Shear-induced deformation of polystyrene coils in dilute solution from small angle neutron scattering 2. Variation of shear gradient, molecular mass and solvent viscosity

Abstract

The technique of small angle neutron scattering (SANS) has been used to study the conformation of polystyrene chains in dilute solution under a constant shear gradient. The experiments reveal a distinct anisotropy of the molecular dimensions with regard to the directions parallel and perpendicular to the flow direction on the 2D-multidetector. The deformation ratio of the single polymer chain (〈R ²〉/〈R ²_iso 〉)−1 as a function of the reduced shear gradientβ=([η] · η · M _w G)/RT shows a transition from the idealβ ²-behaviour for dynamic infinitely flexible coils found at small gradients, to a behaviour with smaller increase at largerβ. These results are qualitatively consistent with the theory of Cerf for a polymer with finite internal viscosity in a shear gradient. At lowβ(β<1), a better agreement with the model of a free-draining coil (Rouse behaviour) than with the Zimm model is observed.