Semi-Convertible Hydrogel Enabled Photoresponsive Lubrication

A semi-convertible hydrogel with reversible photo responsive supra-molecular lubricating ability is demonstrated by integrating a responsive supra molecular system of alpha-cyclodextrins/polyethylene glycol (alpha-CD/PEG) and competitive guest 1-[p-(phenylazo) benzyl] pyridinium bromide (AzoPB) within a poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm) framework. The competitive host-guest interaction between alpha-CD/PEG supramolecular network and AzoPB after UV and visible-light irradiation enables the appearance and disappearance of the sol-state layer on the hydrogel surface while the PVA and PAAm consistently keeps the framework. This semi convertible process realizes the reversible photo responsive lubricating ability and variable toughness. We envision that this finding will offer a possible way for fabricating novel smart devices far beyond lubrication, leading to an emerging branch of interdisciplinary materials science that integrates supramolecular chemistry, hydrogel, and surface science.