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 $\mathrm{[\eta ]}$ 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 ${\mathrm{[\eta ]}}_0$ . The effect of excluded volume on the behavior of ${\mathrm{[\eta ]\hspace{0.17em}/\hspace{0.17em}[\eta ]}}_0‐\mathrm{vs}\mathrm{‐\beta }$ (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 $\text{p\hspace{0.17em}=\hspace{0.17em}2}$ , and those in good solvents resemble that of $\text{p\hspace{0.17em}=\hspace{0.17em}3}$ 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 $\beta$ , the ${\mathrm{[\eta ]\hspace{0.17em}/\hspace{0.17em}[\eta ]}}_0‐\mathrm{vs}\mathrm{‐\beta }$ curve decreases continuously with increasing $\beta$ , 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.