Osmocapillary phase separation

A covalent network of polymer can imbibe a solvent to form a gel. In a cavity on the surface of the gel, capillary force may suck the solvent out of the gel to form a pure liquid phase. We show that such osmocapillary phase separation occurs when capillarity balances osmosis, and when the diffusion of solvent in the gel prevails over the condensation of solvent from the vapor. Osmocapillary phase separation can occur even when the gel is isolated from the vapor, or when the solvent is nonvolatile. We relate osmocapillary phase separation to phenomena of practical significance, including the wettability of gels, the transparency of gels, the liquid bridge at the tip of an atomic force microscope, the adhesion between a gel and another substance, the surface morphology of gels, and the production of tight oil.