Molecular design of N-oxide zwitterions for supreme salinity tolerance and substrate adaptability in aqueous lubrication

Hydration lubrication is the core mechanism of water-based lubrication, enabling low friction through biomimetic interfacial hydration layers. Zwitterionic materials, with their outstanding hydration capabilities have recently emerged as key choices for constructing superlubricant interface materials. In the study, inspired by the natural osmolyte trimethylamine N -oxide (TMAO), we designed and synthesized a novel class of N -oxide zwitterionic lubricants featuring a direct N⁺-O⁻ bond. Unlike conventional zwitterions such as sulfobetaine and carboxybetaine, these materials possess a smaller bond dipole and induce stronger water polarization, resulting in a robust hydration layer even under high-salinity conditions. The resulting lubricants exhibit excellent salinity tolerance and substrate adaptability, maintaining a low coefficient of friction (COF) across various surfaces. Together with their inherent biocompatibility and universal lubricating performance, these properties underscore the strong potential of N⁺-O⁻ zwitterions for biomedical and advanced interfacial applications.