Glass transition and dynamics of poly(vinyl pyrrolidone)-water mixture

Abstract

Broadband dielectric measurements of poly(vinyl pyrrolidone) (PVP)-water mixture were performed in a frequency range of 10 mHz - 50 GHz and at temperatures between 118 K and 318 K. The relaxation processes caused by the reorientational motion of water molecules (h-process) and the local chain motion of PVP (m-process) were observed without crystallization of water. The relaxation time of the m-process, τm, obeys the Vogel-Fulcher law, and the glass transition temperature, Tg, of PVP in the mixture, at which τm being 100 s is 237 K. The relaxation time of the h-process, τh, obeys the Vogel-Fulcher law above Tg = 237 K, and it turns to obey the Arrhenius law below Tg. The relaxation strength of the m-process, Δεm, increases with decreasing temperature. The relaxation strength of the h-process, Δεh, increases with decreasing temperature above the crossover temperature, TC (TC = 272 K), and it turns to be almost constant below TC. The temperature dependences of τm and τh are the same as those of the α- and the ν-processes observed in various kinds of water mixtures. In contrast, the temperature dependence of Δεh is different from that observed in various kinds of water mixtures. The characteristic property of Δεh could be related to the highest Tg of neat PVP in those of the solutes of other water mixtures.