EXPERIMENTAL-STUDY OF SHEAR-INDUCED MIGRATION OF POLYMERS IN DILUTE-SOLUTIONS

The results of an experimental study into the coupling of mass and mom entum transfer for dilute polymer solutions are presented to test the numerous theoretical investigations of this effect. Solutions of high molecular weight, nearly monodisperse, linear polystyrene in oligomeri c polystyrene were sheared in the cone-and-plate geometry. After long times under shear, the concentration of the high molecular weight spec ies was measured as a function of radial position using a gel permeati on chromatography based technique. An increase in polymer concentratio n of over 200% near the apex of the cone and a depletion of polymer ne ar the edge was measured indicating a migration of polymer as a result of shearing the sample. The time evolution of the nonuniform concentr ation profile was found to be very slow and a strong function of both the polymer molecular weight and the applied shear rate. The experimen tal results are compared to theoretical predictions of a dumbbell base d model and measured values of the physical parameters. While the meth od of solution of the highly coupled problem invokes a number of simpl ifying assumptions, the comparison to experimental results suggests th at the theory substantially underestimates the rate of migration. (C) 1996 Society of Rheology.