Controlling interfacial lubrication: Modulating MXene-based hydrogel properties with near-infrared light

Stimuli-responsive polymers have steadily grown in significance over the past decades, with extensive research dedicated to the intelligent design of friction materials inspired by natural processes. In this study, we introduce a hydrogel system, CS-MXene@P(AAc-CaAc-co-HEMA-Br)@PSPMA (M-PAAc@PSPMA), that adeptly modulates its modulus across temperature variations, subsequently influencing the interface friction coefficient. The integration of CS-MXene as a photothermal agent facilitates interface temperature modulation under near-infrared (NIR) light irradiation. By manipulating the temperature, the modulus of the P(AAc-CaAc-co-HEMA-Br) hydrogel is effectively regulated. Moreover, the PSPMA polyelectrolyte brush further refines the lubricating attributes of the system. At ambient conditions, the hydrogel is characterized by a low modulus, heightened flexibility, diminished strength, and a friction coefficient of approximately 0.24. Contrastingly, under NIR irradiation, the hydrogel manifests increased modulus, hardness, and strength, with a friction coefficient plummeting to roughly 0.1. This innovative hydrogel system offers advanced friction control by modulating its modulus, setting a precedent for the future development of intelligent lubricant hydrogels, interface detection, and regulated transmission.