Osmocapillary phase separation at contact lines

Swollen soft materials have various uncommon wetting properties, such as anomalous contact angles, extremely low adhesion, stimuli-responsive adhesion, and time-dependent wetting. These properties are related to the solvent exudation near the contact lines. Existing studies assume that the phenomenon is governed by the elastocapillary effect, predicting that a stiffer material suppresses the solvent exudation. Here we show that the phenomenon is governed by the osmocapillary effect instead, predicting that a stiffer material promotes solvent exudation while a higher osmotic pressure suppresses it. We combine a small-deformation analytical model and nonlinear finite element simulations to develop a model that quantitatively predicts a wide range of existing experimental data with no fitting parameters.