Reversible Photocontrolled Swelling-Shrinking Behavior of Micron Vesicles Self-Assembled from Azopyridine-Containing Diblock Copolymer

Poly(N-isopropylacrylamide)-block-poly{6-[4-(4-pyridyazo)phenoxy] hexylmethacrylate} (PNIPAM-b-PAzPy) was synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization. In a water/tetrahydrofuran (H2O/THF) mixture, amphiphilic PNIPAM-b-PAzPy self-assembles into giant micro-vesicles. Upon alternate ultraviolet (UV) and visible light irradiation, obvious reversible swelling-shrinking of the vesicles was observed directly under an optical microscope. The maximum percentage increase in volume, caused by the UV light, reached 17%. Moreover, the swelling could be adjusted using the UV light power density. The derivation of this effect is due to photoinduced reversible isomerization of azopyridine units in the vesicles.