Calorimetric Study of Dynamical Heterogeneity in Toluene Solutions of Polystyrene

In an effort to clarify the effect of dynamical heterogeneity on the glass transition in binary systems, we measured the heat capacity C p 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 C p vs temperature T curve of the solvent toluene/xylene(90/10) exhibits a sharp stepwise increase of C p at the glass transition temperature T g (= 115 K). In contrast, the C p curves of PS/toluene solutions exhibit a double-sigmoidal shape. The configurational heat capacity Δ C p around T g has been determined by subtracting the heat capacity due to the lattice vibrations and intramolecular vibrations. We have further resolved Δ C p into two sigmoidal curves using an empirical function. The T g s corresponding to the two sigmoids are denoted as T g1 and T g2 ( T g1 > T g2 ). 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 T α and T β are defined as the temperatures at which the dielectric relaxation times for the α and β processes become 10 3 s, respectively. T α and T β agree well with the calorimetric T g1 and T g2, respectively.