Nanoparticle assembly of a photo- and pH-responsive random azobenzene copolymer

Stimuli-responsive polymeric nanoparticles with a core of hydrophobic azobenzene-containing acrylate units and a shell of hydrophilic acrylic acid units were prepared from a novel photo- and pH-responsive amphiphilic random azobenzene copolymer. Upon UV light irradiation, the trans azobenzene changed to the cis form and thus the water contact angle and the absorption of water on the polymer film could be changed, while little effect was exerted on the morphology of the nanoparticles although the polarity of the core of nanoparticles increased. Adjusting pH of the nanoparticle solution could exert a strong effect on the morphology of the nanoparticles. The prime nanoparticles (pH 6) changed to nanoparticle aggregates at pH 3, and to swollen nanoparticles at pH 11. The controlled release of Nile Red from the nanoparticles under the stimuli was demonstrated.