Slow and fast dynamics in glycerol-water mixtures

We discuss the relaxation dynamics of glycerol-water mixtures as studied by broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). BDS studies were performed in a frequency range of 1 Hz to 250 MHz at temperatures ranging from 173 to 323 K and DSC measurements were made between 138 and 313 K. The experimental results obtained for the glycerol-rich mixtures in terms of dielectric loss 'master plots' suggest that the main dielectric relaxation process, as well as the high frequency 'excess wing' and dc-conductivity, follow the same temperature dependence. This result indicates that all of these processes are based on the same physical origin. A new phenomenological relationship for the complex dielectric permittivity is proposed. The structural and dynamic properties of glycerol-water mixtures are discussed. The experimental data for water-rich mixtures show the existence of a critical concentration of 40 mol% of glycerol that relates to the numbers of hydrogen bonds of glycerol and of water molecules. Below this concentration, water cooperative domains appear, coexisting with the glycerol cooperative domains. Below 20 mol% of glycerol, ice nanocrystals appeared that led to three relaxation processes; result from ice, mesoscopic glycerol-water domains, and water on the interface between former two.