Equilibrium and transport properties of polydisperse polyelectrolytes in graft-modified porous charged membranes:: forced permeation-diffusion of lignosulfonate

The convective diffusion of a polydisperse polyelectrolyte (lignosulfonate) through charged porous membranes is studied. The membranes an characterised by potentiometric transport number determination both in the presence and in the absence of lignosulfonate. The convective diffusion experiments are carried out with NaCl and HCl as supporting electrolytes. The effect of using different concentrations of supporting electrolyte in the two cell compartments is also studied. The Donnan equilibrium and steady-state transport of the polyelectrolyte in a convective diffusion cell are theoretically described, and the effects of changing the supporting electrolyte (and pH) are discussed. Good agreement between theoretical and experimental results is obtained. It is shown that the effective membrane fixed charge reverses its sign due to polyelectrolyte adsorption.