(415e) Polyamide-Based Thin Film Cation Exchange Membrane Synthesis

Polymeric membranes with the ability to separate cations from anions or anions from cations have broad implications in the water and energy sectors. In particular, ion exchange membranes (IEMs) containing negative or positive fixed-charged groups enable the targeted removal of specific ions from water in electro-membrane processes such as electrodialysis, bipolar membrane electrodialysis, and Donnan dialysis. Additionally, IEMs are essential in energy conversion and storage technologies to transport ions and isolate electrochemical reactions. Traditional methods of IEM synthesis via solvent casting are expensive, require selective materials, and involve a considerable amount of solvent, leading to safety concerns. Therefore, a new manufacturing approach is necessary to synthesize highly selective, low-resistance, scalable, and inexpensive IEMs to realize the full potential of the technology. Additive manufacturing, electrospray, is a promising method that offers unprecedented control over membrane thickness while reducing material use.

It is known that polyamide membranes widely used in the desalination process synthesize via interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) onto the support. Those membranes mainly consist of two layers (active polyamide layer, responsible for rejection of both cations and anions and support layer mainly responsible for physical durability of a relatively thin and fragile selective layer of membrane). Interestingly, those membranes have shown relatively low ion exchange capacity due to the low amount of negatively charged COOH^- in their structure but those membranes do not contain enough negatively charged COOH^- groups in their structure to achieve a high ion exchange capacity, making these membranes unsuitable for use in electro-membrane processes. The method, interfacial polymerization, is relatively inexpensive and easy to use, but it cannot be adapted to make ion exchange membranes with different materials.

To increase the selectivity between cations and anions, ion exchange capacity, and decrease the electrical resistance of IEMs, charged co-monomers such as the sulfonated analog of MPD (SMPD) are necessary. However, this approach can only be applied by using electrospray due to the reactivity difference between charged and uncharged co-monomers. Additionally, the controls over the deposition of materials via electrospray offer precise control over the thickness and indirect control over electrical resistance. The number of fixed charged groups (ion exchange capacity) in the polymer can also be controlled by the amount of incorporation of SMPD. This approach allows for the synthesis of ion exchange membranes with tunable parameters, specifically designed for applications such as desalination or energy conversion.

In this study, we will synthesize sulfonated polyamide membranes by using both MPD and SMPD and TMC via electrospray by using support membranes. This novel approach has the potential to produce highly selective, low-resistance, scalable, and inexpensive IEMs, enabling the full potential of ion exchange membrane technology to be realized in the water and energy sectors.