Reversible Switching of the Amphiphilicity of Organic–Inorganic Hybrids by Adsorption–Desorption Manipulation

Surfactants are of great significance due to their wide use in fundamental research, industrial production, and daily lives. It remains a grand challenge to design and synthesize surfactants exhibiting reversible amphiphilicity switching. Here, we report on a "hybrid surfactant" prepared by combining an oil-soluble molecule, stearic acid, with water-dispersible Al2O3 nanofibers via chemisorption at the oil–water interface. The long carbon chain of stearic acid functions as the hydrophobic tail of the surfactant, while the inorganic nanofibers can act as the hydrophilic head. This hybrid surfactant exhibits reversible switching between hydrophilic and lipophilic states by manipulating the adsorption–desorption volume of stearic acid attached to the Al2O3 nanofibers. Therefore, the emulsions stabilized by this organic–inorganic hybrid can reversibly transform between oil-in-water and water-in-oil type. Unlike conventional approaches, no other external stimulus is needed to set the amphiphilic properties of the hybrid surfactant. As a bonus, organic–inorganic three-dimensional solid foams can be readily prepared based on the emulsion system, which demonstrates potential applications for remediation of oil spills in the environment.