Prediction of Water Uptake in Ion Exchange Membranes Based on Gel Swelling Models Combined with Ion Sorption Model

Ion sorption and diffusion in ion exchange membranes are significantly influenced by water uptake in the membrane. Therefore, fundamental understanding of the relationship between polymer structure and water uptake contributes better design of the membranes. However, in spite of its huge effect on membrane performance, there have been a smaller number of studies about water uptake prediction model describing the relationship in an ion exchange membrane field compared with ion sorption model.

In this work, prediction models for water uptake are discussed using gel swelling models combined with ion sorption model. Flory-Rehner model was firstly introduced to predict swelling of the polymer networks which have ionic functional group and Gaussian distribution polymer chains. [1] This model has been modified by Tanaka [2] and Peppas [3] in order to incorporate the effects of diluted polymer solution and non-ideality of polymer chains for hydrophilic gels. Recently, Donnan and Manning model was developed to predict coion concentration in ion exchange membranes. [4]

Strongly charged cation and anion exchange membranes were synthesized in this study. Water uptake in those membranes were measured as a function of external NaCl concentration within 0.01 M to 1.0 M, and interpreted using the gel swelling models. Water uptake predicted by Flory-Rehner model which accounted for the effect of diluted polymer solution and non-Gaussian effect showed good agreement with experimentally obtained water uptake. In this presentation, coion concentration was also predicted by Donnan and Manning model, and water uptake prediction based on gel swelling model combined with ion sorption model is also discussed.

[1] P. J. Flory, CRC press, 1953.

[2] T. Tanaka et al., Phys. Rev. Lett., 45(20), 1636-1639, 1980.

[3] Peppas and Lucht, Chem. Eng. Commun., 30.3-5, 291-310, 1984.

[4] J. Kamcev et al., Phys. Chem. Chem. Phys., 18, 6021-6031, 2016.