Macroscale superlubricity achieved between zwitterionic copolymer hydrogel and sapphire in water

• Published in: Materials & design 2020-03, Vol.188, p.108441, Article 108441
• Main Authors: Wang, Zhongnan, Li, Jinjin, Liu, Yuhong, Luo, Jianbin
• Format: Article
• Language: English
• Subjects: Copolymer hydrogels; Hydration lubrication; Sapphire; Superlubricity; Zwitterionic polymers
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2019.108441

Achievement of macroscale superlubricity from the hydration effect could provide a potential application for artificial articular cartilage. In this work, two zwitterionic polymers, 2-methacryloyloxyethyl phosphorylcholine (MPC) and sulfobetaine methacrylate (SBMA), were used to synthesize a P(MPC-co-SBMA) copolymer hydrogel through the additional polymerization of the alkane carbon-carbon double bond. The incorporation of MPC promoted the water-binding property of copolymer hydrogels as well as improved their anti-compression capability. A superlubricity state with a friction coefficient of approximately 0.002 was achieved when a P(MPC-co-SBMA) copolymer hydrogel hemisphere slid on a sapphire in water, which demonstrated its dependence on sliding velocity, load, and aqueous lubricants. The superlubricity mechanism was mainly attributed to the hydration effect from zwitterionic MPC and SBMA polymer chains, which led to the formation of a uniform hydration layer on the hydrogel surface and the strong adsorption of water molecules on the sapphire surface, which provided additional stabilized hydration layers. These findings might provide insight into the superlubricity mechanism of zwitterionic hydrogels based on the hydration effect, thereby broadening their extensive applications. [Display omitted] •A novel macro-scale superlubricity system was established between copolymer hydrogel and sapphire.•MPC provided an improvement in compressive capacity for the copolymer hydrogel's network.•MPC promoted the formation of hydration layer on the hydrogel surfaces and enhanced the lubrication properties of hydrogel.•This work provides an idea for the study of macro-scale superlubricity mechanism of zwitterionic hydrogels.