Research Progress on Lubrication of Zwitterionic Polymers

Zwitterionic polymers are organic polymers containing the same amount of anions and cations in the molecular chain. Due to their strong hydrophilicity and anti-polyelectrolyte behavior, zwitterionic polymers have been widely studied in the field of lubrication. On the one hand, zwitterionic polymers can adsorb free water from the lubrication system on the surfaces of materials through electrostatic interaction to improve the lubrication performance. On the other hand, the surface hydration degree of zwitterionic polymers is affected by the type and concentration of salt ions in the lubrication system, which can change its lubrication behavior easily. In this paper, the forms of lubrication in the friction process were introduced firstly. Then the structure of zwitterionic polymers and the lubrication behavior and mechanism of typical zwitterionic polymers, such as sulfonate anionic zwitterionic polymers, phosphate anionic zwitterionic polymers and carboxylate anionic zwitterionic polymers, were summarized and analyzed. Finally, the existing problems and prospects of the research on the lubrication of zwitterionic polymers were put forward.