Fine structure of a perturbed wetting triple line

Practical and mathematical problems related to the use of Young's and Lapla ce's equations are discussed and it is pointed out how difficulties are oft en encountered when heterogeneous solids are being studied. The shape of a wetting triple line on an otherwise homogeneous solid, yet perturbed locall y by the proximity of a heterogeneity, has been considered in the past by s everal workers including the present author. It has been shown that the wet ting front is deformed to a shape which is closely approximated by a logari thmically decreasing function, sufficiently far from the heterogeneity itse lf. In this article, one of the earlier (Fourier series) solutions, issue f rom the analysis of a sessile drop, is simplified and applied to the limiti ng case of a straight (in its unperturbed form) triple line. The logarithmi c behaviour at long distances is corroborated and, more importantly, fine s tructure of the triple line within the heterogeneous zone is assessed. A ch ange from concave to convex curvature is clearly shown. (C) 1999 Elsevier S cience B.V. All rights reserved.