Photoisomerization Induced Solid–Liquid Transition Polymers Enabling Light Regulated Intelligent Lubrication Behavior

Intelligent materials with adaptable friction in response to external stimuli meet the requirements for lubrication under special conditions that are in high demand in aerospace and hi-tech instruments. Herein, we developed a light-regulated intelligent material derived from an azo-containing polymer, which can reversibly adjust the coefficient of friction. The azo-based intelligent lubricating material was synthesized by the copolymerization of 1-(4-butylphenyl)-2-(4-(hexo-5-ene-1-oxy) phenyl) azoene (BHazo) with polyethylene glycol diacrylate (PEGDA), yielding a slightly cross-linked polymer with an azobenzene side chain mixed with BHazo. The cis-to-trans isomerization of azobenzene under ultraviolet–visible (UV–vis) stimulation resulted in entanglement and internal friction change of the polymer chains, followed by varying viscosity, crystallinity, and transition temperature. This work is an essential step toward realizing light-regulated intelligent lubrication for a variety of substrates.