TOPEM?: Measurement of Phase Transitions of Metastable SystemsMelting and Crystallization of Polymers and Organic Solutions

摘要

The total heat flow measured by DSC can be separated in a sensible and in a latent heat flow.TOPEM? is the technique which allows to measure both directly and independently if adequate conditionsare met. The reversing and non-reversing heat flow measured by conventional temperature modulatedDSC cannot be assigned to the sensible and the latent heat flow.Metastable systems can exist in a state close to equilibrium or far away from it. It will beshown, that the latent heat flow of a system depends on the metastable state or on the actual deviationfrom equilibrium. For example the latent heat flow of a process in equilibrium is zero.The conditions required for analyzing melting processes using TOPEM? are discussed. If theseconditions are fulfilled, the reversing heat flow measures processes that occur under equilibrium conditionsand the non-reversing heat flow processes that involve supercooling or superheating. This distinctionallows melting processes to be classified and crystal structures of differing stability to bedifferentiated. The latent heat flow therefore is a measure of the stability of a thermodynamic system.This will be shown and discussed using the melting and crystallization process of polymers and metastablesolutions of organic materials.