Date of Award
Solid state chemistry, Thermal analysis, Pre-melt, Thermal Analysis, Dielectrics, Polarization time, Activation Energy, Tan Delta (ratio of loss factor/ permittivity), Solid Chemicals, Purity (E 928), Active Pharmaceutical Ingredients, Polymers, Organic Compounds
I have observed unique variations in AC electrical conductivity of solids by dielectric analysis (DEA or DETA) when studied with respect to temperature and frequency. A wide range of solids were examined for this study e.g. organics, polymers, carbohydrates, API's (active pharmacy ingredients) and amino acids. Experimental results clearly show novel dielectric behavior of a linear increase in a log ionic conductivity vs. temperature in the pre-melt (20 to 30oC below the melt temperature) and melt transition regions. We have differentiated the solids which show the conductivity variations in pre-melt from those which do not e.g. pre-melt conductivity variations observed with polar polymers such as nylons and acetal vs. not observed in nonpolar polymers such as polyethylene, polypropylenes and long chain alkanes e.g. tetraconsane and pentacosane. Isothermal dielectric analysis was used to study the cause of this variation in solids which yielded a polarization time property. The effect of various experimental factors on the results such as the effect of heating rate, varying the frequency, and sample size on the dielectric variations in the pre-melt temperature range have been studied. 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 E928-08 "Standard Test Method for Purity by Differential Scanning Calorimetry (DSC)" was employed to verify the purity of the experimental chemicals used in this study e.g. Acetanilide, Acetophenitidine and Vanillin. Activation energies were calculated based on Arhennius behavior to better interpret the changes in the solid. 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. Morphological studies done by scanning electron microsco
Mantheni, Dhruthiman R., "Novel Solid State Properties of Drugs, Polymers and Various Chemicals by Thermal and Analytical Techniques" (2012). ETD Archive. 192.