photorheological fluids, viscosity, azobenzene polymer, lubrication


Fluid viscosity is ubiquitous property and is of practical importance in intelligent fluids, industrial lubrication, and pipeline fluid transportation. Recently, there has been a surging interest in viscosity regulation. Here, we have developed a group of photorheological fluids by utilizing azobenzene polymers with a light-induced microstructure transformation. In this work, a photosensitive polymer with 4,4'-bis-hydroxyazobenzene as the main chain was designed and synthesized as a pivotal functional material. The sufficiently large structural difference under ultraviolet and near-infrared light makes it possible to regulate the viscosity of a polyethylene glycol solution. The viscosity of the photosensitive rheological fluids under ultraviolet light radiation is found to be up to 45.1% higher than that under near-infrared light radiation. To explore this intelligent lubricating technology, the friction regulation of ceramic sliding bearings was investigated utilizing photosensitive rheological fluids. Reversible friction regulation with a ratio of up to 3.77 has been achieved by the alternative irradiation of near-infrared and ultraviolet light, which can be attributed to the differences in mechanical properties and molecular structures under ultraviolet and near-infrared light according to both simulations and experiments. Such photorheological fluids will have promising applications in controllable lubrication, intelligent rheological fluids, and photosensitive dampers.

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