Activity-driven emulsions in binary mixtures and droplet self-propulsion

Systems containing active components are intrinsically out of equilibrium, while binary mixtures reach their equilibrium configuration when complete phase separation is achieved. Active particles are found to stabilise non-equilibrium morphologies in phase separating binary mixtures by arresting coarsening, exerting active pressure that competes with surface tension driving forces. For moderate activities, an emulsion morphology is stabilised, where the droplet size is well-defined and controlled by activity. Conversely, the ability of active particles to drive phase-separated mixtures away from their equilibrium configuration is shown. A rich co-assembly behaviour is shown due to the competing energy scales involved in the system. In systems formed by droplets enclosing active particles, it is found that activity enhances shape fluctuations of the interface, matching recent experimental results using Quincke rollers. Furthermore, droplets containing polar active particles display active motion.