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Thermoresponsive surface-grafted gels: Controlling the bulk volume change properties by surface-localized polymer grafting with various densities

Langmuir, 33, 13828-13833 (2017).

Ko Matsukawa, Tsukuru Masuda, Youn Soo Kim, Aya M. Akimoto*, and Ryo Yoshida*



We prepared thermoresponsive bulk gels with poly(N-isopropylacrylamide) (PNIPAAm) grafted only in the surface region with various graft densities and investigated the effect of the graft density on the bulk volume change properties. The surface-grafted gels induced the formation of skin layers during the shrinking process in response to a temperature increase, and their permeability strongly depended on the graft density. The graft density also controlled the kinetics of the swelling behavior in response to a temperature decrease. These physical properties were discussed on the basis of Young’s modulus of the surface determined by an atomic force microscopy force curve measurement and the homogeneity of the surface polymer network observed by cryo-scanning electron microscopy. This makes it possible to arbitrarily control the characteristics of gels as open or semiclosed systems, which was uniquely determined by the designs of the surface gel networks.

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