To Wet or Not to Wet: That Is the Question

Abstract

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H 2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, H 2 O, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth ε of the adsorbate-adsorbate mutual interaction. At the wetting temperature, T w , the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluidsurface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.

Structures, Energetics, and Dynamics of Helium Adsorbed on Isolated Fullerene Ions

“…The binding of inert gases to graphite is relatively strong; for helium it exceeds the binding between the gas atoms [1]. In addition to coverage and temperature, the corrugation of the surface, its curvature, and dimensionality control the physical properties of the adsorbate.…”

Wetting, Prewetting and Superfluidity

“…2. We found that for 4 He on Cs, T w ≈ 2.0 ± 0.1 K and T pwc ≈ 2.5 K. We also found that at coexistence, the wetting transition was extremely hysteretic. If a dry state was prepared on the coexistence curve below T w , it would spontaneously wet at T = T w as the temperature was raised.…”

“…3 He wets Cs at all temperatures, but the formation of a thick film proceeds via an approximately first order prewetting-like transition [20]. The liquid-vapor surface tension of 3 He is less than for 4 He, so the film state corresponding to Fig. 1B is stable even at T = 0.…”

“…The interactions with the wall will typically prefer one phase over another, and that phase will wet the wall. Typical examples of A and B include: two distinct phases of a single component system such as liquid and vapor or solid and liquid; a binary mixture of two immiscible liquids with different concentrations such as 3 He- 4 He mixtures The grand free energy of each configuration must be evaluated to determine the stable state. σ sv , σ sl , and σ lv , are the solid-vapor, solid-liquid and liquid-vapor surface tensions.…”

“…The basic inputs required for this calculation are the interfacial energies and the substrate potential. A detailed discussion of the theoretical basis for a quantitative analysis is presented in [3] and [4].…”