Polymer brush-functionalized surfaces with unique reversible double-stimulus responsive wettability

This paper presents the first fabrication of smart films with unique reversible double-stimulus responsive wettability. In this method, the ABC-type triblock copolymers synthesized through the sequential living radical polymerizations of 2-(diisopropylamino)ethyl methacrylate (DPAEMA), 2-hydroxyethyl methacrylate (HEMA), and (4-(2-methylacryloyloxy) ethyloxy-4'-trifluoromethoxy) azobenzene (MAAZO) mediated by a reversible addition-fragmentation chain transfer (RAFT) process, were grafted onto the surfaces of SiO2 films through the reactions between the hydroxyl groups of the PHEMA middle segments and the acyl chloride groups of the SiO2 film surfaces to form specific V-shaped polymer brushes, leaving highly free PDPAEMA and PMAAZO chains. The as-obtained V-shaped polymer brush-functionalized film exhibited a peculiar reversible double-stimulus responsive wettability, which was triggered only by the joint action of pH and UV light irradiation rather than either single stimulus. This unique wettability should be attributed to the changes of the chemical state of functional groups and the distribution of surface polymer brushes under different stimuli.