Shape-Transforming Block Copolymer Particles Driven by Photoisomerizable Surfactants

Shape-transformable particles by light are useful for developing active, programmable smart materials. In this work, we report block copolymer (BCP) particles with reversible shape-changing property activated by wavelength-selective light irradiation. We design the spiropyran-based surfactants, which can be isomerized between ring-opening and ring-closing structure by UV or visible light irradiation, respectively. This photoisomerization of the spiropyran surfactant effectively tunes the wetting behavior of BCP chains. In the UV light irradiation, spherical BCP particles with hydrophilic outermost layer are generated. By contrast, surfactants of ring-closed form under visible light provide a neutral surrounding to the BCP particles, producing oblate or prolate ellipsoids. We also demonstrate the reversibility of these shape transformations of the BCP particles by sequential UV or visible light irradiation.