MODERATELY CONCENTRATED-SOLUTIONS OF POLYSTYRENE .5. STATIC AND DYNAMIC LIGHT-SCATTERING IN BIS(2-ETHYLHEXYL) PHTHALATE

Static and dynamic light scattering data are reported on dilute and mo derately concentrated solutions of a high molecular weight polystyrene (M(W) = 3.61 x 10(6)) in bis(2-ethylhexyl) phthalate under Flory Thet a conditions. The data cover a concentration range with 0.03 less than or equal to [eta]c less than or equal to 3.5, with several concentrat ions large enough that the product cM(W) exceeds the value necessary f or entanglement behavior. The results show that a certain intermolecul ar scattering function H(q,c) often approximated by unity should not b e neglected in the evaluation of the correlation length in the static scattering from moderately concentrated solutions of flexible chain po lymers. An approximate form for H(q,c) for moderately concentrated sol utions is consistent with a soft spherically symmetric repulsive poten tial among the chains. The dynamic scattering show two distinct groups of relaxation rates at ail concentrations, but the interpretation of the two modes changes as the concentration increases from low concentr ations ([eta]c < 1) to higher concentrations. At low concentrations th e slower mode corresponds to mutual diffusion, and the faster mode to intramolecular dynamics. For concentrations with [eta]c > 2.4 the slow mode is viscoelastic in origin, and the faster mode is diffusive. The behavior is compared with theoretical predictions in both regimes.