Dependence of the macroscopic contact angle on the liquid-solid interaction parameters and temperature

Abstract

The solid-vapor and solid-liquid surface tensions of a fluid in contact with smooth solid surfaces as well as the liquid-vapor surface tension are determined on the basis of a nonlocal density functional theory in wide ranges of temperature and parameters of Lennard-Jones potentials used to represent the fluid-fluid and fluid-solid interactions. The contact angle theta of a macroscopic drop on the solid surface, calculated using the Young equation at various temperatures and various values of the hard core parameter sigma(fs) of the fluid-solid interaction potential, exhibited a simple linear dependence on the fluid-solid energy parameter epsilon(fs). At a certain (critical) value epsilon(fs) = epsilon(0) which depends on sigma(fs), the contact angle acquires a value theta(0) which is almost independent of temperature and sigma(fs). If a drop makes with the surface a contact angle theta > theta(0) (this occurs for epsilon(fs) < epsilon(0)), then theta increases with increasing temperature. Vice versa, if on a given surface theta < theta(0) (epsilon(fs) > epsilon(0)) then theta decreases with increasing temperature. The simple expression derived previously (G. O. Berim and E. Ruckenstein, J. Chem. Phys. 130, 044709 (2009)) for a nanodrop on a solid surface, which relates in a unified form the contact angle theta to the parameters of the interaction potentials and temperature, remains valid for macroscopic drops with some parameters slightly modified.