Physical Mechanisms of Vacuole Formation in Liquid Condensates

A liquid droplet's surface tension disfavours excess interface area, driving its relaxation to a spherical shape. However, recent experiments have observed the emergence of vacuoles (solvent-rich regions inside liquid condensates) across a wide range of systems, from bimolecular condensates to droplets composed of synthetic macromolecules. It was proposed that vacuoles may form, for example, through chemical reactions or surfactant molecules. In this work, we show that a common mechanism underlies vacuole formation in all such systems, which is related to a local instability within the droplets. We consider different scenarios for triggering these instabilities, including temperature quenching and chemical reactions. Using concepts from non-equilibrium statistical physics, we develop a theoretical framework to explore various conditions under which vacuoles are favoured or suppressed. We scrutinize this framework against experiments on RNA nanostars performed by William Verstraeten in the Göpfrich group, finding excellent agreement with the experimental data. Our theory suggests ways to control vacuole formation in different complex systems.