SHEAR FLOW RHEOLOGY OF MICELLAR SOLUTIONS CONTAINING 'LIVING' POLYMER CHAINS

C.-M. Huang¹, J.J. Magda¹, R.G. Larson², D. Pine³, C.-H. Liu⁴

¹University of Utah, ²AT&T Bell Labs, ³University of California Santa Barbara, ⁴Xerox Corp.

(Proceeding of the XIIth International Congress on Rheology, Edited by A. Ait-Kadi, J.M. Dealy, D.F. James and M.C. Williams, Canadian Rheology Group, Quebec City, pp. 217-218, 1996)

CONCLUSION

Dilute aqueous solutions of worm-like micelles exhibit an apparent shear-thickening transition characterized by a large increase in the time-dependent values of the viscosity and the first normal stress difference. At the critical shear rate, there is an induction period of flow before shear-thickening occurs. This induction period is observed both with fresh samples, and with samples which have already undergone shear-thickening and have been given only two minutes of recovery time. The critical shear rate for onset of shear-thickening depends strongly on cone angle and is thus not a true material property. These results are consistent with the hypothesis that an elastic flow instability occurs in torsional rheometry shortly after the formation of shear-induced micellar structures. If so, then torsional rheometry cannot be used to measure meaningful values for the rheological properties after shear-thickening, since the velocity field in the rheometer will be unknown. It is also clear that the critical shear rate for onset of shear-thickening in rectilinear flows (if it occurs at all) is not simply related to the critical shear rate measured in torsional rheometers.