Shape-switchable particles in response to light are very attractive to develop programmable smart materials with superior spatial and temporal resolution. In this work, a facile but robust strategy for light-responsive, shape-switchable block copolymer (BCP) particles is presented. The key strategy is the introduction of azobenzene-grafted Au nanoparticles (Au@Azo NPs) as photo-responsive surfactants by exploiting the photoisomerization of Azo ligands. Under visible light, spherical onion-like polystyrene-<i>block</i>-poly(2-vinylpyridine) (PS-<i>b</i>-P2VP) BCP particles are formed due to the presence of the non-polar trans-Azo ligands, while irradiation with UV light induces the isomerization of the Azo surfactants into cis-isomer and thereby transforms these spheres into ellipsoids with PS and P2VP domains exposed on the particle surfaces. This photo-induced shape switching is fully reversible over multiple cycles. The reversible shape evolution induced by Au@Azo NP surfactants is further elucidated using a cryogenic electron microscope. Lastly, light-dependent fluorescence driven by shape-switching of the BCP particles is demonstrated, allowing the visualization of the changes in particle shape into an optical signal.

Light-responsive, shape-switchable block copolymer particles using azobenzene-grated Au nanoparticle surfactants

ACS Spring 2022

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