Shear-Rate Dependence of the Intrinsic Viscosity of Flexible Linear Macromolecules. II. Solvent Effect

Abstract

Measurements of the shear-rate dependence of the intrinsic viscosity [η] were made on polystyrenes in several solvents, each of which differs in solvent power and solvent viscosity. Low-shear capillary viscometers of the Maron–Belner type were used: shear stresses can be varied continuously from about 10 to a few tenths of a dyn/cm2, which is low enough to measure the zero-shear intrinsic viscosity [η]0. The effect of excluded volume on the behavior of [η] / [η]0-vs-β (the generalized shear-rate) curve was examined. The curves at and near the θ condition resemble that of Saito–Scheraga's prolate ellipsoid with axial ratio p = 2, and those in good solvents resemble that of p = 3 ellipsoid; the variation with solvent power is not so large as the theory of either Fixman or Chikahisa predicts. In the region of moderate to large β, the [η] / [η]0-vs-β curve decreases continuously with increasing β, as contrasted to the behavior of the ellipsoid, which levels off rather rapidly. The non-Newtonian behavior is practically unaffected by solvent viscosity. In addition, the effect of polydipersity was discussed briefly.