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

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 θ of a macroscopic drop on the solid surface, calculated using the Young equation at various temperatures and various values of the hard core parameter σ_fs of the fluid-solid interaction potential, exhibited a simple linear dependence on the fluid-solid energy parameter ϵ_fs . At a certain (critical) value ϵ_fs=ϵ ₀which depends on σ_fs , the contact angle acquires a value θ ₀which is almost independent of temperature and σ_fs . If a drop makes with the surface a contact angle θ > θ ₀ (this occurs for ϵ_fs<ϵ₀ ), then θ increases with increasing temperature. Vice versa, if on a given surface θ<θ₀ (ϵ_fs>ϵ₀) then θ 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 θ to the parameters of the interaction potentials and temperature, remains valid for macroscopic drops with some parameters slightly modified. © 2009 American Institute of Physics. [DOI: 10.1063/1.3133327]