pH and light-triggered shape transformation of block copolymer particles in emulsion droplets

Abstract

Dual-responsive shape-transformable block copolymer (BCP) particles have arisen great attentions because of their tunable physical and chemical characteristics triggered by external stimuli. Herein, we developed a simple yet effective strategy to realize pH and light dual-triggered shape-switchable BCP particles through the co-assembly of BCPs with photo-responsive additive 4-hydroxyazobenzene (Azo-OH) within the evaporation emulsion droplets. The formation of hydrogen bonding interactions between the Azo-OH and 4-vinylpyridine (4VP) unit increases the volume fraction of P4VP domain, in turn leading to a morphological transition of the particles from onions to pupas by tuning the Azo-OH content. Subsequent light-induced trans–cis transition of the Azo unit induces the enhancement of the hydrophilicity of the P4VP domains, giving rise to internal shape transitions of the BCP particles from pupas to onions with P4VP at the outmost-layer. Furtherly, since the hydrogen bonds between Azo-OH and 4VP group are sensitive to pH, the interfacial properties of the emulsion droplets and the assembled structures are tuned through adjusting the environment pH of the aqueous solution, causing the formation of various particle shape, including pupas, raspberries, and onions. This work offers a promising method to engineer the microstructures of polymeric assemblies, which may attract more attention on the applications of the stimuli-responsive particles.