Effect of Photoisomerizable Surfactant on Light-Responsive Shape Transformation of Block Copolymer Particles

Photoactive shape-changing particles offer a promising platform for smart materials with tunable properties at high spatiotemporal resolutions. Herein, a series of spiropyran (SP)-based surfactants with different alkyl spacer lengths are developed to achieve photoactive, shape-changing PS-b-P4VP particles from the evaporative emulsion. The length of the alkyl chain spacer between the SP head group and ionic chain end is modulated from hexyl to ethyl decanoate to provide surfactants with tunable amphiphilicity. Under UV light, the hydrophilic merocyanine surfactants produce onion-like microspheres with a P4VP surface. Conversely, exposure of visible light yields striped ellipsoids with axially stacked PS and P4VP blocks. This shape transition is only observed for surfactants that contain spacers longer than or equal to octyl. The effects of photoswitchable surfactants on their interfacial properties and the corresponding morphological evolution of the particles are investigated to elucidate the shape transition mechanism. Finally, 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.