Investigation of ionic stability criteria for ion-permeable charged membranes

The flocculation criteria in the DLVO theory of colloid stability are applied to ion-permeable membranes containing ionizable fixed groups. These groups are not restricted to the membrane surface but are uniformly distributed throughout a thick surface layer. The flocculation concentrations for such membranes are calculated by using a numerical method to solve the nonlinear Poisson-Boltzmann equation. Results are compared with calculations previously carried out for more restrictive models of biological membranes. The flocculation concentrations are shown to depend on the density of ionizable groups, the dissociation constant of these groups, and the pH of the bulk solution.