Light-Responsive, Reversibly Shape-Changing 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 smart materials with superior spatial and temporal resolution. Herein, a facile strategy for light-responsive, shape-changing block copolymer (BCP) particles is developed. We designed the azobenzene-grafted Au (Au@Azo) nanoparticles as photo-switchable surfactants through photoisomerization of Azo ligands. Under visible light, onion-like polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP particles with PS outer layers form due to the non-polar nature of trans-Azo ligands, whereas the isomerization to polar cis-Azo with UV irradiation transforms to ellipsoids with both PS and P2VP exposed on their surfaces. This light-driven shape change is fully reversible over multiple irradiation cycles. The reversible shape evolution between spherical and ellipsoidal BCP particles induced by photo-active Au@Azo surfactants is elucidated using a cryogenic electron microscope. Furthermore, light-dependent fluorescence and shape of the BCP particle is successfully demonstrated, enabling the visualization of particle shape into an optical signal.