UV-enhanced Ordering in Azobenzene-Containing Polystyrene-block-Poly(n-Butyl Methacrylate) Copolymer Blends

作者：Chen Wei; Wang Jia Yu; Wei Xinyu; Xu Ji; Balazs Anna C; Matyjaszewski Krzysztof; Russell Thomas P^*

来源：Macromolecules, 2011, 44(2): 278-285.

DOI：10.1021/ma102005s

Reversible photocontrol on the ordering of block copolymers through the disorder-to-order transition (DOT) is important to promote long-range laterally ordered nanostructures over a macroscopic scale by "photo-combing", similar to the classic zone refining used to produce highly pure, large single crystals. In this report, we have synthesized two deuterated polystyrene-b-poly(n-butyl -methacrylater2-(4-(phenylazo)benzoate)ethyl methacrylate) (PS-d(8)-b-P(nBMA-r-AzoEMA)) block copolymers containing photoisomerizable azobenzene functionalities. These two block copolymers and their binary mixtures exhibit an entropy-driven lower DOT (LDOT). Upon UV irradiation, the photoisomerization of azobenzene led to a gain in entropy, originating from conformational changes and density variations. Such an increase in entropic contributions significantly enhanced the ordering, thereby driving the phase-mixed-copolymer blends toward a fully ordered state, as evidenced by small-angle neutron scattering (SANS) and specular neutron reflectivity (NR). This process could also be reversed by exposure to visible light via photoinduced cis-trans isomerization of azobenzene.

• 出版日期2011-1-25