ABSTRACT
This chapter describes the application of through-vial impedance spectroscopy (TVIS) for the characterization of the ice formation process in terms of the onset time and temperature of nucleation and ice growth, and the solidification end point. These observations are based on the transition between two dielectric mechanisms as the material changes from liquid to solid. The dielectric mechanism in the liquid state is a Maxwell-Wagner (MW) process, in which the glass wall of the vial is charged through the solution resistance; whereas the dielectric mechanism in the solid state is due to the relaxation of ice. By selecting a frequency at the high end of the measured impedance spectrum (>100 kHz) it is possible to accurately determine the solidification end point while the temperature of the material continues to change (as it releases the excess thermal energy from the ice formation process). This is because the permittivity of ice at high frequencies (which is in fact the instantaneous permittivity) has almost no temperature dependence, whereas the Maxwell-Wagner polarization of the glass wall is strongly temperature dependent.
