(398x) Prediction of Water Uptake in Ion Exchange Membranes Using Gel Swelling Models

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

In this work, predictive models for water uptake are discussed using gel swelling models which have been developed for crosslinked polymer networks with ionic functional groups. Flory-Rehner model was firstly introduced to predict swelling of the polymer networks which have ionic functional groups and polymer chains with Gaussian distribution. [1] This model has been modified by Tanaka [2] and Peppas [3] to account for the effects of diluted polymer solution and non-ideality of polymer chains for hydrophilic gels.

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 showed good agreement with experimentally obtained water uptake. Furthermore, the model which accounted for non-Gaussian effect in addition to diluted polymer solution showed better prediction. These results suggest water uptake in ion exchange membranes can be predicted by Flory-Huggins interaction parameter between polymer networks and water, crosslinking density of polymer networks, and ion concentration in the membrane. In this presentation, water uptake prediction based on gel swelling model combined with ion sorption model [4] is also discussed.

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

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

[3] N. A. Peppas and L. M. Lucht, Chem. Eng. Commun., 30, 291-310, 1984.

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