DIVERGENCE OF THE POINT TENSION AT WETTING

The line tension, tau (free energy associated with the line of contact) is expected to have interesting singular behaviour at the wetting transition, as has already been inferred from mean field theory and scaling arguments. In order to investigate this behaviour, we consider an exactly soluble two-dimensional Ising model with appropriate wetting boundary conditions and investigate suitable definitions of tau, now a point tension, associated with the junction of an interface tilted with average angle theta(c) and another lying along the substrate. Size-dependent fluctuations in the point of contact indicate that tau be defined through a convolution sum. Hence tau almost-equal-to ln (1/theta(c)) as theta(c) down 0 (wetting transition), which can be understood as a consequence of the entropic repulsion of the tilted part of the interface against the substrate, This logarithmic divergence is consistent with the recent scaling hypothesis of Indekeu and Robledo.