Dielectric study of the glass transition: correlation with calorimetric data

TL;DR

This study uses thermally stimulated depolarization currents and calorimetry to analyze the glass transition in poly(ethylene terephthalate), demonstrating the decomposition of relaxation processes and modeling kinetics to correlate with calorimetric data.

Contribution

It introduces a method to decompose the glass transition into elementary components using TSDC and models the kinetics to match calorimetric results in polar polymers.

Findings

TSDC can decompose the glass transition into elementary modes.

Kinetic parameters vary with polarization temperature, indicating different activation energies.

Modeling TSDC kinetics can qualitatively reproduce DSC results.

Abstract

The glass transition in amorphous poly(ethylene terephthalate) is studied by thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The ability of TSDC to decompose a distributed relaxation, as the glass transition, into its elementary components is demonstrated. Two polarization techniques, windows polarization (WP) and non-isothermal windows polarization (NIW), are employed to assess the influence of thermal history in the results. The Tool-Narayanaswami-Moynihan (TNM) model has been used to fit the TSDC spectra. The most important contributions to the relaxation comes from modes with non-linearity (x) around 0.7. Activation energies yield by this model are located around 1eV for polarization temperature (Tp) below 50C and they raise up to values higher than 8eV as Tp increases (up to 80C). There are few differences between results obtained with WP and NIW but, nonetheless, these are discussed. The obtained kinetic parameters are tested against DSC results in several conditions. Calculated DSC curves at several cooling and heating rates can reproduce qualitatively experimental DSC results. These results also demonstrate that modelization of the non-equilibrium kinetics involved in TSDC spectroscopy is a useful experimental tool for glass transition studies in polar polymers.