title: Tuning self-assembly and photo-responsive behavior of azobenzene-containing triblock copolymers by combining homopolymers.
abstract: The self-assembly behavior of azobenzene-based triblock copolymers poly(ethylene oxide)-block-polystyrene-block-poly[6-(4-methoxy-4'-oxy-azobenzene) hexyl methacrylate] (PEO-b-PS-b-PMMAZO) and their mixtures with PS or PMMAZO homopolymers was studied by means of transmission electron microscopy, scanning electron microscopy, laser light scattering and UV-vis spectrophotometry. It was found that pure block copolymers self-assembled into spherical micelles with core-shell structures. The addition of PS or PMMAZO homopolymers can not only increase the aggregate size but also have a significant influence on the photo-isomerization behavior and photo-deformation behavior of the aggregate. The photo-isomerization study revealed that a complete  trans-cis or  cis-trans isomerization of azobenzene chromophores can be acquired when irradiated with UV or visible light for polymers both in organic solutions and in micelles. The photo-isomerization rate of azobenzene chromophores increases when PS homopolymers were incorporated into micelles, while with the addition of PMMAZO homopolymers, it decreases. The photo-induced elongation of the aggregates by irradiation of a linearly polarized laser was observed for all the samples, and the deformation degree increases with the weight fraction of azobenzene groups in the parent copolymers, as well as the PMMAZO content for the mixture micelles.
authors: Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai, People's Republic of China.
authors: Shaoliang
authors: S
authors: Lin
authors: Yingying
authors: Y
authors: Wang
authors: Chunhua
authors: C
authors: Cai
authors: Yaohui
authors: Y
authors: Xing
authors: Jiaping
authors: J
authors: Lin
authors: Tao
authors: T
authors: Chen
authors: Xiaohua
authors: X
authors: He