(180ao) Devitrification of Polymer Glasses

An experimental program is being carried out in our lab to show whether polymer glasses display universal phenomena independent of any difference in the chemical structure.  Our experiments are designed to teach us how polymer glasses turn from brittle fracture to ductile yielding across a small temperature range and what is the origin of the “strain hardening” observed to occur during uniaxial extension of ductile glasses after the neck has consumed the entire specimen.  The experimental systems involve melt-stretched polymer glasses that are brittle at room temperature in its isotropic state such PS as well as glasses that are ductile at room temperature such as PC.  Our experiments reveal and study several types of yielding associated with the devitrification of the primary structure and shear yielding of the chain network as well as re-vitrification processes.  The experimental tools used in this study include Dynamic Mechanical Analysis (DMA), DSC and dielectric spectroscopy in addition to Instron tensile stretcher.