Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Abstract

Confinement of the glass-forming regions in the nanometer range influences the (x-relaxation which is associated with the glass transition. These effects were investigated for semicrystalline poly(ethylene terephthalate) by dielectric spectroscopy and differential scanning calorimetry. The. results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of glass transition. Both experiments showed a dependence of the glass transition on the mean thickness of the amorphous layers. For the dielectric relaxation, the loss maximum was found to shift to higher temperatures with decreasing thickness of the amorphous layers, but no differences 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 shape did correlate with the layer thickness of the mobile amorphous fraction. From the structure parameters, a characteristic length of approximately (2.5+1) nm was estimated for the unconfined glass relaxation (transition).

Effect of gamma irradiation on the dielectric relaxation of uniaxially oriented low density polyethylene

“…Moreover, investigation of the relaxation intensity in most semicrystalline polymers shows that not all the non-crystalline fraction participates in the glass transition. 11 Therefore, a rigid amorphous and mobile amorphous fraction has been postulated. The mobile amorphous fraction contributes to the glass transition.…”

Separation of components of different molecular mobility by calorimetry, dynamic mechanical and dielectric spectroscopy

“…(1) we can calculate the mobile amorphous fraction related to the local movements from the relaxation strength of the ~-relaxation. We compare the results with that of the dynamic glass transition (main-, a-relaxation) [6].…”

Study of reorientational dynamics during real-time crystallization of absorbable poly(p-dioxanone) by dielectric relaxation spectroscopy

“…In an earlier study on isothermal crystallization of poly(aryl ether ketone ketone), Ezquerra et al 19 showed a very strong correlation between the strength of the dielectric relaxation, ⌬⑀ ϭ ⑀ 0 Ј Ϫ ⑀ ϱ Ј (where ⑀ ϱ Ј is the unrelaxed, highfrequency permittivity) and the crystallinity, as calculated from X-ray images. This and other studies 9,13,16,31,32 have shown that the extrapolation of crystallinity to ⌬⑀ ϭ 0 yields in some polymers a predicted crystallinity somewhat lower than 100%. However, we felt justified in using dielectric measurements to determine relative crystallization kinetics for our isothermally grown PDS films because this material typically crystallizes under good conditions to only about 40%.…”