Showing papers on "Wetting transition published in 1987"
TL;DR: In this article, the phase transition from partial to complete wetting at a single adsorbing wall is shifted to lower temperatures and tends to become first-order when the more realistic SDA is employed.
Abstract: Phase transitions at fluid interfaces and in fluids confined in pores have been investigated by means of a density functional approach that treats attractive forces between fluid molecules in mean-field approximation and models repulsive forces by hard-spheres. Two types of approximation were employed for the hard-sphere free energy functional: (a) the well-known local density approximation (LDA) that omits short-ranged correlations and (b) a non-local smoothed density approximation (SDA) that includes such correlations and therefore accounts for the oscillations of the density profile near walls. Three different kinds of phase transition were considered: (i) wetting transition. The transition from partial to complete wetting at a single adsorbing wall is shifted to lower temperatures and tends to become first-order when the more-realistic SDA is employed. Comparison of the results suggests that the LDA overestimates the contact angle γ in a partial wetting situation. (ii) capillary evaporation of a fluid...
576 citations
TL;DR: In this paper, a system close to a bulk phase transition presents peculiar response to external boundaries, a single wall may induce the presence of wetting layers, with the appearance of a surface phase transition and critical point.
Abstract: A system close to a bulk phase transition presents peculiar response to external boundaries, a single wall may induce the presence of wetting layers, with the appearance of a surface phase transition and critical point. The confinement of the system between the two parallel walls or cylindrical tube, produces a shift of the bulk phase transition, which may be observed in a gravitational field as the capillary rise. The two phenomena may interact: the capillary properties are strongly affected by the wetting regime and the prewetting transition may be frustated by the capillary shift of the bulk transition. Symmetry breaking phase transitions present also the competition between conmensurate and inconmensurate structures which produce a richer variety of phenomena.
143 citations
TL;DR: In this paper, it was shown that the solid strain combined with the Laplace pressure may modify contact angle equilibrium on a mesoscopic scale, situated between that of the molecular structure of the triple line and the macroscopic behavior observed in quotidian contact angle assessment.
Abstract: At a triple wetting line, the liquid-fluid tension may produce a wetting ridge in sufficiently soft solids. By employing variational methods, it has been shown that the solid strain combined with the Laplace pressure may modify contact angle equilibrium on a mesoscopic scale, situated between that of the molecular structure of the triple line and the macroscopic behavior observed in quotidian contact angle assessment. Young's equation remains perfectly valid in the latter regime. Some possible consequences are discussed.
103 citations
TL;DR: In this article, a macroscopic static theory of the morphological stability of partial wetting is developed, which is based on the Young condition on the contact angle made at the contact line where the free surface of liquid meets the solid surface.
93 citations
TL;DR: Measurements of the state of wetting of two liquid mixtures at coexistence near their respective critical consolute temperatures yield surprising results which may be understood as a consequence of long-range forces.
Abstract: We report measurements of the state of wetting of two liquid mixtures at coexistence near their respective critical consolute temperatures. Borosilicate glass capillary tubes were reacted with hexamethyldisilazane to produce substrates of uniform and controlled silylation. Surfaces of low coverage exhibit a series of first-order partial to complete wetting transitions and obey a short-range force scaling relation. Surfaces of high coverage yield surprising results which may be understood as a consequence of long-range forces.
49 citations
TL;DR: In this paper, a contact angle procedure, involving the measurements of four initial wetting angles, is suggested for the estimation of the equilibrium values of the polar and dispersion components of the surface free energies of polymeric surfaces equilibrated in both polar and nonpolar environments.
48 citations
TL;DR: In this article, the equilibrium statistical mechanics of the semi-infinite Ising model, interpreted as a model of a binary system near a wall, are studied and the wetting transition is analyzed.
Abstract: We study the equilibrium statistical mechanics of the semi-infinite Ising model, interpreted as a model of a binary system near a wall. In particular, the wetting transition is analyzed. In dimensionsd≧3 and at low temperature, we prove the existence of a layering transition which is of first-order.
48 citations
TL;DR: In this article, the authors derived the generalized Young equation for anisotropic models using thermodynamic considerations and showed that the surface tension may be computed explicitly as a simple integral, which depends upon the orientation of the interface.
Abstract: This paper is devoted to the study of the Young equation, which gives a connection between surface tensions and contact angle. We derive the generalized form of this equation for anisotropic models using thermodynamic considerations. In two dimensions with SOS-like approximations of the interface, we prove that the surface tension may be computed explicitly as a simple integral, which of course depends upon the orientation of the interface. This allows a complete study of the wetting transition when a constant wall “attraction” is taken into account within the SOS and Gaussian models. We therefore give a complete analysis of the variation of the contact angle with the temperature for those models. It is found that for certain values of the parameters, two wetting transitions may successively appear, one at low temperature and one at high temperature, giving the following states: film—droplet—film. This study rests upon the generalized Young equation, the validity of which is proved for the Gaussian model with a constant wall attraction, using microscopic considerations.
38 citations
TL;DR: Wetting phenomena near the bulk critical point of an adsorbate are examined for the realistic case of long-ranged (e.g., van der Waals) forces, with use of mean-field theory for an Ising lattice-gas system.
Abstract: Wetting phenomena near the bulk critical point of an adsorbate are examined for the realistic case of long-ranged (e.g., van der Waals) forces, with use of mean-field theory for an Ising lattice-gas system. For moderately strong long-ranged forces new critical behavior appears at and near ${\mathrm{T}}_{\mathrm{c}}$, accompanied by both reentrant wetting and dewetting transitions and the appearance of two distinct wetting phases.
37 citations
TL;DR: In this article, the authors derived a time-dependent Ginzburg-Landau equation with a timedependent boundary condition at the surface in a mean-field approximation of a purely relaxational lattice model.
Abstract: The dynamic behavior at wetting transitions is studied for systems with short-range forces and nonconserved order parameter. From a continuum limit of a purely relaxational lattice model in mean-field approximation, a time-dependent Ginzburg-Landau equation with a time-dependent boundary condition at the surface is derived in the long wavelength approximation. The dynamics of relaxation close to stable and metastable states is treated in linear response. A divergence of the relaxation time occurs both for critical wetting and along the surface spinodal lines (in the case of first-order wetting), although the static surface layer susceptibilities χ1, χ11 stay finite at the surface spinodal in the non-wet region of the phase diagram.
34 citations
TL;DR: Aqueous wetting films on a plane quartz plate are studied experimentally to elucidate some of the details of the transition region between the film and the plane Quartz plate as discussed by the authors.
TL;DR: It is shown that there are two distinct dynamical regimes with crossover from fluctuation-dominated logarithmic growth for large L and short time t to quasi-one-dimensional diffusive growth for small L and large t.
Abstract: We present the first Monte Carlo study of the dynamics of the formation of the wet phase far from the wetting transition for a short-range attractive wall potential. A nearest-neighbor, simple-cubic, ferromagnetic Ising lattice gas with single spin-flip dynamics in a slab geometry (L\ifmmode\times\else\texttimes\fi{}L cross section) is used. We show that there are two distinct dynamical regimes with crossover from fluctuation-dominated logarithmic growth for large L and short time t to quasi-one-dimensional diffusive growth for small L and large t. For any finite system, the long-time behavior (i.e., t\ensuremath{\gg}${L}^{4}$[ln(L${)}^{2}$]) is predicted to always be quasi-one-dimensionally diffusive in nature.
TL;DR: In this article, the convergence rate of the Van der Waals transition in a model with exponential attractions is investigated. But, in practice, this numerical procedure is not able to locate precisely the tricritical line in the parameter space separating regions with a first-order transition from those with a continuous wetting transition.
Abstract: The wetting transition in a model with exponential attractions is investigated within the framework of modern Van der Waals theory. The transition is first studied by a numerical procedure due to Tarazona and Evans. The basis for this procedure is scrutinized and found to be sound in principle. Semi-quantitative estimates for the convergence rate are given. However, in practice, this numerical procedure is not able to locate precisely the tricritical line in the parameter space separating regions with a first-order transition from those with a continuous wetting transition. For this purpose an analytic approach is developed, asymptotically exact as the wall-fluid and fluid-fluid forces become equal. The tricritical line is located and found to have qualitatively different properties from those found in previous work on this model. Wetting exponents, including a new exponent describing the energy barrier in a weakly first-order transition, are determined. In large parts of the parameter space they are found to be non-universal, changing with the model parameters in a continuous manner.
TL;DR: In this article, the surface tension, adsorption and density-orientational profiles at the interface of ternary mixtures with one amphiphilic component were calculated as a function of the bulk composition of C in the two liquid phase region.
Abstract: We use a mean field theory for non-uniform molecular fluids to study the interfacial properties of the AB liquid-liquid interface of model ternary mixtures (A, B, C) with one amphiphilic component (C). We calculate the surface tension, adsorption and density-orientational profiles at the interface as a function of the bulk composition of C in the two liquid phase region. The latter terminates at a plait, tricritical or triple point depending on the values of the external fields (temperature and pressure) and on the parameters characterizing the intermolecular interactions. The surface tension of the AB interface decreases rapidly with the bulk concentration of C and vanishes at the plait and tricritical points. Under conditions of three phase equilibria the AB interface is characterized, in general, by low surface tensions and may undergo a wetting transition.
TL;DR: In this paper, the authors investigated the spreading of nonvolatile liquids on smooth and on rough surfaces and found that the radius of the wetted spot was consistent with scaling laws (t 1/10 for capillarity driven and t 1/8 for gravity driven spreading).
Abstract: The rate of spreading of non-volatile liquids on smooth and on rough surfaces was investigated. The radius of the wetted spot was found to agree with recently proposed scaling laws (t 1/10 for capillarity driven and t 1/8 for gravity driven spreading) when the surface was smooth. However, the crossover between these regimes was not observed at a constant value of the radius. Rough surfaces exhibited at least four spreading regimes which could be rationalized in terms of a macroscopic contact angle and macroscopic deviations thereof. An interesting feature is the appearance of a wetted rim around the central drop. This rim follows a diffuce spreading law (t 1/2). Partially wetting liquids followed the same dynamics provided the spreading conditions was fulfilled.
TL;DR: In this paper, a new generalization of the Sullivan model for the wetting transition is constructed, and a simplified version of the model allows a more quantitative criterion for a first-order transition to be formulated.
Abstract: A new generalization of the Sullivan model for the wetting transition is constructed. To the exponential wall potential of the Sullivan model is added a square well of arbitrary depth and range. Although explicit solutions cannot be given, the different possible types of density profiles are systematically classified. It is argued that for shallow wells of long range, the wetting transition is of first order. Shallow wells of short range give continuous transitions, and the shift from the Sullivan case is calculated explicitly. A simplified version of the model allows a more quantitative criterion for a first-order transition to be formulated. It also points to the possibility that a continuous wetting transition is preceded by a first-order transition between two distinct, partially wet, states.
TL;DR: In this paper, a model for interface detachment due to thermal fluctuations is first worked out, and an empirical framework for distinguishing between first-order and continuous wetting transitions is then set up, and quantified by the introduction of the van der Waals mean field model.
Abstract: The wetting of an attractive planar wall by liquid at liquid-gas coexistence is investigated from a microscopic point of view. A model for interface detachment due to thermal fluctuations is first worked out. An empirical framework for distinguishing between first-order and continuous wetting transitions is then set up, and quantified by the introduction of the van der Waals mean field model. This is solved for strong, short-range and weak, long-range forces. The role of fluctuations is reconsidered, and the nature of the required corrections examined, both for wall-fluid and fluid-fluid interfaces.
AT&T1
TL;DR: In this paper, a photolithographically-prepared, parallel-grooved surface on silica has been employed as a model to study the influence of roughness on the spreading equilibrium of liquid drops.
Abstract: A photolithographically-prepared, parallel-grooved surface on silica has been employed as a model to study the influence of roughness on the spreading equilibrium of liquid drops. The equations generated by Oliver, Huh and Mason for cylindrically shaped drops were extended to account for wetting by liquid crystals. The observed drop shapes were dependent upon surface roughness. The equilibrium contact angles on a smooth surface can be calculated from the roughness, contact angles both parallel and perpendicular to the grooves, and the drop shape. Reasonably good agreement with experimental contact angles was obtained.
TL;DR: In this article, the authors present evidence for the occurrence of a wetting transition in the adsorption of Kr and Xe on exfoliated graphite (Grafoil MAT).
Abstract: Evidence is presented for the occurrence of a wetting transition in the adsorption of Kr and Xe on exfoliated graphite (Grafoil MAT). The estimated wetting temperatures are 82·95 ± 0·1 for Kr and 116·3 ± 0·1 K for Xe. In relation to the critical temperature T c of the bulk adsorbate, these temperatures correspond to T w/T c = 0·396 and 0·401 respectively. An earlier study of the adsorption of CH4 on the same substrate yielded T w = 75·5 ± 0·1 K and T w/T c = 0·397. The experiments consisted of precise measurements of adsorption isotherms at seven temperatures for Kr and at four temperatures for Xe up to the equivalent of as many as eleven layers adsorbed. Just as for the example of the CH4/gr aphite system [1], in the region T < T w, the results are described well by Here n a is the amount adsorbed (at temperature T) where the adsorption is observed to change from type I (complete wetting) to type II (incomplete wetting). The adsorption isotherms are consistent with those measured previously by others.
TL;DR: Unusual temperature dependence and the first experimental evidence of a possible "partial drying" transition recently predicted by Ebner and Saam for the case of strong short-range substrate-liquid forces opposed by a weak long-range force are found.
Abstract: Measurements are presented of the state of wetting of a binary liquid mixture on heavily silylated glass, which are believed to probe a new region of the wetting phase diagram. We find unusual temperature dependence and the first experimental evidence of a possible "partial drying" transition recently predicted by Ebner and Saam for the case of strong short-range substrate-liquid forces opposed by a weak long-range force.
TL;DR: Determination of contact angle is important to several areas of dentistry, denture retention being one, but published reports attribute spurious significance to advancing and retreating angles, which are not in general interpretable thermodynamically.
TL;DR: In this article, a phenomenological theory of the liquid wetting layer is presented, and its predictions are compared to those of earlier simpler models as well as to recent experimental results.
Abstract: A phenomenological theory of the liquid wetting layer is presented. Its predictions are compared to those of earlier simpler models as well as to recent experimental results. Special attention is given to the critical region and to the crossover from the complete wetting regime to the critical wetting regime.
TL;DR: In this paper, the authors studied the melting of pure solid helium at pressures between 240 and 1700 bar and found that the contact angle between the helium solid and the substrate (Vespel SP-1) changes from 0° to between 60 and 90°.
Abstract: Fast melting of pure solid hcp and fcc 4He at pressures between 240 and 1700 bar was studied. It was found that under these conditions solid helium exhibits properties which are quite different from those observed under near equilibrium conditions. For melting rates exceeding a certain value, and under constant volume conditions competition between surface and bulk melting was observed. Melting under these conditions starts as surface melting. During the last stage of melting a wetting transition takes place, during which the contact angle between the helium solid and the substrate (Vespel SP-1) changes from 0° to between 60 and 90°. The wetting transition is followed by continuous melting throughout the solid. The most likely mechanism of continuous melting is a disordering process i.e., the spontaneous generation of high concentrations of thermal vacancies.
TL;DR: In this article, the generalized Sullivan model is reconsidered on the basis of a formulation of the problem as one in classical dynamics, and a discussion of the order of transition when the difference in interaction range is not small.
Abstract: The generalized Sullivan model, in which the wall and fluid-fluid potentials are of exponential form, but with different renge, allows, within a Van der Walls framework, both continuous and first-order wetting transitions. This model is reconsidered on the basis of a formulation of the problem as one in classical dynamics. Recent non-trivial results on the locus of tricriticality, when the difference in range is small, are rederived from this point of view. The dynamics approach, in addition, allows a discussion of the order of transition when the difference in interaction range is not small. Pade approximants are used for an accurate determination of the locus of tricriticality in the high temperature region.
TL;DR: In this article, the authors derived the capillary parameter for the partially miscible binary liquid system acetonitrile + cyclohexane and fitted it to a power law σ=0.061 (Tc-T)1.26.
Abstract: The determination of the capillary parameter for the partially miscible binary liquid system acetonitrile + cyclohexane has been reported. The system has closely matched densities and the data points are affected by gravity only when the fractional change of the temperature from the critical temperature is about 10−6. The system also exhibits very interesting wetting properties. The interfacial tension has been fitted to a power law σ=0.061 (Tc-T)1.26. The effect of doping with water and the instability of the wetting layer, which crucially depends on the interfacial tension, are studied.
TL;DR: In this article, the authors studied the kinetics of domain growth in the uniaxial (4*1) phase of the two-dimensional ANNNI model by Monte Carlo methods and showed that an abrupt change of the anisotropic growth mode due to the effect of a wetting transition is observed.
Abstract: The kinetics of domain growth in the uniaxial (4*1) phase of the two-dimensional ANNNI model is studied by Monte Carlo methods. An abrupt change of the anisotropic growth mode due to the effect of a wetting transition is observed. To explain this, a theory of domain growth developed for the clock model is extended to include the uniaxial (4*1) phase. In addition, it is shown that the ANNNI model with conserved density and a model with a symmetric p=4 phase studied recently belong to different dynamical universality classes.
TL;DR: In this paper, the authors revisited the wetting transition by looking at the contact angle of a macroscopic droplet, in a microscopic statistical-mechanical study, for anisotropic media.
Abstract: The wetting transition is revisited by looking at the contact angle of a macroscopic droplet, in a microscopic statistical-mechanical study, for anisotropic media. As an example, we consider the (1 + 1)-dimensional continuous SOS model with a contact wall potential, which is exactly solvable. It is shown that zero, one or two wetting transitions may occur as the temperature is varied. Typical of a second-order transition, the contact angle vanishes linearly with the temperature at the transition, and the prefactor is exactly computed.
TL;DR: In this article, the phase diagram is analyzed rigorously, and in particular the wetting transition is discussed, and the phase transition is shown to be linear in the length of the transition.
Abstract: The phase diagram is analyzed rigorously, and in particular the wetting transition is discussed.