Elastocapillary deformations on partially-wetting substrates: rival contact-line models

Abstract

A partially-wetting liquid can deform the underlying elastic substrate upon which it rests. This situation requires the development of theoretical models to describe the wetting forces imparted by the drop onto the solid substrate, particularly those at the contact-line. We construct a general solution using a displacement potential function for the elastic deformations within a finite elastic substrate associated with these wetting forces, and compare the results for several different contact-line models. Our work incorporates internal contributions to the surface stress from both liquid/solid $\Sigma_{ls}$ and solid/gas $\Sigma_{sg}$ solid surface tensions (surface stress), which results in a non-standard boundary-value problem that we solve using a dual integral equation. We compare our results to relevant experiments and conclude that the generalization of solid surface tension $\Sigma_{ls} \neq \Sigma_{sg}$ is an essential feature in any model of partial-wetting. The comparisons also allow us to systematically eliminate some proposed contact-line models.