Calorimetric Study of Dynamical Heterogeneity in Toluene Solutions of Polystyrene

摘要

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 DELTAC_P around T_g has been determined by subtracting the heat capacity due to the lattice vibrations and intramolecular vibrations.We have further resolved DELTAC_p,into two sigmoidal curves using an empirical function.The T_gs corresponding to the two sigmoids are denoted as T_(g1) and T_(g2) (T_(g1) > T_(g2)).Two dielectric loss peaks termed a and beta are assigned to segmental motions of PS and rotation of the toluene molecules,respectively.The dielectric glass transition temperatures T_(alpha) and T_(beta) are defined as the temperatures at which the dielectric relaxation times for the a and beta processes become 10~3 s,respectively.T_(alpha) and T_(beta) agree well with the calorimetric T_(g1) and T_(g2),respectively.