Reversible Shape- and Color- Changing Block Copolymer Particles Driven by Photoisomerizable Surfactant

Abstract

Polymer particles that switch their shape and color in response to light are of great interest to develop programmable smart materials. Herein, we report block copolymer (BCP) particles with reversible shapes and colors, activated by irradiation with UV and visible lights. This shape transformation of the BCP particles is achieved by a spiropyran-based surfactant (SP-DTAB) that changes its amphiphilicity upon photoisomerization. Under UV light (365 nm) irradiation, the hydrophilic ring-opened merocyanine form of SP-DTAB surfactant affords the formation of spherical, onion-like BCP particles. In contrast, when exposed to visible light, surfactants with the ring-closed form yields prolate or oblate BCP ellipsoids with axially stacked nanostructures. Importantly, the change in BCP particle morphology between spheres and ellipsoids is reversible over multiple UV and visible light irradiation cycles. In addition, the shape- and color-switchable BCP particles are integrated to form a composite hydrogel, demonstrating their potential as high-resolution displays with reversible patterning capabilities.