DYNAMICS IN CONCENTRATED POLYMER-SOLUTIONS BY POLARIZED RAYLEIGH-BRILLOUIN SCATTERING AND DYNAMIC LIGHT-SCATTERING

Solutions of polystyrene in toluene in the concentration range 0.1-1.0 g/ml have been examined using polarized Rayleigh-Brillouin scattering and dynamic light scattering. The purpose was to extend measurements to the hitherto little studied interval between semidilute solutions and the bulk polymer. The Brillouin shift increases monotonically with polymer volume fraction (PHI-p) and a linewidth maximum is observed at about PHI-p = 0.6. Up to PHI-p = 0.56, a single cooperative diffusion mode is found, which passes through a broad maximum at PHI-p = 0.5. For the sample with PHI-p = 0.78, the nature of the main component depends sensitively on temperature. At 17-degrees-C it is purely relaxational (q independent), while at 40 and 50-degrees-C, it is diffusive. At intermediate temperatures, mixed behavior is noted where the dynamic processes overlap because the slower relaxational mode has a stronger temperature dependence. At PHI-p = 0.89, the correlation functions are highly nonexponential and strongly temperature dependent. The bimodal correlation function contains contributions from both concentration fluctuations due to cooperative diffusion and density fluctuations arising from segmental motions in the polymer.