Mixed surfactants for stabilizing and controlling water transport in double emulsions

Double emulsions, comprising an aqueous droplet enclosed within an oil shell, hold great potential as versatile microcompartments for a variety of applications. However, their widespread utility is often limited by inherent instability and uncontrolled water transport. In this study, we use droplet microfluidics to prepare double emulsions with uniform thin oil shells stabilized by mixed surfactant systems. By combining monomeric and polymeric surfactants, we demonstrate that polymeric surfactants enhance stability by preventing oil shell drainage, while monomeric surfactants substantially increase water transport above a critical concentration, albeit reducing the emulsion lifespan. Swelling kinetics experiments, coupled with small-angle neutron scattering analysis, reveal that interface-controlled water transport occurs via mixed reverse micelle solubilization. This study provides valuable insights into designing double emulsions with optimized surfactant compositions, enabling enhanced stability and tunable water transport, with potential applications across food, cosmetics, and drug delivery systems.