A spectroscopic study of polyelectrolyte solutions under shear

Abstract

The chain segment orientation of the polyelectrolyte poly(styrene sulfonate), PSS, in glycerol solutions under shear have been studied using a novel Ultra Violet rheo-optic technique. The extinction coefficient of the polyelectrolyte in solution, ϵ, was measured using unpolarised light perpendicular to the direction of flow and is shown to decrease upon the application of shear. When the incident light was polarised with the direction of shear the reduced change in extinction coefficient of the polyelectrolyte became more negative with shear. For light polarised perpendicular to the shear direction the reduced change in extinction coefficient of the polyelectrolyte increased, became more positive, with the application of shear. There was no shear-induced change in the reduced change in extinction coefficient of the polyelectrolyte backbone for light polarised at 67° to the direction of shear. All shear-spectroscopic behaviour may be explained by the alignment of the polarised PSS monomer units in the direction of shear. The maximum dichroic ratio for the polyelectrolyte chain is related to the chain polarisability and was predicted from the angular dependence of the change in extinction measurements to be approximately 2.35.