Uematsu Ikuo, Jimbo Toshihiko, Tanioka Akihiko
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan.
J Colloid Interface Sci. 2002 Jan 15;245(2):319-24. doi: 10.1006/jcis.2001.8016.
An amphoteric membrane consists of both positively and negatively fixed charge groups chemically bound to the polymer chains. If the external solution is changed from alkali to acid, it is possible to obtain an experimental result in which the membrane potential changes from positive to negative through the isoelectric point. It was characterized by examining the relationship between membrane potential and proton concentration (pH) obtained from both experimental and theoretical considerations. The Nernst-Planck flux equation and the Donnan equilibrium theory were also solved for a four-component system combined with the dissociation constant, in order to discuss the pH dependence of membrane potential in a weak amphoteric membrane by comparing the experimental results with the calculated results. It was proven that the calculated results substantially deviated from the theoretical results despite a similar tendency. Such a deviation was caused by the fact that the original theory disregarded the activity coefficient and the ionic mobility, which were dependent on the fixed charge concentration in a membrane. The original theoretical model was modified by adding the effect of a fixed charge group to the activity coefficient and ionic mobility. The calculated results using the modified model explained well the experimental results if the parameter called charge effectiveness, phi, was introduced into the equations. Introduction of phi into the prediction of membrane potential was already done by Kobatake et al. in a system of a strong polyelectrolyte monopolar membrane/salt aqueous solution. In this study, it was proved that phi can also be introduced into a weak amphoteric polymer membrane/salt aqueous solution system. Finally it was also concluded that the Donnan equilibrium and the Nernst-Planck flux equation were still applicable for examining the transport phenomena for the system of a weak amphoteric charged membrane and electrolyte solutions at various pH.
两性膜由化学键合到聚合物链上的带正电和带负电的固定电荷基团组成。如果将外部溶液从碱性变为酸性，有可能获得这样一个实验结果：膜电位通过等电点从正变为负。通过研究从实验和理论两方面得到的膜电位与质子浓度（pH）之间的关系对其进行了表征。还针对结合了离解常数的四组分体系求解了能斯特 - 普朗克通量方程和唐南平衡理论，以便通过将实验结果与计算结果进行比较来讨论弱两性膜中膜电位对pH的依赖性。结果表明，尽管趋势相似，但计算结果与理论结果存在显著偏差。这种偏差是由于原始理论忽略了与膜中固定电荷浓度相关的活度系数和离子迁移率。通过将固定电荷基团的影响添加到活度系数和离子迁移率中，对原始理论模型进行了修正。如果将称为电荷有效性的参数φ引入方程中，使用修正模型得到的计算结果能很好地解释实验结果。Kobatake等人已经在强聚电解质单极膜/盐水溶液体系中，将φ引入了膜电位的预测中。在本研究中，证明了φ也可以引入弱两性聚合物膜/盐水溶液体系中。最后还得出结论，唐南平衡和能斯特 - 普朗克通量方程仍然适用于研究不同pH下弱两性带电膜和电解质溶液体系的传输现象。
