Concentration and its distribution at and near the concentrating side surface (interfaces) of ion exchange membranes were estimated. Electrodialysis was carried out at 2 or 4 A/dm2 and 25°C, and 0.5 N-NaCl solution was used as raw solution. The estimation was done by Schlieren-Diagonal method previously reported. A process of concentration change in the interfaces during the concentrating process from O.5 N-NaCl to equilibrated concentration was shown by photographs. Concentration distributions in the interfaces under the equilibrium were observed to be a straight line in the Schlieren patterns, which showed that concentration differences in the interfaces from that of bulk solution could be expressed by quadratic equations of distance from membrane surface. Cencentration at membrane surfaces increased with current density increased. Concentration difference there between anion and cation exchange membrane, however, increased at increased current density. Concentration at membrane surface Ci, on the other hand, could be expressed by a linear equation of that of bulk solution Cb as Ci=αCb+Co. Both of constants α and Co were characteristic to membrane species and particularly,α was independent of current density. This relationship was seemed to be useful for a “dynamic characterization” of membranes which had previously been proposed.
