A robust method for quantification of surface elasticity in soft solids

TL;DR

This paper introduces a new method to accurately measure surface elastic constants of soft solids by analyzing droplet deformations, avoiding nonlinearities of previous techniques, and providing analytical solutions for different deformation modes.

Contribution

It presents an analytical approach coupled with experimental procedures to quantify surface elasticity in soft solids using droplet deformation analysis.

Findings

Derived analytical solutions for droplet shape under uniaxial deformation.

Developed a minimization procedure to extract surface elastic parameters.

Proposed coupling of mechanical deformation with droplet dissolution for sensitivity assessment.

Abstract

We propose an approach to measure surface elastic constants of soft solids. Generally, this requires one to probe interfacial mechanics at around the elastocapillary length scale, which is typically microscopic. Deformations of microscopic droplets embedded in soft solids are particularly attractive, because they avoid intrinsic nonlinearities associated with previous experiments such as the equilibrium of contact lines and the relaxation of patterned surfaces. We derive analytical solutions for the shape of droplets under uniaxial deformation and for the radius of droplets upon hydrostatic inflation. We couple mechanical deformations to the dissolution of droplets to assess experimental sensitivities. Combined with experimental data from both modes of deformation, one should be able to reliably extract the complete set of isotropic surface material parameters following a specific minimization procedure.