Dynamics of Water in Partially Crystallized Polymer/Water Mixtures Studied by Dielectric Spectroscopy
详细信息 查看全文
- 作者：Naoki Shinyashiki ; Mayumi Shimomura ; Takahiko Ushiyama ; Takashi Miyagawa ; Shin Yagihara
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：August 30, 2007
- 年：2007
- 卷：111
- 期：34
- 页码：10079 - 10087
- 全文大小：255K
- 年卷期：v.111,no.34(August 30, 2007)
- ISSN：1520-5207
文摘
The dielectric relaxation process of water was investigated for polymer/water mixtures containing poly(vinylmethyl ether), poly(ethyleneimine), poly(vinyl alcohol), and poly(vinylpyrrolidone) with a polymer concentration of up to 40 wt % at frequencies between 10 MHz and 10 GHz in subzero temperatures down to -55 
C.These polymer/water mixtures have a crystallization temperature TC of water at -10 to -2 C. Below TC,part of the water crystallized and another part of the water, uncrystallized water (UCW), remained in a liquidstate with the polymer in an uncrystallized phase. The dielectric relaxation process of UCW was observed,and reliable dielectric relaxation parameters of UCW were obtained at temperatures of -26 to -2 C. At TC,the relaxation strength, relaxation time, and relaxation time distribution change abruptly, and their subsequentchanges with decreasing temperature are larger than those above TC. The relaxation strength of UCW decreases,and the relaxation time and dynamic heterogeneity (distribution of relaxation time) increase with decreasingtemperature. These large temperature dependences below TC can be explained by the increase in polymerconcentration in the uncrystallized phase Cp,UCP with decreasing temperature. Cp,UCP is independent of theinitial polymer concentration. In contrast to the relaxation times above TC, which vary with the chemicalstructure of the polymer and its concentration, the relaxation times of UCW are independent of both of them.This indicates that the factor determining whether the water forms ice crystals or stays as UCW is the mobilityof the water molecules.
C.These polymer/water mixtures have a crystallization temperature TC of water at -10 to -2 C. Below TC,part of the water crystallized and another part of the water, uncrystallized water (UCW), remained in a liquidstate with the polymer in an uncrystallized phase. The dielectric relaxation process of UCW was observed,and reliable dielectric relaxation parameters of UCW were obtained at temperatures of -26 to -2 C. At TC,the relaxation strength, relaxation time, and relaxation time distribution change abruptly, and their subsequentchanges with decreasing temperature are larger than those above TC. The relaxation strength of UCW decreases,and the relaxation time and dynamic heterogeneity (distribution of relaxation time) increase with decreasingtemperature. These large temperature dependences below TC can be explained by the increase in polymerconcentration in the uncrystallized phase Cp,UCP with decreasing temperature. Cp,UCP is independent of theinitial polymer concentration. In contrast to the relaxation times above TC, which vary with the chemicalstructure of the polymer and its concentration, the relaxation times of UCW are independent of both of them.This indicates that the factor determining whether the water forms ice crystals or stays as UCW is the mobilityof the water molecules.