Contact lines on stretched soft solids: Modeling anisotropic surface stresses

TL;DR

This paper develops analytical models for the deformation of stretched soft substrates caused by wetting droplets, incorporating anisotropic surface stresses and pre-strain effects, and compares these models to experimental data.

Contribution

It extends existing models to include uniaxial pre-strains and finite kinematics, providing improved fits to experimental wetting ridge shapes and revising surface elastic constant values.

Findings

Finite kinematics better capture opening angles at higher strains.

Models successfully fit experimental wetting ridge profiles.

Revised surface elastic constants align with experimental observations.

Abstract

We present fully analytical solutions for the deformation of a stretched soft substrate due to the static wetting of a large liquid droplet, and compare our solutions to recently published experiments (Xu et al, Soft Matter 2018). Following a Green's function approach, we extend the surface-stress regularized Flamant-Cerruti problem to account for uniaxial pre-strains of the substrate. Surface profiles, including the heights and opening angles of wetting ridges, are provided for linearized and finite kinematics. We fit experimental wetting ridge shapes as a function of applied strain using two free parameters, the surface Lame coefficients. In comparison with experiments, we find that observed opening angles are more accurately captured using finite kinematics, especially with increasing levels of applied pre-strain. These fits qualitatively agree with the results of Xu et al, but revise values of the surface elastic constants.