LIGHT-SCATTERING-STUDIES ON THE DYNAMICS OF LONG-CHAIN MACROMOLECULESIN SHEAR-FLOW

By use of the Springer-Wolfle rheophotometer, the shear-induced orient ation of high-molar-mass polystyrene (M(w) = 10.3 x 10(6) g mol(-1)) i s investigated in dilute solution. It is known that the degree of mole cular orientation in extremely good and poor solvents is significantly different and, furthermore, that its dependence on shear rate is a fu nction of solvent power. For this reason, the present investigation de als with polystyrene in solvents of intermediate quality, represented by binary mixtures of poly(methylvinylether) (PMVE) and toluene. Owing to the variation of the PMVE fraction, which builds an isorefractive pair with toluene, a variation of both solvent quality and viscosity i s realized. This investigation proves that the degree of orientation i s induced not only by hydrodynamic interaction but also by thermodynam ic interaction, and therefore describes a non-linear function of solve nt power. The observed dependence of the rheo-optically detected molec ular orientation on solution properties is interpreted and discussed i n the light of various theoretical predictions.