Wetting of a symmetrical binary fluid mixture on a wall - art. no. 031201

We study the wetting behavior of a symmetrical binary fluid below the demix ing temperature at a nonselective attractive wall. Although it demixes in t he bulk, a sufficiently thin liquid film remains mixed. On approaching liqu id vapor coexistence, however, the thickness of the liquid film increases a nd it may demix and then wet the substrate. We show that the wetting proper ties are determined by an interplay of the two length scales related to the density and the composition fluctuations. The problem is analyzed within t he framework of a generic two component Ginzburg-tandau functional (appropr iate for systems with short-ranged interactions). This functional is minimi zed both numerically and analytically within a piecewise parabolic potentia l approximation. A number of surface transitions are found, including first -order demixing and prewetting, continuous demixing, a tricritical point co nnecting the two regimes, or a critical end point beyond which the prewetti ng line separates a strongly and a weakly demixed film. Our results are sup ported by detailed Monte Carlo simulations of a symmetrical binary Lennard- Jones fluid at an attractive wall.