Shaping Capillary Solids from Statics to Dynamics

The shape of a soft solid is largely determined by the balance between elastic and surface energies with capillarity becoming important at length scales smaller than the elastocapillary length, which approaches the millimeter scale for the softest hydrogels, leading to many new and surprising phenomena. This review is focused on describing recent experimental and theoretical progress on the deformations of soft solids due to capillarity in two-phase systems for both statics and dynamics. Relative to rigid solids, surface tension can lead to the rounding of sharp corners, wrinkling and creasing, and general morphological shape change of the static equilibrium configuration, beyond a critical elastocapillary number. With regard to dynamics, both surface tension and viscoelasticity affect wave number selection in a number of dynamic pattern formation phenomena in soft solids, such as elastocapillary-gravity waves, Rayleigh-Taylor instability, Plateau-Rayleigh instability, Faraday waves, and drop oscillations, all of which have direct analogs with classical hydrodynamic instabilities helping to interpret the relevant physics.