of Small Capillary Length Liquid in Super-repelled State.
Liu, Tingyi Leo; Kim, Chang-Jin Cj
2017-04-07
The difficulty of measuring very large contact angles (>150 degrees) has become more relevant with the increased popularity of super-repellent surfaces. Measurement is more difficult for dynamic contact angles, for which theoretical profiles do not fit well, and small capillary length liquids, whose sessile droplets sag by gravity. Here, we expand the issue to the limit by investigating dynamic contact angles of liquids with an extremely small capillary length (<1.0 mm), empowered by the superomniphobic surface that can super-repel even fluorinated solvents, which highly wet all materials. Numerically simulating and experimentally testing 13 different liquids on the superomniphobic surface, we discover their dynamic contact angles can be measured with a consistent accuracy despite their vastly different capillary lengths if one keeps the lens magnification inversely proportional to the capillary length. Verifying the droplet equator height is a key parameter, we propose a new Bond number defined by the equator height and optical resolution to represent the measurement accuracy of large contact angles. Despite negligible improvement for most liquids today, the proposed approach teaches how to measure very large contact angles with consistent accuracy when any of the liquids in consideration has a capillary length below 1.0 mm.
Assessing the accuracy of contact angle measurements for sessile drops on liquid-repellent surfaces.
Srinivasan, Siddarth; McKinley, Gareth H; Cohen, Robert E
2011-11-15
Gravity-induced sagging can amplify variations in goniometric measurements of the contact angles of sessile drops on super-liquid-repellent surfaces. The very large value of the effective contact angle leads to increased optical noise in the drop profile near the solid-liquid free surface and the progressive failure of simple geometric approximations. We demonstrate a systematic approach to determining the effective contact angle of drops on super-repellent surfaces. We use a perturbation solution of the Bashforth-Adams equation to estimate the contact angles of sessile drops of water, ethylene glycol, and diiodomethane on an omniphobic surface using direct measurements of the maximum drop width and height. The results and analysis can be represented in terms of a dimensionless Bond number that depends on the maximum drop width and the capillary length of the liquid to quantify the extent of gravity-induced sagging. Finally, we illustrate the inherent sensitivity of goniometric contact angle measurement techniques to drop dimensions as the apparent contact angle approaches 180°.
Effect of contact angle on capillary displacement curvatures in pore throats formed by spheres
Mason, G. . Dept. of Chemical Engineering); Morrow, N.R. )
1994-11-01
The curvature of an interface in a pore depends upon the shape of the pore and the operative contact angle that the interface makes with the solid surface. Even relatively simple pores formed by the surfaces of equal spheres have a complex shape including nonaxisymmetric cross-section and converging-diverging geometry. For such pores, a theory for meniscus behavior has been devised that uses a combination of a theory for meniscus curvature in rods together with the toroidal approximation of Purcell. The results of the theory show that converging-diverging geometry tends to compensate for the effect of contact angle. This is because the position at which the nonzero contact angle meniscus has maximum curvature in a converging-diverging pore is not the narrowest part of the pore throat. Due to this compensation, the effect of contact angle on maximum meniscus curvatures for drainage is approximately proportional to cos 2/3 [theta] (rather than the cos [theta] appropriate for cylindrical tubes). Experiments on pores formed by PTFE spheres using partially wetting liquids confirmed the theoretical prediction. Contact angle measurements on the PTFE spheres also demonstrated that, because of microscopic surface roughness, receding contact angles (these being operative with respect to drainage) on ground surfaces are significantly lower than values for smooth surfaces.
Contact angle goniometry on single micron-scale fibers for composites
NASA Astrophysics Data System (ADS)
Hansen, Daniel; Bomholt, Niels; Jeppesen, Jonas Camillus; Simonsen, Adam Cohen
2017-01-01
Probing the wetting properties of microfibers by polymer resins is of significant interest for the rational design of composite materials. Here, we demonstrate the measurement of contact angles on wetted micron scale fibers by imaging the fluid meniscus with telecentric optics at a spatial resolution of 4 μm followed by automated image analysis. The meniscus is described as a catenary in the zero gravity approximation and by fitting this to the measured profile, the contact angle is obtained at the intersection between the fluid and the fiber surface. The method is validated by measuring agreement between contact angles for the PMMA/H2O system for fibers with diameters 20-800 μm and for sessile drops. The ability of the method to discriminate contact angles for a series of commercial glass fibers against epoxy resin is successfully demonstrated. AFM imaging shows that the surface topography of the fibers does not have a simple relationship with the variation in contact angles. Contact angle goniometry by imaging of micron scale fibers appears as a viable alternative to Wilhelmy type measurements and the measurement principle could readily be extended to dynamic wetting experiments.
Experimental evidence of nonlocal hydrodynamic influence on the dynamic contact angle
NASA Astrophysics Data System (ADS)
Blake, T. D.; Bracke, M.; Shikhmurzaev, Y. D.
1999-08-01
The dynamic contact angle formed when a liquid curtain impinges onto a moving solid is measured for aqueous glycerol solutions in different flow regimes. It is usually assumed that the dynamic contact angle is simply a function of the contact-line speed and the material properties of the contacting media. The new results show that this is not the case. For a given gas/liquid/solid combination and a given contact-line speed, the dynamic contact angle can be varied by varying the flow rate of the liquid and/or the curtain height, that is by varying the flow field near the contact line. The possibility of attributing this effect merely to free-surface bending and interpreting the results in terms of the so-called "apparent" contact angle is discussed and ruled out on the basis of some general qualitative arguments and analysis of the characteristic length scales involved. A probable connection between the observed effect and the physical mechanism of interface disappearance and formation incorporated in a recently developed theory of wetting is discussed.
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.
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.
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.
Wang, Liming; McCarthy, Thomas J
2013-06-25
Water capillary bridges are prepared that span hydrophilic pinning features on parallel opposing smooth, flat, and hydrophobic surfaces. These bridges are distorted by shearing the parallel plates at a low rate. The capillary bridges lengthen and distort to balance Laplace pressure (equilibrate mean curvature) as the features are separated and eventually rupture at a distance that is a function of the liquid volume, the advancing and receding contact angles of the surfaces, the separation between the parallel surfaces, and in particular, the shape and orientation of the hydrophilic pinning features. Two modes of capillary bridge failure are observed: (1) tensile, in which the capillary bridge breaks to form sessile drops on both the upper and lower surfaces, and (2) sessile, in which sessile capillary bridge rupture occurs on one surface to form a puddle (contact-line-distorted sessile drop) on the feature and a retained capillary bridge spanning the hydrophobic surface and the hydrophilic feature on the opposing surface. The shape and orientation of the features control the mode of capillary bridge failure as well as the distribution of water between the two separate sessile drops or the retained capillary bridge and the puddle.
Dilatational viscosity of dilute particle-laden fluid interface at different contact angles
NASA Astrophysics Data System (ADS)
Lishchuk, Sergey V.
2016-12-01
We consider a solid spherical particle adsorbed at a flat interface between two immiscible fluids and having arbitrary contact angle at the triple contact line. We derive analytically the flow field corresponding to dilatational surface flow in the case of a large ratio of dynamic shear viscosities of two fluids. Considering a dilute assembly of such particles we calculate numerically the dependence on the contact angle of the effective surface dilatational viscosity particle-laden fluid interface. The effective surface dilatational viscosity is proportional to the size and surface concentration of particles and monotonically increases with the increase in protrusion of particles into the fluid with larger shear viscosity.
Color-gradient lattice Boltzmann model for simulating droplet motion with contact-angle hysteresis.
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.
NASA Astrophysics Data System (ADS)
Ramírez-Flores, Juan Carlos; Bachmann, Jörg; Marmur, Abraham
2010-03-01
SummaryAn accurate method to determine contact angles (CA) of soils as a measure of water repellency is still missing. In the present research, we evaluated and compared different methods to determine the CA of dry soil samples. Experiments were made by using a set of porous materials (silt, sand and glass beads) with different levels of water repellency. The CAs were measured with the Capillary Rise Method ( θCRM; liquid penetration into a 3-d system), the Wilhelmy plate method ( θWPM; measurement of capillary forces acting on a plane sample) and the Sessile Drop Method ( θSDM; optical CA analysis of drop contour on a plane sample). Results were compared with the CAs calculated from capillary rise in long vertical columns ( θECR), where liquid profiles of the final capillary rise of water and ethanol, respectively, were used to derive the contact angle under the assumed equilibrium conditions. The results showed the overestimation of the CA by using the well established bi-liquid CRM technique for porous materials, in particular for material with a low degree of water repellency (CA < 40°) and for the finer textured materials. In contrast, a variant of the Wilhelmy plate method, i.e. the cosine-averaged advancing CA and receding CA ( θEWPM), as well as the Sessile Drop CA, θSDM, were close to the ones of θECR. We concluded that θEWPM and θSDM are apparent CA, but nevertheless able to predict the impact of wettability on the final capillary rise which is affected by pore topology as well as by wettability.
Xu, Z N; Wang, S Y
2015-02-01
To improve the accuracy in the calculation of dynamic contact angle for drops on the inclined surface, a significant number of numerical drop profiles on the inclined surface with different inclination angles, drop volumes, and contact angles are generated based on the finite difference method, a least-squares ellipse-fitting algorithm is used to calculate the dynamic contact angle. The influences of the above three factors are systematically investigated. The results reveal that the dynamic contact angle errors, including the errors of the left and right contact angles, evaluated by the ellipse-fitting algorithm tend to increase with inclination angle/drop volume/contact angle. If the drop volume and the solid substrate are fixed, the errors of the left and right contact angles increase with inclination angle. After performing a tremendous amount of computation, the critical dimensionless drop volumes corresponding to the critical contact angle error are obtained. Based on the values of the critical volumes, a highly accurate dynamic contact angle algorithm is proposed and fully validated. Within nearly the whole hydrophobicity range, it can decrease the dynamic contact angle error in the inclined plane method to less than a certain value even for different types of liquids.
NASA Astrophysics Data System (ADS)
Jafari, Mohammad; Jung, Jongwon
2016-10-01
The performance of a geologic carbon storage site strongly depends on the capillary pressure of sealing rock and formations. While wettability of minerals is a key factor in capillary pressure, published contact angles are inconsistent. This study explores the discrepancy of published contact angles in order to reduce the uncertainty of measured laboratory contact angles, and understand the variation of contact angles at unsaturated CO2-water conditions. A ratio of droplet dimension and triple line (or contact line) are used to explain the observed wide range of contact angles and the variation of contact angle at unsaturated conditions. Results show that the shape factor has a good agreement with contact angle change during CO2 dissolution in water. Silica substrate has clear two pinned and slip stages of triple line during CO2 droplet dissolution, which cause contact angle on silica substrate to increase from 34.5° to 42.1°. However, mica substrate has the repeated pinned and slip stages due to the heterogeneity of mica surface, which cause contact angle to increase dramatically from 25.4° to 68.1°. Thus, both the impact of the unsaturated CO2-water conditions on the wide range of contact angle and the heterogeneity of mineral surface should be considered when one estimates capillary pressure based on contact angle in geological CO2 sequestration.
Analysis of the relationship between liquid droplet size and contact angle.
Vafaei, S; Podowski, M Z
2005-05-30
The purpose of this paper is to present a consistent theoretical concept that can explain the various physical phenomena associated with the effect of droplet size on contact angle for droplets on solid surfaces, and with the geometry of the liquid/gas/solid contact line in general. Two droplet geometries have been considered: uniformly elongated droplets and axisymmetric droplets. It has been shown that the contact angle for elongated droplets is size-independent and, thus, satisfies the Young equation for constant material and interfacial properties. On the other hand, whereas the contact angle for axisymmetric droplets is size-dependent and does not satisfy the original Young equation, it is shown that this contact angle can still be predicted for any combination of droplet and substrate materials, and a given mass of the droplet. The theoretical work has been combined with the development of numerical schemes of solving the Laplace-Young equation for various droplet geometries. The proposed approach has been applied to different material/substrate combinations and validated against several sets of experimental data. As a result, a method has been developed for predicting the contact angle of both long and axisymmetric sessile droplets of arbitrary sizes for given liquid/solid/gas properties.
NASA Technical Reports Server (NTRS)
Zhang, Neng-Li; Chao, David F.
2001-01-01
A new hybrid optical system, consisting of reflection-refracted shadowgraphy and top-view photography, is used to visualize flow phenomena and simultaneously measure the spreading and instant dynamic contact angle in a volatile-liquid drop on a nontransparent substrate. Thermocapillary convection in the drop, induced by evaporation, and the drop real-time profile data are synchronously recorded by video recording systems. Experimental results obtained from this unique technique clearly reveal that thermocapillary convection strongly affects the spreading process and the characteristics of dynamic contact angle of the drop. Comprehensive information of a sessile drop, including the local contact angle along the periphery, the instability of the three-phase contact line, and the deformation of the drop shape is obtained and analyzed.
Apparent Contact Angle Calculated from a Water Repellent Model with Pinning Effect.
Suzuki, Shojiro; Ueno, Kazuyuki
2017-01-10
A set of new theoretical equations for apparent contact angles is proposed. The equations are derived from an equilibrium of interfacial tensions of a three-phase contact line pinned at the edges of a fine structure. These equations are validated by comparison with contact-angle measurement results for 2 μL water droplets on poly(methyl methacrylate) microstructured samples with square pillars or holes. The equilibrium contact angles predicted by the new equations reasonably agree with the experimental results. In contrast, the values predicted by the Cassie-Baxter equation or the Wenzel equation do not qualitatively agree with the experimental results in pillar pattern cases because the Cassie-Baxter equation and the Wenzel equation do not account for the pinning effect.
Experimental Investigation of the Contact Angle at Wetting the Non-ferrous Metals
NASA Astrophysics Data System (ADS)
Feoktistov, D. V.; Orlova, E. G.; Ponomarev, K. O.
2015-10-01
Experimental dependences on the effect of the drop volume from the contact angle under the conditions of the static three-phase contact line formation during wetting the nonferrous metals (aluminium, magnalium, copper and brass) are presented in the work. The surface of the substrates was investigated by modern equipment (profilometer "Micro Measure 3D station" and microscope TM-3000). The drop was placed on the surface by the precision electronic single-channel pipette (Thermo scientific). Shadow method was used to obtain the drop profile; symmetry of the drop was controlled by Schlieren method. The comparison of the methods used to determine the contact angle on the image of the drop profile was executed. It was established that in spite of influencing the friction and gravity forces the structure of metal surfaces affects greatly the value of the contact angle.
Limiting conditions for applying the spherical section assumption in contact angle estimation.
Chatterjee, Jaideep
2003-03-01
The shape of liquid drops on solid surfaces deviates from the spherical as tension decreases and gravity effects start affecting the drop shape. This paper attempts to define this deviation and estimates the dimensionless Eotvos number limits above which the deviation becomes "significant." The use of these limiting values can facilitate estimation of contact angle in the following manner. It is well known that the equilibrium contact angle made by a liquid drop on a solid surface can be estimated from measurements of two drop parameters. These parameters can be any two chosen from the drop volume, height, and wetted radius. In case the effect of gravity on the drop shape is negligible, simple algebraic relations derived from the spherical section assumption exist, from which the contact angle can be estimated. In systems where the "spherical section" assumption is invalid, the Laplace equation for the drop shape has been solved numerically with any two of the above parameters as the constraints, to obtain the contact angle. In this paper, Eotvos numbers at which the deviation of the drop profile from the spherical is significant enough to result in contact angle deviation of 1 degrees are estimated. The limiting values of Eotvos number, expressed as a function of the original contact angle made by the spherical profile, are obtained by solving the Laplace equation for the drop shape with the drop volume and wetted radius constraints for decreasing values of Interfacial tension. These limiting values are also estimated for different drop sizes and for cases where the drop phase is heavier (sessile) and lighter (buoyant) than the surrounding fluid. The independence of the Eotvos number estimates from the sign of the density difference as well as the drop size is shown. These Eotvos number limits can be used to check if the spherical section assumption, with the resulting simple algebraic relations, can be used for contact angle estimation and other shape
Wetting of biopolymer coatings: contact angle kinetics and image analysis investigation.
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.
Effect of Adsorption on the Contact Angle: Water-Glass System
NASA Astrophysics Data System (ADS)
Keshavarz, Ali; Ward, Charles A.
2002-03-01
The contact angle at the line formed by the intersection of solid, liquid and vapor phases is usually assumed to be only a function of temperature. This amounts to neglecting the effects of vapor adsorption. However recent experimental observations made during a Space Shuttle flight raised questions about this view. To explain the observations, it was hypothesized that in the limit of the pressure approaching the saturation vapour pressure, adsorption effects can gave rise to an approximately 20° increase in the contact angle. In a ground-based laboratory, this hypothesis examined. Nine cylinders, each with a different diameters has been partially filled with water, sealed and the miniscule height measured under isothermal conditions. By determining the interface shape from the Laplace equation that has the measured meniscus height, the value of the contact angle and pressure at the three-phase line can be inferred. An equilibrium adsorption isotherm relation is derived using a model of the adsorbate that was previously introduced by Hill. The adsorption isotherm relation this obtained contains three temperature-dependent parameters, and when used with the Gibbs adsorption equation, an expression for the contact angle in terms of these parameters is obtained. Their values at each of 5 different temperatures were determined by fitting theoretical relation to the measured contact angles. This permits the amount adsorbed in the limit of the pressure approaching the saturation vapour pressure to be calculated—a parameter range not previously explored. It also permits one to show that the contact angles measured on the Space Shuttle are completely consistent with those measured in a ground-based larboratory provided one takes adsorption into account. The results suggest the contact angle depends strongly on the pressure and that its pressure-dependence can not be neglected when the pressure at the three phase line is near the saturation vapor pressure.
Rangwalla, Hasnain; Schwab, Alexander D; Yurdumakan, Betül; Yablon, Dalia G; Yeganeh, Mohsen S; Dhinojwala, Ali
2004-09-28
A new and direct approach to verify surface heterogeneity as the microscopic origin of contact-angle hysteresis is demonstrated. IR-visible sum-frequency-generation spectroscopy (SFG) was used to selectively probe the molecules at the interface of an alkyl-side-chain polymer [poly(vinyl n-octadecyl carbamate-co-vinyl acetate)] with water. The spectra indicate that in contact with water, the polymer surface is heterogeneous (having areas of differing surface energies). This evidence of surface heterogeneity supports the hysteresis observed in the advancing and receding contact angles of the polymer surface with water. The same measurements made for the chemically and structurally similar surface of an octadecyltrichlorosilane self-assembled monolayer indicates a homogeneous surface at the water interface. In this case, contact-angle hysteresis measurements implicate surface roughness as the cause of hysteresis. Atomic force microscopy measurements of roughness for these surfaces further support our conclusions. The polymer-water interface was probed using SFG at above-ambient temperatures, and an order-to-disorder transition (ODT) of alkyl side chains at the interface was observed, which closely follows the melting of crystalline side chains in the bulk. This transition explains the increased wettability of the polymer, by water, when the temperature is raised above the bulk melting temperature. Furthermore, the irreversibility of this ODT suggests that the disordered polymer-water interface is the thermodynamic equilibrium state, whereas the before-heating structure of this interface is a kinetically hindered metastable state.
Sarmadivaleh, Mohammad; Al-Yaseri, Ahmed Z; Iglauer, Stefan
2015-03-01
We measured water-CO2 contact angles on a smooth quartz surface (RMS surface roughness ∼40 nm) as a function of pressure and temperature. The advancing water contact angle θ was 0° at 0.1 MPa CO2 pressure and all temperatures tested (296-343 K); θ increased significantly with increasing pressure and temperature (θ=35° at 296 K and θ=56° at 343 K at 20 MPa). A larger θ implies less structural and residual trapping and thus lower CO2 storage capacities at higher pressures and temperatures. Furthermore we did not identify any significant influence of CO2-water equilibration on θ. Moreover, we measured the CO2-water interfacial tension γ and found that γ strongly decreased with increasing pressure up to ∼10 MPa, and then decreased with a smaller slope with further increasing pressure. γ also increased with increasing temperature.
NASA Astrophysics Data System (ADS)
Marshall, K. L.; Didovets, O.; Saulnier, D.
2014-10-01
The exceptionally high 1054-nm laser-damage resistance of photoalignment materials (approaching that of fused silica) has made it possible to fabricate a wide variety of photoaligned liquid crystal (LC) devices for high-peak-power laser applications. Despite these advances, materials selection and photoalignment exposure conditions are still determined using costly and time-consuming "trial-and-error" methods. The contact angle of a fluid droplet on an alignment layer yields important information about LC-surface physicochemical interactions, and as such, it has potential as a rapid and convenient metric for optimizing photoaligned device quality. To this end, we report on efforts to correlate fluid contact angle with surface energy and azimuthal-anchoring energy to aid in the assessment of alignment quality in photoalignment materials systems.
NASA Astrophysics Data System (ADS)
Kubiak, K. J.; Wilson, M. C. T.; Castrejón-Pita, J. R.; Hutchings, I. M.
2011-11-01
Contact Angle Hysteresis (CAH) is usually attributed to surface heterogeneity, contact line pinning, adsorption or interdiffusion. A model of CAH developed recently by Kubiak & Wilson is demonstrated using the lattice Boltzmann method. The model is based on the dynamic surface heterogeneity, reorientation of surface molecules under wetting liquid, physical roughness, chemical heterogeneity and liquid adhesion and evaporation. Once the surface is wetted, the local static contact angle (CA) changes from its advancing value to match the receding static CA over time Ta. When the contact line retracts, the surface recovers its initial properties corresponding to the advancing static CA over time period Te, which corresponds to the physical evaporation. Further development of the model to include surface roughness and chemical heterogeneity is presented. The model shows good agreement with experimental results for several practical configurations i.e. droplet impact and coalescence, drops on tilted surface, and drops on superhydrophobic and non-uniform surfaces etc. The extended model exhibits great potential for predictive modelling using the lattice Boltzmann method, but can be also implemented in other schemes. Research supported by EPSRC EP/F065019/1 and EP/H018913/1.
Fractional Wetting and Contact Angle Dynamics in Water Repellent Soils
NASA Astrophysics Data System (ADS)
Beatty, S. M.; Smith, J. E.
2009-12-01
Soil water repellency is a vadose zone phenomenon most often associated with reduced or impeded infiltration for some time. Even if only short-lived, problems caused by soil water repellency are numerous and significant. In recent years, a substantial interdisciplinary research effort has advanced our knowledge of soil water behavior in these highly complex and non-linear hydrologic systems. However, fundamental understanding of the interdependent relationship between static conditions and dynamic processes is still largely undeveloped. In this study we used Axisymmetric Drop Shape Analysis (ADSA) and instrumented infiltration experiments to systematically measure and quantify static controls and dynamic processes in hydrophobic media. Using natural materials collected from a wildfire site approximately 1.5 years post-fire, we show that infiltration processes within these materials are largely governed by the spatial and temporal variation of wettable and non-wettable fractions. The approach taken 1) facilitated the development of our understanding of the interdependent nature of static and dynamic variables on soil water behavior in these materials and 2) indicates that the dynamic nature of these hydrophobic materials is well expressed empirically over centimeter spatial scales and temporal scales on the order of 10’s of minutes to hours.
Effect of contact angle hysteresis on breakage of a liquid bridge
NASA Astrophysics Data System (ADS)
Chen, H.; Tang, T.; Amirfazli, A.
2015-03-01
In this paper, the importance of considering contact angle hysteresis (CAH) during the process of stretching and breaking a liquid bridge between two solid surfaces is addressed. We clearly show that due to the pinning of contact line at the end of the stretching stage, the contact angle between liquid bridge and surfaces cannot be simply assumed to have a constant value (e.g. receding contact angle, θ r ). Simulation results for stretching a liquid bridge with and without CAH, showed that the contact line pinning can lead to breakage at a larger surface separation and smaller value of pull-off force ( F p ). A systematic study about the effect of CAH and contact line pinning on the value of F p is provided. It is found that when one of the surfaces has a θ r larger than 90∘, F p decreases with the increase of θ r on either surface delimiting the bridge. For the cases where θ r of both surfaces are smaller than 90∘, significantly smaller F p is seen when contact line pinning occurs on both surfaces, as compared to F p when contact line pinning occurs only on one surface. This smaller F p is caused by more curved profile and later breakage of liquid bridge.
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.
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.
Static and dynamic contact angles of evaporating liquids on heated surfaces.
Ajaev, Vladimir S; Gambaryan-Roisman, Tatiana; Stephan, Peter
2010-02-15
We studied both static and dynamic values of the apparent contact angle for gravity-driven flow of a volatile liquid down a heated inclined plane. The apparent contact line is modeled as the transition region between the macroscopic film and ultra-thin adsorbed film dominated by disjoining pressure effects. Four commonly used disjoining pressure models are investigated. The static contact angle is shown to increase with heater temperature, in qualitative agreement with experimental observations. The angle is less sensitive to the details of the disjoining pressure curves than in the isothermal regime. A generalization of the classical Frumkin-Derjaguin theory is proposed to explain this observation. The dynamic contact angle follows the Tanner's law remarkably well over a range of evaporation conditions. However, deviations from the predictions based on the Tanner's law are found when interface shape changes rapidly in response to rapid changes of the heater temperature. The Marangoni stresses are shown to result in increase of the values of apparent contact angles.
NASA Astrophysics Data System (ADS)
Heib, F.; Hempelmann, R.; Munief, W. M.; Ingebrandt, S.; Fug, F.; Possart, W.; Groß, K.; Schmitt, M.
2015-07-01
Contact angles and wetting of solid surfaces are strongly influenced by the physical and chemical properties of the surfaces. These influence quantities are difficult to distinguish from each other if contact angle measurements are performed by measuring only the advancing θa and the receding θr contact angle. In this regard, time-dependent water contact angles are measured on two hydrophobic modified silicon wafers with different physical surface topographies. The first surface is nearly atomically flat while the second surface is patterned (alternating flat and nanoscale rough patterns) which is synthesized by a photolithography and etching procedure. The different surface topographies are characterized with atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS) and Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR). The resulting set of contact angle data obtained by the high-precision drop shape analysis approach is further analyzed by a Gompertzian fitting procedure and a statistical counting procedure in dependence on the triple line velocity. The Gompertzian fit is used to analyze overall properties of the surface and dependencies between the motion on the front and the back edge of the droplets. The statistical counting procedure results in the calculation of expectation values E(p) and standard deviations σ(p) for the inclination angle φ, contact angle θ, triple line velocity vel and the covered distance of the triple line dis relative to the first boundary points XB,10. Therefore, sessile drops during the inclination of the sample surface are video recorded and different specific contact angle events in dependence on the acceleration/deceleration of the triple line motion are analyzed. This procedure results in characteristically density distributions in dependence on the surface properties. The used procedures lead to the possibility to investigate influences on contact
NASA Astrophysics Data System (ADS)
Zhou, X.; Nolte, D. D.; Pyrak-Nolte, L. J.
2014-12-01
Traditionally, capillary pressure is determined by increasing or decreasing external fluid pressures to change the immiscible fluid saturation in a porous medium. The resulting saturation and interfacial area are then linked to the capillary pressure through constitutive equations. A key question is whether externally measured pressures are sensitive to changes in distributions that arise from internal changes in contact angles. As a first step in addressing this question, we investigated the effect of electro-kinetic manipulation on interfacial area and contact angles for a fixed saturation. An EWOD (electro-wetting on dielectric) technique was used to alter the contact angle of single 10 μL droplets of a 1M KCl-H2O solution. A liquid droplet was placed on a glass cover slip (18 mm x 18 mm) coated with a layer of silver (100 nm in thickness) to act as an electrode and then spin-coated with polyimide (a dielectric). A platinum wire was inserted into the droplet and connected to an AC voltage source. The glass plate electrode was connected to ground. Measurements were made for Vrms voltages between 0 to 300 V at a frequency of 50 Hz. Two CCD cameras were used to image changes in the shape of a droplet. One camera was placed on a microscope to capture a top view of a drop in order to measure changes in areal extent and the perimeter of the drop. The second camera imaged a drop from the side to measure contact angles and side-view areal extent and perimeter. At low voltages, the cosine of the contact angle, θ, after applying voltage was linearly dependent on Vrms2. Several experiments showed that the slope of the low-voltage relationship of cos θ vs Vrms2 remained constant for all trials. As the voltage increased, the contact angle saturated. From the side-view images, the contact angle and interfacial length decreased with increasing voltage. From the top-view images, the drop shape changed from circular to elliptical-to irregular as the voltage increased
Contact-Angle Hysteresis Caused by a Random Distribution of Weak Heterogeneities on a Solid Surface.
Öpik
2000-03-15
A model according to which contact-angle hysteresis arises as the result of a random distribution of irregularities on the solid surface is investigated on the basis of probability theory. An estimate is obtained of the mathematical expectation of the number of stable equilibria when the effective angle between the liquid-gas surface and the solid surface with which the liquid is in contact deviates from the value, say theta(0), which would obtain if the solid surface were uniform, i.e., free from irregularities. It is found that when the effective contact angle deviates from theta(0) by less than a critical value, then the expected number of stable equilibria increases exponentially with the length of the contact line; therefore such a contact angle can occur under static conditions. But if the deviation of the contact angle from theta(0) exceeds the critical value, then the expected number of stable equilibria decreases exponentially with the length of the contact line, so a stable equilibrium is not possible for a macroscopic length of the contact line. The method is applicable only if the random deviations of the spreading power (defined as the solid-gas surface tension minus the sum of the liquid-gas and liquid-solid surface tensions) from its average are sufficiently small. It is found that the critical deviation of the contact angle from theta(0) is, apart from a slowly varying logarithmic factor, proportional to H(2)rho(s), where H is a measure of the amplitude of the surface irregularities and rho(s) is the surface density (i.e., number per unit area) of the irregularities. This qualitative feature agrees with the results previously obtained by several other authors, and, moreover, there is a surprisingly close agreement of the proportionality factor with the results of some earlier work in which the method of statistical analysis was much less elaborate than here. The effect of the logarithmic factor is to make the critical deviation of the contact angle
Modulating contact angle hysteresis to direct fluid droplets along a homogenous surface.
Luo, Mingxiang; Gupta, Rohini; Frechette, Joelle
2012-02-01
The shape and motion of drops on surfaces is governed by the balance between the driving and the pinning forces. Here we demonstrate control over the motion of droplets on an inclined surface by exerting control over the contact angle hysteresis. The external modulation of contact angle hysteresis is achieved through a voltage-induced local molecular reorganization within the surface film at the solid-liquid interface. We show that tuning contact angle hysteresis alone is sufficient to direct and deform drops when subjected to a constant external driving force, here gravity, in the absence of a pre-defined surface energy gradient or pattern. We also show that the observed stretching and contraction of the drops mimic the motion of an inchworm. Such reversible manipulation of the pinning forces could be an attractive means to direct drops, especially with the dominance of surface forces at micro-/nanoscale.
Experimental Study on the Effect of Liquid Contact Angle on Bubble Movement under Microgravity
NASA Astrophysics Data System (ADS)
Yanjie, Yang; Li, Shiyou; Yiyong, Huang; Guangyu, Li
2016-07-01
The experimental study of bubble dynamics under microgravity has been conducted utilizing the Drop Tower Beijing(NMLC). A pottery sized of 20mm in length, 10mm in width and 1.2mm in height was used as the heater. The fluid was HFE7500 and distilled water. During the experiment under microgravity the nucleate boiling and film boiling were observed. At the same heating power the bubble of HFE7500 whose contact angle is smaller grew faster and bigger, moved quickly on the heating surface, combined into center big bubble by colliding and reached its CHF earlier to film boiling. The bubble of distilled water whose contact angle is bigger didn't move obviously on heating surface, and it transferred from nucleate boiling to film boiling at its original place meanwhile it absorbed smaller bubble around. Key words: microgravity; bubble movement; contact angle; drop tower
NASA Astrophysics Data System (ADS)
Korsgaard Andersen, Nis; Taboryski, Rafael
2017-04-01
Contact angle measurements are a fast and simple way to measure surface properties and is therefore widely used to measure surface energy and quantify wetting of a solid surface by a liquid substance. In common praxis contact angle measurements are done with sessile drops on a horizontal surface fitted to a drop profile derived from the Young-Laplace equation. When measuring the wetting behaviour by tilting experiments this is not possible since it involves moving drops that are not in equilibrium. Here we present a fitting technique capable of determining the contact angle of asymmetric drops with very high accuracy even with blurry or noisy images. We do this by splitting the trace of a drop into a left and right part at the apex and then fit each side to an ellipse.
A nonmonotonic dependence of the contact angles on the surface polarity for a model solid surface.
Qi, Chonghai; Zhou, Bo; Wang, Chunlei; Zheng, Yujun; Fang, Haiping
2017-03-01
Based on molecular dynamics simulations, we found a nonmonotonic relationship between the contact angle of water droplets and the surface polarity on a solid surface with specific hexagonal charge patterns at room temperature. The contact angle firstly decreases and then increases as polarity (denoted as charge q) increases from 0 e to 1.0 e with a vertex value of q = 0.5 e. We observed a different wetting behavior for a water droplet on a conventional nonwetted solid surface when q ≤ 0.5 e, and a water droplet on an ordered water monolayer adsorbed on a highly polar solid surface when q > 0.5 e. The solid-water interaction, density of water, hydrogen bonds, and water structures were analyzed. Remarkably, there was up to six times difference in the solid-water interactions despite the same value of the apparent contact angle values.
Shape of menisci in spinning horizontal tubes: Application to contact angle determination
Princen, H.M.; Vaidya, R.N.
1995-09-01
The authors have computed the shape of an axisymmetric fluid/liquid meniscus in a capillary that is spun about its horizontal axis. The solutions were used to establish the relationship between the fluid/liquid/solid contact angle on the one hand and several experimentally accessible parameters (tube radius, interfacial tension, densities, angular velocity, and certain meniscus dimensions) on the other. This opens the way to a novel method for determining contact angles. Using the results for single menisci, the authors have in addition developed a method whereby the contact angle may be obtained from the critical speed at which a finite drop (or slug) is either released from the tube wall (if the drop phase is the less dense phase) or penetrated axially by the other phase (if the drop phase is the denser phase).
Contact angles and wettability of ionic liquids on polar and non-polar surfaces†
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
Chemical nano-heterogeneities detection by contact angle hysteresis: theoretical feasibility.
Bittoun, Eyal; Marmur, Abraham
2010-10-19
The theoretical feasibility of detecting chemical nanoheterogeneities on solid surfaces by measurement of contact angle hysteresis (CAH) was studied, using simplified models of cylindrical (2D) and axisymmetric (3D) drops on corresponding models of chemically heterogeneous, smooth solid surfaces. This feasibility depends on the ratio between the external energy input to the drop and the energies needed to deform its liquid-gas interface and move the contact line across energy barriers. A ubiquitous source of external energy is building vibrations, since most contact-angle measurements are done in buildings. The energy barriers that oppose the motion of the contact line were numerically calculated for various parameters of the two systems. The variations of the liquid-gas interfacial energy are discussed in terms of orders of magnitude. By comparing these energies, it is concluded that under regular ("barely perceptible") building vibrations CAH measurements may detect chemical heterogeneities at the few nanometers scale.
Krumpfer, Joseph W; McCarthy, Thomas J
2010-01-01
Contact angle hysteresis is addressed from two perspectives. The first is an analysis of the events that occur during motion of droplets on superhydrophobic surfaces. Hysteresis is discussed in terms of receding contact line pinning and the tensile failure of capillary bridges. The sign of the curvature of the solid surface is implicated as playing a key role. The second is the report of a new method to prepare smooth low hysteresis surfaces. The thermal treatment of oxygen plasma-cleaned silicon wafers with trimethylsilyl-terminated linear poly(dimethylsiloxane) (PDMS - commercial silicone oils) in disposable glass vessels is described. This treatment renders silicon/silica surfaces that contain covalently attached PDMS chains. The grafted layers of nanometre scale thickness are liquid-like (rotationally dynamic at room temperature), decrease activation barriers for contact line motion and minimize water contact angle hysteresis. This simple method requires neither sophisticated techniques nor substantial laboratory skills to perform.
Kong, Bin; Yang, Xiaozhen
2006-02-28
We have studied two types of topological substrates--the continuous solid substrates (CSS) and the discontinuous solid substrates (DSS)--by using the dissipative particle dynamics (DPD) method for a better understanding of the contact angle hysteresis on two such substrates. After the validation of DPD in the system, we found that DSS has a different distribution of the metastable states from that of CSS and that DSS has relatively larger contact angle hysteresis at lower temperature. Obtained results also show that CSS is more suitable for making an ultrahydrophobic or ultralyophobic surface than DSS from the point of view of dynamic wettability.
Apparent Contact Angle and Triple-Line Tension of a Soap Bubble on a Substrate.
Rodrigues, João Filipe; Saramago, Benilde; Fortes, Manuel Amaral
2001-07-15
The contact angle, θ, of a small bubble on a flat solid substrate was measured as a function of bubble radius, R. The observed deviation of the contact angle from 90 degrees can be accounted for in terms of a negative line tension, tau. The measured values of |tau|/gamma(f), where gamma(f) is the film tension, ranged between 0.15 and 0.6 mm and are proportional to the height, h, of the Plateau border, with |tau| congruent with1.7gamma(f)h. Copyright 2001 Academic Press.
A thermodynamic approach for determining the contact angle hysteresis for superhydrophobic surfaces.
Li, W; Amirfazli, A
2005-12-01
Contact angle hysteresis (CAH) is critical to superhydrophobicity of a surface. This study proposes a free energy thermodynamic analysis (of a 2-D model surface) that significantly simplifies calculations of free energy barrier associated with CAH phenomena. A microtextured surface with pillar structure, typical of one used in experimental studies, is used as an example. We demonstrate that the predicted CAH and equilibrium contact angles are consistent with experimental observations and predictions of Wenzel's and Cassie's equations, respectively. We also establish a criterion for transition between noncomposite and composite wetting states. The results and methodology presented can potentially be used for designing superhydrophobic surfaces.
Iliev, Dimitar; Pesheva, Nina; Iliev, Stanimir
2013-05-14
The results of a numerical study of the various characteristics of the static contact of a liquid meniscus with a flat but heterogeneous surface, consisting of two types of homogeneous materials, forming regularly and randomly distributed microscopic defects are presented. The solutions for the meniscus shape are obtained numerically using the full expression of the system free energy functional. The goal is to establish how the magnitude and the limits of the hysteresis interval of the equilibrium contact angle, the Cassie's angle, and the contact line (CL) roughness exponent are related to the parameters, characterizing the heterogeneous surface-the equilibrium contact angles on the two materials and their fractions. We compare the results of different ways of determining the averaged contact angle on heterogeneous surfaces. We study the spread of the CL corrugation along the liquid meniscus. We compare our results with the numerical results, obtained using linearized energy functional, and also with experimental results for the CL roughness exponent. The obtained results support the conclusion that some characteristics depends on the type (regular or random) of the heterogeneity pattern.
Hilpert, Markus
2009-09-01
We generalize Washburn's analytical solution for capillary flow in a horizontally oriented tube by accounting for a dynamic contact angle. We consider two general models for dynamic contact angle: the uncompensated Young force on the contact line depends on the capillary number in the form of either (1) a power law with exponent beta or (2) a power series. By considering the ordinary differential equation (ODE) for the velocity of the gas-liquid interface instead of the ODE for the interface position, we are able to derive new analytical solutions. For both dynamic contact angle models, we derive analytical solutions for the travel time of the gas-liquid interface as a function of interface velocity. The interface position as a function of time can be obtained through numerical integration. For the power law and beta=1 (an approximation of Cox's model for dynamic contact angle), we obtain an analytical solution for both interface position and velocity as a function of time. For the power law and beta=3, we can express the interface velocity as a function of time.
Liquid-bridge stability and breakup on surfaces with contact-angle hysteresis.
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.
Role of contact-angle hysteresis for fluid transport in wet granular matter.
Mani, Roman; Semprebon, Ciro; Kadau, Dirk; Herrmann, Hans J; Brinkmann, Martin; Herminghaus, Stephan
2015-04-01
The stability of sand castles is determined by the structure of wet granulates. Experimental data on the size distribution of fluid pockets are ambiguous with regard to their origin. We discovered that contact-angle hysteresis plays a fundamental role in the equilibrium distribution of bridge volumes, and not geometrical disorder as commonly conjectured. This has substantial consequences on the mechanical properties of wet granular beds, including a history-dependent rheology and lowered strength. Our findings are obtained using a model in which the Laplace pressures, bridge volumes, and contact angles are dynamical variables associated with the contact points. While accounting for contact line pinning, we track the temporal evolution of each bridge. We observe a crossover to a power-law decay of the variance of capillary pressures at late times and a saturation of the variance of bridge volumes to a finite value connected to contact line pinning. Large-scale simulations of liquid transport in the bridge network reveal that the equilibration dynamics at early times is well described by a mean-field model. The spread of final bridge volumes can be directly related to the magnitude of contact-angle hysteresis.
NASA Astrophysics Data System (ADS)
Colinet, Pierre; Tsoumpas, Yannis; Dehaeck, Sam; Rednikov, Alexey
2014-11-01
For volatile liquids, finite contact angles on solid substrates can occur even in the case of perfect wetting, immobile contact lines and ideally smooth surfaces. This is a fluid-dynamic effect due to evaporation typically intensifying towards a small vicinity of the contact line. In the present talk, we first overview recent theoretical results on the subject, where we focus primarily on the case of diffusion-limited evaporation into air. The model is based upon the so-called de Gennes' paradigm, incorporating simultaneously the spreading coefficient and the disjoining pressure in the form of an inverse cubic law. Then we carry out comparison with experimental results for the contact angles of evaporating sessile drops of several perfectly-wetting HFE liquids of different volatility recently obtained by Mach-Zehnder interferometry. The scaling-type theoretical prediction for the apparent contact angle is found to be in good agreement with experimental measurements. Another model based upon the Kelvin effect (curvature dependence of the saturation conditions) is also briefly discussed, an important conceptual feature of which being that contact-line singularities (both evaporation- and motion-induced) can be fully regularized, in contrast with the first model. Support from ESA, BELSPO and FRS-FNRS is gratefully acknowledged.
Chakraborty, Debapriya; Chakraborty, Suman
2008-09-02
The dynamic evolution of an incompressible liquid meniscus inside a microcapillary is investigated, under the combined influences of viscous, capillary, intermolecular, pondermotive, and electroosmotic effects. In the limit of small capillary numbers, an advancing meniscus shape is shown to merge smoothly with the precursor film, using matched asymptotic analysis. A scaling relationship is also established for the dynamic contact angle as a nondimensional function of the capillary number and the applied electrical voltage. The analysis is further generalized by invoking a kinetic slip model for overcoming the constraints of meniscus tip singularity. The kinetic slip model is subsequently utilized to analyze the interfacial dynamics from the perspective of the results obtained from the matched asymptotic analysis. A generalization is achieved in this regard, which may provide a sound basis for controlling the topographical features of a dynamically evolving meniscus in a microcapillary subjected to electrokinetic effects. These results are also in excellent agreement with the experimental findings over a wide range of capillary number values.
Grabowska, I; Dehaen, W; Radecka, H; Radecki, J
2016-05-01
In this article we present the results of the studies on interactions between the VC1 domain of the Receptor for Advanced Glycation End Products (RAGE) and its ligand, the S100B protein, performed by contact angle measurements. Histidine-tagged (His6) VC1-RAGE domain was covalently bonded to Cu(II) or Ni(II) complexes with dipyrromethene (DPM) self-assembled on gold surface. The method based on the theory of van Oss was used for the purpose of determining the Lifshitz-van der Waals (γ(LW)) component as well as the electron acceptor-electron donor (the Lewis acid-base, γ(+)-γ(-)) parameters of the VC1-RAGE-S100B complex. Moreover, the surface free energies of the interactions between the VC1 domain attached to the surface and the ligand present in the aqueous phase were determined. The specificity of the VC1- RAGE interactions with the ligand studied was also proved.
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.
Tuning the Receding Contact Angle on Hydrogels by Addition of Particles.
Boulogne, François; Ingremeau, François; Limat, Laurent; Stone, Howard A
2016-06-07
Control of the swelling, chemical functionalization, and adhesivity of hydrogels are finding new applications in a wide range of material systems. We investigate experimentally the effect of adsorbed particles on hydrogels on the depinning of contact lines. In our experiments, a water drop containing polystyrene microspheres is deposited on a swelling hydrogel, which leads to the drop absorption and particle deposition. Two regimes are observed: a decreasing drop height with a pinned contact line followed by a receding contact line. We show that increasing the particles concentration increases the duration of the first regime and significantly decreases the total absorption time. The adsorbed particles increase the pinning force at the contact line. Finally, we develop a method to measure the receding contact angle with the consideration of the hydrogel swelling.
Colosqui, Carlos E; Kavousanakis, Michail E; Papathanasiou, Athanasios G; Kevrekidis, Ioannis G
2013-01-01
We present a model based on the lattice Boltzmann equation that is suitable for the simulation of dynamic wetting. The model is capable of exhibiting fundamental interfacial phenomena such as weak adsorption of fluid on the solid substrate and the presence of a thin surface film within which a disjoining pressure acts. Dynamics in this surface film, tightly coupled with hydrodynamics in the fluid bulk, determine macroscopic properties of primary interest: the hydrodynamic slip; the equilibrium contact angle; and the static and dynamic hysteresis of the contact angles. The pseudo-potentials employed for fluid-solid interactions are composed of a repulsive core and an attractive tail that can be independently adjusted. This enables effective modification of the functional form of the disjoining pressure so that one can vary the static and dynamic hysteresis on surfaces that exhibit the same equilibrium contact angle. The modeled fluid-solid interface is diffuse, represented by a wall probability function that ultimately controls the momentum exchange between solid and fluid phases. This approach allows us to effectively vary the slip length for a given wettability (i.e., a given static contact angle) of the solid substrate.
Sawane, Yogesh B; Ogale, Satishchandra B; Banpurkar, Arun G
2016-09-14
We demonstrate a consistent electrowetting response on ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) insulator covered with a thin Teflon AF layer. This bilayer exhibits a factor of 3 enhancement in the contact angle modulation compared to that of conventional single-layered Teflon AF dielectric. On the basis of the proposed model the enhancement is attributed to the high value of effective dielectric constant (εeff ≈ 6) of the bilayer. Furthermore, the bilayer dielectric exhibits a hysteresis-free contact angle modulation over many AC voltage cycles. But the contact angle modulation for DC voltage shows a hysteresis because of the field-induced residual polarization in the ferroelectric layer. Finally, we show that a thin bilayer exhibits contact angle modulation of Δθ (U) ≈ 60° at merely 15 V amplitude of AC voltage indicating a potential dielectric for practical low voltage electrowetting applications. A proof of concept confirms electrowetting based rapid mixing of a fluorescent dye in aqueous glycerol solution for 15 V AC signal.
Contact angle and detachment energy of shape anisotropic particles at fluid-fluid interfaces.
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.
On canonical cylinder sections for accurate determination of contact angle in microgravity
NASA Technical Reports Server (NTRS)
Concus, Paul; Finn, Robert; Zabihi, Farhad
1992-01-01
Large shifts of liquid arising from small changes in certain container shapes in zero gravity can be used as a basis for accurately determining contact angle. Canonical geometries for this purpose, recently developed mathematically, are investigated here computationally. It is found that the desired nearly-discontinuous behavior can be obtained and that the shifts of liquid have sufficient volume to be readily observed.
A Langevin model for fluctuating contact angle behaviour parametrised using molecular dynamics.
Smith, E R; Müller, E A; Craster, R V; Matar, O K
2016-12-06
Molecular dynamics simulations are employed to develop a theoretical model to predict the fluid-solid contact angle as a function of wall-sliding speed incorporating thermal fluctuations. A liquid bridge between counter-sliding walls is studied, with liquid-vapour interface-tracking, to explore the impact of wall-sliding speed on contact angle. The behaviour of the macroscopic contact angle varies linearly over a range of capillary numbers beyond which the liquid bridge pinches off, a behaviour supported by experimental results. Nonetheless, the liquid bridge provides an ideal test case to study molecular scale thermal fluctuations, which are shown to be well described by Gaussian distributions. A Langevin model for contact angle is parametrised to incorporate the mean, fluctuation and auto-correlations over a range of sliding speeds and temperatures. The resulting equations can be used as a proxy for the fully-detailed molecular dynamics simulation allowing them to be integrated within a continuum-scale solver.
Forny, Laurent; Saleh, Khashayar; Denoyel, Renaud; Pezron, Isabelle
2010-02-16
Dry water is a very convenient way of encapsulating a high amount of aqueous solutions in a powder form made of hydrophobic silica nanoparticles. It was demonstrated in previous studies that both solid and liquid interfacial properties influence the quality of the final product resulting occasionally in mousse formation. To explain this behavior, contact angles of silica nanoparticles have been measured for water and water/ethanol solution by means of liquid intrusion experiments. It was found that the quality of the final product correlates with the contact angle, i.e., contact angle close to 105 degrees leads to mousse formation whereas a slightly higher value of approximately 118 degrees allows dry water formation. The proposed explanation was based on the energy of immersion and adhesion defined as the energy needed for a spherical particle to respectively penetrate into the liquid or attach at the liquid/air interface. Significantly lower energy of immersion calculated for lower contact angle might account for particle penetration into the liquid phase during processing, leading to continuous network aggregation, air entrapment, and finally mousse formation.
Influence of the dynamic contact angle on the characterization of porous media.
Martic, G; De Coninck, J; Blake, T D
2003-07-01
It has been shown recently that the classical Lucas-Washburn equation, often used to model the dynamics of liquid penetration into porous media, should be modified to take account of the dynamic contact angle between the liquid and the pore. Here we show how neglect of this effect can lead to significant errors in estimation of the effective pore radius.
Effect of the meniscus contact angle during early regimes of spontaneous imbibition in nanochannels.
Karna, Nabin Kumar; Oyarzua, Elton; Walther, Jens H; Zambrano, Harvey A
2016-11-30
Nanoscale capillarity has been extensively investigated; nevertheless, many fundamental questions remain open. In spontaneous imbibition, the classical Lucas-Washburn equation predicts a singularity as the fluid enters the channel consisting of an anomalous infinite velocity of the capillary meniscus. Bosanquet's equation overcomes this problem by taking into account fluid inertia predicting an initial imbibition regime with constant velocity. Nevertheless, the initial constant velocity as predicted by Bosanquet's equation is much greater than those observed experimentally. In the present study, large scale atomistic simulations are conducted to investigate capillary imbibition of water in slit silica nanochannels with heights between 4 and 18 nm. We find that the meniscus contact angle remains constant during the inertial regime and its value depends on the height of the channel. We also find that the meniscus velocity computed at the channel entrance is related to the particular value of the meniscus contact angle. Moreover, during the subsequent visco-inertial regime, as the influence of viscosity increases, the meniscus contact angle is found to be time dependent for all the channels under study. Furthermore, we propose an expression for the time evolution of the dynamic contact angle in nanochannels which, when incorporated into Bosanquet's equation, satisfactorily explains the initial capillary rise.
Influence of temperature and glass composition on aluminum nitride contact angle
NASA Astrophysics Data System (ADS)
Tarnovskiy, R.; Ditts, A.
2016-11-01
Results of research of different glass compositions for possibility of their application in metallization pastes intended for ceramics based on aluminum nitride are presented in this article. It includes research of contact angle of aluminum nitride with glasses of different compositions at different temperatures and different roughness of ceramics.
NASA Astrophysics Data System (ADS)
Colosqui, Carlos E.; Kavousanakis, Michail E.; Papathanasiou, Athanasios G.; Kevrekidis, Ioannis G.
2013-01-01
We present a model based on the lattice Boltzmann equation that is suitable for the simulation of dynamic wetting. The model is capable of exhibiting fundamental interfacial phenomena such as weak adsorption of fluid on the solid substrate and the presence of a thin surface film within which a disjoining pressure acts. Dynamics in this surface film, tightly coupled with hydrodynamics in the fluid bulk, determine macroscopic properties of primary interest: the hydrodynamic slip; the equilibrium contact angle; and the static and dynamic hysteresis of the contact angles. The pseudo-potentials employed for fluid-solid interactions are composed of a repulsive core and an attractive tail that can be independently adjusted. This enables effective modification of the functional form of the disjoining pressure so that one can vary the static and dynamic hysteresis on surfaces that exhibit the same equilibrium contact angle. The modeled fluid-solid interface is diffuse, represented by a wall probability function that ultimately controls the momentum exchange between solid and fluid phases. This approach allows us to effectively vary the slip length for a given wettability (i.e., a given static contact angle) of the solid substrate.
Liquid transfer mechanism between two surfaces and the role of contact angles.
Chen, H; Tang, T; Amirfazli, A
2014-04-21
The transfer ratio of quasi-static liquid transfer was found to strongly depend on the difference between the receding contact angles of the two surfaces. In contrast to traditional thinking, the transfer ratio was quite insensitive to the adhesion force between the solid and the liquid when the liquid bridge broke.
Effect of meniscus contact angle during early regimes of spontaneous capillarity in nanochannels
NASA Astrophysics Data System (ADS)
Karna, N. K.; Oyarzua, Elton; Walther, J. H.; Zambrano, Harvey
2016-11-01
In capillary imbibition, the classical Lucas-Washburn equation predicts a singularity as the fluid enters the channel consisting in an anomalous infinite velocity of the capillary meniscus. The Bosanquet's equation overcomes this problem by taking into account fluid inertia predicting an initial imbibition regime with constant velocity. Nevertheless, the initial constant velocity predicted by Bosanquet's equation is much greater than experimentally observed. In the present study, we conduct atomistic simulations to investigate capillary imbibition of water in silica nanochannels with heights between 4 and 18 nm. We find that the meniscus contact angle remains constant during the inertial regime and its value depends upon the height of the channel. We also find that the meniscus velocity computed at the channel entrance is related to the particular value of the meniscus contact angle. Moreover, after the inertial regime, the meniscus contact angle is found to be time dependent for all the channels under study. We propose an expression for the time evolution of the dynamic contact angle in nanochannels which, when incorporated in Bosanquet's equation, satisfactorily explains the initial capillary rise. We aknowledge financial support from Conicyt project.
2007-03-01
of two methods described in this section. For films, a static contact - angle setup using the sessile drop method was utilized. The setup consists...can’t be used, as fabric roughness causes absorption of the single drop . To measure the liquid-solid contact angle for fabrics, we use the Wilhelmy...polyethylene film. Prior to plasma exposure, a drop of water was placed on the film and the contact angle was 98°. In this case, the surface can be
Fluid epitaxialization effect on velocity dependence of dynamic contact angle in molecular scale.
Ito, Takahiro; Hirata, Yosuke; Kukita, Yutaka
2010-02-07
Molecular dynamics simulations were used to investigate the effect of epitaxial ordering of the fluid molecules on the microscopic dynamic contact angle. The simulations were performed in a Couette-flow-like geometry where two immiscible fluids were confined between two parallel walls moving in opposite directions. The extent of ordering was varied by changing the number density of the wall particles. As the ordering becomes more evident, the change in the dynamic contact angle tends to be more sensitive to the increase in the relative velocity of the contact line to the wall. Stress components around the contact line is evaluated in order to examine the stress balance among the hydrodynamic stresses (viscous stress and pressure), the deviation of Young's stress from the static equilibrium condition, and the fluid-wall shear stress induced by the relative motion between them. It is shown that the magnitude of the shear stress on the fluid-wall surface is the primary contribution to the sensitivity of the dynamic contact angle and that the sensitivity is intensified by the fluid ordering near the wall surface.
Simulations of impinging droplets with surfactant-dependent dynamic contact angle
NASA Astrophysics Data System (ADS)
Ganesan, Sashikumaar
2015-11-01
An arbitrary Lagrangian-Eulerian (ALE) finite element scheme for computations of soluble surfactant droplet impingement on a horizontal surface is presented. The numerical scheme solves the time-dependent Navier-Stokes equations for the fluid flow, scalar convection-diffusion equation for the surfactant transport in the bulk phase, and simultaneously, surface evolution equations for the surfactants on the free surface and on the liquid-solid interface. The effects of surfactants on the flow dynamics are included into the model through the surface tension and surfactant-dependent dynamic contact angle. In particular, the dynamic contact angle (θd) of the droplet is defined as a function of the surfactant concentration at the contact line and the equilibrium contact angle (θe0) of the clean surface using the nonlinear equation of state for surface tension. Further, the surface forces are included into the model as surface divergence of the surface stress tensor that allows to incorporate the Marangoni effects without calculating the surface gradient of the surfactant concentration on the free surface. In addition to a mesh convergence study and validation of the numerical results with experiments, the effects of adsorption and desorption surfactant coefficients on the flow dynamics in wetting, partially wetting and non-wetting droplets are studied in detail. It is observed that the effects of surfactants are more in wetting droplets than in the non-wetting droplets. Further, the presence of surfactants at the contact line reduces the equilibrium contact angle further when θe0 is less than 90°, and increases it further when θe0 is greater than 90°. Nevertheless, the presence of surfactants has no effect on the contact angle when θe0 = 90 °. The numerical study clearly demonstrates that the surfactant-dependent contact angle has to be considered, in addition to the Marangoni effect, in order to study the flow dynamics and the equilibrium states of surfactant
Hilpert, Markus
2010-04-01
We derive new analytical solutions for liquid infiltration into a gas-filled capillary tube, whose inlet is connected to a liquid reservoir held at a constant pressure. We generalize the Lucas-Washburn theory to account for a model for dynamic contact angle that assumes the nonequilibrium Young force to depend linearly on the velocity of the gas-liquid interface. Like Lucas and Washburn, we neglect inertial forces. Using the Lambert function, we derive explicit analytical solutions for the interface position, velocity, and acceleration as a function of time. Consistent with previous work, which used more general models for dynamic contact angle, we can distinguish between five infiltration scenarios: horizontal infiltration, upward infiltration (capillary rise), as well as steady-state, accelerating, and decelerating downward infiltration. We determine the mutually exclusive conditions for the different infiltration scenarios to occur in terms of the nondimensional parameters that define the problem. Moreover, we develop 2D and 3D diagrams that show which parameter combination results in which infiltration scenario. Our analytical solutions are also valid in the limit where the dynamic contact angle becomes constant. For a constant contact angle, accelerating downward infiltration occurs only if the initial interface is not located at the tube inlet but further down the tube. For the special case in which the contact angle is constant, the liquid pressure at the tube inlet is equal to the gas pressure, and the interface is initially located at the tube inlet, our solution for upward infiltration is identical to a solution previously reported in the literature.
Effective Darcy-Scale Contact Angles in Porous Media Imbibing Solutions of Various Surface Tensions
Weisbrod, Noam; McGinnis, Thomas; Rockhold, Mark L.; Niemet, Mike; Selker, John S.
2009-10-17
Surface tensions of high-salinity solutions are significantly different from those of pure water. Our objective was to develop and test a methodology to determine whether these surface-tension effects predictably alter imbibition into dry and moist porous media. Static and dynamic experiments were performed using four grades of quartz sand to determine the effects of solution salinity on imbibition. Results were quantified as apparent contact angles between the sand and three solutions (pure water, 5 molal NaNO3, n-hexane). Contact angles determined using a static method in initially air-dried sand ranged from 23° to 31°, with the same values found for both water and the NaNO3 solution. Effective contact angles determined for the air-dried sand using a dynamic method based on a modified version of the Green and Ampt model were about twice those found using the static method, averaging 45° and 62° for water and the NaNO3 solution, respectively. In pre-wetted sands, the dynamic imbibition data yielded apparent contact angles of 2° and 21° for water and the NaNO3 solution, respectively, with the latter value comparing well to a predicted value of 25° for the NaNO3 solution based solely on surface-tension contrast. The results of this study indicate that on the Darcy-scale, saline solutions appear to follow the relationship of non-zero contact angles with other miscible fluids of different surface tensions used to pre-wet the sand grains, in agreement with the macro-scale infiltration results of Weisbrod et al. [2004].
Small angle slot divertor concept for long pulse advanced tokamaks
NASA Astrophysics Data System (ADS)
Guo, H. Y.; Sang, C. F.; Stangeby, P. C.; Lao, L. L.; Taylor, T. S.; Thomas, D. M.
2017-04-01
SOLPS-EIRENE edge code analysis shows that a gas-tight slot divertor geometry with a small-angle (glancing-incidence) target, named the small angle slot (SAS) divertor, can achieve cold, dissipative/detached divertor conditions at relatively low values of plasma density at the outside midplane separatrix. SAS exhibits the following key features: (1) strong enhancement of the buildup of neutral density in a localized region near the plasma strike point on the divertor target; (2) spreading of the cooling front across the divertor target with the slot gradually flaring out from the strike point, thus effectively reducing both heat flux and erosion on the entire divertor target surface. Such a divertor may potentially provide a power and particle handling solution for long pulse advanced tokamaks.
X-ray computed microtomography for drop shape analysis and contact angle measurement.
Santini, Maurizio; Guilizzoni, Manfredo; Fest-Santini, Stephanie
2013-11-01
The interaction between an atomized fluid and a solid surface has a great importance in many fields, both in adiabatic conditions and when heat transfer is involved. To investigate the behavior of many drops in contact with a surface, the first step is to study a single one of them and in that, surface wettability is key parameter. Wettability analyses are usually performed by contact angle measurement, in most cases using the sessile drop or captive bubble techniques. Such techniques require optical acquisition of a side view of the drop or bubble, with a series of drawbacks when conventional optics are used, in particular for not uniform, not planar or rough base surfaces. X-ray micro-computed tomography is therefore used to acquire a 3D scan of a drop gently deposited on a surface, with the aim to reconstruct the drop surface and to perform contact angle measurements on true cross-sections of the drop-surface couple. Comparison with contact angle measurements performed on conventional images is performed. The results evidence that the proposed technique is very promising for surface characterization and to get more accurate and detailed information about wettability characteristics.
Pressure dependence of the contact angle in a CO2-H2O-coal system.
Siemons, Nikolai; Bruining, Hans; Castelijns, Hein; Wolf, Karl-Heinz
2006-05-15
Carbon dioxide injection into coal layers serves the dual purpose to enhance coal bed methane production (ECBM) and to store CO2. The efficiency of this process is expected to be much higher if water is the non-wetting phase in the coal-water-gas system. Therefore, contact angles in the coal-water-CO2 system have been measured using the captive bubble technique in the pressure range between atmospheric pressure and 141 bar at a temperature of 45 degrees C. At atmospheric pressure the contact angle of a shrinking CO2 droplet increases with time, but stays below 90 degrees . At higher pressures (>2.6 bar) the contact angle increases beyond 90 degrees . The pressure dependence of the contact can be represented by theta=(111 degrees +/-10.5 degrees )+(0.17+/-0.14)P [bar]. The exceptional behavior at atmospheric pressure is possibly related to the stability of water patches on the coal surface. It is concluded that water is the non-wetting phase in this coal-water-CO2 system.
Investigation of Contact Angle Behavior and Stability of Drops to Airflow Forcing on Rough Surfaces
NASA Astrophysics Data System (ADS)
Schmucker, Jason; White, Edward
2011-11-01
A method for measuring full-field, instantaneous drop interface profiles on rough surfaces has been implemented to study contact angles and stability to wind forcing on metallic surfaces with micron-scale roughness. Wind tunnel experiments are conducted to produce criteria for runback of drops and set these thresholds for measured water drops spanning a range of Bond numbers from Bo = 0 . 5 to 5 on roughness in the range of RA = 0 . 8 to 4 . 9 with drop based Reynolds numbers spanning an order of magnitude. More importantly, these stability limits are tested with particular care taken to observe their relation to the behavior of both the contact line and contact angle distribution as the drop adjusts its configuration to find a stable condition until it is no longer able to do so and is blown downstream. Results such as critical shear rates and contact angles are discussed and compared with previous numerical studies in the literature such as Dimitrakopoulos [J.Fluid.Mech. 580, 2007] and Ding and Spelt [J.Coll.Sci. 599, 2008] along with experimental results such as Milne [Langmuir 25:24, 2009].
Effect of contact angle and humidity on evaporation of inkjet-printed colloidal drops
NASA Astrophysics Data System (ADS)
Sun, Ying; Bromberg, Vadim; Gawande, Sailee; Singler, Timothy
2009-11-01
Inkjet printing has attracted much attention in recent years due to its ability to dispense precise amounts of functional materials onto targeted areas. Although evidence exists for a multi-stage evaporation of a sessile drop, the actual evaporation behavior of an inkjetted colloidal drop is not well understood. In this study, a novel visualization technique is developed wherein aqueous suspensions of fluorescent particles are inkjetted onto transparent surfaces and the evaporation dynamics are observed in real-time using a high-power microscope. Two influencing parameters, the ambient humidity and substrate wettability, are systematically varied. It has been confirmed that jetted drops follow a pinned, dewetting, and mixed multi-stage evaporation process. The results also show that the relative humidity acts mainly to accelerate or decelerate the process whereas its relationship to contact angle is not as direct. Contact angle hysteresis plays an important role in controlling the initial pinned mode. For lower contact angle substrates, evaporation drives a flow of particles to deposit near the contact line which set the conditions for the dewetting stage that follows. Finally, a diffusion-controlled evaporation model is used to predict the time internals for each evaporation stage. The model agrees well with the experimental data, especially for the dewetting mode.
Contact angles at the water-air interface of hydrocarbon-contaminated soils and clay minerals
NASA Astrophysics Data System (ADS)
Sofinskaya, O. A.; Kosterin, A. V.; Kosterina, E. A.
2016-12-01
Contact angles at the water-air interface have been measured for triturated preparations of clays and soils in order to assess changes in their hydrophobic properties under the effect of oil hydrocarbons. Tasks have been to determine the dynamics of contact angle under soil wetting conditions and to reveal the effect of chemical removal of organic matter from soils on the hydrophilicity of preparations. The potentialities of static and dynamic drop tests for assessing the hydrophilic-hydrophobic properties of soils have been estimated. Clays (kaolinite, gumbrine, and argillite) have been investigated, as well as plow horizons of soils from the Republic of Tatarstan: heavy loamy leached chernozem, medium loamy dark gray forest soil, and light loamy soddy-calcareous soil. The soils have been contaminated with raw oil and kerosene at rates of 0.1-3 wt %. In the uncontaminated and contaminated chernozem, capillary water capacity has been maintained for 250 days. The contact angles have been found to depend on the degree of dispersion of powdered preparation, the main type of clay minerals in the soil, the presence and amount of oxidation-resistant soil organic matter, and the soil-water contact time. Characteristic parameters of mathematical models for drop behavior on triturated preparations have been calculated. Contamination with hydrocarbons has resulted in a reliable increase in the contact angles of soil preparations. The hydrophobization of soil surface in chernozem is more active than in soils poorer in organic matter. The complete restoration of the hydrophilic properties of soils after hydrocarbon contamination is due to the oxidation of easily oxidizable organic matter at the low content of humus, or to wetting during several months in the absence of the mazut fraction.
Mulroy, Sara J.; Ruparel, Puja; Hatchett, Patricia E.; Haubert, Lisa Lighthall; Eberly, Valerie J.; Gronley, JoAnne K.
2015-01-01
Background: Shoulder loading during manual wheelchair propulsion (WCP) contributes to the development of shoulder pain in individuals with spinal cord injury (SCI). Objective: To use regression analysis to investigate the relationships between the hand contact angle (location of the hand on the pushrim at initial contact and release during the push phase of the WCP cycle) with propulsion characteristics, pushrim forces, and shoulder kinetics during WCP in individuals with paraplegia. Methods: Biomechanical data were collected from 222 individuals (198 men and 24 women) with paraplegia from SCI during WCP on a stationary ergometer at a self-selected speed. The average age of participants was 34.7 years (±9.3), mean time since SCI was 9.3 years (±6.1), and average body weight was 74.4 kg (±15.9). The majority (n = 127; 56%) of participants had lower level paraplegia (T8 to L5) and 95 (42%) had high paraplegia (T2 to T7). Results: Increased push arc (mean = 75.3°) was associated with greater velocity (R = 0.384, P < .001) and cycle distance (R = 0.658, P < .001) and reduced cadence (R = -0.419, P < .001). Initial contact angle and hand release angles were equally associated with cycle distance and cadence, whereas a more anterior release angle was associated with greater velocity (R = 0.372, P < .001). When controlling for body weight, a more posterior initial contact angle was associated with greater posterior shoulder net joint force (R = 0.229, P = .001) and greater flexor net joint moment (R = 0.204, P = .002), whereas a more anterior hand release angle was significantly associated with increased vertical (R = 0.270, P < .001) and greater lateral (R = .293, P < .001) pushrim forces; greater shoulder net joint forces in all 3 planes — posterior (R = 0.164, P = .015), superior (R = 0.176, P = .009), and medial (R = 0.284, P < .001); and greater external rotator (R = 0.176, P = .009) and adductor (R = 0.259, P = .001) net joint moments. Conclusions: Current
An analytical solution for a partially wetting puddle and the location of the static contact angle.
Elena Diaz, M; Fuentes, Javier; Cerro, Ramon L; Savage, Michael D
2010-08-01
A model is formulated for a static puddle on a horizontal substrate taking account of capillarity, gravity and disjoining pressure arising from molecular interactions. There are three regions of interest--the molecular, transition and capillary regions with characteristic film thickness, hm, ht and hc. An analytical solution is presented for the shape of the vapour-liquid interface outside the molecular region where interfacial tension can be assumed constant. This solution is used to shed new light on the static contact angle and, specifically, it is shown that. (i) There is no point in the vapour-liquid interface where the angle of inclination, theta, is identically equal to the static contact angle, theta(o), but the angle at the point of null curvature is the closest with the difference of O(epsilon2) where epsilon2 = ht/hc is a small parameter. (ii) The liquid film is to O(epsilon) a wedge of angle theta(o) extending from a few nanometers to a few micrometers of the contact line. A second analytical solution for the shape of interface within the molecular region reveals that cos theta has a logarithmic variation with film thickness, cos theta=cos theta-ln[1-h2(m)/2h2]. The case, hm = 0, is of special significance since it refers to a unique configuration in which the effect of molecular interactions vanishes, disjoining pressure is everywhere zero and the vapour-liquid interface is now described exactly by the Young-Laplace equation and includes a wedge of angle, theta(o), extending down to the solid substrate.
Non-contact angle measurement based on parallel multiplex laser feedback interferometry
NASA Astrophysics Data System (ADS)
Zhang, Song; Tan, Yi-Dong; Zhang, Shu-Lian
2014-11-01
We present a novel precise angle measurement scheme based on parallel multiplex laser feedback interferometry (PLFI), which outputs two parallel laser beams and thus their displacement difference reflects the angle variation of the target. Due to its ultrahigh sensitivity to the feedback light, PLFI realizes the direct non-contact measurement of non-cooperative targets. Experimental results show that PLFI has an accuracy of 8″ within a range of 1400″. The yaw of a guide is also measured and the experimental results agree with those of the dual-frequency laser interferometer Agilent 5529A.
A Langevin model for the Dynamic Contact Angle Parameterised Using Molecular Dynamics
NASA Astrophysics Data System (ADS)
Smith, Edward; Muller, Erich; Craster, Richard; Matar, Omar
2016-11-01
An understanding of droplet spreading is essential in a diverse range of applications, including coating processes, dip feed reactors, crop spraying and biomedical treatments such as surfactant replacement theory. The default modelling tools for engineering fluid dynamics assume that the continuum hypothesis is valid. The contact line motion is very difficult to capture in this paradigm and requires some form of closure model, often tuned a priori to experiments. Molecular dynamics (MD), by assuming only an inter-molecular potential, reproduces the full detail of the three-phase contact line with no additional modelling assumptions. This provides an ideal test-bed to understand contact line motion. In this talk, MD results for a sheared liquid bridge are presented. The evolution and fluctuations of the dynamic contact angle are paramterised over a range of wall sliding speeds and temperatures. A Langevin model is proposed to reproduce the fluctuations and evolution of the contact angle. Results from this model are compared to molecular simulation data showing excellent agreement. The potential applications of this model, as well as limitation and possible extensions, are discussed. EPSRC UK platform Grant MACIPh (EP/L020564/1).
NASA Astrophysics Data System (ADS)
Chhasatia, Viral H.; Joshi, Abhijit S.; Sun, Ying
2010-12-01
The deposition behavior of inkjet-printed aqueous colloidal drops on a glass substrate has been investigated by using fluorescence microscopy and a high resolution goniometer. Real-time side-view images of a pinned colloidal drop show that the contact angle during evaporation is a function of the relative humidity (RH). The RH also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively driven flow inside the drop that drives the suspended particles toward the contact line. Results show that the particle deposition area and pattern change significantly with the RH.
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.
NASA Astrophysics Data System (ADS)
Linder, Nicklas; Criscione, Antonio; Roisman, Ilia V.; Marschall, Holger; Tropea, Cameron
2015-12-01
Contact line phenomena govern a large number of multiphase flows. A reliable description of the contact line dynamics is therefore essential for prediction of such flows. Well-known difficulties of computation of the wetting phenomena include the mesh dependence of the results caused by flow singularity near the contact line and accurate estimation of its propagating velocity. The present study deals with the computational problem arising from the discontinuity in the dependence of the dynamic contact angle on the propagation velocity, associated with the contact angle hysteresis. The numerical simulations are performed using the volume of fluid method. The boundary conditions in the neighborhood of the contact line are switched depending on the value of the computed current local contact angle between a propagating contact line and a pinning condition. The method is applied to the simulation of the deformation and incipient motion of a shedding drop. The model is validated by comparison of the numerical predictions with experimental data.
Pasquini, Daniel; Belgacem, Mohamed Naceur; Gandini, Alessandro; Curvelo, Antonio Aprigio da Silva
2006-03-01
The surface chemical modification of microcrystalline cellulose and cellulose fibers obtained from different sugar cane bagasse pulping processes, viz. Kraft, organosolv ethanol/water and organosolv/supercritical carbon dioxide, were studied in heterogeneous conditions using modest amounts of octadecanoyl and dodecanoyl chloride. The ensuing surfaces acquired a non-polar character, suitable for incorporating these fibers as reinforcing agents in composite materials based on polymeric matrices. The success of these chemical modifications was assessed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analysis, scanning electron microscopy (SEM) and contact angle measurements. In particular, the dynamic and equilibrium contact angle measurements, before and after the treatments, revealed that the value of the polar component (gamma(s)p) of the surface energy had decreased very considerably following the modification.
Mercury Porosimetry: Contact Angle Hysteresis of Materials with Controlled Pore Structure.
Salmas, Constantinos; Androutsopoulos, George
2001-07-01
Mercury Porosimetry (MP) hysteresis is a commonly observed phenomenon in which mercury retention disguises further the overall hysteresis picture. This article introduces a new interpretation of the MP hysteresis based on the combined effect of pore structure networking and mercury contact angle variation occurring between the mercury penetration and retraction operations. To distinguish the contribution of each factor the following investigations were carried out. Nitrogen sorption (NP) and MP experiments were performed on samples of an anodic aluminum membrane and the results were interpreted in terms of the Corrugated Pore Structure Model (CPSM), i.e., CPSM-Nitrogen and CPSM-Mercury models, respectively. The simulation of the observed hysteresis data using the CPSM model enabled the evaluation of an identical for the two methods intrinsic pore size distribution (PSD) and cumulative surface area in perfect agreement with the respective BET value. Additionally, the CPSM analysis of data resulted in the evaluation of mercury contact angles, i.e., θ(p)=143 degrees and θ(r)=101.7 degrees for the MP penetration and retraction branches of the hysteresis loop, respectively. Moreover, CPSM-Mercury simulations of literature MP hysteresis data, valid for controlled-pore glasses and nuclepore membranes, led to the evaluation of contact angles, i.e., glasses: θ(p)=143 degrees, θ(r)=100.5-107.5 degrees and nuclepore: θ(p)=143 degrees, θ(r)=118- 121 degrees. The latter values are comparable with relevant literature data and approximate those determined for the anodic aluminum membrane. The CPSM model employed herein proved to be a flexible and reliable model for simulating the pertinent hysteresis loops by combining pore networking and contact angle hysteresis phenomena. Copyright 2001 Academic Press.
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.
Dynamic contact angle measurement on materials with an unknown wet perimeter.
Muster, Tim H
2004-09-10
Whilst contact angle measurements obtained using the Wilhelmy balance technique are accurate and reproducible for planar surfaces, their use for characterizing particulate materials is highly dependent upon accurate knowledge of the wet perimeter. This communication suggests that the approach of Pepin et al. [Int. J. Pharm. 152 (1997) 1] for wet perimeter determination using non-polar liquids may lead to erroneous conclusions. Alternative approaches for wet perimeter determination are suggested.
NASA Astrophysics Data System (ADS)
Huang, Haibo; Thorne, Daniel T., Jr.; Schaap, Marcel G.; Sukop, Michael C.
2007-12-01
We propose a method for approximating the adhesion parameters in the Shan and Chen multicomponent, multiphase lattice Boltzmann model that leads to the desired fluid-solid contact angle. The method is a straightforward application of Young’s equation with substitution of the Shan and Chen cohesion parameter and a density factor for the fluid-fluid interfacial tension, and the adhesion parameters for the corresponding fluid-solid interfacial tensions.
NASA Astrophysics Data System (ADS)
Ickes, Luisa; Welti, André; Lohmann, Ulrike
2017-02-01
Heterogeneous ice formation by immersion freezing in mixed-phase clouds can be parameterized in general circulation models (GCMs) by classical nucleation theory (CNT). CNT parameterization schemes describe immersion freezing as a stochastic process, including the properties of insoluble aerosol particles in the droplets. There are different ways to parameterize the properties of aerosol particles (i.e., contact angle schemes), which are compiled and tested in this paper. The goal of this study is to find a parameterization scheme for GCMs to describe immersion freezing with the ability to shift and adjust the slope of the freezing curve compared to homogeneous freezing to match experimental data. We showed in a previous publication that the resulting freezing curves from CNT are very sensitive to unconstrained kinetic and thermodynamic parameters in the case of homogeneous freezing. Here we investigate how sensitive the outcome of a parameter estimation for contact angle schemes from experimental data is to unconstrained kinetic and thermodynamic parameters. We demonstrate that the parameters describing the contact angle schemes can mask the uncertainty in thermodynamic and kinetic parameters. Different CNT formulations are fitted to an extensive immersion freezing dataset consisting of size-selected measurements as a function of temperature and time for different mineral dust types, namely kaolinite, illite, montmorillonite, microcline (K-feldspar), and Arizona test dust. We investigated how accurate different CNT formulations (with estimated fit parameters for different contact angle schemes) reproduce the measured freezing data, especially the time and particle size dependence of the freezing process. The results are compared to a simplified deterministic freezing scheme. In this context, we evaluated which CNT-based parameterization scheme able to represent particle properties is the best choice to describe immersion freezing in a GCM.
Chen, Jianrong; Shen, Liguo; Zhang, Meijia; Hong, Huachang; He, Yiming; Liao, Bao-Qiang; Lin, Hongjun
2016-02-01
Concept of hydrophobicity always fails to accurately assess the interfacial interaction and membrane fouling, which calls for reliable parameters for this purpose. In this study, effects of contact angle on interfacial interactions related to membrane fouling were investigated based on thermodynamic analysis. It was found that, total interaction energy between sludge foulants and membrane monotonically decreases and increases with water and glycerol contact angle, respectively, indicating that these two parameters can be reliable indicators predicting total interaction energy and membrane fouling. Membrane roughness decreases interaction strength for over 20 times, and effects of membrane roughness on membrane fouling should consider water and glycerol contact angle on membrane. It was revealed existence of a critical water and glycerol contact angle for a given membrane bioreactor. Meanwhile, diiodomethane contact angle has minor effect on the total interaction, and cannot be regarded as an effective indicator assessing interfacial interactions and membrane fouling.
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.
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.
On the interfacial behavior of ionic liquids: surface tensions and contact angles.
Restolho, José; Mata, José L; Saramago, Benilde
2009-12-01
In this work the liquid/vapour and the solid/liquid interfaces of a series of ionic liquids: 1-ethyl-3-methylpyridinium ethyl sulfate, [EMPy][EtSO4], 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO4], 1-ethanol-3-methylimidazolium tetrafluoroborate, [C2OHMIM][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF4], were investigated. The surface tension was measured in a wide temperature range, (298-453) K. The contact angles were determined on substrates of different polarities. Both on the polar (glass) and the non-polar substrates ((poly-(tetrafluoroethylene) and poly-(ethylene)), the liquids with maximum and minimum surface tensions lead, respectively, to the highest and the lowest contact angles. The dispersive, gamma(L)(d), and non-dispersive, gamma(L)(nd), components of the liquid surface tension, gamma(L), were calculated from the contact angles on the non-polar substrates using the Fowkes approach. The polarity fraction, gamma(L)(nd)/gamma(L), was compared with the polarity parameter, k, obtained from the fitting of the surface tension vs. temperature data to the Eötvös equation. Good agreement was found for the extreme cases: [OMIM][BF4] exhibits the lowest polarity and [BMIM][BF4], the highest. When compared with the polarity fractions of standard liquids considered as "polar" liquids, the ionic liquids studied may be considered as moderately polar.
The Study of Layer-by-Layer Ultrathin Films by the Dynamic Contact Angle Method.
Chen, Jinyu; Luo, Guobin; Cao, Weixiao
2001-06-01
The self-assembly film fabricated via the layer-by-layer technique was studied by the dynamic contact angle (DCA) method (wilhelmy plate method). The used polyelectrolytes are poly(diallyl-dimethylammonium chloride) (PDDA), poly(etheleneimine) (PEI), diphenylamine-4-diazonium-formaldehyde resin (DR), 2-nitro-N-methyl-4-diazonium-formaldehyde resin (NDR), and poly(sodium-p-styrenesulfonate) (PSS). For the self-assembly systems of PDDA/PSS, PEI/PSS, DR/PSS, and NDR/PSS, their individual contact angle fluctuates regularly with the fabrication of each layer, while the magnitude of different systems' contact angle depends on the participant polycation. The re-organization of components and the adjacent layer interpenetration are presented here to explain this phenomena. We also found that DR or NDR can adsorb itself via the layer-by-layer method to form multilayer film, and the hydrophobic interaction is put forward to effect this process. Moreover, the procedure of washing and drying after adsorption was studied and considered as a prerequisite for the successful fabrication, especially of the same charge carried components. Copyright 2001 Academic Press.
Destgeer, Ghulam; Jung, Jin Ho; Park, Jinsoo; Ahmed, Husnain; Sung, Hyung Jin
2017-01-03
A sessile droplet of water carrying polystyrene microparticles of different diameters was uniformly exposed to high frequency surface acoustic waves (SAWs) produced by an interdigitated transducer (IDT). We investigated the concentration behavior of the microparticles as the SAWs generated a strong acoustic streaming flow (ASF) inside the water droplet and exerted a direct acoustic radiation force (ARF) on the suspended particles, the magnitude of which depended upon the particle diameter. As a result of the ARF, the microparticles were concentrated according to their diameters at different positions inside the sessile droplet placed in the path of the SAW, right in front of the IDT. The microparticle concentration behavior changed as the sessile droplet contact angle with the substrate was varied by adding surfactant to the water or by gradually evaporating the water. The positions at which the smaller and larger microparticles were concentrated remained distinguishable, even at very different experimental conditions. The long-term exposure of the droplets to the SAWs was accompanied by the gradual evaporation of the carrier fluid, which dynamically changed the droplet contact angle as well as the concentration of particles. Complete evaporation of the fluid left behind several concentrated yet separated clusters of particles on the substrate surface. The effect of the droplet contact angle on particles' concentration behavior and consequent separation of particles has been uniquely studied in this SAW-based report.
Effects of synthesizing parameters on surface roughness and contact angles of ZnO nanowire films.
Jing, Weixuan; Wang, Bing; Niu, Lingling; Jiang, Zhuangde; Qi, Han; Chen, Lujia; Zhou, Fan
2014-06-01
Effects of the synthesizing parameters on the surface roughness and the contact angles of ZnO nanowire films were studied in this paper. ZnO nanowire films were synthesized with the hydrothermal method on glass substrates, and the synthesizing parameters include the concentrations of the growth solution and the seed layer solution, the growth time span as well as the temperature. Atomic force microscopy and scanning electron microscopy were employed respectively to characterize the surface and the profile roughness of ZnO nanowire films. The measurement results by atomic force microscopy were in agreement with that by scanning electron microscopy, hence the former was used for the investigation of aforementioned effects. Relationships between the synthesizing parameters, the surface roughness and the contact angles of ZnO nanowire films were established, revealing that the synthesizing parameters affected significantly not only the surface roughness but also the contact angles of ZnO nanowire films. The results can be used for batch fabrication of ZnO nanowire-based structures and these structures-based sensors in a wide variety of applications.
Hsia, Yiao Tee; Jones, Paul; White, Lee R
2004-11-09
The disjoining pressure of lubricant nanofilms used in the magnetic recording industry controls the equilibrium wetting, the dynamics of film restoration, and the evaporation kinetics of the film. It has been claimed that by measuring the contact angle of nonpolar and polar liquids on lubricant films, the disjoining pressure can be extracted using the method of Girafalco and Good, and such analyses have appeared in the literature. The approximations underlying the method have been discussed before in the literature. In view of the importance of measuring disjoining pressure in nanofilms of lubricants, it is timely to revisit these assumptions to understand the validity of the contact-angle method presently in use. We re-derive the relevant equations using a thermodynamic-interaction-energy approach which is free of the problems inherent in the original derivation and make explicit the assumptions which must be made in the derivation. General interaction energy arguments are then invoked to demonstrate that it does not appear possible to obtain the disjoining pressure in the film from contact-angle measurements in an unambiguous manner.
Hilpert, Markus
2010-11-01
In a preceding paper, we derived analytical solutions for the displacement of a gas by a liquid in horizontal and inclined capillary tubes where the tube inlet is connected to a liquid reservoir of constant pressure. We considered quite general models for the dynamic contact angle and were able to derive implicit equations for the velocity of the gas-liquid interface. These solutions allowed us to identify five different flow scenarios for liquid withdrawal that differed in the direction of flow and the sign of the acceleration of the gas-liquid interface. In this paper, we consider the special case where the dynamic contact angle is determined by a nonequilibrium Young force that depends linearly on the capillary number. Thus we can derive explicit and the more traditional implicit analytical solutions for both the position and the velocity of the gas-liquid interface. We also construct diagrams that allow us to predict which of the five flow scenarios will occur depending on the nondimensional parameters that define the problem. The diagrams can be combined with diagrams previously obtained for infiltration and the entire parameter space subdivided into regions that are associated with either liquid withdrawal, liquid infiltration, or metastable and stable equilibrium states. Our solutions are also valid within the limit where the contact angle is constant.
NASA Astrophysics Data System (ADS)
Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.
2016-02-01
The universality of the scaling laws that correlate the hydrodynamic slip length and static contact angle was investigated by introducing the concept of the wettability transparency of graphene-coated surfaces. Equilibrium molecular dynamics simulations of droplet wettability for Si(111), Si(100), and graphene-coated silicon surfaces were performed to determine the conditions required to obtain similar contact angles between bare and graphene-coated surfaces (wettability transparency). The hydrodynamic slip length was determined by means of equilibrium calculations for silicon and graphene-coated silicon nanochannels. The results indicate that the slip-wettability scaling laws can be used to describe the slip behavior of the bare silicon nanochannels in general terms; however, clear departures from a general universal description were observed for hydrophobic conditions. In addition, a significant difference in the hydrodynamic slippage was observed under wettability transparency conditions. Alternatively, the hydrodynamic boundary condition for silicon and graphene-coated silicon nanochannels was more accurately predicted by observing the density depletion length, posing this parameter as a better alternative than the contact angle to correlate with the slip length.
Bortolotti, Mauro; Brugnara, Marco; Della Volpe, Claudio; Siboni, Stefano
2009-08-01
Axisymmetric drop shape analysis (ADSA) is a well-established methodology for estimating the contact angle value and the surface tension of liquids starting from sessile drops images. It consists of an iterative procedure in which a best fit between a theoretical axisymmetric Laplacian curve and an experimental drop profile is performed. When only an evaluation of the geometric contact angle value is needed, a similar numerical approach can be adopted by using simpler algebraic models in place of a Laplace profile, thus allowing more straightforward implementations and shorter computation times. In this work the relative merits of the different methodologies are compared. Beside the standard ADSA procedure, four different mathematical models are examined, namely the circular and elliptical models, the first-order perturbative solution of the Laplace equation, and a cubic spline model. Their relative statistical performances are tested on both calculated and experimental drop profiles. For simulated drops, the actual capability of the models to predict the correct contact angle is also investigated.
Sun, Xiaojun; Hasegawa, Yosuke; Kohno, Haruhiko; Jiao, Zhenjun; Hayakawa, Koji; Okita, Kohei; Shikazono, Naoki
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 zirconia 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.
Thin three-dimensional droplets on an oscillating substrate with contact angle hysteresis
NASA Astrophysics Data System (ADS)
Bradshaw, J.; Billingham, J.
2016-01-01
Recent experiments [P. Brunet, J. Eggers, and R. D. Deegan, Phys. Rev. Lett. 99, 144501 (2007), 10.1103/PhysRevLett.99.144501] have shown that a liquid droplet on an inclined plane can be made to move uphill by sufficiently strong, vertical oscillations. In order to investigate this counterintuitive phenomenon we use a model in which liquid inertia and viscosity are assumed negligible so that the motion of the droplet is dominated by the applied acceleration due to the oscillation of the plate, gravity, and surface tension. We explain how the leading order motion of the droplet can be separated into a spreading mode and a swaying mode. For a linear contact line law, the maximum rise velocity occurs when these modes are in phase. We show that, both with and without contact angle hysteresis, the droplet can climb uphill and also that, for certain contact line laws, the motion of the droplet can produce footprints similar to experimental results. We show that if the two modes are out of phase when there is no contact angle hysteresis, the inclusion of hysteresis can force them into phase. This in turn increases the rise velocity of the droplet and can, in some cases, cause a sliding droplet to climb.
Thin three-dimensional droplets on an oscillating substrate with contact angle hysteresis.
Bradshaw, J; Billingham, J
2016-01-01
Recent experiments [P. Brunet, J. Eggers, and R. D. Deegan, Phys. Rev. Lett. 99, 144501 (2007)10.1103/PhysRevLett.99.144501] have shown that a liquid droplet on an inclined plane can be made to move uphill by sufficiently strong, vertical oscillations. In order to investigate this counterintuitive phenomenon we use a model in which liquid inertia and viscosity are assumed negligible so that the motion of the droplet is dominated by the applied acceleration due to the oscillation of the plate, gravity, and surface tension. We explain how the leading order motion of the droplet can be separated into a spreading mode and a swaying mode. For a linear contact line law, the maximum rise velocity occurs when these modes are in phase. We show that, both with and without contact angle hysteresis, the droplet can climb uphill and also that, for certain contact line laws, the motion of the droplet can produce footprints similar to experimental results. We show that if the two modes are out of phase when there is no contact angle hysteresis, the inclusion of hysteresis can force them into phase. This in turn increases the rise velocity of the droplet and can, in some cases, cause a sliding droplet to climb.
A simple method for measuring the superhydrophobic contact angle with high accuracy.
Hung, Yi-Lin; Chang, Yao-Yuan; Wang, Meng-Jiy; Lin, Shi-Yow
2010-06-01
A modified selected-plane method for contact angle (theta) measurement is proposed in this study that avoids the difficulty of finding the real contact point and image-distortion effects adjacent to the contact point. This method is particularly suitable for superhydrophobic surfaces. The sessile-drop method coupled with the tangent line is the most popular method to find the contact angle in literature, but it entails unavoidable errors in determining the air-solid base line due to the smoothness problem and substrate tilting. In addition, the tangent-line technique requires finding the actual contact point. The measurement error due to the base line problem becomes more profound for superhydrophobic surfaces. A larger theta deviation results from a more superhydrophobic surface with a fixed base line error. The proposed modified selected-plane method requires only four data points (droplet apex, droplet height, and two interfacial loci close to the air-solid interface), avoiding the problem of the sessile-drop-tangent method in finding the contact point and saving the trouble of the sessile-drop-fitting method for best fitting of the numerous edge points with the theoretical profile. A careful error analysis was performed, and a user-friendly program was provided in this work. This method resulted in an accurate theta measurement and a method that was much improved over the classical selected plane and the sessile-drop-tangent methods. The theta difference between this method and the sessile-drop-fitting method was found to be less than three degrees.
A simple method for measuring the superhydrophobic contact angle with high accuracy
NASA Astrophysics Data System (ADS)
Hung, Yi-Lin; Chang, Yao-Yuan; Wang, Meng-Jiy; Lin, Shi-Yow
2010-06-01
A modified selected-plane method for contact angle (θ) measurement is proposed in this study that avoids the difficulty of finding the real contact point and image-distortion effects adjacent to the contact point. This method is particularly suitable for superhydrophobic surfaces. The sessile-drop method coupled with the tangent line is the most popular method to find the contact angle in literature, but it entails unavoidable errors in determining the air-solid base line due to the smoothness problem and substrate tilting. In addition, the tangent-line technique requires finding the actual contact point. The measurement error due to the base line problem becomes more profound for superhydrophobic surfaces. A larger θ deviation results from a more superhydrophobic surface with a fixed base line error. The proposed modified selected-plane method requires only four data points (droplet apex, droplet height, and two interfacial loci close to the air-solid interface), avoiding the problem of the sessile-drop-tangent method in finding the contact point and saving the trouble of the sessile-drop-fitting method for best fitting of the numerous edge points with the theoretical profile. A careful error analysis was performed, and a user-friendly program was provided in this work. This method resulted in an accurate θ measurement and a method that was much improved over the classical selected plane and the sessile-drop-tangent methods. The θ difference between this method and the sessile-drop-fitting method was found to be less than three degrees.
A simple method for measuring the superhydrophobic contact angle with high accuracy
Hung, Yi-Lin; Chang, Yao-Yuan; Wang, Meng-Jiy; Lin, Shi-Yow
2010-06-15
A modified selected-plane method for contact angle ({theta}) measurement is proposed in this study that avoids the difficulty of finding the real contact point and image-distortion effects adjacent to the contact point. This method is particularly suitable for superhydrophobic surfaces. The sessile-drop method coupled with the tangent line is the most popular method to find the contact angle in literature, but it entails unavoidable errors in determining the air-solid base line due to the smoothness problem and substrate tilting. In addition, the tangent-line technique requires finding the actual contact point. The measurement error due to the base line problem becomes more profound for superhydrophobic surfaces. A larger {theta} deviation results from a more superhydrophobic surface with a fixed base line error. The proposed modified selected-plane method requires only four data points (droplet apex, droplet height, and two interfacial loci close to the air-solid interface), avoiding the problem of the sessile-drop-tangent method in finding the contact point and saving the trouble of the sessile-drop-fitting method for best fitting of the numerous edge points with the theoretical profile. A careful error analysis was performed, and a user-friendly program was provided in this work. This method resulted in an accurate {theta} measurement and a method that was much improved over the classical selected plane and the sessile-drop-tangent methods. The {theta} difference between this method and the sessile-drop-fitting method was found to be less than three degrees.
Effect of tibial tuberosity advancement on femorotibial contact mechanics and stifle kinematics.
Kim, Stanley E; Pozzi, Antonio; Banks, Scott A; Conrad, Bryan P; Lewis, Daniel D
2009-01-01
Objective- To evaluate the effects of tibial tuberosity advancement (TTA) on femorotibial contact mechanics and 3-dimensional kinematics in cranial cruciate ligament (CrCL)-deficient stifles of dogs. Study Design- In vitro biomechanical study. Animals- Unpaired pelvic limbs from 8 dogs, weighing 28-35 kg. Methods- Digital pressure sensors placed subjacent to the menisci were used to measure femorotibial contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 135 degrees . Three-dimensional static poses of the stifle were obtained using a Microscribe digitizing arm. Each specimen was tested under normal, CrCL-deficient, and TTA-treated conditions. Repeated measures analysis of variance with a Tukey post hoc test (P<.05) was used for statistical comparison. Results- Significant disturbances to all measured contact mechanic parameters were evident after CrCL transection, which corresponded to marked cranial tibial subluxation and internal tibial rotation in the CrCL-deficient stifle. No significant differences in any contact mechanic and kinematic parameters were detected between normal and TTA-treated stifles. Conclusion- TTA eliminates craniocaudal stifle instability during simulated weight-bearing and concurrently restores femorotibial contact mechanics to normal. Clinical Relevance- TTA may mitigate the progression of stifle osteoarthritis in dogs afflicted with CrCL insufficiency by eliminating cranial tibial thrust while preserving the normal orientation of the proximal tibial articulating surface.
NASA Astrophysics Data System (ADS)
Guan, Dongshi; Wang, Yong Jian; Charlaix, Elisabeth; Tong, Penger
We report direct atomic-force-microscope measurements of capillary force hysteresis and relaxation of a circular moving contact line (CL) formed on a long micron-sized hydrophobic fiber intersecting a water-air interface. The measured capillary force hysteresis and CL relaxation show a strong asymmetric speed dependence in the advancing and receding directions. A unified model based on force-assisted barrier-crossing is utilized to find the underlying energy barrier Eb and size λ associated with the defects on the fiber surface. The experiment demonstrates that the pinning (relaxation) and depinning dynamics of the CL can be described by a common microscopic frame-work, and the advancing and receding CLs are influenced by two different sets of relatively wetting and non-wetting defects on the fiber surface. Work supported in part by the Research Grants Council of Hong Kong SAR.
Mobarak, K A; Espeland, L; Krogstad, O; Lyberg, T
2001-04-01
The objective of this cephalometric study was to compare skeletal stability and the time course of postoperative changes in high-angle and low-angle Class II patients after mandibular advancement surgery. The subjects were 61 consecutive mandibular retrognathism patients whose treatment included bilateral sagittal split osteotomy and rigid fixation. The patients were divided according to the preoperative mandibular plane angle; the 20 patients with the lowest mandibular plane angle (20.8 degrees +/- 4.9 degrees ) constituted the low-angle group, while the 20 cases with the highest mandibular plane angle (43.0 degrees +/- 4.0 degrees ) represented the high-angle group. Lateral cephalograms were taken on 6 occasions: immediately before surgery, immediately after surgery, 2 and 6 months after surgery, and 1 and 3 years after surgery. Results demonstrated that the high-angle and low-angle groups had different patterns of surgical and postoperative changes. High-angle patients were associated with both a higher frequency and a greater magnitude of horizontal relapse. While 95% of the total relapse took place during the first 2 months after surgery in the low-angle group, high-angle patients demonstrated a more continuous relapse pattern, with a significant proportion (38%) occurring late in the follow-up period. Possible reasons for the different postsurgical response are discussed.
Extrand, C W; Moon, Sung In
2010-11-16
Measurement of contact angles on super hydrophobic surfaces by conventional methods can produce ambiguous results. Experimental difficulties in constructing tangent lines, gravitational distortion or erroneous assumptions regarding the extent of spreading can lead to underestimation of contact angles. Three models were used to estimate drop shape and perceived contact angles on completely nonwetting super hydrophobic surfaces. One of the models employed the classic numerical solutions from Bashforth and Adams. Additionally, two approximate models were derived as part of this work. All three showed significant distortion of microliter-sized drops and similar trends in perceived contact angles. Liquid drops of several microliters are traditionally used in sessile contact angle measurements. Drops of this size are expected to and indeed undergo significant flattening on super hydrophobic surfaces, even if the wetting interactions are minimal. The distortion is more pronounced if the liquid has a lesser surface tension or greater density. For surfaces that are completely nonwetting, underestimation of contact angles can be tens of degrees. Our modeling efforts suggest that accurate contact angle measurements on super hydrophobic surfaces would require very small sessile drops, on the order of hundreds of picoliters.
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.
NASA Astrophysics Data System (ADS)
Zhang, Xuening; Han, Qinkai; Peng, Zhike; Chu, Fulei
2015-05-01
A great deal of research work has been done on the dynamic behaviors of the rotor-bearing system. However, the important effects of load and variation of contact angle on the bearing performance have not been focused on sufficiently. In this paper, a five-degree-of-freedom load distribution model is set up considering the bearing preload and the loads due to the rotor imbalance. Utilizing this model, the variation of the bearing contact angle is investigated thoroughly. The comparisons of the obtained contact angle against the results from literature validate that the proposed load distribution model is effective. With this model, the static ball deformations are obtained considering variation of the contact angle. Through resolving the dynamic displacements of the rotor, the dynamic ball deformations could also be obtained. Then the total restoring forces and moments of the bearings could be formulated. By introducing these nonlinear forces and moments into the rotating system, a new dynamic model considering the preload and the variation of contact angle is set up. The present analyses indicate that the bearing contact angle will be changed remarkably with the effect of bearing load. The deflection vibration of the rotor-bearing system will be underestimated without considering the varying contact angle. With the effect of varying contact angle, the ball passage frequency and its combinations with the shaft rotating frequency become more noticeable. The main resonance regions for the rotor-bearing system shift to the lower speed ranges when the variation of contact angle is taken into account.
Zanini, Michele; Isa, Lucio
2016-08-10
Micro and nanoparticles at fluid interfaces have been attracting increasing interest in the last few decades as building blocks for materials, as mechanical and structural probes for complex interfaces and as models for two-dimensional systems. The three-phase contact angle enters practically all aspects of the particle behavior at the interface: its thermodynamics (binding energy to the interface), dynamics (motion and drag at the interface) and interactions with the interface (adsorption and wetting). Moreover, many interactions among particles at the interface also strongly depend on the contact angle. These concepts have been extensively discussed for non-deformable, homogeneous and mostly spherical particles, but recent progress in particle synthesis and fabrication has instead moved in the direction of producing more complex micro and nanoscale objects, which can be responsive, deformable, heterogenous and/or anisotropic in shape, surface chemistry and material properties. These new particles have a much greater potential for applications and new science, and the study of their behavior at interfaces has only very recently started. In this paper, we critically review the current state of the art of the experimental methods available to measure the contact angle of micro and nanoparticles at fluid interfaces, indicating their strengths and limitations. We then comment on new particle systems that are currently attracting increasing interest in relation to their adsorption and assembly at fluid interfaces and discuss if and which ones of the current techniques are suited to investigate their properties at interfaces. Based on this discussion, we will finally try to indicate a direction in which new experimental methods should develop in the future to tackle the new challenges posed by the novel types of particles that more and more often are used at interfaces.
Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?
Malavasi, Ileana; Veronesi, Federico; Caldarelli, Aurora; Zani, Maurizio; Raimondo, Mariarosa; Marengo, Marco
2016-06-28
It is well known that a superhydrophobic surface may not be able to repel impacting droplets because of the so-called Cassie-to-Wenzel transition. It has been proven that a critical value of the receding contact angle (θR) exists for the complete rebound of water, recently experimentally measured to be 100° for a large range of impact velocities. On the contrary, in the present work, no rebound was observed when low-surface-tension liquids such as hexadecane (σ = 27.5 mN/m at 25 °C) are concerned, even for very low impact velocities and very high values of θR and low contact angle hysteresis. Therefore, the critical threshold of θR ≈ 100° does not sound acceptable for all liquids and for all hydrophobic surfaces. For the same Weber numbers, a Cassie-to-Wenzel state transition occurs after the impact as a result of the easier penetration of low-surface-tension fluids in the surface structure. Hence, a criterion for the drop rebound of low-surface-tension liquids must consider not only the contact angle values with surfaces but also their surface tension and viscosity. This suggests that, even if it is possible to produce surfaces with enhanced static repellence against oils and organics, generally the realization of synthetic materials with self-cleaning and antisticking abilities in dynamic phenomena, such as spray impact, remains an unsolved task. Moreover, it is demonstrated that the chemistry of the surface, the physicochemical interactions with the liquid drops, and the possible wettability gradient of the surface asperity also play important roles in determining the critical Weber number above which impalement occurs. Therefore, the classical numerical simulations of drop impact on dry surfaces are definitively not able to capture the final outcomes of the impact for all possible fluids if the surface topology and chemistry and/or the wettability gradient in the surface structure are not properly reflected.
Combined in-situ dilatometer and contact angle studies of interfacial reaction kinetics in brazing.
Dave, V. R.; Javernick, D. A.; Thoma, D. J.; Cola, M. J.; Hollis, K. J.; Smith, F. M.; Dauelsberg, L. B.
2001-01-01
Multi-component dissimilar material braze joints as shown in Figure 1 consisting of dissimilar base materials, filler materials and wetting agents are of tantamount importance in a wide variely of applications. This work combines dilatometry and contact angle measurements to characterize in-situ the multiple interfacial reaction pathways that occur in such systems. Whereas both of these methods are commonly used tools in metallurgical investigation, their combined use within the context of brazing studies is new and offers considerable additional insight. Applications are discussed to joints made between Beryllium and Monel with TiH{sub 2} as the wetting agent and Cu-28%Ag as the filler material.
Force of adhesion upon loss of contact angle hysteresis: when a liquid behaves like a solid.
Escobar, Juan V; Castillo, Rolando
2013-11-27
The theoretically predicted vanishment of the macroscopic contact angle hysteresis is found experimentally along with a small but finite force of adhesion (F(Ad)≈-0.5 μN) that, unexpectedly, is independent of the history of the preload. Our results agree with the prediction of a model in which the surface tension of the liquid provides the counterpart of the restoring force of an elastic solid, evidencing that the dewetting of a liquid in the absence of strong pinning points is equivalent to the detachment of an elastic solid.
Kennedy, John M.; Kim, Sunwoo; Kim, Kwang J.
2009-10-06
Phase change heat transfer is notorious for increasing the irreversibility of, and therefore decreasing the efficiency of, geothermal power plants. Its significant contribution to the overall irreversibility of the plant makes it the most important source of inefficiency in the process. Recent studies here have shown the promotion of drop wise condensation in the lab by means of increasing the surface energy density of a tube with nanotechnology. The use of nanotechnology has allowed the creation of surface treatments which discourage water from wetting a tube surface during a static test. These surface treatments are unique in that they create high- contact angles on the condensing tube surfaces to promote drop wise condensation.
Investigation of the surface of implanted silicon crystal by the contact angle
Lebedeva, N.N.; Bakovets, V.V.; Sedymova, E.A.; Pridachin, N.B.
1987-03-01
The authors study the dependence of the critical contact angle of silicon upon the dose of its irradiation by argon and boron ions. It is established that the system of immiscible liquids ether-water can be successfully used to study the influence of ion implantation of silicon on its wettability by water. The change in the wettability of implanted silicon is related to the increase in the level of the defect state of the layer surface. Wetting of implanted silicon by melts at high temperatures can be used for studying the kinetics and the annealing mechanism of defects.
Nishimura, T; Doi, K; Fujimoto, H
2015-08-01
Touch-sensitive screen terminals enabling intuitive operation are used as input interfaces in a wide range of fields. Tablet terminals are one of the most common devices with a touch-sensitive screen. They have a feature of good portability, enabling use under various conditions. On the other hand, they require a GUI designed to prevent decrease of usability under various conditions. For example, the angle of fingertip contact with the display changes according to finger posture during operation and how the case is held. When a human fingertip makes contact with an object, the contact area between the fingertip and contact object increases or decreases as the contact angle changes. A touch-sensitive screen detects positions using the change in capacitance of the area touched by the fingertip; hence, differences in contact area between the touch-sensitive screen and fingertip resulting from different forefinger angles during operation could possibly affect operability. However, this effect has never been studied. We therefore conducted an experiment to investigate the relationship between size/spacing and operability, while taking the effect of fingertip contact angle into account. As a result, we have been able to specify the button size and spacing conditions that enable accurate and fast operation regardless of the forefinger contact angle.
Welzel, Petra B; Rauwolf, Cordula; Yudin, Olexandr; Grundke, Karina
2002-07-01
The interaction of inorganic ions with low-energy hydrophobic surfaces was examined using model systems of solid polymers without ionizable functional surface groups in aqueous electrolyte solutions. Low-rate dynamic contact angle measurements with captive bubbles in conjunction with axisymmetric drop shape analysis (ADSA) were performed to study the influence of electrolyte ions (in the aqueous test solutions) on the wettability of the polymers. When various types of ions were used, no significant change in advancing and receding contact angles was observed. The contact angle hysteresis was small. The zeta potential of the model polymers in aqueous electrolyte solutions was determined from streaming potential measurements. The variation of the zeta potential at different pH levels indicates preferential adsorption of hydroxyl ions at this interface. However, the presence of electrolytes at the interface between water and the different model polymers did not influence the macroscopic contact angle. The results may suggest the absence of any specific interaction between the ions and the solid polymer, as this should result in changes of hydrophobicity. Similar to the air/water interface, the composition and the potential of the polymer/water interface are obviously determined predominantly by the aqueous phase with only slight influence from the solid phase.
NASA Astrophysics Data System (ADS)
Escobar, Juan V.; Garza, Cristina; Alonso, Juan Carlos; Castillo, Rolando
2013-05-01
Increased roughness is known to enhance the natural wetting properties of surfaces, making them either more hydrophobic or more hydrophilic. In this work we study the wetting properties of water and mercury drops in contact with boron doped diamond films with progressively increased surface roughnesses. We show how thermal oxidation of a microcrystalline film creates pyramids decorated with sub-micron protrusions that turn its naturally mercuryphobic surface into super-mercuryphobic. With this liquid, we observe the vanishment of the contact angle hysteresis that is expected for rough surfaces as the contact angle approaches 180˚, making small drops of mercury roll along out of the surface at an apparent zero tilt-angle. In contrast, the incorporation of nano-globules on the oxidized surface through a silanization process is necessary to increase the hydrophobic properties of the film for which the contact angle with water reaches 138°. The wetting states that dominate in each case are discussed.
Lehr, C M; Bouwstra, J A; Boddé, H E; Junginger, H E
1992-01-01
The possible role of surface energy thermodynamics in mucoadhesion was investigated with Polycarbophil and pig intestinal mucosa. In separate experiments, the surface energy parameters of the substrate (mucosa) and the adhesive (polymer film) were determined by contact angle measurements on captive air/octane bubbles in three physiologically relevant test fluids (isotonic saline, artificial gastric fluid, and artificial intestinal fluid). Whereas the swollen Polycarbophil films were relatively hydrophilic as indicated by small water contact angles (22, 23, and 16 degrees), the water contact angles measured on mucosal tissue were significantly larger (61, 48, and 57 degrees). Hence, mucus was found to possess an appreciable hydrophobicity. The measured adhesive performance (force of detachment) between Polycarbophil and pig small intestinal mucosa was highest in nonbuffered saline medium, intermediate in gastric fluid, and minimal in intestinal fluid. In agreement with this trend, the mismatch in surface polarities between substrate and adhesive, calculated from the contact angle data, increased in the same order.
Muster, Tim H; Prestidge, Clive A
2002-03-02
The time-dependent wetting of sulfathiazole compacts with sessile water drops was evaluated using video microscopy. The influence of sulfathiazole crystalline form, particle size, pre-saturation with water, humidity and compaction pressure on the droplet spreading kinetics and contact angles are reported. The rate and extent of droplet spreading decreased for compact surfaces of high microscopic roughness; this was determined by atomic force microscopy (AFM). Pre-saturation of powder compacts with water (pre-saturated with sulfathiazole) enhanced droplet spreading and enabled pseudo-equilibrium contact angles to be determined for up to 10 min. Sessile-drop contact angles on both sulfathiazole powder compacts and single crystals are compared with particle contact angles determined by liquid penetration. This study has led to an improved understanding of the influence of physical heterogeneities and the face-specific surface chemistry of individual crystals on the wetting characteristics of pharmaceutical compacts.
Gupta, Pooja; Ulman, Abraham; Fanfan, Stephanie; Korniakov, Alexander; Loos, Katja
2005-01-12
We present the first study of mixed alkanethiolate SAMs on ultrasmooth gold surfaces. By eliminating surface roughness, it became possible, for the first time, to investigate wetting properties as a function of surface chemical composition. In three different surface compositions, it was found that contact-angle hysteresis apparently vanished. This suggests that surface chemical heterogeneity does not contribute to contact-angle hysteresis in mixed SAMs on ultrasmooth gold surfaces.
Letellier, Pierre; Mayaffre, Alain; Turmine, Mireille
2007-10-15
We applied the concepts of nonextensive thermodynamics [Turmine et al., J. Phys. Chem. B 108 (2004) 18980], to describe the equilibrium of a liquid drop placed on a solid substrate. This approach provides a consistent formal framework for analyzing the contact angle according to the nature and structure of the substrate, and also the size of the drops. The introduction, for the solid/liquid interface, of the concept of "fuzzy interface" characterized by a thermodynamic dimension, different from 2/3 (surface) allowed description of the case of substrates with ill-defined geometry (such as porous, structured systems, fractal structure systems, etc.) and straightforward explanation of the phenomenon of super hydrophobicity without using a layer of trapped air in possible anfractuosities. The application of the nonextensive thermodynamics relationships, allowed explanation of all the usual behaviors described in the literature (Young, modified Young, Wenzel, Cassie-Baxter) including the case of the composite interfaces made of materials with different natures and spatial structures (smooth, rough, homogeneous and heterogeneous surfaces). We show that the contact angle can vary with the drop volume according to a power law, and this was validated against values published in the literature. This study also has consequences for the relations between "thermodynamic dimension" and "fractal dimension."
Mattia, Davide; Starov, Victor; Semenov, Sergey
2012-10-15
While the stability of liquid films on substrates is a classical topic of colloidal science, the availability of nanostructured materials, such as nanotubes, nanofibres and nanochannels, has raised the question of how the stability of liquid films and their wetting behaviour is affected by nanoscale confinement. This paper will present the conditions for the stability of liquid films on and inside cylindrical solid substrates with nanometre scale characteristic dimensions. It is shown that the stability is determined by an effective disjoining/conjoining pressure isotherm which differs from the corresponding disjoining/conjoining pressure isotherm of flat liquid films on flat solid substrates. From the former, the equilibrium contact angles of drops on an outer or inner surface of a cylindrical capillary have been calculated as a function of surface curvature, showing that the expressions for equilibrium contact angles vary for different geometries, in view of the difference in thickness of the film of uniform thickness with which the bulk liquid (drops or menisci) is at equilibrium. These calculations have been extended to the case of glass nanocapillaries and carbon nanotubes, finding good agreement with experimental results in the literature.
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.
Mesoscopic modeling of a two-phase flow in the presence of boundaries: The contact angle.
Benzi, R; Biferale, L; Sbragaglia, M; Succi, S; Toschi, F
2006-08-01
We present a mesoscopic model, based on the Boltzmann equation, for the interaction between a solid wall and a nonideal fluid. We present an analytic derivation of the contact angle in terms of the surface tension between the liquid-gas, the liquid-solid, and the gas-solid phases. We study the dependency of the contact angle on the two free parameters of the model, which determine the interaction between the fluid and the boundaries, i.e. the equivalent of the wall density and of the wall-fluid potential in molecular dynamics studies. We compare the analytical results obtained in the hydrodynamical limit for the density profile and for the surface tension expression with the numerical simulations. We compare also our two-phase approach with some exact results obtained by E. Lauga and H. Stone [J. Fluid. Mech. 489, 55 (2003)] and J. Philip [Z. Angew. Math. Phys. 23, 960 (1972)] for a pure hydrodynamical incompressible fluid based on Navier-Stokes equations with boundary conditions made up of alternating slip and no-slip strips. Finally, we show how to overcome some theoretical limitations connected with the discretized Boltzmann scheme proposed by X. Shan and H. Chen [Phys. Rev. E 49, 2941 (1994)] and we discuss the equivalence between the surface tension defined in terms of the mechanical equilibrium and in terms of the Maxwell construction.
Hilpert, Markus
2010-07-15
The displacement of a gas by a liquid in both horizontal and inclined capillary tubes where the tube inlet is connected to a liquid reservoir of constant pressure can be described by the Lucas-Washburn theory. One can also use the Lucas-Washburn theory to model the reverse flow, that is, liquid withdrawal, even though the latter case has received relatively little attention. In this paper, we derive analytical solutions for the travel time of the gas-liquid interface as a function of interface velocity. The interface position can be obtained by numerically integrating the numerically inverted interface velocity. Therefore we refer to these solutions as (semi)-analytical. We neglect inertial forces. However, we account for a dynamic contact angle where the nondimensional non-equilibrium Young force depends on the capillary number in the form of either a power law or a power series. We explore the entire nondimensional parameter space. The analytical solutions allow us to show that five different liquid withdrawal scenarios may occur that differ in the direction of flow and the sign of the acceleration of the gas-liquid interface: horizontal, upward, steady-state downward, accelerating downward, and decelerating downward flow. In the last case, the liquid is withdrawn from the tube either completely or partially. The (semi)-analytical solutions are also valid within the limit where the contact angle is constant.
Adsorption of modified dextrins on molybdenite: AFM imaging, contact angle, and flotation studies.
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.
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.
Liquid transfer between two solid surfaces with the effect of contact angle hysteresis
NASA Astrophysics Data System (ADS)
Chen, Huanchen; Tang, Tian; Amirfazli, Alidad
2013-11-01
Drop transfer from one solid surface to another (e.g. due to the approach of a surface from top to a sessile drop resting on a lower surface) is widely observed in many industrial areas, e.g. offset printing. This process is governed by many factors such as the contact angle (CA) and contact angle hysteresis (CAH) of surfaces, viscosity of the liquid and the rate at which the donor and acceptor surfaces are separated. In this work, an experimental apparatus is developed to study the transfer of liquid drop between surfaces, with the particular focus on addressing the effect of the surfaces' CAH when the loading speed is low (transfer is quasi-static). In the experiment, a liquid bridge between the two surfaces is first formed by compression; then stretched to the point of breakage. By using surfaces that have similar CA but dissimilar CAH, the liquid transfer ratio (the amount of liquid transferred to the acceptor surface over the total amount of liquid) is found to be significantly influenced by CAH. In addition, as a result of CAH, the maximum compression of the liquid bridge is found to play an important role in determining the transfer ratio. These findings can be very helpful for the design of surfaces and loading conditions to achieve desired transfer ratios in practice.
Investigation of energy dissipation due to contact angle hysteresis in capillary effect
NASA Astrophysics Data System (ADS)
Athukorallage, Bhagya; Iyer, Ram
2016-06-01
Capillary action or Capillarity is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity. Three effects contribute to capillary action, namely, adhesion of the liquid to the walls of the confining solid; meniscus formation; and low Reynolds number fluid flow. We investigate the dissipation of energy during one cycle of capillary action, when the liquid volume inside a capillary tube first increases and subsequently decreases while assuming quasi-static motion. The quasi-static assumption allows us to focus on the wetting phenomenon of the solid wall by the liquid and the formation of the meniscus. It is well known that the motion of a liquid on an non-ideal surface involves the expenditure of energy due to contact angle hysteresis. In this paper, we derive the equations for the menisci and the flow rules for the change of the contact angles for a liquid column in a capillary tube at a constant temperature and volume by minimizing the Helmholtz free energy using calculus of variations. We describe the numerical solution of these equations and present results from computations for the case of a capillary tube with 1 mm diameter.
Sedeva, Iliana G; Fetzer, Renate; Fornasiero, Daniel; Ralston, John; Beattie, David A
2010-05-15
The adsorption of three dextrin-based polymers, regular wheat dextrin (Dextrin TY), phenyl succinate dextrin (PS Dextrin), and styrene oxide dextrin (SO Dextrin) on a model hydrophobic surface, consisting of a mixed alkanethiol layer on gold, has been characterized using the quartz crystal microbalance with dissipation monitoring (QCM-D). The three polymers exhibited varying affinities and capacity for adsorption on the hydrophobic substrate. Atomic force microscope (AFM) imaging of the polymer layers indicates that all three polymers fully cover the surface. The effect of the three polymers on the static contact angle of the surface was studied using captive bubble contact angle measurements. The three polymers were seen to reduce the receding contact angle by similar amounts (approximately 14°) in spite of having varying adsorbed amounts and differences in adsorbed layer water content. Although no differences were observed in the ability of the polymers to reduce the static contact angle, measurements of the dynamic contact angle between a rising air bubble and the polymer covered substrate yielded stark differences between the polymers, with one polymer (SO Dextrin) slowing the dewetting by an order of magnitude more than the other two polymers. The differences in dewetting behavior correlate with the adsorbed layer characteristics determined by QCM-D and AFM. The role of the dynamic and static contact angle in the performance of a polymer as depressant is discussed.
Contact angles for evaporating liquids predicted and compared with existing experiments
NASA Astrophysics Data System (ADS)
Morris, S. J. S.
2001-04-01
The stationary meniscus of an evaporating, perfectly wetting system exhibits an apparent contact angle [Theta] which vanishes with the applied temperature difference [Delta]T, and is maintained for [Delta]T > 0 by a small-scale flow driven by evaporation. Existing theory predicts [Theta] and the heat flow q[low asterisk] from the contact region as the solution of a free-boundary problem. Though that theory admits the possibility that [Theta] and q[low asterisk] are determined at the same scale, we show that, in practice, a separation of scales gives the theory an inner and outer structure; [Theta] is determined within an inner region contributing a negligible fraction of the total evaporation, but q[low asterisk] is determined at larger scales by conduction across an outer liquid wedge subtending an angle [Theta]. The existence of a contact angle can thus be assumed for computing the heat flow; the problems for [Theta] and q[low asterisk] decouple. We analyse the inner problem to derive a formula for [Theta] as a function of [Delta]T and material properties; the formula agrees closely with numerical solutions of the existing theory. Though microphysics must be included in the model of the inner region to resolve a singularity in the hydrodynamic equations, [Theta] is insensitive to microphysical detail because the singularity is weak. Our analysis shows that [Theta] is determined chiefly by the capillary number Ca = [mu]lVl/[sigma] based on surface tension [sigma], liquid viscosity [mu]l and a velocity scale Vl set by evaporation kinetics. To illustrate this result of our asymptotic analysis, we show that computed angles lie close to the curve [Theta] = 2.2Ca1/4; a small scatter of ±15% about that curve is the only hint that [Theta] depends on microphysics. To test our scaling relation, we use film profiles measured by Kim (1994) to determine experimental values of [Theta] and Ca; these are the first such values to be published for the evaporating meniscus
A method of estimating the contact angle of a sissle drop on a clean, level surface, is developed for drops whose profiles are so low that the...contact angles are too small to measure. A simple geometric relationship between the drop’s volume and its contact angle is demonstrated, both
Evaporation stains: suppressing the coffee-ring effect by contact angle hysteresis.
Li, Yueh-Feng; Sheng, Yu-Jane; Tsao, Heng-Kwong
2013-06-25
A ring-shaped stain is frequently left on a substrate by a drying drop containing colloids as a result of contact line pinning and outward flow. In this work, however, different patterns are observed for drying drops containing small solutes or polymers on various hydrophilic substrates. Depending on the surface activity of solutes and the contact angle hysteresis (CAH) of substrates, the pattern of the evaporation stain varies, including a concentrated stain, a ringlike deposit, and a combined structure. For small surface-inactive solutes, the concentrated stain is formed on substrates with weak CAH, for example, copper sulfate solution on silica glass. On the contrary, a ringlike deposit is developed on substrates with strong CAH, for example, a copper sulfate solution on graphite. For surface-active solutes, however, the wetting property can be significantly altered and the ringlike stain is always visible, for example, Brij-35 solution on polycarbonate. For a mixture of surface-active and surface-inactive solutes, a combined pattern of a ringlike and concentrated stain can appear. For various polymer solutions on polycarbonate, similar results are observed. Concentrated stains are formed for weak CAH such as sodium polysulfonate, and ring-shaped patterns are developed for strong CAH such as poly(vinyl pyrrolidone). The stain pattern is actually determined by the competition between the time scales associated with contact line retreat and solute precipitation. The suppression of the coffee-ring effect can thus be acquired by the control of CAH.
Spreading dynamics and dynamic contact angle of non-Newtonian fluids.
Wang, X D; Lee, D J; Peng, X F; Lai, J Y
2007-07-17
The spreading dynamics of power-law fluids, both shear-thinning and shear-thickening fluids, that completely or partially wet solid substrate was investigated theoretically and experimentally. An evolution equation for liquid-film thickness was derived using a lubrication approximation, from which the dynamic contact angle versus the contact line moving velocity relationship was evaluated. In the capillary spreading regime, film thickness h is proportional to xi3/(n+2) (xi is the distance from the contact line), whereas in the gravitational regime, h is proportional to xi1/(n+2), relating to the rheological power exponent n. The derived model fit the experimental data well for a shear-thinning fluid (0.2% w/w xanthan solution) or a shear-thickening fluid (7.5% w/w 10 nm silica in polypropylene glycol) on a completely wetted substrate. The derived model was extended using Hoffmann's proposal for partially wetting fluids. Good agreement was also attained between model predictions and the shear-thinning fluid (1% w/w cmc solution) and shear-thickening fluid (10% w/w 15 nm silica) on partially wetted surfaces.
Mettu, Srinivas; Chaudhury, Manoj K
2011-08-16
Hysteresis of wetting, like the Coulombic friction at solid/solid interface, impedes the motion of a liquid drop on a surface when subjected to an external field. Here, we present a counterintuitive example, where some amount of hysteresis enables a drop to move on a surface when it is subjected to a periodic but asymmetric vibration. Experiments show that a surface either with a negligible or high hysteresis is not conducive to any drop motion. Some finite hysteresis of contact angle is needed to break the periodic symmetry of the forcing function for the drift to occur. These experimental results are consistent with simulations, in which a drop is approximated as a linear harmonic oscillator. The experiment also sheds light on the effect of the drop size on flow reversal, where drops of different sizes move in opposite directions due to the difference in the phase of the oscillation of their center of mass.
The contact angle for a droplet on homogeneous and spherical concave surfaces
NASA Astrophysics Data System (ADS)
Hu, Ai-Jun; Lv, Bao-Zhan; Wang, Xiao-Song; Zhou, Long
2016-03-01
Wetting of droplets on homogeneous and spherical concave rough surfaces is investigated based on thermodynamics. In this study, neglecting the droplet gravity and the thickness of the precursor film of the liquid-vapor interface, the three-phase system is divided into six parts using Gibbs concept of dividing surface. The system Helmholtz free energy is established based on thermodynamics. Supposing the temperature and chemical potential to be constant, a new generalized Young’s equation of the equilibrium contact angle for a spherical droplet on a spherical concave rough surfaces is obtained including the line tension effects. Under certain conditions, this generalized Young’s equation is the same as the Rusanov’s equation.
Zhou, Jian; Zhang, Renyun; Li, Xiaomao; Gutmann, Sebastian; Lv, Gang; Wang, Xuemei
2007-08-01
Fe3O4 nanoparticles are the most commonly used magnetic materials with promising applications in biomedical and biochemical engineering. In this study, a novel application of the tetraheptylammonium capped Fe3O4 nanoparticles in controllable biorecognition process of anticancer drug doxorubicin through combination with external static magnetic field has been demonstrated. Our AFM and electrochemical studies illustrate that the presence of the tetraheptylammonium capped Fe3O4 nanoparticles could promote the binding behavior of doxorubicin to DNA. And the results of the electrochemical contact angle measurements indicate that the controllable biomolecular recognition of doxorubicin could be readily achieved by combining these functionalized Fe3O4 nanoparticles with changing the positions of external magnetic field.
Arif, Muhammad; Al-Yaseri, Ahmed Z; Barifcani, Ahmed; Lebedev, Maxim; Iglauer, Stefan
2016-01-15
Precise characterization of wettability of CO2-brine-rock system and CO2-brine interfacial tension at reservoir conditions is essential as they influence capillary sealing efficiency of caprocks, which in turn, impacts the structural and residual trapping during CO2 geo-sequestration. In this context, we have experimentally measured advancing and receding contact angles for brine-CO2-mica system (surface roughness ∼12nm) at different pressures (0.1MPa, 5MPa, 7MPa, 10MPa, 15MPa, 20MPa), temperatures (308K, 323K, and 343K), and salinities (0wt%, 5wt%, 10wt%, 20wt% and 30wt% NaCl). For the same experimental matrix, CO2-brine interfacial tensions have also been measured using the pendant drop technique. The results indicate that both advancing and receding contact angles increase with pressure and salinity, but decrease with temperature. On the contrary, CO2-brine interfacial tension decrease with pressure and increase with temperature. At 20MPa and 308K, the advancing angle is measured to be ∼110°, indicating CO2-wetting. The results have been compared with various published literature data and probable factors responsible for deviations have been highlighted. Finally we demonstrate the implications of measured data by evaluating CO2 storage heights under various operating conditions. We conclude that for a given storage depth, reservoirs with lower pressures and high temperatures can store larger volumes and thus exhibit better sealing efficiency.
NASA Technical Reports Server (NTRS)
deGroh, Kim; Berger, Lauren; Roberts, Lily
2009-01-01
The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 x 10(exp 15) atoms/sq cm/sec, and each polymer was exposed to a maximum fluence of 5.16 x 10(exp 20) atoms/sq cm.
Linking fractional wettability and contact angle dynamics in water repellent soils
NASA Astrophysics Data System (ADS)
Beatty, Sarah; Smith, James
2016-04-01
Dynamic soil water repellency has become a highly documented soil phenomenon across a range of environmental conditions and investigated within a range of disciplines. With global climate change at the environmental science fore, there is growing concern and need for accurate quantification of fundamental soil hydraulic properties and model parameterization. In the presence of soil water repellency, however, substantial unknowns remain in terms of characterizing repellency and drawing linkages to fundamental hydraulic parameters. This is often related to the complexity of investigating soil water repellency, which is often a challenging environment because of its spatially and temporally variable nature. To help bridge this gap, this work reports on different approaches using various technologies to explore opportunities that yield greater quantification and parametrization of soil water repellency in natural hydrologic systems at different scales. These approaches include X-ray microtomography (μXCT), Axisymmetric Drop Shape Analysis (ADSA), Drop Penetration tests (MED/WDPT), and Tension Infiltrometry. This work has shown the strength of conceptually linking contact angle dynamics and fractional wettability as a means to understand the nature of infiltration in water repellent soils and provide a mechanistic foundation upon which repellency can be quantified and related to fundamental hydraulic properties. Contact angle dynamics and fractional wettability are complimentary terminology that appear in the multiphase flow and soil physics literature, but have largely/essentially only been applied in synthetic systems. Their utility in natural environments is potentially significant and conceptually useful since they can readily incorporate existing characterizations while providing greater opportunity for articulating and defining specific behaviours in systems with high spatial and temporal heterogeneity.
Krumpfer, Joseph W; Bian, Pei; Zheng, Peiwen; Gao, Lichao; McCarthy, Thomas J
2011-03-15
Silicon/silicon dioxide surfaces containing 3 μm (width) × 6 μm (length) × 40 μm (height) staggered rhombus posts were prepared using photolithography and hydrophobized using a perfluoroalkyl-containing monofunctional silane. These surfaces exhibit water contact angles of θ(A)/θ(R) = 169°/156°. Water drops come to rest on a carefully aligned horizontal sample but roll when the surface is tilted slightly. No visible trail or evidence of water "left behind" at the receding edge of the drop is apparent on surfaces that water drops have rolled on or on samples removed from water through the air-water interface. When dimethylbis(β-hydroxyethyl)ammonium methanesulfonate (N(+)S(-), a nonvolatile ionic liquid) is used as the liquid probe fluid (instead of water), contact angles of θ(A)/θ(R) = 164°/152° are observed and ∼3-μm-diameter sessile drops are visible (by scanning electron microscopy - SEM) on the top of every post of a sample drawn out of this liquid. We interpret the formation of these sessile microdrops as arising from microcapillary bridge failure that occurs during receding events and emphasize that the capillary bridges rupture in primarily a tensile failure mode. Smaller sessile drops could be prepared using mixtures of water and N(+)S(-). Microdroplets of N(+)S(-) were also observed to form selectively at particular features on surfaces containing square holes separated by ridges. This suggests that pinning sites can be identified using microscopy and this ionic liquid probe fluid.
New procedure to measure simultaneously the surface tension and contact angle.
Champmartin, S; Ambari, A; Le Pommelec, J Y
2016-05-01
This paper proposes a new procedure to simultaneously measure the static contact angle and the surface tension of a liquid using a spherical geometry. Unlike the other existing methods, the knowledge of one of both previous parameters and the displacement of the sphere are not mandatory. The technique is based on the measurement of two simple physical quantities: the height of the meniscus formed on a sphere at the very contact with a liquid bath and the resulting vertical force exerted on this object at equilibrium. The meniscus height, whose exact value requires the numerical resolution of the Laplace equation, is often estimated with an approximate 2D model, valid only for very large spheres compared to the capillary length. We develop instead another simplified solution of the Young-Laplace equation based on the work of Ferguson for the meniscus on a cylinder and adapted for the spherical shape. This alternative model, which is less restrictive in terms of the sphere size, is successfully compared to numerical solutions of the complete Young-Laplace equation. It appears to be accurate for sphere radii larger than only two capillary lengths. Finally the feasibility of the method is experimentally tested and validated for three common liquids and two "small" steel spheres.
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.
Dynamic contact angle effects onto the maximum drop impact spreading on solid surfaces
NASA Astrophysics Data System (ADS)
Vadillo, D. C.; Soucemarianadin, A.; Delattre, C.; Roux, D. C. D.
2009-12-01
This paper reports experimental investigations of drop impacts onto chemically treated surfaces with wettability from 5° to 160°. To follow in time the drop spreading, a high speed video camera was used, and it allows us to determine precisely the expansion of the drop and the profile of the free surface at the contact line. By changing the impact velocity, between less than 0.5 and 5 m/s, and the viscosity, from 1 to 100 mPa s, at constant surface tension, a broad range of Reynolds and Weber numbers is explored. This paper is divided into two parts. In the first part, the experimental drop evolution during spreading is directly reported and compared with previous works. Secondly, the emphasis is on the importance of the apparent dynamic contact angle for the prediction of the maximum spreading diameter. This achievement is manifested at low Reynolds numbers at which the matching between the experiment and the model is improved greatly.
New procedure to measure simultaneously the surface tension and contact angle
NASA Astrophysics Data System (ADS)
Champmartin, S.; Ambari, A.; Le Pommelec, J. Y.
2016-05-01
This paper proposes a new procedure to simultaneously measure the static contact angle and the surface tension of a liquid using a spherical geometry. Unlike the other existing methods, the knowledge of one of both previous parameters and the displacement of the sphere are not mandatory. The technique is based on the measurement of two simple physical quantities: the height of the meniscus formed on a sphere at the very contact with a liquid bath and the resulting vertical force exerted on this object at equilibrium. The meniscus height, whose exact value requires the numerical resolution of the Laplace equation, is often estimated with an approximate 2D model, valid only for very large spheres compared to the capillary length. We develop instead another simplified solution of the Young-Laplace equation based on the work of Ferguson for the meniscus on a cylinder and adapted for the spherical shape. This alternative model, which is less restrictive in terms of the sphere size, is successfully compared to numerical solutions of the complete Young-Laplace equation. It appears to be accurate for sphere radii larger than only two capillary lengths. Finally the feasibility of the method is experimentally tested and validated for three common liquids and two "small" steel spheres.
Contact angle measurements of Sn-Ag and Sn-Cu lead-free solders on copper substrates
NASA Astrophysics Data System (ADS)
Arenas, Mario F.; Acoff, Viola L.
2004-12-01
In this study, the contact angles of four lead-free solders, namely, Sn-3.5Ag, Sn-3.5Ag-4.8Bi, Sn-3.8Ag-0.7Cu, and Sn-0.7Cu (wt.%), were measured on copper substrates at different temperatures. Measurements were performed using the sessile-drop method. Contact angles ranging from 30° to 40° after wetting under vacuum with no fluxes and between 10° and 30° with rosin mildly activated (RMA) and rosin activated (RA) fluxes were obtained. The Sn-3.5Ag-4.8Bi exhibited the lowest contact angles, indicating improved wettability with the addition of bismuth. For all soldering alloys, lower contact angles were observed using RMA flux. Intermetallics formed at the solder/Cu interface were identified as Cu6Sn5 adjacent to the solder and Cu3Sn adjacent to the copper substrate. The Cu3Sn intermetallic phase was generally not observed when RMA flux was used. The effect of temperature on contact angle was dependent on the type of flux used.
Wang, Qiuling; Graber, Ellen R; Wallach, Rony
2013-04-15
Understanding the role of geometry, inertia, and dynamic contact angle on wetting and dewetting of capillary tubes has theoretical and practical aspects alike. The specific and synergistic effects of these factors were studied theoretically using a mathematical model that includes inertial and dynamic contact angle terms. After validating the model for capillaries of uniform cross section, the model was extended to capillaries with sinusoidal modulations of the radius, since in practice, capillaries rarely have uniform cross-sections. The height of the meniscus during wetting and dewetting was significantly affected by the relations between the local slope of the capillary surface and the Young contact angle. Non-dimensional variables were defined using viscous effects and gravity as the scaling parameters. Simulations using the dimensionless model showed that the inertial and dynamic contact angle terms can be neglected for narrow capillaries of uniform cross-section but not for uniform, wide cross-section capillaries. Moreover, nonuniformity in cross-sectional area induced hysteresis, deceleration, blocking, and metastable equilibrium locations. An increase in contact angle further amplified the effect of geometry on wetting and dewetting processes. These results enable characterization and modeling of fluid retention and flow in porous structures that inherently consist of capillaries of varying cross section.
NASA Astrophysics Data System (ADS)
Prajitno, D. H.; Maulana, A.; Syarif, D. G.
2016-08-01
Contact angles play an important role in the mass and heat transfer. Stainless steel 304 has been used for nuclear power plan structure material until now. An experiment to measure contact angle of demineralized aqua and nanofluid containing nano particle of zirconia on metal surface of stainless steel 304 with sessile drop method was conducted. The measurement to measure the static contact angle and drop of nano fluid containing nano particle zirconia on stainless steel with different surface roughness was carried out. It was observed that stainless steel 304 was good hydrophylic properties with decreasing surface roughness of stainless steel during drop of aqua demineralized and nano fluid respectively. As a result the contact angle of demineralized aqua is decreased from 97.39 to 78.42 and contact angle of nano fluid from 94.3 to 67.50, respectively with decreasing surface roughness of stainless stee 304. Wettability of nanofluid on surface stainless steel 304 is better than aqua demineralized.
Advances in Non-Contact Measurement of Creep Properties
NASA Technical Reports Server (NTRS)
Hyers, Robert; Canepari, Stacy; White, Erica Bischoff; Cretegny, Laurent; Rogers, jan
2009-01-01
As the required service temperatures for superalloys increases, so do the demands on testing for development of these alloys. Non-contact measurement of creep of refractory metals using electrostatic levitation has been demonstrated at temperatures up to 2300 C using samples of only 20-40 mg. These measurements load the spherical specimen by inertial forces due to rapid rotation. However, the first measurements relied on photon pressure to accelerate the samples to the high rotational rates of thousands of rotations per second, limiting the applicability to low stresses and high temperatures. Recent advances in this area extend this measurement to higher stresses and lower-temperatures through the use of an induction motor to drive the sample to such high rotational speeds. Preliminary results on new measurements on new materials will be presented.
NASA Astrophysics Data System (ADS)
Wu, Cyuan-Jhang; Li, Yueh-Feng; Woon, Wei-Yen; Sheng, Yu-Jane; Tsao, Heng-Kwong
2016-11-01
Contact angle hysteresis (CAH) on graphitic surfaces, including chemical vapor deposition (CVD) graphene, reduced electrophoretic deposition (EPD) graphene, highly oriented pyrolytic graphite (HOPG), and polished graphite sheet, has been investigated. The hysteresis loops of water drops on the first three samples are similar but the receding contact angle is particularly small for the polished graphite sheet.The significant CAH observed on CVD graphene and HOPG associated with atom-scale roughness has to be attributed mainly to adhesion hysteresis (surface relaxation), instead of roughness or defects.The difference of the wetting behavior among those four graphitic samples has been further demonstrated by hexadecane drops. On the surface of HOPG or CVD graphene,the contact line expands continuously with time, indicating total wetting for which the contact angle does not exist and contact line pinning disappears. In contrast, on the surface of reduced EPD graphene, spontaneous spreading is halted by spikes on it and partial wetting with small contact angle (θ≈4°) is obtained. On the surface of polished graphite sheet, the superlipophilicity and porous structure are demonstrated by imbibition and capillary rise of hexadecane. Consequently, an oil-infused graphite surface can be fabricated and the ultralow CAH of water (∆θ≈2°) is achieved.
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.
Digilov, Rafael M
2008-12-02
The impact of non-Newtonian behavior and the dynamic contact angle on the rise dynamics of a power law liquid in a vertical capillary is studied theoretically and experimentally for quasi-steady-state flow. An analytical solution for the time evolution of the meniscus height is obtained in terms of a Gaussian hypergeometric function, which in the case of a Newtonian liquid reduces to the Lucas-Washburn equation modified by the dynamic contact angle correction. The validity of the solution is checked against experimental data on the rise dynamics of a shear-thinning cmc solution in a glass microcapillary, and excellent agreement is found.
Afferrante, Luciano; Carbone, Giuseppe
2014-06-14
In the present paper, we propose a new theoretical approach to evaluate the shape and apparent contact angle (ACA) of a drop gently deposited on microstructured superhydrophobic surfaces. We exploit the very large separation of scales between the drop size and the features of the micromorphology of the interface to propose a numerical methodology to calculate the apparent contact area and apparent contact angle. In agreement with very recent experiments, calculations show that, in the case of surfaces made of conical micropillars, the ACA may take values very close to 180° not depending on the size of the liquid drop. At large drop volumes, the shape of the drop deviates from the spherical one as a result of the gravity effects, but it is noteworthy that the apparent contact angle does not change at all. Our calculations shows that this holds true also for different pillar shapes, showing that, for any given Young contact angle of the solid constituting the pillars, the ACA is an intrinsic property of the surface microgeometry.
Astrand, Anders P; Jalkanen, Ville; Andersson, Britt M; Lindahl, Olof A
2013-04-01
Human tissue stiffness can vary due to different tissue conditions such as cancer tumours. Earlier studies show that stiffness may be detected with a resonance sensor that measures frequency shift and contact force at application. Through the frequency shift and the contact force, a tissue stiffness parameter can be derived. This study evaluated how the probe application angle and indentation velocity affected the results and determined the maximum parameter errors. The evaluation was made on flat silicone discs with specified hardness. The frequency shift, the force and the stiffness parameter all varied with contact angle and indentation velocity. A contact angle of ≤10° was acceptable for reliable measurements. A low indentation velocity was recommended. The maximum errors for the system were <1.1% of the measured values. It was concluded that contact angle and indentation velocity have to be considered in the clinical setting. The angular dependency is especially important in clinical use for studying stiffness of human soft tissue, e.g. in prostate cancer diagnosis.
Hurley, Claire R; Leggett, Graham J
2009-08-01
Studies of the UV-induced photodegradation of poly(ethylene terephthalate) (PET) have been carried out using contact-angle goniometry, X-ray photoelectron spectroscopy (XPS), and friction force microscopy (FFM). The advancing contact angle of water, theta, decreased following exposure of free-standing PET films to UV light. Measurements of surface friction by FFM showed that the coefficient of friction mu increased as the degradation proceeded, reaching a limiting value after ca 200 min, in agreement with the contact angle data. Using a modified form of the Cassie equation, a quantitative analysis of the extent of modification could be carried out. There was a very close correlation between the coefficient of friction determined by FFM and the value of cos theta. XPS provided more detailed information on surface bonding that also correlated closely with the FFM data. Although FFM provides quantitative data on surface modification with nanometer-scale spatial resolution, it does not provide detailed structural information such as is provided by XPS. The oxygen content at the surface was found to increase as photo-generated radicals within the PET reacted with atmospheric oxygen. Increases in both ester and carbonyl contributions within XPS data accompanied this increase. It was concluded that the photodegradation process follows mainly Norrish type I reaction pathways, following previous work by Fechine et al and Grosstete et al.
Dingle, Nicole M; Harris, Michael T
2005-06-15
The pendant and sessile drop profile analysis using the finite element method (PSDA-FEM) is an algorithm which allows simultaneous determination of the interfacial tension (gamma) and contact angle (theta(c)) from sessile drop profiles. The PSDA-FEM algorithm solves the nonlinear second-order spherical coordinate form of the Young-Laplace equation. Thus, the boundary conditions at the drop apex and contact position of the drop with the substrate are required to solve for the drop profile coordinates. The boundary condition at the position where the drop contacts the substrate may be specified as a fixed contact line or fixed contact angle. This paper will focus on the fixed contact angle boundary condition for sessile drops on a substrate and how this boundary condition is used in the PSDA-FEM curve-fitting algorithm. The PSDA-FEM algorithm has been tested using simulated drop shapes with and without the addition of random error to the drop profile coordinates. The random error is varied to simulate the effect of camera resolution on the estimates of gamma and theta(c) values obtained from the curve-fitting algorithm. The error in the experimental values for gamma from sessile drops of water on acrylic and Mazola corn oil on acrylic falls within the predicted range of errors obtained for gamma values from simulated sessile drop profiles with randomized errors that are comparable in magnitude to the resolution of the experimental setup.
NASA Astrophysics Data System (ADS)
Hancer, Mehmet; Arkaz, Harun
2015-11-01
Although there are many viable approaches to induce hydrophobicity, a superhydrophobic surface could only be fabricated by combination of surface chemistry modification and roughness enhancement. In this study, surface roughness was obtained by 12 nm SiO2 nanoparticles (NPs) which were chemically modified using a self-assembled monolayer of perfluorodecyltrichlorosilane. The SiO2 NPs which were rendered hydrophobic, then successfully dispersed into a poly silicon (silsesquioxane) matrix at varying concentrations from 0.5 to 4%. The NPs dispersed polymer suspension was then spray coated on to glass and aluminum coupons in order to achieve polymer thin film nanocomposites. The results were revealed a superhydrophobic surface with a water contact angle exceeding 178° with low hysteresis and bouncing water droplet behavior. Furthermore the composite film reliability (hot-humid and ice build-up) was tested in an environmental control chamber by precisely adjusting both temperature (85 °C) and relative humidity (85 RH). Taber abrasion testing was applied in order to gain insights into the abrasion resistance of nanocomposite film. Finally, ice formation was simulated at -20 °C on the superhydrophobic nanocomposite film coated substrates.
Belman, Nataly; Jin, Kejia; Golan, Yuval; Israelachvili, Jacob N; Pesika, Noshir S
2012-10-16
Self-assembled monolayers (SAMs) are known to form on a variety of substrates either via chemisorption (i.e., through chemical interactions such as a covalent bond) or physisorption (i.e., through physical interactions such as van der Waals forces or "ionic" bonds). We have studied the behavior and effects of water on the structures and surface energies of both chemisorbed octadecanethiol and physisorbed octadecylamine SAMs on GaAs using a number of complementary techniques including "dynamic" contact angle measurements (with important time and rate-dependent effects), AFM, and electron microscopy. We conclude that both molecular overturning and submolecular structural changes occur over different time scales when such SAMs are exposed to water. These results provide new insights into the time-dependent interactions between surfaces and colloids functionalized with SAMs when synthesized in or exposed to high humidity or bulk water or wetted by water. The study has implications for a wide array of phenomena and applications such as adhesion, friction/lubrication and wear (tribology), surfactant-solid surface interactions, the organization of surfactant-coated nanoparticles, etc.
Metastable nanobubbles at the solid-liquid interface due to contact angle hysteresis.
Nishiyama, Takashi; Yamada, Yutaka; Ikuta, Tatsuya; Takahashi, Koji; Takata, Yasuyuki
2015-01-27
Nanobubbles exist at solid-liquid interfaces between pure water and hydrophobic surfaces with very high stability, lasting in certain cases up to several days. Not only semispherical but also other shapes, such as micropancakes, are known to exist at such interfaces. However, doubt has been raised as to whether or not the nanobubbles are gas-phase entities. In this study, surface nanobubbles at a pure water-highly ordered pyrolytic graphite (HOPG) interface were investigated by peak force quantitative nanomechanics (PF-QNM). Multiple isolated nanobubbles generated by the solvent-exchange method were present on the terraced areas, avoiding the steps of the HOPG surface. Adjacent nanobubbles coalesced and formed metastable nanobubbles. Coalescence was enhanced by the PF-QNM measurement. We determined that nanobubbles can exist for a long time because of nanoscale contact angle hysteresis at the water-HOPG interface. Moreover, the hydrophilic steps of HOPG were avoided during coalescence, providing evidence that the nanobubbles are truly gas phase.
Adão; Saramago; Fernandes
1999-09-01
The surface free energy per unit area of a solid, gamma(S), is a fundamental property of materials and determines their surface and interfacial behavior in processes like wetting and adhesion. In this study the gamma(S) of a series of styrene-acrylonitrile random copolymers is evaluated. Three different approaches are used to determine the components in which the surface free energy can be decomposed. Using the geometric and the harmonic mean approach, the dispersive, gamma(d), and polar, gamma(p), components of the solid surface free energy were determined and compared to the Lifshitz-van der Waals, gamma(LW), and acid-base, gamma(AB), components using the approach developed by C. J. van Oss et al. (1987, Adv. Colloid Interface Sci. 28, 35). The acid-base approach was also used to evaluate the work of adhesion of the test liquids: water, glycerol, and thiodiglycol. It was found that the contact angles of these liquids follow closely the predictions of Cassie equation. The evaluation of the surface free energy components on one hand and the relative magnitude of the work of adhesion components on the other hand, suggest that below 50% of acrylonitrile the polystyrene repeating units are preferentially at the surface. Above 50% of acrylonitrile the segregation of the low-energy homopolymer at the surface decreases. Copyright 1999 Academic Press.
Benni, Safiya; Mora, Laurence
2014-01-01
Atherosclerosis is a major cardiovascular disease. One of the side effects is restenosis. The aim of this work was to study the coating of stents by dextran derivates based polyelectrolyte's multilayer (PEM) films in order to increase endothelialization of injured arterial wall after stent implantation. Films were composed with diethylaminoethyl dextran (DEAE) as polycation and dextran sulphate (DS) as polyanion. One film was composed with 4 bilayers of (DEAE-DS)4 and was labeled D−. The other film was the same as D− but with an added terminal layer of DEAE polycation: (DEAE-DS)4-DEAE (labeled D+). The dynamic adsorption/desorption of proteins on the films were characterized by dynamic contact angle (DCA) and atomic force microscopy (AFM). Human endothelial cell (HUVEC) adhesion and proliferation were quantified and correlated to protein adsorption analyzed by DCA for fibronectin, vitronectin, and bovine serum albumin (BSA). Our results showed that the endothelial cell response was optimal for films composed of DS as external layer. Fibronectin was found to be the only protein to exhibit a reversible change in conformation after desorption test. This behavior was only observed for (DEAE-DS)4 films. (DEAE-DS)4 films could enhance HUVEC proliferation in agreement with fibronectin ability to easily change from conformation. PMID:25276808
Benni, Safiya; Avramoglou, Thierry; Hlawaty, Hanna; Mora, Laurence
2014-01-01
Atherosclerosis is a major cardiovascular disease. One of the side effects is restenosis. The aim of this work was to study the coating of stents by dextran derivates based polyelectrolyte's multilayer (PEM) films in order to increase endothelialization of injured arterial wall after stent implantation. Films were composed with diethylaminoethyl dextran (DEAE) as polycation and dextran sulphate (DS) as polyanion. One film was composed with 4 bilayers of (DEAE-DS)4 and was labeled D-. The other film was the same as D- but with an added terminal layer of DEAE polycation: (DEAE-DS)4-DEAE (labeled D+). The dynamic adsorption/desorption of proteins on the films were characterized by dynamic contact angle (DCA) and atomic force microscopy (AFM). Human endothelial cell (HUVEC) adhesion and proliferation were quantified and correlated to protein adsorption analyzed by DCA for fibronectin, vitronectin, and bovine serum albumin (BSA). Our results showed that the endothelial cell response was optimal for films composed of DS as external layer. Fibronectin was found to be the only protein to exhibit a reversible change in conformation after desorption test. This behavior was only observed for (DEAE-DS)4 films. (DEAE-DS)4 films could enhance HUVEC proliferation in agreement with fibronectin ability to easily change from conformation.
Pinho, Ana C; Piedade, Ana P
2013-08-28
The sputtering deposition of gold (Au) and poly(tetrafluoroethylene) (PTFE) was used to prepare a nanocomposite hybrid thin film suitable for protein adsorption while maintaining the native conformation of the biological material. The monolithic PTFE and the nanocomposite PTFE/Au thin films, with Au content up to 1 at %, were co-deposited by r.f. magnetron sputtering using argon as a discharge gas and deposited onto 316L stainless steel substrates, the most commonly used steel in biomaterials. The deposited thin films, before and after bovine serum albumin (BSA) adsorption, were thoroughly characterized with special emphasis on the surface properties/characteristics by atomic force microscopy (AFM), zeta potential, and static and dynamic contact angle measurements, in order to assess the relationship between structure and conformational changes. The influence of a pre-adsorbed peptide (RGD) was also evaluated. The nanotopographic and chemical changes induced by the presence of gold in the nanocomposite thin films enable RGD bonding, which is critical for the maintenance of the BSA native conformation after adsorption.
Haagh, M E J; Siretanu, I; Duits, M H G; Mugele, F
2017-04-11
The effectiveness of water flooding oil recovery depends to an important extent on the competitive wetting of oil and water on the solid rock matrix. Here, we use macroscopic contact angle goniometry in highly idealized model systems to evaluate how brine salinity affects the balance of wetting forces and to infer the microscopic origin of the resultant contact angle alteration. We focus, in particular, on two competing mechanisms debated in the literature, namely, double-layer expansion and divalent cation bridging. Our experiments involve aqueous droplets with a variable content of chloride salts of Na(+), K(+), Ca(2+), and Mg(2+), wetting surfaces of muscovite and amorphous silica, and an environment of ambient decane containing small amounts of fatty acids to represent polar oil components. By diluting the salt content in various manners, we demonstrate that the water contact angle on muscovite, not on silica, decreases by up to 25° as the divalent cation concentration is reduced from typical concentrations in seawater to zero. Decreasing the ionic strength at a constant divalent ion concentration, however, has a negligible effect on the contact angle. We discuss the consequences for the interpretation of core flooding experiments and the identification of a microscopic mechanism of low salinity water flooding, an increasingly popular, inexpensive, and environment-friendly technique for enhanced oil recovery.
Ho, Raimundo; Hinder, Steven J; Watts, John F; Dilworth, Sarah E; Williams, Daryl R; Heng, Jerry Y Y
2010-03-15
The sensitivity of two techniques in tracking changes in surface energetics was investigated for a crystalline excipient, D-mannitol. Macroscopic crystals of D-mannitol were grown from saturated water solution by slow cooling, and sessile drop contact angle was employed to measure the anisotropic surface energy. The facet-specific surface energy was consistent with localised hydroxyl group concentrations determined by X-ray photoelectron spectroscopy (XPS), and was also in excellent agreement with the surface energy distribution of the powder form of mannitol measured via a new methodology using inverse gas chromatography (IGC) at finite concentrations. The gamma(SV)(d) was found to vary between 39.5 mJ/m(2) and 44.1 mJ/m(2) for contact angle and between 40 mJ/m(2) and 49 mJ/m(2) for IGC measurements. We report here, a high level of surface heterogeneity on the native mannitol crystal surfaces. When the surfaces of both D-mannitol samples (powder and large single crystals) were modified by dichlorodimethylsilane to induce surface hydrophobicity, both IGC and contact angle revealed a homogeneous surface due to functionalisation of mannitol crystal surface with methyl groups resulting in gamma(SV)(d) of approximately 34 mJ/m(2). It was shown that both IGC and contact angle techniques are able to detect surface chemical variations and detailed surface energetic distribution.
Pichot, R; Spyropoulos, F; Norton, I T
2012-07-01
The effect of surfactants' type and concentration on the interfacial tension and contact angle in the presence of hydrophilic silica particles was investigated. Silica particles have been shown to have an antagonistic effect on interfacial tension and contact angle in the presence of both W/O and O/W surfactants. Silica particles, combined with W/O surfactant, have no effect on interfacial tension, which is only dictated by the surfactant concentration, while they strongly affect interfacial tension when combined with O/W surfactants. At low O/W surfactant, both particles and surfactant are adsorbed at the interface, modifying the interface structure. At higher concentration, interfacial tension is only dictated by the surfactant. By increasing the surfactant concentration, the contact angle that a drop of aqueous phase assumes on a glass substrate placed in oil media decreases or increases depending on whether the surfactant is of W/O or O/W type, respectively. This is due to the modification of the wettability of the glass by the oil or water induced by the surfactants. Regardless of the surfactant's type, the contact angle profile was dictated by both particles and surfactant at low surfactant concentration, whereas it is dictated by the surfactant only at high concentration.
Effect of dynamic contact angle in a volume of fluid (VOF) model for a microfluidic capillary flow.
Ashish Saha, Auro; Mitra, Sushanta K
2009-11-15
We perform three-dimensional numerical and experimental study of the dynamic contact angle using volume of fluid (VOF) method applied to microfluidic channels with integrated pillars. Initially, we evaluated different dynamic contact angle models (hydrodynamic, molecular kinetic and empirical) for capillary filling of a two-dimensional microchannel using analytical formulation. Further, the models which require a minimum prescription of adjustable parameters are only used for the study of capillary filling of microchannels with integrated pillars using different working fluids such as DI water, ethanol and isopropyl alcohol. Different microchannel geometry with varying diameter/height/spacing were studied for circular pillars. Effect of square pillars and changing the overall number of pillars on the capillary phenomena were also simulated. Our study demonstrated that the dynamic contact angle models modifies the transient response of the meniscus displacement and also the observed trends are model specific for the various microchannel geometries and working fluids. However, the different models have minimal effect on the meniscus profile. Different inlet boundary conditions were applied to observe the effect of grid resolution selected for numerical study on the capillary filling time. A grid dependent dynamic contact angle model which incorporates effective slip in the model was also used to observe the grid convergence of the numerical results. The grid independence was shown to improve marginally by applying the grid dependent dynamic contact angle model. Further we did numerical experiments of capillary filling considering variable surface wettability on the top and bottom walls of the microchannel with alternate hydrophilic-hydrophobic patterns. The meniscus front pinning was noticed for a high wetting contrast between the patterns. Non uniform streamline patterns indicated mixing of the fluid when using patterned walls. Such a microfluidic device with
Donelli, Ilaria; Taddei, Paola; Smet, Philippe F; Poelman, Dirk; Nierstrasz, Vincent A; Freddi, Giuliano
2009-08-01
The purpose of this study was to investigate the changes induced by a lypolytic enzyme on the surface properties of polyethylene terephthalate (PET). Changes in surface hydrophilicity were monitored by means of water contact angle (WCA) measurements. Fourier Transform Infrared spectroscopy (FTIR) in the Attenuated Total Reflectance mode (ATR) was used to investigate the structural and conformational changes of the ethylene glycol and benzene moieties of PET. Amorphous and crystalline PET membranes were used as substrate. The lipolytic enzyme displayed higher hydrolytic activity towards the amorphous PET substrate, as demonstrated by the decrease of the WCA values. Minor changes were observed on the crystalline PET membrane. The effect of enzyme adhesion was addressed by applying a protease after-treatment which was able to remove the residual enzyme protein adhering to the surface of PET, as demonstrated by the behavior of WCA values. Significant spectral changes were observed by FTIR-ATR analysis in the spectral regions characteristic of the crystalline and amorphous PET domains. The intensity of the crystalline marker bands increased while that of the amorphous ones decreased. Accordingly, the crystallinity indexes calculated as band intensity ratios (1,341/1,410 cm(-1) and 1,120/1,100 cm(-1)) increased. Finally, the free carboxyl groups formed at the surface of PET by enzyme hydrolysis were esterified with a fluorescent alkyl bromide, 2-(bromomethyl)naphthalene (BrNP). WCA measurements confirmed that the reaction proceeded effectively. The fluorescence results indicate that the enzymatically treated PET films are more reactive towards BrNP. FTIR analysis showed that the surface of BrNP-modified PET acquired a more crystalline character.
Settens, Charles M.
2015-01-01
Simultaneous migration of planar transistors to FinFET architectures, the introduction of a plurality of materials to ensure suitable electrical characteristics, and the establishment of reliable multiple patterning lithography schemes to pattern sub-10 nm feature sizes imposes formidable challenges to current in-line dimensional metrologies. Because the shape of a FinFET channel cross-section immediately influences the electrical characteristics, the evaluation of 3D device structures requires measurement of parameters beyond traditional critical dimension (CD), including their sidewall angles, top corner rounding and footing, roughness, recesses and undercuts at single nanometer dimensions; thus, metrologies require sub-nm and approaching atomic level measurement uncertainty. Synchrotron critical dimension small angle X-ray scattering (CD-SAXS) has unique capabilities to non-destructively monitor the cross-section shape of surface structures with single nanometer uncertainty and can perform overlay metrology to sub-nm uncertainty. In this dissertation, we perform a systematic experimental investigation using CD-SAXS metrology on a hierarchy of semiconductor 3D device architectures including, high-aspect-ratio contact holes, H2 annealed Si fins, and a series of grating type samples at multiple points along a FinFET fabrication process increasing in structural intricacy and ending with fully fabricated FinFET. Comparative studies between CD-SAXS metrology and other relevant semiconductor dimensional metrologies, particularly CDSEM, CD-AFM and TEM are used to determine physical limits of CD-SAXS approach for advanced semiconductor samples. CD-SAXS experimental tradeoffs, advice for model-dependent analysis and thoughts on the compatibility with a semiconductor manufacturing environment are discussed.
Muthu, Satish; Childress, Amy; Brant, Jonathan
2014-08-15
Membrane fouling assessed from a fundamental standpoint within the context of the Derjaguin-Landau-Verwey-Overbeek (DLVO) model. The DLVO model requires that the properties of the membrane and foulant(s) be quantified. Membrane surface charge (zeta potential) and free energy values are characterized using streaming potential and contact angle measurements, respectively. Comparing theoretical assessments for membrane-colloid interactions between research groups requires that the variability of the measured inputs be established. The impact that such variability in input values on the outcome from interfacial models must be quantified to determine an acceptable variance in inputs. An interlaboratory study was conducted to quantify the variability in streaming potential and contact angle measurements when using standard protocols. The propagation of uncertainty from these errors was evaluated in terms of their impact on the quantitative and qualitative conclusions on extended DLVO (XDLVO) calculated interaction terms. The error introduced into XDLVO calculated values was of the same magnitude as the calculated free energy values at contact and at any given separation distance. For two independent laboratories to draw similar quantitative conclusions regarding membrane-foulant interfacial interactions the standard error in contact angle values must be⩽2.5°, while that for the zeta potential values must be⩽7 mV.
Kalantarian, A; David, R; Chen, J; Neumann, A W
2011-04-05
Axisymmetric drop-shape analysis-no apex (ADSA-NA) is a recent drop-shape method that allows the simultaneous measurement of contact angles and surface tensions of drop configurations without an apex (i.e., a sessile drop with a capillary protruding into the drop). Although ADSA-NA significantly enhanced the accuracy of contact angle and surface tension measurements compared to that of original ADSA using a drop with an apex, it is still not as accurate as a surface tension measurement using a pendant drop suspended from a holder. In this article, the computational and experimental aspects of ADSA-NA were scrutinized to improve the accuracy of the simultaneous measurement of surface tensions and contact angles. It was found that the results are relatively insensitive to different optimization methods and edge detectors. The precision of contact angle measurement was enhanced by improving the location of the contact points of the liquid meniscus with the solid substrate to subpixel resolution. To optimize the experimental design, the capillary was replaced with an inverted sharp-edged pedestal, or holder, to control the drop height and to ensure the axisymmetry of the drops. It was shown that the drop height is the most important experimental parameter affecting the accuracy of the surface tension measurement, and larger drop heights yield lower surface tension errors. It is suggested that a minimum nondimensional drop height (drop height divided by capillary length) of 1.7 is required to reach an error of less than 0.2 mJ/m(2) for the measured surface tension. As an example, the surface tension of water was measured to be 72.46 ± 0.04 at 24 °C by ADSA-NA, compared to 72.39 ± 0.01 mJ/m(2) obtained with pendant drop experiments.
NASA Astrophysics Data System (ADS)
Pogorzelski, Stanisław J.; Berezowski, Zdzisław; Rochowski, Paweł; Szurkowski, Janusz
2012-02-01
The aim of the paper is to propose a quantitative description of dental surface modifications, resulting from application of Corega and oral cavity liquids, with several surface parameters derived from liquid/solid contact angle measurements. In particular, to predict the long-term effectiveness of denture cleansers in prosthetics, it is necessary to determine surface wettability variations for model dental materials/probe liquid systems related to the contamination effect caused by substances found in the oral cavity. A novel simple low-cost methodology, based on liquid drop contact angle hysteresis CAH approach developed by Chibowski, was adopted to trace solid surface free energy changes in the model PMMA-Corega Tabs interfacial layer. Contact angle and its hysteresis were studied with a sessile drop-inclined plate method in contact with a cleanser (Corega Tabs) and model liquids found in the oral cavity. The apparent solid surface free energy, adsorptive film pressure, work of adhesion and spreading were derived from contact angle hysteresis data for both model solid surfaces (reference) and samples affected by different reactive liquids for a certain time. A time-dependent surface wettability changes of dentures were expressed quantitatively in terms of the corresponding variations of the surface energy parameters which turned out to be unequivocally related to the cleanser exposure time and polarity of the liquids applied to the dental material. The novel methodology appeared to be a useful tool for long term surface characterization of dental materials treated with surfactants-containing liquids capable of forming adhesive layers. The time of optimal use and effectiveness of cleansers are also reflected dynamically in the corresponding variations of the surface wettability parameters. Further studies on a large group of dental surface-probe liquid systems are required to specify the role played by other important factors (liquid polarity, pH and temperature).
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
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.
2016-11-01
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 c}\\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.
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.
Yoshida, Kenichiro; Ohkubo, Kohji; Ojima, Nobutoshi; Iwata, Kayoko
2013-03-01
We adapted the critical angle method for measuring rough surfaces under partial contact to acquire an in vivo skin refractive index (RI). Assuming that the total reflection is the simple sum of reflection from areas that are in contact and reflection from those that are not in contact, the RI can be estimated even for partial contact with a rough surface. We found that cheek skin is sufficiently soft that a sufficiently large area can be in contact and that the critical angle was detectable. The RIs of the cheeks of adult females were measured. The RI range was about 1.51 to 1.53, at a wavelength of 550 nm, without considering systematic errors. The RIs of cheeks are significantly correlated with their conductance, which corresponds to their water content. We determined the relationship between the RI and conductance within the variation of skin under normal conditions; this relationship was theoretically obtained in previous studies. In the present study, a direct in vivo measurement method was developed that enabled us to measure the RI in daily life, although this method contains errors for several reasons, including disregarding absorption.
Experimental investigation of evaporation from low-contact-angle sessile droplets.
Dhavaleswarapu, Hemanth K; Migliaccio, Christopher P; Garimella, Suresh V; Murthy, Jayathi Y
2010-01-19
Evaporating sessile drops remain pinned at the contact line during much of the evaporation process, and leave a ring of residue on the surface upon dryout. The intensive mass loss near the contact line causes solute particles to flow to the edge of the droplet and deposit at the contact line. The high vapor diffusion gradient and the low thermal resistance of the film near the contact line are responsible for very efficient mass transfer in this region. Although heat and mass transfer at the contact line have been extensively studied, well-characterized experiments remain scarce. The local mass transport in a 100-400 microm region near the contact line of a water droplet of radius 1810 microm on a glass substrate is experimentally quantified in the present work. Microparticle image velocimetry measurements of the three-dimensional flow field near the contact line are conducted to map the velocity field. Combined with high-resolution transient liquid profile shapes, the measured velocity field yields transient local evaporative mass fluxes near the contact line. The spatial and temporal distribution of the local evaporative flux is also documented. The temperature distribution in the droplet near the contact line is deduced from the local evaporative fluxes and interface mass transport theory.
Measurement of contact angle in a clearance-fit pin-loaded hole
NASA Technical Reports Server (NTRS)
Prabhakaran, R.; Naik, R. A.
1986-01-01
A technique which measures load-contact variation in a clearance-fit, pin-loaded hole is presented in detail. A steel instrumented pin, which activates a make-or-break electrical circuit in the pin-hole contact region, was inserted into one aluminum and one polycarbonate specimen. The resulting load-contact variations are indicated schematically. The ability to accurately determine the arc of contact at any load was crucial to this measurement. It is noted that this simple experimental technique is applicable to both conducting and nonconducting materials.
NASA Astrophysics Data System (ADS)
Zhao, Cunhua; Liang, Huiqin; Cui, Dongqing; Hong, Xinhua; Wei, Daling; Gao, Changliu
2011-08-01
In the ultralight or ultrathin applied domain of zoom lens, the traditional glass / plastic lens is limited for manufacture technology or cost. Therefore, a liquid lens was put forward to solve the problems. The liquid zoom lens has the merits of lower cost, smaller volume, quicker response, lower energy consumption, continuous zoom and higher accuracy. In liquid zoom lens the precise focal length is obtained by the contact angle changing to affect the curvature radius of interface. In our works, the relations of the exerted voltage, the contact angle, the curvature radius and the focal length were researched and accurately calculated. The calculation of the focal length provides an important theoretical basis for instructing the design of liquid zoom lens.
Mugikura, Y.; Selman, J.R.
1996-08-01
The wetting of metals and oxides by molten carbonate is an important factor affecting the performance of a molten carbonate fuel cell (MCFC). The distribution of the electrolyte among electrodes and matrix in the MCFC is dominated by the pore characteristics and wetting properties of these components. However, data on wetting, especially under load (current passage), are limited. In this study, the behavior of the meniscus at a metal is used to obtain information on wetting and electrochemical reactions. Meniscus height and current were measured under various atmospheres. The contact angle was calculated from the meniscus height. The electrolyte distribution in the MCFC was estimated using contact angles thus obtained in oxidant and reducing atmospheres. The results suggest that upon application of load the electrolyte moves from the anode to the cathode and that capillary effects can worsen the performance of a cell, especially if it is in an unbalanced state of electrolyte filling.
Okon, Kufre Edet; Lin, Fengcai; Chen, Yandan; Huang, Biao
2017-05-15
The effect of silicone oil heat treatment (SOTH) on the chemical composition, cellulose crystalline structure, thermal degradation and contact angle of Chinese parasol wood were examined in this study. Samples were heated at 150°C, 180°C and 210°C for 2h and 8h, after SOHT chemical composition, fourier transformed infrared (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) of the treated samples were evaluated. Results showed that the chemical components of the wood were affected after SOHT particularly when treated at 210°C for 8h. Changes in the chemical components was due to the degradation of biopolymer components of the wood during SOHT. The crystallinity index of cellulose and contact angle of the SOHT samples was increased. The findings demonstrate the potential of SOHT for modification of wood. Thus an economical and eco-friendly approach to thermally modified wood was achieved in this study.
Advances in contact algorithms and their application to tires
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.; Tanner, John A.
1988-01-01
Currently used techniques for tire contact analysis are reviewed. Discussion focuses on the different techniques used in modeling frictional forces and the treatment of contact conditions. A status report is presented on a new computational strategy for the modeling and analysis of tires, including the solution of the contact problem. The key elements of the proposed strategy are: (1) use of semianalytic mixed finite elements in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynomials in the meridional direction; (2) use of perturbed Lagrangian formulation for the determination of the contact area and pressure; and (3) application of multilevel iterative procedures and reduction techniques to generate the response of the tire. Numerical results are presented to demonstrate the effectiveness of a proposed procedure for generating the tire response associated with different Fourier harmonics.
NASA Astrophysics Data System (ADS)
Babu, Keshak; Pal, Nilanjan; Bera, Achinta; Saxena, V. K.; Mandal, Ajay
2015-10-01
New synthesized polymeric surfactants have immensely attracted the researchers for further development of chemical enhanced oil recovery method particularly in surfactant flooding. Contact angle and interfacial tension measurement tests are the effective ways to identify proper chemicals/surfactants for enhanced oil recovery by chemical/surfactant flooding. In the present study a new polymeric surfactant was synthesized from pre-synthesized sodium methyl ester sulfonate (surfactant) and acrylamide for application in chemical enhanced oil recovery. The synthesized surfactant and polymeric surfactant were used to measure interfacial tension between their aqueous phase and crude oil phase to investigate the efficiency of the surfactants in reduction of interfacial tension. The synthesized polymeric surfactant has also ability to control the mobility because of its viscous nature in aqueous solution. Contact angles of solid-crude oil-surfactant interface were also measured to study the effect of the synthesized surfactant and polymeric surfactant on wettability alteration mechanism. Synergistic effect was studied by using NaCl and synthesized surfactants on interfacial tension. Dynamic interfacial tensions of the surfactant and polymeric surfactant solutions with crude oil were measured at different NaCl concentrations. Interfacial tension was found to be lowered up to 10-2 to 10-3 mN/m which is effective for oil recovery. Measurement of contact angle indicates the wettability change of the quartz surface. Comparative studies on efficiencies of synthesized sodium methyl ester sulfonate surfactant and polymeric surfactant were also carried out with respect to interfacial tension reduction and contact angle change.
Advances in reduction techniques for tire contact problems
NASA Technical Reports Server (NTRS)
Noor, Ahmed K.
1995-01-01
Some recent developments in reduction techniques, as applied to predicting the tire contact response and evaluating the sensitivity coefficients of the different response quantities, are reviewed. The sensitivity coefficients measure the sensitivity of the contact response to variations in the geometric and material parameters of the tire. The tire is modeled using a two-dimensional laminated anisotropic shell theory with the effects of variation in geometric and material parameters, transverse shear deformation, and geometric nonlinearities included. The contact conditions are incorporated into the formulation by using a perturbed Lagrangian approach with the fundamental unknowns consisting of the stress resultants, the generalized displacements, and the Lagrange multipliers associated with the contact conditions. The elemental arrays are obtained by using a modified two-field, mixed variational principle. For the application of reduction techniques, the tire finite element model is partitioned into two regions. The first region consists of the nodes that are likely to come in contact with the pavement, and the second region includes all the remaining nodes. The reduction technique is used to significantly reduce the degrees of freedom in the second region. The effectiveness of the computational procedure is demonstrated by a numerical example of the frictionless contact response of the space shuttle nose-gear tire, inflated and pressed against a rigid flat surface. Also, the research topics which have high potential for enhancing the effectiveness of reduction techniques are outlined.
High Yield of GaAs Nanowire Arrays on Si Mediated by the Pinning and Contact Angle of Ga.
Russo-Averchi, Eleonora; Vukajlovic Plestina, Jelena; Tütüncüoglu, Gözde; Matteini, Federico; Dalmau-Mallorquí, Anna; de la Mata, Maria; Rüffer, Daniel; Potts, Heidi A; Arbiol, Jordi; Conesa-Boj, Sonia; Fontcuberta i Morral, Anna
2015-05-13
GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfill this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work, we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90°, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon.
Hysteretic memory in pH-response of water contact angle on poly(acrylic acid) brushes.
Yadav, Vivek; Harkin, Adrienne V; Robertson, Megan L; Conrad, Jacinta C
2016-04-21
We investigated the pH-dependent response of flat polyacid brushes of varying length and dispersity in the extended brush regime. Our model system consisted of poly(acrylic acid) brushes, which change from hydrophobic and neutral at low pH to hydrophilic and negatively charged at high pH, synthesized on silicon substrates using a grafting-from approach at constant grafting density. We observed three trends in the pH-response: first, the dry brush thickness increased as the pH was increased for brushes above a critical length, and this effect was magnified as the dispersity increased; second, the water contact angle measured at low pH was larger for brushes of greater dispersity; and third, brushes of sufficient dispersity exhibited hysteretic memory behavior in the pH-dependence of the contact angle, in which the contact angle upon increasing and decreasing pH differed. As a consequence, the pKa of the brushes measured upon increasing pH was consistently higher than that measured upon decreasing pH. The observed pH response is consistent with proposed changes in the conformation and charge distribution of the polyelectrolyte brushes that depend on the direction of pH change and the dispersity of the brushes.
NASA Astrophysics Data System (ADS)
Azeredo, Bruno P.; Yeratapally, Saikumar R.; Kacher, Josh; Ferreira, Placid M.; Sangid, Michael D.
2016-11-01
Decorating 1D nanostructures (e.g., wires and tubes) with metal nanoparticles serves as a hierarchical approach to integrate the functionalities of metal oxides, semiconductors, and metals. This paper examines a simple and low-temperature approach to self-assembling gold nanoparticles (Au-np)—a common catalytic material—onto silicon nanowires (SiNWs). A conformal ultra-thin film (i.e., <15 nm thick) is deposited onto SiNWs and thermally dewetted, forming nanoparticles in the 6-70 nm range. Two parameters of its morphology are dependent upon dewetting conditions: particle size and particle contact angle. Using transmission electron microscopy imaging, it is found that annealing temperature profile has a strong effect on the particle size. Additionally, the contact angle is found to be dependent on particle size and temperature even below the eutectic temperature of the Au-Si alloy. Molecular dynamics simulations were performed to investigate potential explanations for such experimental observation. In this temperature regime, the simulations reveal the formation of an amorphous phase at the interface between the catalyst and SiNW that is sensitive to temperature. This amorphous layer increases the adhesion energy at the interface and explains the contact angle dependence on temperature.
Ahfat, N M; Buckton, G; Burrows, R; Ticehurst, M D
2000-01-01
Surfaces of pharmaceutical powders have been assessed using contact angle, inverse phase gas chromatography (IGC) and triboelectric (electrostatic) charging techniques. The suitability of the Dynamic Angle Tester (DAT), an instrument based on the sessile drop technique, in determining contact angles and then the surface energy of pharmaceutical powders was assessed. The dispersive components of the surface energy of powders determined from the DAT and IGC method ranked the powders in the same order. The dispersive component values obtained by IGC were, as expected, higher than those from the DAT, due to IGC probing the highest energy sites on the powder surface. IGC and triboelectric studies allow materials to be characterised in terms of their electron donating-accepting tendencies, so inter-relationships between the data from the two techniques were explored. Although the data set was limited, there appeared to be a correlation between the charges developed by the powders on contact with stainless steel and the ratio of the electron-donating to electron-accepting tendencies of the materials as obtained from IGC.
Cabezas, M Guadalupe; Bateni, Arash; Montanero, José M; Neumann, A Wilhelm
2006-11-21
Drop shape techniques, such as axisymmetric drop shape analysis, are widely used to measure surface properties, as they are accurate and reliable. Nevertheless, they are not applicable in experimental studies dealing with fluid configurations that do not present an apex. A new methodology is presented for measuring interfacial properties of liquids, such as surface tension and contact angles, by analyzing the shape of an axisymmetric liquid-fluid interface without use of apex coordinates. The theoretical shape of the interface is generated numerically as a function of surface tension and some geometrical parameters at the starting point of the interface, e.g., contact angle and radius of the interface. Then, the numerical shape is fitted to the experimental profile, taking the interfacial properties as adjustable parameters. The best fit identifies the true values of surface tension and contact angle. Comparison between the experimental and the theoretical profiles is performed using the theoretical image fitting analysis (TIFA) strategy. The new method, TIFA-axisymmetric interfaces (TIFA-AI), is applicable to any axisymmetric experimental configuration (with or without apex). The versatility and accuracy of TIFA-AI is shown by considering various configurations: liquid bridges, sessile and pendant drops, and liquid lenses.
Zigelman, Anna; Manor, Ofer
2016-06-29
We propose a model for the pattern deposition of the solute from an evaporating drop of a dilute solution on a horizontal substrate. In the model we take into account the three-phase contact angle hysteresis and the deposition of the solute whenever its concentration exceeds the solubility limit. The evaporating drop is governed by a film equation. We show that unless for a very small three-phase contact angle or a very rapid evaporation rate the film adopts a quasi-steady geometry, satisfying the Young-Laplace equation to leading order. The concentration profile is assumed to satisfy an advection diffusion equation subject to the standard Fick's law for the diffusive flux. We further use an integral boundary condition to describe the dynamics of the concentration in the vicinity of the three-phase contact line; we replace an exact geometric description of the vicinity of the contact line, which is usually assumed such that mathematical singularities are avoided, with general insights about the concentration and its flux. We use our model to explore the relationships between a variety of deposition patterns and the governing parameters, show that the model repeats previous findings, and suggest further insights.
Soil-water contact angle of some soils of the Russian Plane
NASA Astrophysics Data System (ADS)
Bykova, Galina; Tyugai, Zemfira; Milanovskiy, Evgeny; Shein, Evgeny
2016-04-01
INTRODUCTION Soil wettability affects the aggregate water resistance, the movement of moisture and dissolved substances, preferential flows, etc. There are many factors affecting the soil's wettability (the content of organic matter (OM), soil's mineralogical composition, particle size distribution), so it can reflect changes in the soil, including results of human impact. The quantitative characteristic of soil wettability is a contact angle (CA), its measurement is a new and difficult problem because of the complexity, heterogeneity and polydispersity of the object of investigation. The aim of this work is to study soil-water CA of some soils of the Russian Plane. MATERIALS AND METHODS The objects of study were sod-podzolic (Umbric Albeluvisols Abruptic, Eutric Podzoluvisols), grey forest non-podzolised (Greyic Phaeozems Albic, Haplic Greyzems), typical Chernozems (Voronic Chernozems pachic, Haplic Chernozems) - profiles under the forest and the arable land, and the chestnut (Haplic Kastanozems Chromic, Haplic Kastanozems) soils. The CA's determination was performed by a Drop Shape Analyzer DSA100 by the static sessile drop method. For all samples was determined the content of total and organic carbon (OC and TC) by dry combustion in oxygen flow. RESULTS AND DISCUSSION There is CA increasing from 85,1° (5 cm) to 40-45° (deeper, than 45 cm) in the sod-podzolic soil; OC content is changed at the same depths from 1,44 to 0.22%. We can see the similar picture in profiles of chernozems. In the forest profile the highest OC content and CA value are achieved on the surface of profile (6,41% and 78,1°), and by 90 cm these values are 1.9% and 50.2°. In the chernozem under the arable land the OC content is almost two times less and the profile is more wettable (from 50° to 19° at 5 and 100 cm). Corresponding with the OC content, the curve describing changes of CA in the profile of grey forest soil is S-shaped with peaks at 20 and 150 cm (81,3° and 70° respectively
Hybrid bearing technology for advanced turbomachinery: Rolling contact fatigue testing
Dill, J.F.
1996-01-01
The purpose of this paper is to describe the basic structure and results to date of a major ARPA funded effort to provide a tribological performance database on ceramic bearing materials and their interaction with standard bearing steels. Program efforts include studies of material physical properties, machining characteristics, and tribological performance. The majority of the testing completed to date focuses on rolling contact fatigue testing of the ceramic materials, including efforts to arrive at optimum approaches to evaluating ceramic/steel hybrid combinations in rolling contact fatigue.
NASA Astrophysics Data System (ADS)
Zhuang, Shoubing
2013-05-01
Nonlinear contact analysis including forming simulation via finite element methods has a crucial and practical application in many engineering fields. However, because of high nonlinearity, nonlinear contact analysis still remains as an extremely challenging obstacle for many industrial applications. The implicit finite element scheme is generally more accurate than the explicit finite element scheme, but it has a known challenge of convergence because of complex geometries, large relative motion and rapid contact state change. It might be thought as a very painful process to diagnose the convergence issue of nonlinear contact. Most complicated contact models have a great many contact surfaces, and it is hard work to well define the contact pairs using the common contact definition methods, which either result in hundreds of contact pairs or are time-consuming. This paper presents the advanced techniques of nonlinear contact analysis and forming simulation via the implicit finite element scheme and the penalty method. The calculation of the default automatic contact stiffness is addressed. Furthermore, this paper presents the idea of selection groups to help easily and efficiently define contact pairs for complicated contact analysis, and the corresponding implementation and usage are discussed. Lastly, typical nonlinear contact models and forming models with nonlinear material models are shown in the paper to demonstrate the key presented method and technologies.
Dey, Tania; Naughton, Daragh
2017-04-06
Glass surface cleaning is the very first step in advanced coating deposition and it also finds use in conserving museum objects. However, most of the wet chemical methods of glass cleaning use toxic and corrosive chemicals like concentrated sulfuric acid (H2SO4), piranha (a mixture of concentrated sulfuric acid and 30% hydrogen peroxide), and hydrogen fluoride (HF). On the other hand, most of the dry cleaning techniques like UV-ozone, plasma, and laser treatment require costly instruments. In this report, five eco-friendly wet chemical methods of glass cleaning were evaluated in terms of contact angle (measured by optical tensiometer), nano-scale surface roughness (measured by atomic force microscopy or AFM), and elemental composition (measured by energy dispersive x-ray spectroscopy or SEM-EDX). These glass cleaning methods are devoid of harsh chemicals and costly equipment, hence can be applied in situ in close proximity with plantation such as greenhouse or upon subtle objects such as museum artifacts. Out of these five methods, three methods are based on the chemical principle of chelation. It was found that the citric acid cleaning method gave the greatest change in contact angle within the hydrophilic regime (14.25° for new glass) indicating effective cleansing and the least surface roughness (0.178 nm for new glass) indicating no corrosive effect. One of the glass sample showed unique features which were traced backed to the history of the glass usage.
Wetting and nanodroplet contact angle of the clay 2:1 surface: The case of Na-montmorillonite (001)
NASA Astrophysics Data System (ADS)
Zheng, Y.; Zaoui, A.
2017-02-01
Molecular dynamics simulation method is performed to study the wetting and contact angle between a water nanodroplet and a surface of Na-montmorillonite (Na-MMT). The nanodroplet of 256, 500 and 1000 water molecules, based on SPC and TIP4P water models, is handled by means of Monte Carlo and Molecular Dynamics simulation methods The spreading of water molecules on Na-MMT's surface is not uniform. In fact, the contact line is not perfectly circlar; it depends on the distribution of cations on clay's surface. The average contact angle of air/water/clay corresponds to 25° for all cases of nanodroplets studied here, which reveals that Na-MMT is definitely hydrophilic. In the nanodroplet, most of water molecules remain at a distance between 3.5 and ∼4 Å to the clay's surface. However, at the edge of nanodroplet, water molecules are caught by the clay's surface oxygen and thus enter into the 0-3 Å zone, which blocks the spreading of nanodroplet.
How Does a Liquid Wet a Solid? Hydrodynamics of Dynamic Contact Angles
NASA Technical Reports Server (NTRS)
Rame, Enrique
2001-01-01
A contact line is defined at the intersection of a solid surface with the interface between two immiscible fluids. When one fluid displaces another immiscible fluid along a solid surface, the process is called dynamic wetting and a "moving" contact line (one whose position relative to the solid changes in time) often appears. The physics of dynamic wetting controls such natural and industrial processes as spraying of paints and insecticides, dishwashing, film formation and rupture in the eye and in the alveoli, application of coatings, printing, drying and imbibition of fibrous materials, oil recovery from porous rocks, and microfluidics.
Prediction of Unsteady Blade Surface Pressures on an Advanced Propeller at an Angle of Attack
NASA Technical Reports Server (NTRS)
Nallasamy, M.; Groeneweg, J. F.
1989-01-01
The numerical solution of the unsteady, three-dimensional, Euler equations is considered in order to obtain the blade surface pressures of an advanced propeller at an angle of attack. The specific configuration considered is the SR7L propeller at cruise conditions with a 4.6 deg inflow angle corresponding to the plus 2 deg nacelle tilt of the Propeller Test Assessment (PTA) flight test condition. The results indicate nearly sinusoidal response of the blade loading, with angle of attack. For the first time, detailed variations of the chordwise loading as a function of azimuthal angle are presented. It is observed that the blade is lightly loaded for part of the revolution and shocks appear from hub to about 80 percent radial station for the highly loaded portion of the revolution.
Prediction of unsteady blade surface pressures on an advanced propeller at an angle of attack
NASA Technical Reports Server (NTRS)
Nallasamy, M.; Groeneweg, J. F.
1989-01-01
The paper considers the numerical solution of the unsteady, three-dimensional, Euler equations to obtain the blade surface pressures of an advanced propeller at an angle of attack. The specific configuration considered is the SR7L propeller at cruise conditions with a 4.6 deg inflow angle corresponding to the +2 deg nacelle tilt of the Propeller Test Assessment (PTA) flight test condition. The results indicate nearly sinusoidal response of the blade loading, with angle of attack. For the first time, detailed variations of the chordwise loading as a function of azimuthal angle are presented. It is observed that the blade is lightly loaded for part of the revolution and shocks appear from hub to about 80 percent radial station for the highly loaded portion of the revolution.
Hagens, R; Mann, T; Schreiner, V; Barlag, H G; Wenck, H; Wittern, K-P; Mei, W
2007-08-01
Substantivity of sunscreen formulations is affected by the wash-out rate of ultraviolet-absorber and -reflector compounds in water. Water-resistance of sunscreen formulations is currently determined according to a standardized European Cosmetic Toiletry and Perfumery Association (COLIPA) protocol, encompassing the determination of a minimal erythemal dose before and after a defined immersion step in water. It can be supposed that the higher the wettability of a treated skin area, the higher is the wash-out rate of sunscreen compounds. This present report addresses the validity of determining the wettability of treated skin alone as a measure for the water-resistance of sunscreen products. The report addresses the robustness, accuracy and congruence of a recently developed wettability test, based on the measurement of the contact angle (CA) of a sessile water drop on treated skin areas. Contact angle data of 66 sunscreen formulations are compared with the corresponding results of 81 water-resistance tests, using the sun protection factor (SPF)/immersion/SPF method. Sunscreen products tested by the CA method were applied to the skin of the volar forearm of test subjects at a defined dose and drying-time, using a standardized application and recording device. Contact angles between a sessile water drop and skin were recorded by a Charge-Coupled Device (CCD) camera and subjected to automatic contour analysis. Taking the SPF/immersion/SPF method as gold standard, accuracy parameters of the CA method were determined. By using an appropriate cut-off level of CAs, the CA method has a specificity and positive-predictive value of 100%, and turns out to be a reliable screening method to identify water-resistant formulations. Based on our findings, those formulations that give CAs above 30 degrees may be categorized water-proof without further testing by the COLIPA water-resistance method.
Rüttermann, Stefan; Trellenkamp, Taina; Bergmann, Nora; Raab, Wolfgang H-M; Ritter, Helmut; Janda, Ralf
2011-03-01
The purpose of the present study was to identify novel delivery systems and active agents which increase the water contact angle and reduce the surface free energy when added to resin-based dental restorative materials. Two delivery systems based on zeolite or novel polymeric hollow beads (Poly-Pore), loaded with two low surface tension active agents (hydroxy functional polydimethylsiloxane and polydimethylsiloxane) or a polymerizable active agent (silicone polyether acrylate) were used to modify commonly formulated experimental dental resin composites. The non-modified resin was used as a standard (ST). Flexural strength, flexural modulus, water sorption, solubility, polymerization shrinkage, surface roughness Ra, contact angle θ, total surface free energy γS, and the apolar γSLW, polar γSAB, Lewis acid γS+ and base γS- components, and the active agents surface tensions γL were determined (P<0.05). The active agents did not differ in γL. The modified materials had significantly higher θ but significantly lower γS, γSAB and γS- than the ST. A Poly-Pore/polydimethyl siloxane delivery system yielded the highest θ (110.9±3.5°) acceptable physical properties and the lowest values for γSLW and γS-. Among the modified materials the polymerizable materials containing active agents had the lowest γAB and the highest γS+ and γS-. Although not significant, both of the zeolite delivery systems yielded higher γSLW, γS+ and γS- but lower γSAB than the Poly-Pore delivery systems. Poly-Pore based delivery systems highly loaded with low surface tension active agents were found not to influence the physical properties but to significantly increase the water contact angle and thus reduce surface free energy of dental resin composites.
Song, Bo; Chen, Kun; Schmittel, Michael; Schönherr, Holger
2016-11-01
All experimental findings related to surface nanobubbles, such as their pronounced stability and the striking differences of macroscopic and apparent nanoscopic contact angles, need to be addressed in any theory or model of surface nanobubbles. In this work we critically test a recent explanation of surface nanobubble stability and their consequences and contrast this with previously proposed models. In particular, we elucidated the effect of surface chemical composition of well-controlled solid-aqueous interfaces of identical roughness and defect density on the apparent nanoscopic contact angles. Expanding on a previous atomic force microscopy (AFM) study on the systematic variation of the macroscopic wettability using binary self-assembled monolayers (SAMs) on ultraflat template stripped gold (TSG), we assessed here the effect of different surface chemical composition for macroscopically identical static water contact angles. SAMs on TSG with a constant macroscopic water contact angle of 81 ± 2° were obtained by coadsorption of a methyl-terminated thiol and a second thiol with different terminal functional groups, including hydroxy, amino, and carboxylic acid groups. In addition, surface nanobubbles formed by entrainment of air on SAMs of a bromoisobutyrate-terminated thiol were analyzed by AFM. Despite the widely differing surface potentials and different functionality, such as hydrogen bond acceptor or donor, and different dipole moments and polarizability, the nanoscopic contact angles (measured through the condensed phase and corrected for AFM tip broadening effects) were found to be 145 ± 10° for all surfaces. Hence, different chemical functionalities at identical macroscopic static water contact angle do not noticeably influence the apparent nanoscopic contact angle of surface nanobubbles. This universal contact angle is in agreement with recent models that rely on contact line pinning and the equilibrium of gas outflux due to the Laplace pressure and
Raya, Jésus; Perrone, Barbara; Hirschinger, Jérôme
2013-02-01
A simple multiple-contact cross-polarization (CP) scheme is applied to a powder sample of ferrocene and β-calcium formate under static and magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. We show that multiple equilibrations-re-equilibrations with the proton spin bath improves the polarization transfer efficiency at short contact times and provides higher signal enhancements than state-of-the art techniques such as adiabatic passage through the Hartmann-Hahn condition CP (APHH-CP) when MAS is applied. The resulting chemical shift powder spectra then are identical to the ones obtained by using ROtor-Directed Exchange of Orientations CP (APHH-RODEO-CP) with intensity gains of a factor 1.1-1.3.
NASA Astrophysics Data System (ADS)
Raya, Jésus; Perrone, Barbara; Hirschinger, Jérôme
2013-02-01
A simple multiple-contact cross-polarization (CP) scheme is applied to a powder sample of ferrocene and β-calcium formate under static and magic-angle spinning (MAS) conditions. The method is described analytically through the density matrix formalism. We show that multiple equilibrations-re-equilibrations with the proton spin bath improves the polarization transfer efficiency at short contact times and provides higher signal enhancements than state-of-the art techniques such as adiabatic passage through the Hartmann-Hahn condition CP (APHH-CP) when MAS is applied. The resulting chemical shift powder spectra then are identical to the ones obtained by using ROtor-Directed Exchange of Orientations CP (APHH-RODEO-CP) with intensity gains of a factor 1.1-1.3.
NASA Astrophysics Data System (ADS)
Kawamura, Go; Ema, Tomoyuki; Sakamoto, Hisatoshi; Wei, Xing; Muto, Hiroyuki; Matsuda, Atsunori
2014-04-01
Multilayer structures composed of poly(allylamine hydrochloride) (PAH) and Nafion were fabricated on glass substrates by layer-by-layer assembly. Some of the multilayers demonstrated spontaneous changes in contact angle of water and oil due to flip-flop movements of free sulfo groups in the Nafion layer, and the multilayers eventually possessed water repellency in air and oil repellency in water. The repellencies were enhanced by applying primer layers that were formed using SiO2 fine particles to increase surface roughness. Compared to typical hydrophobic and oleophobic surfaces, the multilayers showed practical levels for a use as soil release coatings.
NASA Astrophysics Data System (ADS)
Iwamae, A.; Ogawa, H.; Sugie, T.; Kusama, Y.
2011-03-01
The in situ calibration method for the impurity influx monitor (divertor) is experimentally examined. The total reflectance of the optical path from the focal point of the Cassegrain telescope to the first mirror is derived using a micro retroreflector array. An optical fiber with angled physical contact (APC) connectors reduces the return edge reflection. APC fibers and a multimode coupler increase the signal-to-noise ratio by about one order compared to that of triple-branched fibers and enable measurement of the wavelength dependence of the total reflectance of the optical system even after potential deterioration of mirror surfaces reduces reflectance.
NASA Astrophysics Data System (ADS)
Piri, Mohammad; Blunt, Martin J.
2004-12-01
We use the Helmholtz free energy balance and the Mayer-Stowe-Princen method to derive general expressions governing multiphase pistonlike displacements in noncircular capillary elements with arbitrary wettability. We take into account hysteresis in oil/water, gas/water, and gas/oil contact angles. We study both two- and three-phase systems. We find threshold capillary pressures for gas invasion into oil, oil invasion into gas, and water invasion into oil for capillaries with an irregular triangular cross section. Finally we study the effects of shape factor, oil/water capillary pressure, and oil/water and gas/oil contact angles on the threshold capillary pressure for gas invasion into oil for spreading and nonspreading systems. In many cases the threshold pressures of the three-phase displacements are not the same as those of the equivalent pseudo-two-phase displacements. It is possible that gas invasion can occur resulting in a configuration without oil layers, even if oil layers are geometrically possible. This emphasizes the distinction between geometric and thermodynamic stability—it is the latter that controls threshold pressures.
Piri, Mohammad; Blunt, Martin J
2004-12-01
We use the Helmholtz free energy balance and the Mayer-Stowe-Princen method to derive general expressions governing multiphase pistonlike displacements in noncircular capillary elements with arbitrary wettability. We take into account hysteresis in oil/water, gas/water, and gas/oil contact angles. We study both two- and three-phase systems. We find threshold capillary pressures for gas invasion into oil, oil invasion into gas, and water invasion into oil for capillaries with an irregular triangular cross section. Finally we study the effects of shape factor, oil/water capillary pressure, and oil/water and gas/oil contact angles on the threshold capillary pressure for gas invasion into oil for spreading and nonspreading systems. In many cases the threshold pressures of the three-phase displacements are not the same as those of the equivalent pseudo-two-phase displacements. It is possible that gas invasion can occur resulting in a configuration without oil layers, even if oil layers are geometrically possible. This emphasizes the distinction between geometric and thermodynamic stability-it is the latter that controls threshold pressures.
Bouteau, Murielle; Cantin, Sophie; Fichet, Odile; Perrot, Françoise; Teyssié, Dominique
2010-11-16
The large application ranges of polydimethylsiloxane (PDMS) and poly(ethylene oxide) (PEO) based materials justify the importance of controlling polymer surface properties including morphology and wettability behavior. However, it appears that the reported contact angle values of PDMS surfaces show significant scattering which cannot always be interpreted in terms of sole chemical data. In addition, few values are reported concerning pure PEO surfaces, since the polymer generally swells in the presence of water. Thus, in order to correlate surface properties with sample preparation, several single PDMS and PEO polymer networks were synthesized with varying cross-linkers and different cross-linking densities. First, the sample surface topography was systematically analyzed by atomic force microscopy (AFM). It was proven that the removal process of the polymer film from the mold plays a significant role in surface topography according to the vitreous or rubbery state of the given polymer network at room temperature irrespective of mold surface treatment. AFM-scale smooth surfaces can be obtained for all the samples by removing them systematically from the mold at a temperature below the α-relaxation temperature. Dynamic water contact angles were then measured and the values analyzed as a function of cross-linker nature and cross-linking density.
Liakos, Ioannis L; Newman, Roger C; McAlpine, Eoghan; Alexander, Morgan R
2007-01-30
We report the development of a method to determine the aqueous stability of self-assembled monolayers (SAMs) using the Wilhelmy plate dynamic contact angle (DCA) experiment. The DCA is measured in solutions over a range of pH values for alkyl carboxylic and alkyl phosphonic acid SAMs formed on magnetron-sputtered aluminum. The change in DCA on repeated immersion is used as a measure of the degradation of the SAMs by hydrolytic attack. The short and intermediate chain length alkyl acids are not stable in water of neutral pH, whereas molecules with the longest alkyl chains show considerably greater stability in neutral and both high and low pH solutions. The packing density inferred from the DCA and the contact angle hysteresis suggests the C18CO2H monolayer to be slightly less well packed than that of the C18P(=O)(OH)2; this is consistent with related friction force microscopy and infrared reflection absorption spectroscopy findings published elsewhere (Foster, T. T.; Alexander, M. R.; Leggett, G. J.; McAlpine, E. Langmuir 2006, 22, 9254-9259). The resistance of the SAMs to acid and alkaline environments is discussed in the context of aluminum oxide solubility, SAM packing density, and the resistance of the interfacial phosphate and carboxylate functionalities to different aqueous conditions.
Paquette, M R; Milner, C E; Melcher, D A
2017-02-01
Foot strike pattern and movement variability have each been associated with running injuries. Foot contact angle (FCA) is a common measure of strike pattern. Thus, variability in FCA could be an important running injury risk factor. The purposes of this study were to compare (a) foot contact angle (FCA) and its variability between runners with and without injury history and, (b) FCA variability between habitual rearfoot strike (RFS) and non-RFS runners during a prolonged run. Twenty-three runners with and 21 without injury history participated. Motion capture was used to collect kinematic data during a 40 min treadmill run. Average FCA and its variability were compared between injury groups and among four time points. FCA and its variability were not different between runners with and without injury history or among time points during the run. FCA variability was lower in non-RFS compared to RFS runners (P < 0.001). Lower FCA variability in non-RFS runners may have implications for higher injury risks due to repeated localized tissue loading. Prospective analyses on the effects of lower FCA variability on injury risk are needed.
Low Angle Contact Between the Oaxaca and Juárez Terranes Deduced From Magnetotelluric Data
NASA Astrophysics Data System (ADS)
Arzate-Flores, Jorge A.; Molina-Garza, Roberto; Corbo-Camargo, Fernando; Márquez-Ramírez, Víctor
2016-10-01
We present the electrical resistivity model along a profile perpendicular to the Middle America trench in southern Mexico that reveals previously unrecognized tectonic features at upper to mid-crustal depths. Our results support the hypotheses that the upper crust of the Oaxaca terrane is a residual ~20 km thick crust composed by an ~10 km thick faulted crustal upper layer and an ~10 km thick hydrated and/or mineralized layer. Oaxaca basement overthrust the younger Juárez (or Cuicateco) terrane. The electrical resistivity model supports the interpretation of a slab subducting at a low angle below Oaxaca. Uplift in the Oaxaca region appears to be related to fault reactivation induced by low angle subduction. In the Juárez terrane, isostatic forces may contribute to uplift because it is largely uncompensated. In the Sierra Madre del Sur, closer to the coast, uplift is facilitated by slab-dehydration driven buoyancy. Both gravity and resistivity models are consistent with a thinned upper crust in the northeast end of the profile.
Mohan, Rayapudi Phani; Pai, Annappa Raghavendra Vivekananda
2015-01-01
Aim: The aim was to assess the influence of two irrigation regimens having ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetraacetic acid with cetrimide (EDTAC) as final irrigants, respectively, on the dentine wettability for AH Plus sealer by comparing its contact angle formed to the irrigated dentine. Materials and Methods: Study samples were divided into two groups (n = 10). The groups were irrigated with 3% sodium hypochlorite (NaOCl) solution followed by either 17% EDTA or 17% EDTAC solution. AH Plus was mixed, and controlled volume droplet (0.1 mL) of the sealer was placed on the dried samples. The contact angle was measured using a Dynamic Contact Angle Analyzer and results were analyzed using SPSS 21.0 and 2 sample t-test. Results: There was a significant difference in the contact angle of AH Plus formed to the dentine irrigated with the above two regimens. AH Plus showed significantly lower contact angle with the regimen having EDTAC as a final irrigant than the one with EDTA (P < 0.05). Conclusion: An irrigation regimen consisting of NaOCl with either EDTA or EDTAC solution as a final irrigant influences the dentine wettability and contact angle of a sealer. EDTAC as a final irrigant facilitates better dentin wettability than EDTA for AH Plus to promote its better flow and adhesion. PMID:26180409
Theory of Wetting-Induced Fluid Entrainment by Advancing Contact Lines on Dry Surfaces
NASA Astrophysics Data System (ADS)
Ledesma-Aguilar, R.; Hernández-Machado, A.; Pagonabarraga, I.
2013-06-01
We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension.
Theory of wetting-induced fluid entrainment by advancing contact lines on dry surfaces.
Ledesma-Aguilar, R; Hernández-Machado, A; Pagonabarraga, I
2013-06-28
We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension.
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.
Foran, Philip S; Boxall, Colin; Denison, Kieth R
2012-12-21
Transparent TiO(2) thin films were prepared on quartz substrates via a reverse micelle, sol-gel, spin-coating technique. The time dependence of the TiO(2) film photoinduced superhydrophilicity (PISH) was measured by goniometric observation of the contact angle, θ, of sessile water drops at the film surfaces. In these measurements, the TiO(2) substrate was illuminated by 315 nm light and drops were sequentially applied at a range of illumination times. Using a model for the wetting of heterogeneous surfaces derived by Israelachvili and Gee, these measurements were used to calculate the time dependence of f(2), the fractional surface coverage of the TiO(2) surface by adventitious contaminating organics (Israelachvili, J. N.; Gee, M. L. Contact angles on chemically heterogeneous surfaces. Langmuir 1989, 5, 288). Extending this model to include a Langmuir-Hinshelwood based kinetic analysis of f(2) as a function of time allowed for calculation of an expected value for θ immediately prior to illumination, that is, at illumination time t = 0. Such expected values of θ at t = 0 were calculated using two possible values of θ(1), the contact angle on a pristine unilluminated homogeneous TiO(2) surface: (i) θ(1) = 4° as suggested by, inter alia, Zubkov et al. (Zubkov, T.; Stahl, D.; Thompson, T. L.; Panayotov, D.; Diwald, O.; Yates, J. T. Ultraviolet Light-Induced Hydrophilicity Effect on TiO(2)(110)(1 × 1). Dominant Role of the Photooxidation of Adsorbed Hydrocarbons Causing Wetting by Water Droplets. J. Phys. Chem. B2005, 109, 15454); and (ii) where θ(1) = 25°, as suggested by Fujishima et al., representative of a more hydrophobic homogeneous TiO(2) surface that reconstructs upon exposure to ultraband gap illumination into a hydrophilic surface where θ(1) → 0° (Fujishima, A.; Zhang, X.; Tryk, D. A. TiO(2) photocatalysis and related surface phenomena Surf. Sci. Rep.2008, 63, 515). Analysis of data from our experiments and from selected literature sources
NASA Astrophysics Data System (ADS)
Yu, Yang; Conroy, Mike; Smith, Richard
2012-10-01
Advanced metrology plays an important role in the research, production and quality control of optical components. With surface finish, form error and other parameter specifications becoming more stringent, precision measurements are increasingly demanded by optics manufacturers and users. The modern metrologist now has both contact and noncontact measurement solutions available and a combination of these techniques now provides a more detailed understanding of optical components. Phase Grating Interferometry (PGI) with sub-nanometre vertical resolution and sub-micron lateral resolution can provide detailed characterization of a wide range of components including shallow and steep-sided optics. PGI is ideal for precision form measurement of a comprehensive range of lenses, moulds and other spherical or aspheric products. Because of the complex nature of these components, especially precision aspheric and asphero-diffractive optics, control of the form is vital to ensure they perform correctly. Recent hardware and software developments now make it possible to gain a better understanding and control of the form and function of this optics. Another change is the use of high speed 3D non-contact measurement of optics which is becoming more popular. Often scanning interferometric techniques such as coherence correlation interferometry (CCI) can be used to study components not suited to 2D contact analysis, including fragile surfaces and structured surfaces. Scanning interferometry can also be used to measure film thickness and uniformity of any coating present. In this paper the use of both PGI and CCI to measure optical lenses and coatings is discussed.
Measurement and prediction of contact angles of Pb-free Sn-Ag solder alloys on Cu substrate
NASA Astrophysics Data System (ADS)
Erer, A. M.; Candan, E.; Güven, M. H.; Turen, Y.
2011-04-01
The contact angle (Θ) of molten Sn and Sn-Ag alloys (0.5, 1.5, 3.5, 6 wt.% Ag) on Cu substrates have been studied by using sessile drop method at various temperatures (230, 250, 275 and 300 °C). Experimental results showed that additions of Ag to Sn resulted in a continuous decrease in the Θ up to 3.5 wt.% above which the Θ value was increased. Increasing alloy temperature also decreased the Θ proportionally. Experimental results revealed that a correlation between the Θ, alloy composition and the alloy temperature exists which yielded an empirical model to predict the Θ at a given Ag content and temperature for a given Sn-Ag alloy. The empirical model predicts the Θ reasonably well with the present work and the other published works.
Melnichenko, Yuri B; Lavrik, N V; Popov, E; Bahadur, J; He, L; Kravchenko, I I; Smith, G; Pipich, V; Szekely, N K
2014-08-26
The structure of deterministically nanopatterned surfaces created using a combination of electron beam lithography and reactive ion etching was evaluated using small-angle neutron scattering (SANS). Samples exhibit 2D neutron scattering patterns that confirm the presence of ordered nanoscale cavities consistent with the targeted morphologies as well as with SEM data analysis. Comparison of SANS intensities obtained from samples in air and in contact with an aqueous phase (pure deuterium oxide, D2O, or a contrast matched mixture of D2O + H2O) reveals formation of stable gaseous nanobubbles trapped inside the cavities. The relative volume of nanobubbles depends strongly on the hydrophobicity of the cavity walls. In the case of hydrophobic surfaces, nanobubbles occupy up to 87% of the total cavity volume. The results demonstrate the high degree of sensitivity of SANS measurements for detecting and characterizing nano- and mesoscale bubbles with the volume fraction as low as ∼10(-6).
NASA Astrophysics Data System (ADS)
Kuisma, R.; Pesonen-Leinonen, E.; Redsven, I.; Kymäläinen, H.-R.; Saarikoski, I.; Sjöberg, A.-M.; Hautala, M.
2005-06-01
The tendency to soil and cleanability of ten commercial plastic floor coverings: eight vinyl (PVC) floor coverings, one vinyl composite tile and one plastic composite tile, were examined. Floor coverings were soiled with inorganic, organic and biological soil. The cleanability was measured both by bioluminescence of ATP (adenosine triphosphate) and colorimetrically. The surface topography was studied by AFM, SEM and with a profilometer. From the 2D- and 3D-profilometric measurements several characteristic parameters of the surface profiles were extracted. The tendency to soil and cleanability were compared with the characteristics of the surface. A weak correlation was found between roughness and soilability but no correlation between roughness and cleanability. Roughness had no correlation with contact angle.
Jung, Sung Ho; Kim, Ka Young; Ahn, Ahreum; Choi, Myong Yong; Jaworski, Justyn; Jung, Jong Hwa
2016-06-08
Spectroscopic techniques exist that may discern between enantiomers and assess chiral purity. A nonspectroscopic approach that may be directly observed could provide numerous benefits. Using chiral alanine-appended benzene-tricarboxamide gelators, we reveal a methanol gel system that is capable of providing visual discrimination between enantiomers of various diamines. Specifically, gelation is induced by supramolecular nanofiber assembly resulting from interaction between a chiral gelator and a diamine of opposing chirality (i.e., a heterochiral system). Upon further implementing the chiral gelator in electrospun fibers as solid state films, we revealed enantioselective surface wetting properties that allowed for determining chirality through contact angle measurements. While these two approaches of observable gelation and surface wetting offer nonspectroscopic approaches, we also find that the supramolecular nanofiber assembly was able to enhance the induced circular dichroism signal resulting from addition of chiral diamines, allowing precise quantification of their enantiomeric purity.
NASA Astrophysics Data System (ADS)
Redsven, I.; Kymäläinen, H.-R.; Pesonen-Leinonen, E.; Kuisma, R.; Ojala-Paloposki, T.; Hautala, M.; Sjöberg, A.-M.
2007-04-01
Detection of adenosine triphosphate (ATP) by bioluminescence is used, for instance, in the food industry and in hospitals to assess the hygiene status of surfaces. The aim of this laboratory study was to investigate the feasibility of the ATP method for estimating the cleanability of resilient floor coverings from biological soil. The surfaces were worn using a Soiling and Wearing Drum Tester, and soiled and cleaned with an Erichsen Washability and Scrubbing Resistance Tester. In the laboratory test carried out with the bioluminescence method, most of the new and worn floor coverings that were biologically soiled were cleaned efficiently. According to this study, the semiquantitative ATP screening method can be used for hygiene monitoring of flooring materials. No correlation was found between cleanability and contact angles or surface topography measured using a profilometer. However, by revealing local irregularities and damage on surfaces, scanning electron micrographs appeared useful in explaining differences in cleanability.
Yin, Tsung-I; Zhao, Yunpeng; Horak, Josef; Bakirci, Huseyin; Liao, Hsin-Hao; Tsai, Hann-Huei; Juang, Ying-Zong; Urban, Gerald
2013-03-07
Cantilever sensors have been extensively explored as a promising technique for real-time and label-free analyses in biological systems. A major sensing principle utilized by state-of-the-art cantilever sensors is based on analyte-induced surface stress changes, which result in static bending of a cantilever. The sensor performance, however, suffers from the intrinsically small change in surface stress induced by analytes, especially for molecular recognition such as antigen-antibody binding. Through the contact angle change on a tailored solid surface, it is possible to convert a tiny surface stress into a capillary force-a much larger physical quantity needed for a practical sensor application. In this work, a micro-cantilever sensor based on contact angle analysis (CAMCS) was proposed to effectively enhance the sensitivity of a sensor in proportion to the square of the length to thickness ratio of the cantilever structure. CAMCS chips were fabricated using a standard complementary-metal-oxide-semiconductor (CMOS) process to demonstrate a 1250-fold enhancement in the sensitivity of surface stress to bioanalyte adsorption using a piezoresistive sensing method. A real-time and label-free troponin I (cTnI) immunoassay, which is now widely used in clinics and considered a gold standard for the early diagnosis and prognosis of cardiovascular disease, was performed to demonstrate cTnI detection levels as low as 1 pg mL(-1). The short detection time of this assay was within several minutes, which matches the detection time of commercially available instruments that are based on fluorescence-labeling techniques.
A new in-situ technique for the determination of small scale spatial distribution of contact angles
NASA Astrophysics Data System (ADS)
Lamparter, Axel; Bachmann, Jörg; Woche, Susanne K.
2010-05-01
Water repellency is a common phenomenon in soils around the world. Its hydraulic impact reaches from decreased infiltration rates to preferential flow of water through the soil. The contact angle</