Thermal transitions and dynamics in nanocomposite hydrogels
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Hydrogels based on nanocomposites of statistical poly(hydroxyethyl acrylate-co-ethyl acrylate) and silica, prepared by simultaneous copolymerization and generation of silica nanoparticles by sol–gel process at various copolymer compositions and silica contents, characterized by a fine dispersion of filler, were investigated with respect to glass transition and polymer dynamics by dielectric techniques. These include thermally stimulated depolarization currents and dielectric relaxation spectroscopy, covering together broad ranges of frequency and temperature. In addition, equilibrium water sorption isotherms were recorded at room temperature (25 °C). Special attention was paid to the investigation of effects of silica on glass transition, polymer dynamics (secondary γ and β sw relaxations and segmental α relaxation), and electrical conductivity in the dry systems (xerogels) and in the hydrogels at various levels of relative humidity/water content. An overall reduction of molecular mobility is observed in the nanocomposite xerogels, in particular at high silica contents. Analysis of the results and comparison with previous work on similar systems enable to discuss this reduction of molecular mobility in terms of constraints to polymeric motion imposed by interfacial polymer–filler interactions and by the formation of a continuous silica network interpenetrated with the polymer network at filler contents higher than about 15 wt%.
KeywordsPoly(hydroxyethyl acrylate-co-ethyl acrylate)/silica hydrogels Glass transition Segmental dynamics Electrical conductivity
The research leading to these results has received support from the program for basic research PEBE 2010 funded by the National Technical University of Athens.
- 1.Peppas NA, editor. Hydrogels in medicine and pharmacy, vol. I. Boca Raton, FL: CRC Press; 1986.Google Scholar
- 2.Stoy V, Kliment C. Hydrogels: speciality plastics for biomedical and pharmaceutical applications. Basel: Technomic; 1996.Google Scholar
- 7.Gomez Ribelles JL, Monleon Pradas M, Gallego Ferrer G, Peidro Torres N, Perez Gimenez V, Pissis P, Kyritsis A. Poly(methyl acrylate)/poly(hydroxyethyl acrylate) sequential interpenetrating polymer networks. Miscibility and wáter sorption behavior. J Polym Sci Part B Polym Phys. 1999;37:1587–99.CrossRefGoogle Scholar
- 17.Kremer F, Schoenhals A, editors. Broadband dielectric spectroscopy. Berlin: Springer; 2002.Google Scholar
- 18.Donth E. The glass transition: relaxation dynamics in liquids and disordered materials. Berlin: Springer; 2001.Google Scholar
- 19.Havriliak S Jr, Havriliak SJ. Dielectric and mechanical relaxation in materials. Munich: Hanser; 1997.Google Scholar
- 27.Klonos P, Panagopoulou A, Bokobza L, Kyritsis A, Peoglos V, Pissis P. Comparative studies on effects of silica and titania nanoparticles on crystallization and complex segmental dynamics in poly(dimethylsiloxane). Polymer. 2010;51:5490–9.Google Scholar
- 28.Napolitano S, Wuebbenhorst M. The lifetime of the deviations from bulk behavior in polymers confined at the nanoscale. Nat Commun. 2011;2:260. doi: 10.1038/incomms1259.