Rheology and viscosity scaling of the polyelectrolyte xanthan gum

Abstract

Abstract The viscosity as a function of concentration for xanthan gum in both salt‐free solution and in 50 m M NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt‐free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed ( c* ≈ 70 ppm, c e ≈ 400 ppm, and c D ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed ( c* ≈ 200 ppm and c e ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity‐concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt‐free and 50 m M NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009