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Traditional industrial lubricating emulsions usually contain a variety of constituents to fulfill their functional requirements in long-term stability, lubrication, and anticorrosion. The complexity of the constituents may produce difficulties for their preparation, storage, and recycling. To address this issue, here we design and prepare simple-component, switchable, and multifunctional Pickering emulsions using the green lubricating base oil polydimethylsiloxane, water, and silica nanoparticles modified with a series of magnetic surfactants (CnH2n+1N+(CH3)3XCl3Br−, n = 12, 14, and 16, X = Ce, Fe, and Gd) as compositions. The Pickering emulsions are demonstrated to be highly stable, lubricative, and anticorrosive. Their magneto-responsiveness indicates a potential application as smart lubricants. Their reversible emulsification and demulsification, which allows an effective recycling and reuse of the composite nanoparticles, can be regulated by alternative centrifugation and homogenization or successive addition of the anionic surfactant sodium dodecyl sulfate and the magnetic cationic surfactants. Both their stability and lubricity can be optimized by using surfactant C16H33N+(CH3)3CeCl3Br− (CTACe) as the surface coating for the silica particles. The deposition of CTACe-modified silica nanoparticles endows a metallic material with a high resistance to abrasion and corrosion. We envision that such emulsions, consisting of eco-friendly, biocompatible, and low-cost materials, could find extensive applications in sustainable chemistry and engineering.
Chen et al. (Mon,) studied this question.