Hydrogel triggered liquid-liquid phase separation in ternary mixtures

Liquid-liquid phase separation (LLPS) is ubiquitous in nature and engineering. In mundane situations, mixing Ouzo and water yields spontaneous emulsification, while similar demixing effects are used to manufacture porous membranes. Furthermore, LLPS have been shown to underly the formation of membraneless compartments in cells. While bulk phase separation has received most of the attention in recent years, the influence of surfaces on this complex physico-chemical processes remains poorly understood. Here, we study the phase separation of a ternary water-oil (DEP)-ethanol mixture on the surface of a hydrogel. The absorption of ethanol and release of water from the hydrogel perturbs the chemical composition locally, triggering the phase separation on the hydrogel surface and the formation of a phase separated layer. We analyze the dynamics of this process in a simplified Hele-Shaw geometry and draw the parallel between liquid-liquid phase separation and the surface induced solidification of a melt, or Stefan problem.