直流偏压下透折膜/水溶液体系的介电解析

Abstract

在直流偏压下,结合I-V特征曲线对由VISkIng透析膜和水溶液构成的体系在100Hz-13MHz的频率范围进行了介电测量.当直流偏压超过I-V特征曲线所给出的极限电流密度时,该体系显示了一个显著的介电弛豫,它是由于在膜表面产生的浓度极化层引起的.在农度极化层和体相溶液的串联回路模型基础上,对此介电弛豫进行了介电解析,进而从实验上测得的介电参数获得了特征浓度极化层构造的参数,以及体相溶液的电导和电容的值.这些值与在离子义换膜体系得到的结果相比较,可认为这种透析膜在稀溶液中是呈弱荷电性质的.进一步,用介电弛豫的圆弧规则进行了电容和电导的频率依存性算,其结果证明该弛豫具有驰豫时间分布,它可考虑为是一种与浓度极化层有关的非均匀分布的介电弛豫机理.

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.