Dynamic features of glycerol-water mixtures

We performed broadband dielectric spectroscopy (BDS) measurements of glycerol-water mixture from 0 % to 100 mol% glycerol concentrations with 5 mol% interval in a frequency range from 1 Hz to 250 MHz at temperatures between 173 K and 323 K. Differential scanning calorimetry (DSC) measurements from 138 to 313 K were also provided. The experimental results obtained for the glycerol-rich mixtures in terms of dielectric loss "master plots" suggest that the main dielectric relaxation process, the high frequency "excess wing (EW)" and de-conductivity, all follow the same temperature dependence. This result indicates that all of these processes have the same origin. A new phenomenological relationship for complex dielectric permittivity is proposed in order to provide a comprehensive fitting of the experimental data covering conductivity, main process and EW. Experimental data in water-rich mixtures show the existence of a critical concentration of 40 mol% of glycerol that relates to the number of hydrogen bonds of glycerol and of water molecules. Below this concentration, water cooperative domains appeared, coexisting with glycerol cooperative domains. Furthermore in the water-rich region, ice particles appeared that led to three relaxation processes due to ice, the mesoscopic glycerol-water domain, and water on the interface between former two. The ice nanocrystals showed broad melting behavior (BMB) with increasing temperature that was explained by kinetic description of the water-exchange rates between water molecules in the mesoscopic domain, ice nanocrystals, and the interfacial water. The mole fractions of these water states were determined, and the minimum number of water molecules that can gain bulk ice properties was estimated.