Surfactant-induced core/shell phase equilibrium in hydrogels.

The formation of core/shell structures in hydrogels upon interaction with surfactants is a well-known phenomenon, but whether they are equilibrium states or not is still under debate. This paper presents an equilibrium theory of phase coexistence in hydrogels meant to answer the question of the stability of core/shell separation. The theory suggests that core/shell separation caused by surfactants can indeed be thermodynamically stable if the amount of added surfactant is not too large, but that the exact phase behaviour is governed by both the volume and concentration of the added surfactant solution.