(415c) Investigation and Optimization of Reactive Ink Formulation for Controlled Membranes Functionalization

Chemically patterned membranes with engendered useful characteristics can offer improved selective transport of electrolytes and material durability. Chemical patterning across the membrane surface (charge-patted mosaic membranes) [1] is achieved by inkjet printing while patterning across membrane depth (Janus membrane) [2] is obtained by casting and sequential spray. Both types of patterning approaches involve the use of a reactive ink (or casting solution) with the nanostructured substrates, where the functionality is induced to the membrane surface and pore walls. Hoffman et al. [3] demonstrated that fast kinetics that remains the membrane functionalization process in the transport-limited regime is the key to ensure precise control of the pattern.

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) “click” reaction offers a promising technique for the precisely controlled fabrication of chemically patterned membranes due to its rapid nature and high conversions under mild conditions. [4] The CuAAC reactive ink formulation comprises a sequence of reactions occurring between reactants, i.e., copper sulfate, ascorbic acid, and an alkyne-terminated reactant, to facilitate the formation of the dinuclear copper-alkyne complex (DNCuAC). The “click” between the DNCuAC and azide moieties of the copolymer membrane [5,6] results in the completion of the CuAAC reaction process and the formation of a triazole group. The triazole group can provide a net positive charge due to the presence of the protonated amine. [7] Negative charge functionality or zwitterionic moieties can be generated by a further reaction. [8] The concentration of the DNCAC is essential for the CuAAC reaction to proceed and therefore is responsible for controlling the functionalization rate of the membrane. [9] However, a fast “click” reaction for additive manufacturing of membranes involves an excess load of harmful components (i.e., copper), which hinders high-performance chemical patterned membranes to be commercialized.

The unclarity in the mechanism underlying the CuAAC reaction presents difficulties when trying to formulate reactive ink with minimal copper and guarantee the transport-limited regime at the same time. First, the conversion from Cu(II) to the catalytically-active Cu(I) is incomplete and subject to a series of equilibrium with ascorbic acid. Subsequently, the alkyne-terminated reactant can exist in several coordinated states with the catalytic Cu(I) species. The complicated, and not fully understood reaction network needed to form DNCAC results in its concentration depending strongly on the formulation of the reactive solution.

We recently developed a dynamic mathematical model for the primary step of the batch reactive-ink formulation considering an ink mixture of copper sulphate and ascorbic acid, and we argued that pH measurements are insufficient to identify all the rate constants. [10] In this talk, we demonstrate our investigation and experimental design process to elucidate the CuAAC reaction mechanism. We verify the presence of two side reactions for 3-dimethylamino-1-propyne (DMA) through experimental design and quantify their effects in ink formulation preparation. Informed by Fourier Transform Infrared Spectroscopy (FTIR), we develop a dynamic model describing both the diffusion of DNCuAC and the “click” reaction in the membrane functionalization process. Building off the knowledge of the reaction network, we are able to optimize the reactive ink formulation that follows the fast reaction regime while minimizing the amount of copper based on specific coating time requirements. The workflow for ink formulation optimization here is applicable to other alkyne systems, which will not only promote the innovations of the chemically patterned membrane, but also develop the potential of CuAAC-based processes in other applications.

References

1. Gao, P., Hunter, A., Summe, M. J., & Phillip, W. A. (2016). A method for the efficient fabrication of multifunctional mosaic membranes by inkjet printing. ACS applied materials & interfaces, 8(30), 19772-19779.
2. Liu, Y., Xiao, T., Bao, C., Fu, Y., & Yang, X. (2018). Fabrication of novel Janus membrane by nonsolvent thermally induced phase separation (NTIPS) for enhanced performance in membrane distillation. Journal of membrane science, 563, 298-308.
3. Hoffman, J. R., Mikes, A. D., Gao, F., & Phillip, W. A. (2019). Controlled Postassembly Functionalization of Mesoporous Copolymer Membranes Informed by Fourier Transform Infrared Spectroscopy. ACS Applied Polymer Materials, 1(8), 2120-2130.
4. Kolb, H. C., Finn, M. G., & Sharpless, K. B. (2001). Click chemistry: diverse chemical function from a few good reactions. Angewandte Chemie International Edition, 40(11), 2004-2021.
5. Zhang, Y., Sargent, J. L., Boudouris, B. W., & Phillip, W. A. (2015). Nanoporous membranes generated from self‐assembled block polymer precursors: Quo Vadis?. Journal of Applied Polymer Science, 132(21).
6. Zhang, Y., Almodovar-Arbelo, N. E., Weidman, J. L., Corti, D. S., Boudouris, B. W., & Phillip, W. A. (2018). Fit-for-purpose block polymer membranes molecularly engineered for water treatment. npj Clean Water, 1(1), 2.
7. Wade Jr, L. G., & Simek, J. W. (2017). Organic Chemistry 9th edn.
8. Hoffman, J. R., & Phillip, W. A. (2020). Dual-functional nanofiltration membranes exhibit multifaceted ion rejection and antifouling performance. ACS applied materials & interfaces, 12(17), 19944-19954.
9. Worrell, B. T., Malik, J. A., & Fokin, V. V. (2013). Direct evidence of a dinuclear copper intermediate in Cu (I)-catalyzed azide-alkyne cycloadditions. Science, 340(6131), 457-460.
10. Liu, X., De, R., Pérez, A., Hoffman, J. R., Phillip, W. A., & Dowling, A. W. (2022). Mathematical Modelling of Reactive Inks for Additive Manufacturing of Charged Membranes. In Computer Aided Chemical Engineering (Vol. 49, pp. 1063-1068). Elsevier.