Electric Birefringence of Electrolytes near Charged Surfaces, II: Effect of Polymeric Additives

Abstract

Electric birefringence of electrolytes containing linear polyacrylamide and polyethylene oxide near a negatively charged silica glass surface is studied using evanescent wave laser polarimetry. We find that addition of polymers to electrolytes near charged surfaces leads to substantially larger levels of electric birefringence than the already anomalously large electric birefringence observed in pure electrolytes near charged surfaces. The polymer contribution to the birefringence increases with surface charge, ionic strength of the electrolyte, and electric field, but is only a weak function of polymer molecular weight and polymer concentration. Unusually high levels of polymer orientation are observed for moderate electric fields (10-30 V/cm). These observations are discussed in terms of large local shear gradients experienced by polymer chains subject to electro-osmotic flow in the electric double layer near charged surfaces.