Showing papers on "Wetting transition published in 1985"
TL;DR: In this paper, the authors present an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
6,042 citations
TL;DR: In this article, partial compatible binary mixtures of linear flexible polymers are considered in the presence of a wall which preferentially adsorbs one component, and it is shown that in typical cases at two-phase coexistence the wall is always "wet", i.e. coated with a macroscopically thick layer of the preferred phase, and the transition to the non-wet state occurs at volume fractions of the order of 1/n (where N is the chain length) at the coexistence curve.
Abstract: Partially compatible binary mixtures of linear flexible polymers are considered in the presence of a wall which preferentially adsorbs one component. Using a Flory-Huggins type mean field approach, it is shown that in typical cases at two-phase coexistence the wall is always « wet », i.e. coated with a macroscopically thick layer of the preferred phase, and the transition to the non wet state occurs at volume fractions of the order of 1/~N (where N is the chain length) at the coexistence curve. Both first and second order wetting transitions are found, and the variation of the surface layer thickness, surface excess energy and related quantities through the transition is studied. We discuss both the validity of the long wavelength approximation involved in our treatment, and pos- sible fluctuation effects for « critical wetting », comparing our results to Monte Carlo simulations of wetting in Ising models. The relation of our results to previous work and possible experimental consequences are also briefly mentioned.
168 citations
TL;DR: A unified treatment of the wetting transition in three dimensions with short-range interactions is given and it appears that the possible effects of the nonlinear terms in the renormalization group do not alter the critical behavior found using the truncated linear renormalized group.
Abstract: A linear functional renormalization group is introduced as a framework in which to treat various wetting transitions of films on substrates. A unified treatment of the wetting transition in three dimensions with short-range interactions is given. The results of Br\'ezin, Halperin, and Leibler in their three different regimes are reproduced along with new results on the multicritical behavior connecting the various regimes. In addition, the critical behavior as the coexistence curve is approached at complete wetting is analyzed. Wetting in the presence of long-range substrate-film interactions that fall off as power laws is also studied. The possible effects of the nonlinear terms in the renormalization group are examined briefly and it appears that they do not alter the critical behavior found using the truncated linear renormalization group.
139 citations
TL;DR: In this article, a density functional for inhomogeneous single-component fluids capable of describing both the short-range structure as well as coexistence phenomena such as wetting and drying is derived.
Abstract: A density functional for inhomogeneous single-component fluids capable of describing both the short-range structure as well as coexistence phenomena such as wetting and drying is derived. The formalism utilizes a coarse-grained reference density ${n}_{0}$(r\ensuremath{\rightarrow}) in addition to the full density n(r\ensuremath{\rightarrow}). Equilibrium profiles are obtained by finding the extrema of the density functional with respect to both densities. Density profiles for a Lennard-Jones fluid at both a hard wall and a 3-9 wall near the complete wetting transition are presented.
129 citations
TL;DR: In this article, the authors investigate the equilibrium merging of a liquid-vapor interface and of a solid surface with a weak and random heterogeneity in the mechanical approximation, and show that the contact angle hysteresis is much smaller than the surface heterogeneity when this one is small and at random.
92 citations
TL;DR: In this article, the effects on contact angle and capillary rise hysteresis of a specific pattern of mixed wettability are examined, where the average rise height lies near those stripe boundaries where the material with smaller equilibrium contact angle lies above the other material.
87 citations
TL;DR: In this paper, explicit corrections to the classical macroscopic formulae for the pressure at which capillary condensation occurs and for capillary rise are derived by means of a density functional treatment and a slab model for the density profile of the fluid.
79 citations
01 Oct 1985
TL;DR: In this article, a sequence of contact angle experiments is suggested to estimate the instantaneous as well as equilibrium surface energetic properties of a polymeric solid in an aqueous environment and the time required for the polymeric surface to attain its equilibrium wetting characteristics in the annealing environment.
Abstract: In the conventional methods of estimating the wetting characteristics of solids from contact angle experiments, the surface energetic properties of the solid are assumed to be identical in the environments of both the surrounding medium and probe fluids. While this assumption is suitable for solids which possess rigid surface structures (such as glasses, ceramics, and metals for example), it is generally inapplicable to polymeric solids, since the surfaces of the latter are relatively mobile so as to be able to adopt considerably different configurations in different environments. Based on a recognition of this feature of polymeric surfaces, a sequence of contact angle experiments is suggested to estimate: (a) the instantaneous as well as equilibrium surface energetic properties of a polymeric solid in an aqueous environment and (b) the time required for the polymeric surface to attain its equilibrium wetting characteristics in the aqueous environment. In order to illustrate the applicability of the suggested contact angle procedure, it is necessary to prepare model polymeric surfaces, which are smooth in surface texture, nonporous, and also chemically homogeneous. Such model surfaces were prepared in this study, by radio frequency sputter deposition of thin solid films of oxidized fluorocarbon compounds (from a Teflon FEP target) onto the smooth surfaces of highly polished, single crystal silicon substrates. The estimation of the wetting characteristics of the sputtered polymer films in an aqueous environment was then carried out by the suggested contact angle procedure. The results of the contact angle experiments indicate that the solid-water interfacial free energy of the sputtered polymer film which was initially equilibrated in an octane environment, decreases from an instantaneous value of 50.88 dyn/cm to an equilibrium value of 26.59 dyn/cm, over a duration of about 24 h. Such a change in the solid-water interfacial free energy of these model polymeric surfaces can arise due to a time-dependent reorientation of the buried polar groups of the solid from its bulk to its surface, when it is placed in contact with a strongly polar liquid like water. This interpretation was found to be consistent with the results of ESCA characterization, which indicated that the outer surface layers of the sputtered polymeric specimen contained a fair amount of the polar oxygen atoms that are capable of reorienting themselves from either the interior of the solid to its surface or vice versa, depending on their surrounding environment.
75 citations
TL;DR: It is shown that, for a suitable choice of potentials, critical wetting can occur and be observed explicitly for the first time and this contrasts with all previous calculations and with claims in the literature that first-order wetting is generic.
Abstract: We solve the mean-field equations for a lattice gas in the presence of a substrate. All forces in the system are long ranged. We show that, for a suitable choice of potentials, critical wetting can occur and we observe it explicitly for the first time. This contrasts with all previous calculations and with claims in the literature that first-order wetting is generic.
56 citations
TL;DR: For the critical wetting transition, MF theory is correct for d > dl, l3 and for dl > d > do fluctuations are strong enough to renormalize the exponents but there is no shift of the MF wetting temperature, and all wetting transitions (including those described by MF theory to be first order) are continuous and belong to the same universality class.
Abstract: The nature of the various types of wetting transitions for a given form of interaction potential is still somewhat controversial14 In particular, the systematics of these transitions for inverse-power-law potentials is still an open In this Rapid Communication we investigate this problem for coarse-grained order-parameter interaction potentials of the general form w (r) - r(d+u) as rA‘Â 00, with u > 1 where d is the spatial dimension After establishing the existence of stable mean-field (MF) profiles for u > 1 we determine the correct form of the effective Hamiltonian for I, the interface-substrate separation It is then shown that there is a sequence of upper critical dimensions (UCD) in the problem and that for a given type of critical or multicritical transition three distinct types of behavior are possible, depending on the spatial dimension d Denoting the jth UCD by dl, j"0, 1, , we show that for the potential V(l) given in (3b) below, a', is the spatial dimension where the operator l-("Â¥+j-l is marginal In particular, for the critical wetting transition we find that (i) MF theory is correct for d > dl, l3 (ii) for dl > d > do fluctuations are strong enough to renormalize the exponents but there is no shift of the MF wetting temperature, and (iii) for do > d the wetting temperature is renormalized and all wetting transitions (including those described by MF theory to be first order) are continuous and belong to the same universality class A similar sequencing occurs for all multicritical transitions New results for the critical exponents in the intermediate dimension interval described in (ii) above are also derived and it is argued that for all d S 3, q, the anomalous dimension of the interface degree of freedom 1 is zero Finally, these effects are illustrated by exact results for d = 2 The model we consider is described by the free-energy functional
45 citations
TL;DR: In this article, the authors reviewed the recent studies on wetting behavior of physisorbed films and showed that the wetting of solud films can be complete or incomplete and that incomplete wetting is a wide-spread phenomenon.
TL;DR: In this paper, the authors investigated the water wettability of surfaces, whose surface conditions are comparable to those used in heat and mass transfer equipment, and provided a physically based explanation for the characteristic wetting behaviour of industrial surfaces found experimentally.
Abstract: The water wettability of surfaces, whose surface conditions are comparable to those used in heat and mass transfer equipment, has been investigated experimentally and theoretically. In the first part, results of contact angle measurements for water on metal and non-metal surfaces are reported. With hydrophobic non-metal surfaces (e.g. Teflon) water forms large advancing and receding contact angles, and the contact angle hysteresis is small. Surface contamination is of minor influence. Hydrophilic metal surfaces (copper, nickel) are completely wetted by water only if the surfaces are extremely clean. Surface contamination reduces the wettability drastically. Under most industrial conditions advancing contact angles between 40° and 80°, and receding contact angles smaller than 20° can be expected, and the contact angle hysteresis is large. Corrosion can enhance the water wettability. In the second part, a thermodynamic analysis of the wetting of heterogeneous surfaces is presented. Equilibrium considerations for a model surface consisting of two components of different wettability provide the advancing and receding contact angles for a heterogeneous surface as a function of the equilibrium contact angles, surface fractions, and the distribution function of the two components. The advancing and receding contact angles as well as all the intermediate contact angles indicate metastable states of equilibrium of the system. The results of the model calculations give a physically based explanation for the characteristic wetting behaviour of industrial surfaces found experimentally.
TL;DR: In this article, the authors investigated the nature of adsorption at the interface between a model binary fluid mixture and a solid substrate using a two-density free-energy functional and showed that the solid-vapour interface can be wet by a double wetting film which is a composite of both phase-separated liquids.
Abstract: The nature of adsorption at the interface between a model binary fluid mixture and a solid substrate is investigated using a two-density free-energy functional. For model fluids which exhibit a liquid-liquid upper critical end point we show that the solid-vapour interface can be wet by a ‘double’ wetting film which is a composite of both phase-separated liquids. The structure and growth of such composite films is described and their possible observation discussed briefly. Results of calculations of the density profiles, relative adsorption and surface tension of the solid-vapour interface are presented. For certain choices of the substrate-fluid potential the binary fluid can exhibit re-entrant partial wetting as the temperature is increased, i.e. the solid-vapour interface undergoes transitions from partial wetting, to complete wetting by one liquid phase, to partial wetting and, finally, to wetting by the common liquid phase that occurs above the critical end point.
TL;DR: Une methode asymptotique permettant d'etudier analytiquement l'energie libre de surface en fonction du recouvrement permet de determiner l'ordre de la transition de mouillage.
Abstract: En se fondant sur la theorie de van der Waals du mouillage, on propose une methode asymptotique permettant d'etudier analytiquement l'energie libre de surface en fonction du recouvrement. Cette methode permet de determiner l'ordre de la transition de mouillage
TL;DR: In this paper, the authors apply the GvdW functionals, previously successfully applied to both adsorption and gas/liquid interfaces in simple fluids to the wetting problem, and focus their attention on the role of non-local entropy.
Abstract: The prediction by Cahn (1977, J. chem. Phys., 66, 3677) that a two phase fluid at a wall shows a wetting transition accompanied by a thick-thin film (prewetting) transition as the temperature increases towards the critical value where the fluid becomes uniform has been supported by a number of workers using free energy density functional theory. Due to the use of strong and varying approximations the support is of a qualitative nature and, in the absence of simulation verification of wetting-prewetting in simple solid-fluid systems, the quantitative aspects of the phenomenon are controversial. In this work we apply the GvdW functionals, previously successfully applied to both adsorption and gas/liquid interfaces in simple fluids to the wetting problem. The system consists of a carbon dioxide wall represented as a uniform continuum and an argon fluid interacting within itself and with the wall by appropriate Lennard-Jones (12–6) potentials. We focus our attention on the role of non-local entropy (responsib...
TL;DR: Ellipsometric measurements of the thickness of the wetting layer of sulfur hexafluoride that forms on a fused-silica surface partially immersed in the liquid are presented and are compared in detail to the theory of Dzyaloshinskii et al. (1961).
Abstract: Ellipsometric measurements of the thickness of the wetting layer of sulfur hexafluoride that forms on a fused-silica surface partially immersed in the liquid are presented. The components of the experiment included a He-Ne laser (0.6328 micron), polarizer, and quarter-wave plate with 45-deg azimuth. An optical-grade fused-silica prism was polished to wavelength/20, and strain-induced birefringence was accounted for. It was found that the layer thickness decreases from 40 to 20 nm with a height increase from 0.7 to 3 mm above the liquid-vapor interface. The thickness is independent of the temperature between 10 and 0.1 K below the critical temperature (319 K). The results are compared in detail to the theory of Dzyaloshinskii et al. (1961), and are noted to coincide closely.
TL;DR: In this article, a cylinder of radius b immersed in a two fluid binary mixture A/B produces preferential adsorption of A, described by a surface field h 1, and reduction of A/b interactions near the wall.
Abstract: A cylinder of radius b immersed in a two fluid binary mixture A/B produces two effects : (1) preferential adsorption of A, described by a surface field h1 ; (2) reduction of A/B interactions near the wall (neglected here). Using the Cahn mean-field theory [1], we find that perfect wetting occurs only for cylinders of radius b > bc(h 1). Then near the critical point, wetting is found at temperatures T > T w(b, h1). At Tw the transition is first order. It becomes second order when b = bc.
TL;DR: In this paper, the effect of the angle of a line contact on the constriction resistance and the contact resistance was analyzed theoretically by solving Laplace's equation subject to boundary conditions determined by a modeled morphology of the contact.
Abstract: It can generally be considered that an actual contact makes an angle with the extension of the contact surface, because the tip of a contact element is convex in shape (macroscopically) and has surface roughness (microscopically). There are, however, few studies that have taken into account the effect of this angle on the constriction resistance or the contact resistance. A line contact is taken as an example, and the effect of space angle is analyzed theoretically by solving Laplace's equation subject to boundary conditions determined by a modeled morphology of the contact. The analysis leads to modified formulas for the constriction resistance and the contact resistance, which show that the effect can not always be neglected.
TL;DR: In this article, the consequences of the Rayleigh-Taylor mode of instability in the semicritical wetting layer in a binary liquid mixture are investigated, and experimental observations in support of their theory are reported.
Abstract: In critical wetting phenomena, the situation of a heavier liquid residing on top of lighter liquid is observed. The consequences of the Rayleigh-Taylor mode of instability in the semicritical wetting layer in a binary liquid mixture are investigated. We also report experimental observations in support of our theory, in the critical binary liquid mixture cyclohexane + acetonitrile.
TL;DR: In this article, it was shown that the upper critical dimension is three and fluctuations lead, in dimension three, to strong deviations from mean field theory, presumably because long range forces lead to a first order transition.
Abstract: Critical wetting has never been observed, presumably because long range forces lead to a first order transition. If it were observed the properties would be quite interesting. Indeed the upper critical dimension is three and fluctuations lead, in dimension three, to strong deviations from mean field theory.
TL;DR: In this paper, the authors studied the spreading of a superfluid helium drop totally wetting a smooth solid plane at very low temperatures (T∼0) and constructed an exact self-similar solution describing the spreading.
Abstract: We study the spreading of a superfluid helium drop totally wetting a smooth solid plane at very low temperatures (T∼0). For macroscopic drops, the dominant forces are capillary forces. a) When Antonov's rule holds (i.e. when we are just at a wetting transition) the dynamic contact angle θ d is equal to the static contact angle θ e =0, the spreading velocity reaches a finite value at long times. We construct an exact self-similar solution describing the spreading. b) In conditions of dry spreading with a spreading coefficient S>0 we do not know what will happen, but we list three different possibilities, depending on the ultimate fate of the capillary energy (kinetic energy, capillary waves vorticity). For microscopic drops, the dominant forces are the long range van der Waals forces. The spreading time is finite. For these two situations, we determine the self-similar profiles of the drop Etude de l'etalement d'une goutte de He superfluide, qui mouille totalement une surface solide plane a T∼0. Cas des gouttes macroscopiques (forces capillaires dominantes): a) angles de contact statique et dynamique egaux quand la regle d'Antonov est verifiee (transition de mouillage); vitesse d'etalement tendant vers une limite finie aux temps d'etalement longs; construction d'un profil de goutte self-similaire exact; b) trois manieres possibles de dissiper l'energie capillaire (energie cinetique, ondes capillaires, vorticite) dans les conditions de mouillage sec avec un profil d'etalement S>0. Cas des gouttes microscopiques (forces de van der Waals dominantes a longue portee): profil self-similaire de la goutte
TL;DR: In this article, complete wetting of adsorbed He films is treated by a classical liquid slab model near T = 0. Several contributions to the chemical potential at coexistence are examined: cohesion, adhesion, compression and solidification by the substrate field, and interfacial energies.
TL;DR: The presence of long-range van der Waals forces in a system which undergoes a critical wetting transition gives rise to an unusually large relaxation time which scales as $\ensuremath{\Vert}T-${T}_{w}$, where ${T}$ is the wetting temperature.
Abstract: The presence of long-range van der Waals forces in a system which undergoes a critical wetting transition gives rise to an unusually large relaxation time \ensuremath{\tau} which scales as \ensuremath{\Vert}T-${T}_{w}$${\ensuremath{\Vert}}^{\mathrm{\ensuremath{-}}5}$, where ${T}_{w}$ is the wetting temperature.
TL;DR: In this paper, the wetting characteristics of polyacetylene films were determined by using a standard series of wetting liquids, and the results were interpreted with respect to surface oxidation and tested by examining an oxidized film.
Abstract: The wetting characteristics of free-standing polyacetylene films were determined by using a standard series of wetting liquids. As-prepared films of cis-polyacetylene were found to contain a significant polar contribution to the surface free energy, which became nearly entirely dispersive upon thermal isomerization to the trans form. Both isomeric forms are characterized by a critical surface tension of wetting γc ≈ 51 mN/m, which is considerably higher than that normally obtained from organic polymers. These results have been interpreted with respect to surface oxidation and tested by examining an oxidized film.
01 Jan 1985
TL;DR: In this paper, the authors studied the statistics of a wiggly contact line on a heterogeneous solid, both for totally or partially wetting fluids, and showed that the contact angle hysteresis of the contact line is very sensitive to surface heterogeneities.
Abstract: The wetting properties of a solid surface by a liquid are very sensitive to surface heterogeneities: the contact line becomes wiggly, and the final equilibrium structure of the liquid droplet or liquid film on the surface is history dependent on a heterogeneous surface (in the case of partial wetting, this phenomenon is known as contact angle hysteresis). We study here the statistics of a wiggly contact line on a heterogeneous solid, both for totally or partially wetting fluids.