A Microemulsion Superlubricant with Largely Switchable Friction

Abstract Superlubrication has been discovered in van der Waals 2D materials and dispersions of lipids, polymers and nanoparticles, but not in microemulsions consisting of oil, water and surfactants, although they have been extensively applied in industrial fields. Here, for the first time, we create a microemulsion displaying superlubricity in a broad temperature from -30 to 20 ºC using n-hexane, water, surfactant DDACe ((C12H25)2N+(CH3)2[CeCl4]-) and ethylene glycol as compositions. The microemulsion is capable of abruptly and dramatically switching its coefficient of friction by approximately 25 folds based on a thermoreversible microemulsion-emulsion transition, thus showing great potentials in smart devices and controllable transportation. Its anti-freezing performance allows it to provide excellent lubrication even when the surrounding temperature attains as low as -60 ºC. Together with its facile preparation, high colloidal stability and magneto responsiveness, such novel smart microemulsion superlubricant is envisioned to find widespread applications in engineering, industry, materials science and tribology.