Instabilities and coarsening in active binary fluids

Interfacial instabilities between immiscible fluids are ubiquitous across scales in nature, appearing in systems ranging from geophysical flows to biological systems. I will present how various aspects of liquid-liquid phase separation are modified when one of the phases is an active fluid. I will describe the mechanisms that govern the growth of phase-separated condensates in a self-stirring active fluid, the origin of the non-self-similarity, and of the continuously varying coarsening exponents. I will then turn to active condensates with reduced surface tension, where passive capillary stresses become comparable to the stresses generated by the active phase. In this regime, the active–passive interface deforms, giving rise to morphological instabilities and asymmetric curvature fluctuations. These findings broaden our understanding of phase separation far from equilibrium, with potential implications for materials science and biology.