Solid- and liquid-state studies of a wide range of chemicals by isothermal and scanning dielectric thermal analysis

Abstract

We have observed unique variations in AC electrical conductivity of solids when studied with respect to temperature, time, and frequency. A wide range of solids were examined for this study e.g., organics, polymers, carbohydrates, active pharmacy ingredients (APIs), and amino acids. The observed dielectric analysis conductivity for this great number of organic materials follows an Arrhenius plot of log polar ionic conductivity which is linearly related to reciprocal temperature and the correlation of coefficient is 0.992–0.999. These experimental observations support the polaron hopping conduction model. Experimental results clearly show novel dielectric behavior of a linear increase in a log ionic conductivity versus temperature in the pre-melt/solid-state transition regions. We have differentiated the solids which show the conductivity variations in pre-melt from those which do not. Isothermal dielectric analysis was used to study the cause of this variation in solids which yielded the measure of behavior, i.e., the polarization time property. We have also studied the effect of various experimental factors (e.g., moisture and purity) on the results. Correlating dielectric with calorimetric analyses gave us a better understanding of solid-state properties. Calorimetric analysis was used to assure that the observed variations in the solid-state properties are not due to moisture or impurities present in the sample. The ASTM E698 “purity method” was employed to verify the purity of the chemicals. Activation energies were calculated based on Arrhenius behavior to better interpret the solid-state properties. As the different chemicals were heat–cool cycled they were more amorphous, as evidenced by the decreasing activation energy for charge transfer with an increasing amorphous content.