Thin-Thick Film Transitions on a Planar Solid Surface: A Density Functional Study

A weighted density functional theory is proposed to predict the surface tension and thin-thick film transition of a Lennard-Jones fluid on a planar solid surface. The underlying density functional theory for the Lennard-Jones fluid at low temperature is based on a modified fundamental measure theory for the hard-core repulsion, a Taylor expansion around zero-bulk-density for attraction, and a correlation term evaluated by the weighted density approximation with a weight function of the Heaviside step function. The predicted surface tension and thin-thick film transition agree well with the results from the Monte Carlo simulations, better than those from alternative approaches. For the Ar/CO₂ system, the prewetting line has been calculated. The predicted reduced surface critical temperature is about 0.97, and the calculated wetting temperature is below the triple-point temperature. This is in agreement with the experimental observation.