An obvious example of such morphological engineering is shown in Figure 1, where a fine asymmetric hollow fiber with an external skin is shown. The ultrathin dense skin and porous support layer in this fiber allow rapid permeation in membrane applications. Nevertheless, the molecular scale processes controlling permeation across the dense skin in Figure 2 are identical to those in thicker common films mentioned above. Our group has contributed significantly to the development of processes for formation of these complex asymmetric structures. The work relies upon an integrated knowledge of thermodynamics, phase separation kinetics, and interphase mass transfer to capture the desired asymmetry in the morphology. The ability to control highly asymmetric morphologies in hollow fibers and the ability to select suitable materials based on specific separation requirements make revolutionary separation processes possible.
Work is also underway in our group to form "mixed matrix composite" membrane comprised of blends of molecular sieving entities within the matrix of a conventional polymer. This project seeks to achieve ultra high permeation membrane properties without sacrificing the ease of membrane formation associated with conventional polymers.
Fascinating effects due to non-equilibrium thermodynamic and non-Fickian transport phenomena are additional topics our group studies. Long-lived conditioning effects due to exposure of membranes and barriers to elevated concentrations of certain penetrants are typical of such non-equilibrium phenomena. Protracted aging of glassy polymers, carbons and inorganic membranes after formation or conditioning treatments also are of interest to us. In many cases, these effects seem to defy logic ?until one realizes that an expanded set of rules governs these out-of-equilibrium materials.
- Chandra, P. and W. J. Koros, "Sorption of lower alcohols in poly(ethylene terephthalate)", Polymer, 50(17), 4241-4249 (2009).
- Husain, S. and W. J. Koros, "Macrovoids in hybrid organic/inorganic hollow fiber membranes",Industrial & Engineering Chemistry Research, 48(5), 2372-2379 (2009).
- Lee, J. S.; Madden, W.; Koros, W. J., "Antiplasticization and plasticization of Matrimid asymmetric hollow fiber membranes." , Journal of Membrane Science , 350(1+2), 242-251 (2010)
- Omole, I.C.; Adams, R. T. Miller, S. J.; Koros, W. J., "Effects of CO2 on high performance hollow-fiber membrane for natural gas purification", Industrial & Engineering Chemistry Research , 49 (10), 4887-4896.
- Kratochvil, A. M.; Koros, W. J.; "Effects of supercritical CO2 conditioning on cross-linked polyimide membranes", Macromolecules, 43 (10) , 4679-4687 (2010).
- Kiyono, M.; Williams, P. J.; Koros, W. J., "Effects of pyrolysis atmosphere on separation performance of carbon molecular sieve membranes" , Journal of Membrane Science, 359 (1+2), 2-10 (2010).
- Qui, W. L.; Zhang, K. A., Liu, J. Q.; Sun, Q. H.; Deng, Y. L., " Macropourous polymeric sorbents with high selectivity for separation of phenols", Polymer, 51 (15) 4442-4449 (2010).
- Lively, R. P.; Chance, R. R.; Koros, W. J., "Enabling Low-cost CO2 capture via heat integration", Industrial & Engineering Chemistry Research , 49 (16), 7550-7562 (2010).
- Das, M.; Perry, J. D.; Koros, W. J., "Gas-transport property performance of hybrid molecular sieve-polymer materials" , Industrial & Engineering Chemistry Research , 49 (19), 9310-9321 (2010).
- Adams, R.; Carson, C.; Ward J.; Tannenbaum, R.; Koros, W. J.; "Metal organic framework mixed matrix membranes for gas separations", Microporous & Mesoporous Materials, 131(1-3), 13-20 (2010).