Effect of Alkyl Spacer Length on Light-Responsive Block Copolymer Particles in Photo-Responsive Surfactants

Abstract

Here, we investigated the effect of the spacer length of the surfactant on the light-responsive block copolymer (BCP) particles, whose shape can be determined by wavelength-selective light irradiation. We synthesized the series of spiropyran (SP)-based surfactants by modulating the length of the alkyl spacer of the surfactant molecules: SP-C6, SP-C8, SP-C10, SP-C12, and SP-C14. When generating PS-b-P4VP particles, no light-responsive shape change was observed by using SP-C6. However, light-responsive shape transformation between sphere and ellipsoid was achieved when using the surfactant whose spacer length was more than 8. With PS-b-P2VP, only the SP-C14 could induce the light-responsive shape change of BCP particles. It was systematically analyzed with interfacial tension and concluded that the key of the light-responsive shape determination is 1) the light-induced amphiphilicity change of surfactant by SP head group and 2) its amphipathic shift through the spacer length control.