Elastocapillarity: Surface Tension and the Mechanics of Soft Solids

TL;DR

This paper reviews the emerging field of elastocapillarity, exploring how surface stresses influence the mechanics of soft solids, leading to deviations from classical theories in wetting, adhesion, and composites.

Contribution

It provides a comprehensive overview of surface stress theory and its impact on soft solid mechanics, highlighting phenomena where surface stresses dominate behavior.

Findings

Surface stresses significantly affect soft solid mechanics.

Deviations from classical wetting and adhesion theories are observed.

Surface stress to elastic modulus ratio determines dominant length scales.

Abstract

It is widely appreciated that surface tension can dominate the behavior of liquids at small scales. Solids also have surface stresses of a similar magnitude, but they are usually overlooked. However, recent work has shown that these can play an central role in the mechanics of soft solids such as gels. Here, we review this emerging field. We outline the theory of surface stresses, from both mechanical and thermodynamic perspectives, emphasizing the relationship between surface stress and surface energy. We describe a wide range of phenomena at interfaces and contact lines where surface stresses play an important role. We highlight how surface stresses causes dramatic departures from classic theories for wetting (Young-Dupr\'{e}), adhesion (Johnson-Kendall-Roberts), and composites (Eshelby). A common thread is the importance of the ratio of surface stress to an elastic modulus, which defines a length scale below which surface stresses can dominate.