Light-Active, Reversibly Shape-Shifting Block Copolymer Particles using Photo-Switchable Au Nanoparticle Surfactants

Abstract

Dynamic particles with switchable shapes in response to light have attracted great interest to develop programmable smart materials with superior spatial and temporal resolution. Herein, a facile strategy for light-responsive, shape-changing block copolymer (BCP) particles is developed. Key to this strategy is the design of azobenzene-grafted Au nanoparticles (Au@ Azo NPs) as photoswitchable surfactants through photoisomerization of Azo ligands. Under visible light, onion-like polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP particles with PS outer layer form due to the nonpolar nature of trans-Azo ligands, whereas the isomerization to polar cis-Azo surfactants with UV irradiation transforms these spheres into ellipsoids with both PS and P2VP exposed on their surfaces. This light-driven shape change is robust and reversible over multiple irradiation cycles. The reversible shape evolution between spherical and ellipsoidal BCP particles induced by photoactive Au@Azo NP surfactants is elucidated using a cryogenic electron microscope. Furthermore, light-dependent fluorescence and shape of the BCP particles are successfully demonstrated, enabling the visualization of particle shape into an optical signal.