Unravelling the multiscale surface mechanics of soft solids

TL;DR

This study investigates the multiscale surface mechanics of soft solids, revealing a complex interplay of properties near the interface of silicone gels through displacement measurements.

Contribution

It provides experimental evidence of multiscale surface responses and surface excess elasticity, challenging existing molecular-scale theories.

Findings

Shear modulus decreases by half within 20 microns of the interface.

Surface excess elasticity depends on history and outer medium composition.

Discovered multiscale response challenges previous assumptions about soft solid interfaces.

Abstract

Soft solids and their surface deformations control the response of many natural and artificial systems. Yet, their underlying properties are vigorously debated, particularly for polymer networks. While molecular-scale theories predict no interfacial changes with macroscopic deformation, multiple experiments suggest otherwise. To settle this issue, we measure displacement fields near the interface of a silicone gel, in the limit of small deformations. We discover an unexpected multiscale response. The shear modulus decreases smoothly by half with 20 microns of the interface. At the same time we observe a surface excess elasticity, that depends on history and outer medium composition. These results reveal the fundamentally multiscale nature of polymeric surfaces, and call for further experimental and theoretical investigations into the basic understanding of soft solid interfaces