Dynamics in concentrated polymer solutions studied using dynamic light scattering.

Concentrated solutions (volume fraction 0.1-0.9) of polystyrene (PS) in toluene and of polybutylacrylate (PBA) in dioxane have been examined using dynamic light scattering (DLS) as a function of angle and temperature. With PS there is a pronounced maximum in the cooperative diffusion coefficient (Dc) at about Φ=0.5 as the glassy state is approached. By contrast, with PBA, which has a very low Tg, there is a crossover to a stronger concentration dependence for Dc, which is attributed to an increase in solvent mobility. In the PS/toulene system at Φ=0.78 a transition is noted between the diffusion mode and the main relaxational mode. At 17°C q-independence is observed and at 50 °C q2-dependence. At Φ=0.89, both relaxations are observed simultaneously in the DLS time window, the slower process being a structural relaxation. [ABSTRACT FROM AUTHOR]