Isoconversional kinetics by fast scanning calorimetry

Abstract

Over the past decade the isoconversional methodology has become a major tool for exploring the kinetics of chemical and physical process. This chapter demonstrates that the application area of the isoconversional kinetics expands dramatically when the methodology is combined with fast scanning calorimetry (FSC). FSC allows one to perform reliable kinetic studies of the processes that occur too fast to be measured by regular DSC, to extend significantly the temperature range of the studies, and to accomplish various short-lived metastable states. Examples considered in this chapter include the notoriously fast crystallization polytetrafluoroethylene (PTFE) melt and atypical gelation of a gelatin solution that occurs on heating. Isoconversional analysis of FSC data on PTFE crystallization has revealed a change in the process mechanism that has never been detected by other techniques. It has also been discovered that at the smallest and largest supercooling the process follows the same crystallization mechanism. For a gelatin solution, it is possible to cool it fast enough to avoid gelation and initiate the process on slower heating of the supercooled solution. Isoconversional analysis applied to FSC data on the atypical gelation has revealed a positive temperature coefficient (effective activation energy), whereas the regular gelation on cooling demonstrates a negative coefficient.