Evaluation of the relaxation time for the amorphous styrene oligomer PSA-500 obtained from various measurement methods near the glass-transition temperature

Abstract

In this paper, we study relaxation phenomena in the styrene oligomer PSA-500 around the glass-transition temperature (Tg) using adiabatic calorimetry, thermally modulated differential-scanning calorimetry (TMDSC), dynamic light-scattering (DLS) measurements, viscoelastic measurements, and dielectric-relaxation measurements. Except for the relaxation times determined from DLS and from adiabatic calorimetry below Tg, the relaxation times evaluated from each measurement show the same temperature dependence over a wide range of timescales (10−6 to 102s). The relaxation phenomena above Tg observed using adiabatic calorimetry, TMDSC, and dielectric-relaxation measurements are due to the α-process, which governs the viscosity and is directly related to the glass transition. The relaxation phenomena studied using DLS correspond to simple diffusion. Although the relaxation phenomena observed using adiabatic calorimetry below Tg are also due to the α-process, they exhibit a different temperature dependence from the other α-process observations, because the measurements were obtained under thermodynamically nonequilibrium conditions.