title: Photochemical control of network structure in gels and photo-induced changes in their viscoelastic properties.
abstract: Poly(amide acid) gels containing photosensitive azobenzene groups in the main chain have been synthesized and their viscoelastic properties before and after light irradiation have been investigated by dynamic viscoelasticity measurements. It was found that 405 nm light induced a local volume change and a two-fold increase in the storage modulus of the gels. We discuss the change in storage modulus upon light irradiation quite simply in terms of classical rubber elasticity theory, which cannot explain this large increase in storage modulus. The photo-induced increase in storage modulus may result from an increase in entanglement interactions of topological constraints fixed in the network structure, caused by photoisomerization of the azobenzene moieties. We suggest that topological constraints in the network structure of the gels were realized by light irradiation and calculate the resulting slip link ratio (index of the topological constraints) in the gel network.
authors.affiliation: Graduate School of Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-shi, Tokyo 184-8588, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Hosono
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Furukawa
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Masubuchi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Horie
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry / Q000528:radiation effects; D001391:Azo Compounds / Q000737:chemistry / Q000528:radiation effects; D001550:Benzamidines / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D004548:Elasticity; D005782:Gels / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D008956:Models, Chemical; D015394:Molecular Structure; D010777:Photochemistry / Q000379:methods; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D014783:Viscosity; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D001391:Azo Compounds; D001550:Benzamidines; D003432:Cross-Linking Reagents; D005782:Gels; D011108:Polymers; D000099166:Polyacrylamides; C074442:1,3-bis(4-amidinophenoxy)-2-(4-amidinophenoxymethyl)ethylpropane; C009850:azobenzene