Empty liquid state and re-entrant phase behavior of the patchy colloids confined in porous media

Patchy colloids with three and four equivalent patches, confined in an attractive random porous medium, undergo re-entrant gas-liquid phase separation with the liquid phase density approaching zero at low temperatures. The (bonding) colloid-colloid interaction causes the liquid-gas phase separation, which is modulated by the presence of the randomly distributed hard-sphere obstacles, attracting the colloids via Yukawa potential. Due to this interaction, a layer of mutually bonded colloids around the obstacles is formed. The network becomes nonuniform, with colloid particles locally centered on the obstacles. Features described in this article may open possibilities to produce equilibrium gels with predefined nonuniform distribution of particles and indicate how complicated the phase behavior of biological macromolecules in a crowded environment may be.