Correlation between temperature–pressure dependence of the α-relaxation and configurational entropy for a glass-forming polymer

Abstract

In this work we investigated the temperature–pressure dependence of the relaxation time of the α-relaxation process of poly(vinyl acetate) (PVAc). By means of dielectric spectroscopy technique the relaxation time of the α-process was measured over a broad range of frequencies (10 −1–10 7 Hz), pressures (0–300 MPa) and temperatures (320–460 K). Two different approaches were used to analyze the temperature–pressure dependence of the relaxation time: the phenomenological Vogel–Fulcher–Tammann (VFT) equation and the pressure extended Adam–Gibbs (PEAG) equation recently proposed. We compared both results and discussed the validity of the VFT approach for PVAc at different pressures. We found an excellent agreement between the experimental data and the PEAG equation, which only needs four parameters to describe the complete temperature–pressure dependence of the relaxation time of the α-process. Finally, we showed that the thermal and volumetric contributions to the configurational entropy are clearly separated for PVAc.