Electrolytes in narrow pores / Electrolyten in engen Poren

Abstract

Abstract Mean electrolyte concentration Cm in narrow charged pores decreases as a result of repulsion of co-ions from charged walls. The theory of electrical double layers (EDL) was used for calculation of this effect in dependence on surface potential values Φ1 and concentration C0 of bulk electrolyte solutions. The calculations were limited to the case of 1-1 electrolytes and low values of surface potentials Φ1 when simple analytical solutions may be used. Mean concentration of chloride ions and neutral solution in narrow negatively charged slit pores of different thickness h was calculated in dependence on Φ1 and Debye radius values. It was shown that the effect is more pronounced in narrow pores at relatively high absolute values of surface potentials and at low concentration of a bulk solution. In narrow hydrophilic pores, a decrease in mean electrolyte concentration results from the effect of dielectric exclusion caused by decreasing values of dielectric constant of water ef. The calculations were performed using Born equation that relates the self-energy of ions W with the 8f values and ion radii. Comparing the results obtained with measured values of rejection coefficients of electrolyte solutions in reverse osmosis membranes, the dependence of £f values on pore sizes was calculated. Repulsive forces arising in narrow pores as a result of overlapping of EDL are calculated in dependence on slit thickness, bulk solution concentration and surface potentials in the framework of the theory of electrostatic component of disjoining pressure. In the case of hydrophilic silica systems molecular attraction forces and repulsive structural forces were also taken into account. The arising structural forces are caused by overlapping of boundary layers of water with modified structure