Photoresponsive submicron-sized hollow spheres obtained from amphiphilic azobenzene-containing random copolymer

This article reports the formation, morphology control, and photoresponsive properties of submicron-sized hollow spheres of an amphiphilic azobenzene-containing random copolymer (PEAPE). The hollow spheres were obtained by diluting the polymer disperse at 50 vol% water content with THF-water (v:v = 1:1) and slowly removing THF by evaporation. The size and shell thickness of the hollow spheres were determined by the polymer initial concentration in THF, water addition rate, and diluent volume. The ratio of the average shell thickness to the hollow sphere size was mainly affected by the diluent volume. By adjusting these factors, the size and shell thickness of the hollow spheres could be well controlled. The photoisomerization study indicated that hollow spheres possessed a compactly packed shell with density similar to that of their counterparts with solid interiors. Upon UV light irradiation, the hollow spheres in dispersions showed different photoresponsive properties depending on their size and shell thickness. For the “vesicle-like” spheres with a thin shell, photoinduced disaggregation was observed when irradiated with the 365 nm UV light.