Symbiosis between the components of a soft composite material responding to osmotic shock: The case of three-liquid systems.

Abstract Hypothesis For conventional high internal phase emulsions (HIPEs) with an external osmotic pressure greater than Laplace pressure, once the osmotic balance is broken, the swelling or shrinking of the aqueous phase can easily trigger phase separation. Mixing two immiscible dispersed phases in a double HIPE can evolve differently following an osmotic shock, which is expected to create a synergistic effect that can frustrate the phase separation of the system. Experiments Osmotic responses of double HIPEs were studied at the surface of a NaCl solution at a range of molarities. Fluorescence confocal microscopy studies were carried out to track the responses on microscopic scales. Measurements on surface tensions revealed the interfacial behaviors of the used surfactant. Findings A synergistic effect is achieved by a symbiotic process between the dispersed oils, where one type of droplets become more stable and pack around the other ones to halt their coalescence. The essential drive comes from the adsorption/desorption of surfactant molecules at oil–water interfaces. By directly adjusting the osmotic pressure difference, transitions between osmotic down-shock and osmotic up-shock can also be realized. This symbiosis greatly expands the potential technological applications of multiple-liquid systems, and can be used to design novel multi-functional composite materials.