Low frequency dielectric investigations into the relaxation behavior of frozen polyvinylpyrrolidone-water systems

The low frequency dielectric response of aqueous solutions containing 0, 1, 5, and 10% w/v polyvinylpyrrolidone (PVP) was studied to characterize the low temperature relaxation behavior of these systems. Complementary modulat ed temperature differential scanning calorimetry (MTDSC) studies allowed me asurement of the glass transition temperature for these materials, correspo nding to the behavior of the nonfrozen phase. Dielectric investigations in the frequency range of 10(6) to 10(-2) Hz were performed on the systems in the liquid state, with a Maxwell-Wagner response noted for both the PVP sol utions and water. The solid-phase responses were studied over a range of te mperatures down to -70 degreesC, with a relaxation peak observed for the PV P systems in the kilohertz region. The spectra were modeled using the Havri liak-Negami equation and the corresponding relaxation times were calculated , with a satisfactory fit to the Arrhenius equation noted. The calculated a ctivation energies were similar to literature values for the dielectric rel axation of water. It is suggested that the dielectric response is primarily a reflection of the relaxation behavior of the water molecules in the nonf rozen fraction, thereby indicating that the dielectric technique may yield insights into specific components of frozen aqueous systems. (C) 2001 Wiley -Liss, Inc.