DIFFUSION IN NON-IONIC AND IONIC POLYMER SOLUTIONS: EFFECTS OF SHEAR RATE AND POLYMER CONCENTRATION

Diffusion coefficients for ferricyanide ions in aqueous polymer solutions have been calculated from laminar flow mass transfer data obtained in a concentric annulus apparatus by the electrochemical voltammetric method. The electrolyte solutions containing one to five percent polyvinyl alcohol or polyacrylic acid were pumped through the annulus. Flow was longitudinal, and the shear rate ranged from 7 to 800 s-1 The diffusion coefficient for ferricyanide in the polymer solutions depended on polymer concentration in a different way for the non-ionic (polyvinyl alcohol) solutions compared to the polyelectrolyte (polyacrylic acid) solutions. Over the range of concentrations studied, the diffusion coefficient as a function of polymer concentration for polyacrylic acid solutions reached a minimum, increased to a maximum, and then decreased slightly.The polyvinyl alcohol data showed minimum and maximum but no decrease, and the minimum occurred at a higher polymer concentration. For each type of solution, the diffusion coefficient decreased from five to twenty percent as the shear rate was increased from 100 to 800 s-1.The diffusion data can be related to polymer molecule uncoiling and stretching in the flowing solution and to solvation of the molecules present.