Soft wetting ridge rotation in sessile droplets and capillary bridges

TL;DR

This paper investigates how soft solid layers deform and rotate at the contact line with droplets and capillary bridges, revealing how Laplace pressure influences contact angles and droplet motion control.

Contribution

It introduces a model incorporating surface tension balance to analyze wetting ridge rotation and contact angle changes in soft solids with droplets and capillary bridges.

Findings

Wetting ridge rotation aligns with Laplace pressure sign.

Softer solids generally decrease contact angle in droplets.

Negative Laplace pressure increases contact angle in capillary bridges.

Abstract

We study the deformation of soft solid layers in the presence of sessile droplets or capillary bridges. By incorporating the surface tension balance at the contact line, we examine the rotation of the wetting ridge and the corresponding change in the contact angle. Our findings reveal that the rotation direction of the wetting ridge aligns with the sign of the Laplace pressure. Notably, while a softer solid layer typically decreases the contact angle for sessile droplets, a negative Laplace pressure in a hydrophilic capillary bridge pulls the solid-liquid interface, leading to an increased contact angle. The interplay between soft layer deformation and droplet contact angle modulation offers insights for controlling droplet motion through elastocapillarity.