(695a) Template Particle & Solvent Evaporation Assisted Phase Inversion: Easy and Robust Control of Filtration Membrane Morphologies for Various Applications

Authors: 
Hess, S. C., ETH-Zürich
Stark, W. J., ETH-Zürich
Grass, R. N., ETH-Zürich
Raso, R. A., ETH-Zürich
Kohll, X., ETH-Zürich
Schumacher, C. M., ETH Zurich
We present a robust platform allowing the controlled nanoparticle assisted formation of porous polymer membranes.1 Applications for porous membranes range from drinking water purification,2 gas separation,3 biotechnological downstream processing,4 battery separators,5 reverse osmosis,6 food separation processes7 to porous scaffolds for tissue engineering.8

Depending on the membraneâ??s specific application, different morphologies are required. For example, the convenient separation of particles such as tiny parvoviruses from pharmaceutical goods, requires membranes thick and flexible enough to be mechanically stable while exhibiting appropriate pore sizes. Furthermore for maximizing the flux rate, asymmetric membranes are mostly preferred, as they comprise thin selective layers containing small pores.

Our filtration membrane fabrication procedure allows the simple and exact shaping of porous polymer membranes with previously unmaintained asymmetric properties.1 The membrane formation is enabled by solvent evaporation induced spinodal decomposition of particles containing liquids and the usage of template particles9 as such. Membranes produced with varying concentrations of ingredients were analyzed on their morphology at different steps during membrane synthesis. This allowed deciphering mechanistic aspects of the membrane formation, as well as the key parameters for controlling the pore size and pore size gradient. By only varying the concentration ratio of non-solvent and ZnO nanoparticles within a specific polymer dispersion, selective pore sizes form sub-20 nm up to 100 nm and various pore size gradients could be reproducibly created. A selection of membranes with different pore sizes, was finally tested on pure water flux rates as well as silica nanoparticle retention rates, and compared to commercially available high-end virus filters.

Very recently, we discovered the benefit of pore directed ZnO nanoparticles for the synthesis of MOF-polymer composite membranes. The synthesis of MOF-polymer composite membranes depends on MOF-precursors which are ideally in close contact with the membrane. For synthesis of MOF-polymer composite membranes the ZnO-nanoparticles, instead of being dissolved, were maintained within the pores and used as zinc source for the solvothermal synthesis of mechanically flexible ZIF-8 composite membranes. ZIF-8-polymer composite membranes were tested on H2, N2 and CO2 single gas permeation values.

In addition to the methodâ??s simplicity and the large scale availability of all the ingredients, it has great upscale-potential via roll-to-roll coating.10

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8. Madihally, S. V.; Matthew, H. W. T. Porous chitosan scaffolds for tissue engineering. Biomaterials 1999, 20, 1133-1142.

9. Kellenberger, C. R.; Luechinger, N. A.; Lamprou, A.; Rossier, M.; Grass, R. N.; Stark, W. J. Soluble nanoparticles as removable pore templates for the preparation of polymer ultrafiltration membranes. J Membrane Sci 2012, 387, 76-82.

10. Kellenberger, C. R.; Hess, S. C.; Schumacher, C. M.; Loepfe, M.; Nussbaumer, J. E.; Grass, R. N.; Stark, W. J. Roll-to-Roll Preparation of Mesoporous Membranes by Nanoparticle Template Removal. Ind Eng Chem Res 2014, 53, 9214-9220.