Assessment of the diffusional behavior of polystyrene sulfonates in the dilute regime by hollow-fiber flow field flow fractionation

We applied flow field flow fractionation in a ceramic tubular membrane to s tudy the diffusional behavior of sodium polystyrene sulfonate (NaPSS) as a function of salt and polyelectrolyte concentrations in the dilute concentra tion regime. NaPSS standards were fractionated in an aqueous carrier liquid with salt concentrations of 1-100 mmol L-1 and injected amounts of 0.2-20 mug. A sharp increase in the apparent diffusion coefficients, due to peak o verloading, occurred at a critical polyelectrolyte concentration at the acc umulation wall. A model has been developed that compares repulsive electros tatic interactions, calculated from the Derjaguin-Landau-Verweij-Overbeek t heory, to the thermal energy. It was found that the observed critical conce ntration approximated the concentration of a closely packed lattice of hard spheres within an order of magnitude. The critical concentration appeared to be dependent on the salt concentration, but the influence of the molecul ar mass was less clear. Expressions for the migration velocity in overloade d channels were derived and confirmed experimentally for the two lowest mol ecular masses. Deviations occurred for high molecular mass NaPSS, possibly because of mutual attraction. These experiments confirmed the observations made by small-angle neutron scattering and dynamic light scattering that th e ordering of polyelectrolytes already occurred in the dilute regime. (C) 2 001 John Wiley & Sons, Inc.