FLUID WETTING ON MOLECULARLY ROUGH SURFACES

We examine the effects of structural changes of solid surfaces on flui d wetting by performing molecular dynamics simulations on a model syst em. The system consists of a Lennard-Jones fluid confined between two identical solid surfaces under conditions that induce the formation of both a liquid and vapor region. The smooth surface is three layer sol id particles arranged in a perfect fee lattice. We represent a molecul arly rough surface by adding to the smooth surface a fourth layer cons isting of less than a full monolayer of solid particles. This model co rresponds to some physical situations where there is surface irregular ity, such as surface defects due to vacancies or surface structures ca used by adsorption of foreign particles onto a perfect surface. The fl uid density profiles near the rough surfaces are different from those near the smooth surface and reflect the detailed molecular structure o f the surfaces. More importantly, the changes in surface structure alt er significantly the contact angle between the liquid-vapor interface and the solid surface, which is determined by measuring the interfacia l tensions between liquid, vapor, and solid phases. The wetting transi tion on molecularly rough surfaces occurs at a higher value of the liq uid-solid interaction strength than that for a smooth surface. (C) 199 5 American Institute of Physics.