DIELECTRIC-SPECTROSCOPY AND CALORIMETRY IN THE GLASS-TRANSITION REGION OF SEMICRYSTALLINE POLY(ETHYLENE-TEREPHTHALATE)

Confinement of the glass-forming regions in the nanometer range influe nces the alpha-relaxation which is associated with the glass transitio n. These effects were investigated for semicrystalline poly(ethylene t erephthalate) by dielectric spectroscopy and differential scanning cal orimetry. The results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of g lass transition. Both experiments showed a dependence of the glass tra nsition on the mean thickness of the amorphous layers. For the dielect ric relaxation, the loss maximum was found to shift to higher temperat ures with decreasing thickness of the amorphous layers, but no differe nces were observed in the curve shape for the differently crystallized samples. For the calorimetric measurements, in contrast, there was no correlation for the glass transition temperature, whereas the curve s hape did correlate with the layer thickness of the mobile amorphous fr action. From the structure parameters, a characteristic length of appr oximately (2.5+/-1) nm was estimated for the unconfined glass relaxati on (transition).