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

Stimulus-responsive polymers have steadily grown in significance over the past few 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 can be effectively regulated. Moreover, the poly(3-sulfopropyl methacrylate potassium) (PSPMA) polyelectrolyte brush further refines the lubricating attributes of the system. Under ambient conditions, the hydrogel is characterized by a low modulus, heightened flexibility, diminished strength, and a friction coefficient of approximately 0.24. In contrast, under NIR irradiation, the modulus, hardness, and strength of the hydrogel increased, and the friction coefficient decreased to approximately 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.