Relaxation processes and intermolecular interactions in PVME hydrogels in sub-zero temperatures: Glass transition and pre-melting of ice
Pastorczak, Marcin × Wubbenhorst, Michael Dominguez-Espinosa, Gustavo Okrasa, Lidia Pyda, Marek Kozanecki, Marcin Kadlubowski, Slawomir Ulanski, Piotr Rosiak, Janusz M Ulanski, Jacek #
Polymer vol:53 issue:1 pages:161-168
The phase transition observed by various methods in poly(vinyl methyl ether)/water systems at around 18 degrees C has been assigned by some investigators to the pre-melting of water and by others to a glass transition of the polymer. In this study, broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry were used to identify this transition in radiationally crosslinked poly(vinyl methyl ether) hydrogels, as well as to analyse sub-zero relaxation processes in such a three-phase (polymer/ice/liquid water) system. The process at 18 degrees C was related to the pre-melting of water induced by the segmental motions of the polymer; however, it was seen to be one transition due to the cooperative motions of both compounds. The atypical (two regimes) temperature dependence of the segmental motion process was observed and was related to confinement of the polymer chains between ice clusters below approximately 24 degrees C; furthermore, the main dielectric process of hexagonal ice was identified and a Maxwell-Wagner effect was observed. (C) 2011 Elsevier Ltd. All rights reserved.