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 characterise d 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 us ing different concentrations of supporting electrolyte in the two cell comp artments is also studied. The Donnan equilibrium and steady-state transport of the polyelectrolyte in a convective diffusion cell are theoretically de scribed, and the effects of changing the supporting electrolyte (and pH) ar e discussed. Good agreement between theoretical and experimental results is obtained. It is shown that the effective membrane fixed charge reverses it s sign due to polyelectrolyte adsorption.