Dielectric Study of Concentration Fluctuation in Solutions of Polystyrene

The effect of the solvent quality on local concentration fluctuation was studied for concentrated solutions of polystyrene (PS) in toluene (Tol), ethylbenzene (EtBz), n -propylbenzene (PrBz), and n -butylbenzene (BuBz) by using dielectric spectroscopy. The exponents of the Mark−Houwink−Sakurada equation of those solutions indicate that the solvent quality deteriorates in the order of Tol, EtBz, PrBz, and BuBz. Three dielectric relaxations designated as α, β, and γ are observed in the temperature dependence curves of the dielectric loss in the order of decreasing temperature. According to our previous study on PS/Tol solution, the α, β, and γ relaxations have been assigned to local segmental motions of PS, rotation of the solvent molecules, and the secondary relaxation in the glassy state, respectively. The half-width of the dielectric loss curve Λ α for the α relaxation of PS/Tol solutions is independent of temperature, but the values of Λ α for solutions in EtBz, PrBz, and BuBz increase with decreasing temperature in proportion to ( T − T 0 ) -2 as observed previously for solutions of poly(vinyl acetate) in toluene where T 0 is the critical temperature of the Vogel−Fulcher equation. The slope of the Λ α vs ( T − T 0 ) -2 plots which is a measure of the amplitude of concentration fluctuation increases with the deterioration of the solvent quality, and hence it increases with increasing interaction parameters between the PS chains and the solvent molecules.