Critical Point Wedge Filling

We present results of a microscopic density functional theory study of wedge filling transitions, at a right-angle wedge, in the presence of dispersionlike wall-fluid forces. Far from the corner the walls of the wedge show a first-order wetting transition at a temperature T-w which is progressively closer to the bulk critical temperature T-c as the strength of the wall forces is reduced. In addition, the meniscus formed near the corner undergoes a filling transition at a temperature T-f < T-w, the value of which is found to be in excellent agreement with macroscopic predictions. We show that the filling transition is first order if it occurs far from the critical point but is continuous if T-f is close to T-c even though the walls still show first-order wetting behavior. For this continuous transition the distance of the meniscus from the apex grows as l(w) approximate to (T-f - T)-(beta w) with the critical exponent beta(w) approximate to 0.46 +/- 0.05 in good agreement with the phenomenological effective Hamiltonian prediction. Our results suggest that critical filling transitions, with accompanying large scale universal interfacial fluctuation effects, are more generic than thought previously, and are experimentally accessible. DOI: 10.1103/PhysRevLett.110.166101