Ice Crystals and Glassy Water in Frozen Polymer Gels

To understand the mechanism of ice crystallization during rewarming observed with a frozen crosslinked dextran gel of a certain density of crosslink, DSC, Raman scattering and X ray diffraction-DSC simultaneous measurements were conducted. It was found, as a result, that size of ice crystals as well as freezing behavior depend on the density of crosslink of the gels. By the study of two-dimensional X ray diffraction-DSC simultaneous measurements, formation of small ice crystals was indicated with the gel where ice crystallization during rewarming is observed. Presence of glassy water was also indicated in the frozen state of the gel by the measurement of Raman scattering. Then, it was clarified that ice crystallization in polymer gels is more or less obstructed by the polymer network, and by its change at the time of freezing. From these results together with the knowledge so far obtained, a conceivable mechanism of ice crystallization during rewarming was discussed.