Wetting phenomenon in the liquid-vapor phase coexistence of a partially miscible Lennard-Jones binary mixture

TL;DR

This study uses molecular dynamics simulations to explore wetting phenomena and interfacial properties in a partially miscible Lennard-Jones binary mixture, revealing temperature-dependent wetting transitions and phase behavior.

Contribution

It provides detailed insights into wetting transitions, phase diagrams, and interfacial properties in Lennard-Jones binary mixtures, highlighting the conditions for wetting and the nature of the transition.

Findings

Wetting occurs at certain temperatures for low miscibility parameters.

Wetting transition is of first order, indicated by a jump in adsorption.

Phase diagrams show a tricritical point associated with wetting phenomena.

Abstract

We have carried out extensive equilibrium molecular dynamics (MD) simulations to study the structure and the interfacial properties in the liquid-vapor (LV) phase coexistence of partially miscible binary Lennard-Jones (LJ) mixtures. By analyzing the structural properties as a function of the miscibility parameter, $ \alpha $, we found that at relatively low temperatures the system separates forming a liquid A-liquid B interface in coexistence with the vapor phase. At higher temperatures and, $ 0<\alpha\leq 0.5 $, we found a temperature range, $T^{*}_{w}(\alpha) \leq T^{*} < T^{*}_{cons}(\alpha)$, where the liquid phases are wet by the vapor phase. Here, $ T^{*}_{w}(\alpha) $ represents the wetting transition temperature (WTT) and $T^{*}_{cons}(\alpha)$ is the consolute temperature of the mixture. However, for $ 0.5< \alpha < 1$, no wetting phenomenon occurs. For the particular value, $ \alpha=0.25 $, we analyzed quantitatively the $T^{*}$ versus $\rho^{*}$, and $ P^{*} $ versus $ T^{*} $ phase diagrams and found, $ T^{*}_{c}\simeq 1.25 $, and $T^{*}_{cons}\simeq1.25$. We also studied quantitatively, as a function of temperature, the surface tension and the adsorption of molecules at the liquid-liquid interface. It was found that the adsorption shows a jump from a finite negative value up to minus infinity, when the vapor wets the liquid phases, suggesting that the wetting transition (WT) is of first order. The calculated phase diagram together with the wetting phenomenon strongly suggest the existence of a tricritical point. These results agree well with some experiments carried out in fluid binary mixtures.