Beating surface tension: oxide-skin mediated formation of liquid metal suspensions and emulsions

Room temperature gallium-based liquid metals have surface tension that is about ten times higher than that of water. As a result, the direct mixing of a secondary gas, liquid, or solid phase into the liquid metals is challenging. This presentation will discuss how the few nanometer thin gallium oxide skin that forms rapidly upon exposure to trace amounts of oxygen provides a general path for incorporation of any secondary phase into the liquid metal. Using in-situ imaging in an electron microscope, we show that during shear mixing patches of the oxide stick to even highly "liquid-metal-phobic" solid microparticles and provide local wetting spots for the liquid. This microscale wetting mechanism provides a general path for making liquid metal suspensions with various solid additives [1]. Using high-speed microscopic imaging, we will also show that the incorporation of oxide flakes created during rapid shear mixing of the liquid metal in air allows for making stable liquid metal foams [2]. Mixing these foams with a secondary liquid enables the formation of liquid-in-liquid metal emulsions [3]. These complex suspensions, foams, and emulsions have highly tunable properties and thereby numerous potential applications, including thermal interface materials, soft robotics, and biomedical devices.