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Science 19 April 2002:
Vol. 296. no. 5567, pp. 519 - 522
DOI: 10.1126/science.1069580
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Reports

Ultrapermeable, Reverse-Selective Nanocomposite Membranes

T. C. Merkel,1 B. D. Freeman,2 R. J. Spontak,3 Z. He,4 I. Pinnau,4 P. Meakin,5 A. J. Hill5

Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.

1 Center for Energy Technology, Research Triangle Institute, Research Triangle Park, NC 27709, USA.
2 Department of Chemical Engineering, Center for Energy and Environmental Resources, University of Texas at Austin, Austin, TX 78758, USA.
3 Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695, USA.
4 Membrane Technology and Research, Menlo Park, CA 94025, USA.
5 Commonwealth Scientific and Industrial Research Organisation-Division of Manufacturing Science and Technology, Clayton, Victoria 3168 Australia.
6 School of Chemistry, Monash University, Clayton, Victoria, 3800 Australia.

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