Active mixing of phase separating mixtures

Activity is known to be a generic pathway to phase separation through mechanisms like persistent motility or quorum sensing, but its role in suppressing phase separation is far less explored. Here we examine a model for a mixture of two immiscible liquid crystals and show that endowing one of the components with activity suppresses phase separation, driving the mixture into micro phase separated or uniform states. This suppression arises from the active mixing due to local shear flows that continuously stir the fluid. The self-induced shear generated by active stresses creates an instability of the interface at early times, breaking bulk phase separation. At later times, strong enough active flows keep the system from phase separating again and strongly suppress the coexistence boundary. We relate this result to previous studies of suppressed phase separation in externally sheared mixtures. Our work is directly relevant to recent experiments on DNA-based membraneless condensates immersed in an active liquid crystal.