Nonlinear dependence of the contact angle of nanodroplets on contact line curvature

We have measured the contact angle of microsized and nanosized alkane droplets partially wetting a model substrate using true noncontact atomic force microscopy. The large range of droplet sizes accessible using this technique allowed us to determine the contact line curvature dependence of the contact angle with unprecedented accuracy. Whereas previous studies aimed at explaining such a dependence by a line tension effect, our results and calculations on a model system exclude such an effect and point to an extreme sensitivity to weak substrate heterogeneities confirmed by numerical simulations.     

浸润接触线的摩擦性质与固体表面张力的Wenzel行为

依据Adam和Jessop关于固-液-气三相接触线具有静摩擦性的观点，能从浸润接触角数据推算 出固体的表面张力系数，但结果显然会与摩擦条件的具体形式有关.以报道的不锈钢和聚丙 烯实验数据为例，通过对比Mises和Amonton两种摩擦定律给出的表面张力系数，后者给出的 张力才具有总是随表面粗糙性的增大而增加的Wenzel效应，以及当固-液，固-气界面的张力 系数之差等于液-气界面的张力系数时，退后角将变为零的全浸润条件.这似乎表明用Amonto n定律描写接触线的静摩擦要更为合理. 关键词： 浸润角 静摩擦 固体表面张力     

Test of the stability of a three-phase contact line with negative line tension

The equilibrium structure of a three-phase contact line with negative line tension using a mean-field free-energy functional is calculated in the square-gradient approximation. The equilibrium density profiles are found by solving the Euler—Lagrange equations on a square grid of N ² points covering an area of L ². The fluctuations about the equilibrium structure are analysed via the spectrum of the free energy's second functional derivative. The equilibrium configuration is found to be stable with respect to fluctuations in the structure of the three-phase line and of the interfaces that meet at this line. In addition, the behaviour is investigated numerically of the lowest eigenvalue as the area of the grid is increased. The lowest eigenvalue is always positive and vanishes as 1/L ².     

Effective line tension and contact angles between membrane domains in biphasic vesicles

Inhomogeneities in membranes give rise to localized interactions at the interface between domains in two-component vesicles. The corresponding energy is expressed as a line tension between the two phases. In this paper we study the implications of the thickness mismatch between domains which has been experimentally reported to be of order 20-30% and the conditions under which the induced line tension can destabilize the domains in inhomogeneous vesicles. For asymmetric lipidic membranes we prove an increase of the line tension and the existence of a contact angle. Adsorption of impurities is also examined, our scope being the extension of the Canham-Helfrich model to describe elastic deformations and chemical interactions arising at microscopic scales. This mismatch effect may have important consequences for the stability of very small domains.     

Effect of viscosity and surface tension on erythrocytes adhesion

Cell–cell adhesion is probably the best cell function to be considered for biophysical modeling from micrometer to the molecular level. The aim of this study is to find a relation between the bulk properties of erythrocytes suspension (like surface tension and viscosity) and erythrocytes adhesion. Our results showed that there is a strong correlation between surface tension and adhesion number (r² = 0.85) and moderate correlation between erythrocytes suspension viscosity and adhesion number (r² = 0.55). Our results were indicated that bulk properties of erythrocytes can affect directly on microscopic properties of erythrocytes.     

Three-phase contact line energetics from nanoscale liquid surface topographies

We observed light-induced alignment of the nematic liquid crystal, 4, 4(')-n-pentylcyanobiphenyl (5CB), on a fused quartz. Irradiation of the adsorbed layer with polarized ultraviolet light produced homogeneous alignment in a 5CB-filled liquid crystal cell with the easy orientation axis perpendicular to the polarization direction. The measured anchoring energy increases with illumination up to 10(-4) erg/cm (2). Phase retardation and pretilt measurements confirmed near homogeneous alignment of the LC in a cell, while the polarization dependence of second harmonic generation suggested a near normal alignment of the adsorbed layer. We believe that light-induced rearrangement or phototransformation of the adsorbed layer causes the observed phenomenon.     

Microscopic integral relations for the curvature dependent surface tension in a two-phase multi-component system

In this paper we discuss the thermodynamics and statistical mechanics of a curved fluid interface, in a system containing several chemical components. We derive microscopic integral relations for the Tolman-length, the spontaneous curvature and rigidity constants in a multi-component system. A thorough discussion is given of the dependence of the various relevant quantities on the choice of the dividing surface. Also some choice invariant characteristics quantities are given. We furthermore discuss the small-curvature correction to the Clausius-Clapeyron condition.     

Perturbational approach for the curvature correction to the surface tension via the Hartree-Fock approximation for the plane surface

It is pointed out that the series expansion, used semi-classically to derive a closed formula for the curvature energy, breaks down in the case of the Hartree-Fock approach due to energy density and density fluctuations. The specific curvature energy of a Fermi gas is explicitly shown to be orders of magnitude smaller than that obtained by the standard perturbational procedure. Averaging energy density and density before the evaluation of the standard expression yields reasonable values for the curvature energy in the case of the Fermi gas. Such an averaging procedure is proposed as a way out of the dilemma found in Hartree-Fock calculations of the curvature energy with the standard formula. It is shown that a careful averaging is necessary for the calculation of curvature energies, whereas for surface properties of plane systems rough averaging is also sufficient.     

An investigation on surface tensions of Pb-free solder materials

Surface tensions of some Pb-free solder systems such as Ag–Bi–Sn with cross-sections Ag/Bi = 1/1, Ag/Bi = 1/2, Ag/Bi = 2/1, In–Sn–Zn with cross-sections Sn/In = 1/1, Sn/In = 1/3 and (Ag₇Cu₃)_100?x Sn_x with cross-section Ag/Cu = 7/3 are calculated from the sub-binary surface tension data using the models, such as the Muggianu, Kohler, Toop models, Butler’s equation and Chou’s General Solution Model (GSM) at 873, 923 and 1073 K, respectively. The surface tension of In–Sn–Zn increases wavily with increasing amount of Zn and it is found that the best models are the GSM for both cross-sections in question while GSM becomes the best model for (Ag₇Cu₃)_100?x Sn_x alloy in the whole experimental range. Moreover, the surface tension of (Ag₇Cu₃)_100?x Sn_x decreases slightly with increasing amount of Sn. The Muggianu, Butler and Butler models are determined as the best models for the cross-sections in the order given above for entire measurement range, respectively, and the surface tension of Ag–Bi–Sn decreases slightly with an increasing amount of Bi and Ag but increases with increasing Sn in liquid alloys.     

Effect of fermi surface curvature on low-energy properties of fermions with singular interactions

We discuss the effect of Fermi surface curvature on long-distance or time asymptotic behaviors of two-dimensional fermions interacting via a gapless mode described by an effective gauge-field-like propagator. By comparing the predictions based on the idea of multidimensional bosonization with those of the strong-coupling Eliashberg approach, we demonstrate that an agreement between the two requires a further extension of the former technique.     

On the surface tensions of binary mixtures

For binary mixtures with fixed concentrations of the species, various relationships between the surface tensions and the concentrations are briefly reviewed.     

Determination of surface tension coefficient and contact angle using numerical calculations of equilibrium drop shapes

The technique of determination of the contact angle and surface tension coefficient based on numerical calculation of the geometric characteristics of equilibrium shape of a liquid drop on the horizontal surface is stated. As initial data, the technique suggests using the dimensionless values of drop height and contact-spot radius that are obtained from drop images.     

Step line tension on a metal electrode

The step line tension in electrochemical systems differs conceptually from the line tension on metals in the vacuum because it refers to different boundary conditions. A procedure is established for calculating the electrochemical line tension and is applied to a novel model of the interface comprising both a stepped metal electrode and an electrolyte solution. To first order, the potential dependence of the line tension is governed by the energy of the step dipole in the electric field of the space charge in the solution.     

Effect of local curvature of the coating-substrate interface on deformation and fracture of ceramic coatings under uniaxial tension

Scanning electron microscopy and atomic force microscopy have been applied to study the fracture of SiAlN coatings on Cu substrates under uniaxial tension. It is shown that coating spalling occurs in the zones of local curvature of the SiAlN-Cu interface which form due to dislocation glide in the substrate. Preliminary ion bombardment of the substrate suppresses dislocation-induced kinking at the coating-substrate interface and increases the adhesive strength of the coatings, thus preventing their edge delamination. At the same time, the wavy coatingsubstrate interface resulting from ion bombardment gives rise to normal stresses that lead to the buckling and spalling of the coatings in the zones of positive local curvature of the interface.     

Quasi-static motion of microparticles at the depinning contact line of an evaporating droplet on PDMS surface

In this paper, evaporation of sessile water droplets containing fluorescent polystyrene(PS) microparticles on polydimethylsiloxane(PDMS) surfaces with different curing ratios was studied experimentally using laser confocal microscopy. At the beginning, there were some microparticles located at the contact line and some microparticles moved towards the line. Due to contact angle hysteresis, at first both the contact line and the microparticles were pinned. With the depinning contact line, the microparticles moved together spontaneously. Using the software ImageJ, the location of contact lines at different time were acquired and the circle centers and radii of the contact lines were obtained via the least square method. Then the average distance of two neighbor contact lines at a certain time interval was obtained to characterize the motion of the contact line. Fitting the distance-time curve at the depinning contact line stage with polynomials and differentiating the polynomials with time, we obtained the velocity and acceleration of both the contact line and the microparticles located at the line. The velocity and the maximum acceleration were,respectively, of the orders of 1 μm/s and 20-200 nm/s~2, indicating that the motion of the microparticles located at the depinning contact line was quasi-static. Finally, we presented a theoretical model to describe the quasi-static process, which may help in understanding both self-pinning and depinning of microparticles.     

各向异性表面张力对定向凝固中深胞晶生长的影响

利用匹配渐近展开法和多变量展开法求出定向凝固深胞晶生长的浓度场和界面形态的全局渐近解,研究各向异性表面张力对定向凝固深胞晶生长的影响.结果表明,各向异性表面张力对定向凝固过程深胞晶生长有显著的影响.随着各向异性表面张力增大,胞晶前端部分浓度减小而胞晶界面收缩;胞晶根部的浓度增大而界面曲率增大或根部的曲率半径减小,各向异性表面张力使得深胞晶界面振幅增加.本文结果能够计算定向凝固过程中深胞晶生长的浓度、界面形态.     

界面张力对Rayleigh-Taylor不稳定性的影响

将具有简单速度势的Layzer模型和Zufiria模型推广至非理想流体情况, 并分别利用这两种模型研究了界面张力对Rayleigh-Taylor不稳定性的影响. 首先得到了两种模型下气泡的渐近速度和渐近曲率的解析表达式; 其次系统研究了界面张力对气泡的渐近速度和渐近曲率的影响; 最后将两种模型进行了比较, 并将气泡的渐近速度和数值模拟进行了比较. 研究表明: 界面张力压低了气泡的速度, 但对曲率没有影响; 利用简单速度势的Layzer模型所得的气泡的渐近速度比复杂速度势的Layzer模型的值小, 但是比Zufiria模型的值大; 当阿特伍德数等于1时, 简单速度势的Layzer模型和复杂速度势的Layzer模型给出的结果一致. 关键词： Rayleigh-Taylor不稳定性 界面张力 Layzer模型 Zufiria模型     

Effect of inelastic transitions on the line shape of surface resonances

We show that the inelastic resonant processes discussed by Cantini and Tatarek affect the line shape of elastic resonances. This effect is not included in the Debye-Waller correction to the repulsive matrix elements, as used by Hutchison and others, and may explain the discrepancy between the line strengths predicted by Hutchison's formulae and those observed by Cantini et al.     

各向异性表面张力对深胞晶界面形态稳定性的影响

应用匹配渐近展开法和多变量展开法研究各向异性表面张力对定向凝固中深胞晶界面形态稳定性的影响, 通过寻找定向凝固系统的模式解获得了深胞晶界面形态满足的量子化条件. 结果表明, 与各向同性的定向凝固系统中深胞晶界面形态稳定性比较, 考虑各向异性表面张力的定向凝固中深胞晶生长界面形态也有两种整体不稳定性机制: 整体波动不稳定性和低频不稳定性. 随着各向异性表面张力的增加, 中性模式产生强振荡的枝晶结构的整体波动不稳定性的不稳定区域减小, 中性模式产生弱振荡的胞晶结构的低频不稳定性的不稳定区域增加.     

用CA方法模拟界面能各向异性对胞晶生长形态的影响

用元胞自动机（CellularAutomaton,CA）模型研究了界面能各向异性对二维定向凝固胞晶的生长形态的影响,建立了判定胞晶生长达到稳态的判据．结果显示,当界面能各向异性强度非常小时,胞晶尖端很容易分岔,胞晶形态不容易稳定．而当界面能各向异性强度足够大时,容易形成稳定的胞晶形态,同时界面能各向异性强度会显著影响稳定胞晶的形态,界面能各向异性越强,稳态胞晶间距越小,胞晶尖端半径越小,尖端半径与胞晶间距的比值越小,固液界面前沿的浓度与过冷度越小．