RHEOOPTICAL DETECTION OF SHEAR-INDUCED ORIENTATION OF HIGH MOLAR-MASS POLYSTYRENE IN DILUTE-SOLUTION

The shear-induced orientation of high molar mass polystyrene (M(w) > 9 x 10(6) g mol-1) is investigated by means of rheooptical wide-angle laser light scattering in dilute solution at 20-degrees-C in the near-theta solvent trans-decalin and in thermodynamically good mixed solvents consisting of oligostyrene in toluene. From these measurements the orientation of the macromolecules with respect to the direction of flow is obtained as a function of shear rate and polymer concentration. The orientational behaviour is discussed with respect to the influence of viscosity, solvent power and shear rate, and finally compared with theoretical predictions and with literature data obtained by light scattering and flow birefringence. The results obtained by the new rheooptical light scattering photometer are within the theoretical limits but differ in the degree of orientation, especially at very low shear rates, from the experimental results given in the literature. This deviation is at least partly explained by means of polydispersity and chain stiffness.