Active interfacial stresses drive flow in multiphase fluid

Living and synthetic matter driven out of equilibrium such as active droplets often exhibit rich dynamics driven by active forces at the interfaces. While active matter theories have elucidated active extensile and contractile stresses in scalar, polar, and nematic fluids, it remains unknown how such active interfaces control motion in multiphase fluids. We present a general theory for active interfacial stress in complex fluids where liquid-liquid phase separation occurs and observe new modes of motion due to spontaneous symmetry breaking. These findings provide new insights into the physics of activity-driven pattern formation in complex fluids.