Elastic deformation due to tangential capillary forces

TL;DR

This paper models the detailed capillary forces exerted by a liquid drop on a soft solid substrate, revealing a significant tangential force component that influences elastic deformation.

Contribution

It introduces a density functional theory-based model to quantify both normal and tangential capillary forces, highlighting the importance of tangential forces in substrate deformation.

Findings

Identification of a previously unaccounted tangential force component.

Quantitative analysis of elastic deformation due to capillary forces.

Demonstration of the significance of tangential forces on substrate deformation.

Abstract

A sessile liquid drop can deform the substrate on which it rests if the solid is sufficiently "soft". In this paper we compute the detailed spatial structure of the capillary forces exerted by the drop on the solid substrate using a model based on Density Functional Theory. We show that, in addition to the normal forces, the drop exerts a previously unaccounted tangential force. The resultant effect on the solid is a pulling force near the contact line directed towards the interior of the drop, i.e. not along the interface. The resulting elastic deformations of the solid are worked out and illustrate the importance of the tangential forces.