Dielectric Analysis of Dialysis Membrane/Solution System under DC Bias Voltage Application

Dielectric measurement coupled with measurement of steady current-voltage （ I - V ） characteristics was carried out over a frequency range from 100 Hz -13 MHz on Visking dialysis membrane in 1 mM KC1 solution under the application of d. c. bias voltage. A marked dielectric relaxation was observed when the d. c. bias voltage that yields the limiting current density. The relaxation is caused by concentration polarization laye （CPL） developed alongside the membrane. Further,the dielectric relaxation was analyzed on the basis of the dielectric model of the series combination of the CPL and abulk solution phase. The structural parameters of CPL, capacitance and conductance of the solution phase were obtained from dielectric parameters. These values are comparable with that obtained in the system composed of ion-exchange membrane and distilled water. The results suggest that the dialysis membrane can be considered to be a kind of weak-charged membrane in dilute solution. Numerical calculations by the circular arc rule on dielectric relaxation show that the relaxation is one with a distribution of relaxation frequency. This reason can be considered to be a non-uniform distribution of the relaxation mechanism that is related to the structure of CPL.