Calorimetric Study of Dynamical Heterogeneity in Toluene Solutions of Polystyrene

Abstract

In an effort to clarify the effect of dynamical heterogeneity on the glass transition in binary systems, we measured the heat capacity Cp on concentrated toluene solutions of polystyrene (PS) using an adiabatic calorimeter. We also carried out dielectric measurements on the same system. Results indicate that the Cp vs temperature T curve of the solvent toluene/xylene(90/10) exhibits a sharp stepwise increase of Cp at the glass transition temperature Tg (= 115 K). In contrast, the Cp curves of PS/toluene solutions exhibit a double-sigmoidal shape. The configurational heat capacity ΔCp around Tg has been determined by subtracting the heat capacity due to the lattice vibrations and intramolecular vibrations. We have further resolved ΔCp into two sigmoidal curves using an empirical function. The Tgs corresponding to the two sigmoids are denoted as Tg1 and Tg2 (Tg1 > Tg2). Two dielectric loss peaks termed α and β are assigned to segmental motions of PS and rotation of the toluene molecules, respectively. The dielectric glass transition temperatures Tα and Tβ are defined as the temperatures at which the dielectric relaxation times for the α and β processes become 103 s, respectively. Tα and Tβ agree well with the calorimetric Tg1 and Tg2, respectively.