Effect of water content on dielectric relaxation of gelatin in a glassy state.

Abstract

The dielectric properties of gelatin in the glassy state were measured from 100 Hz to 1 MHz over a temperature range of -20 to 60 degrees C. Samples with different water contents were prepared by varying the drying time for desalted gelatin solution; they were confirmed to be in the glassy state from DSC measurements. The dielectric relaxation (the decrease in dielectric constant, epsilon', and the maximum of the dielectric loss, epsilon' ') was observed for each sample; the relaxation time tau was evaluated from the peak of epsilon' '. The activation energy E obtained from an Arrhenius plot of tau decreased with increasing water content. On the basis of the order of magnitude of E, the dielectric relaxation observed was considered to be beta-relaxation reflecting the local motion of molecules. E and tau seem to describe the enhancement effect of water on the mobility of gelatin molecules in the glassy state; tau and E are considered to be suitable parameters for the characterization of the plasticizing effect of water on a glassy material.