We utilize dielectric relaxation process for the quantitative characterization of antiplasticization of trehalose by glycerol. The high frequency Johari-Goldstein relaxation time was obtained by analyzing the complex permittivity data in terms of the distribution function of relaxation times and a regularization technique. We analyzed the dielectric spectrum without prior assumptions about a spectral function and the number of the relaxation processes. We observe that increasing the glycerol concentration at fixed temperature increases the high frequency relaxation time (τ) extending antiplasticization until a temperature dependent critical plasticization concentration xwp is reached. At a fixed concentration, we find a temperature at which antiplasticization first occurs upon cooling and we designate this as the antiplasticization temperature , Tant. The anti-plasticizing effect becomes more pronounced at low temperatures, and the glycerol concentration at which the maximum in t occurs itself depends on temperature. The relaxation time peaks at about 10-6 s for T = 297 K, while for T = 250 K the maximum is on the order of 10-3 s. At 250 K the peak is located near a 0.35 mass fraction of glycerol. Above this concentration range, t decreases and the antiplasticizing effect apparently no longer exists. The ratio of τ values for the mixture and pure trehalose, antiplasticization factor, is found to provide a useful measure of the extent of antiplasticization. The antiplasticization factor that we describe is applicable to characterize preservation of proteins in sugar formulations and molecular dynamics of synthetic polymers, complex liquids and other glassy materials.
Citation: Journal of Non-Crystalline Solids
Pub Type: Journals
dielectric relaxation, regularization technique, trehalose, antiplasticiztion, biopreservation