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Science 19 May 2006:
Vol. 312. no. 5776, p. 969
DOI: 10.1126/science.312.5776.969f
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This Week in Science
Knudsen diffusion occurs when the mean free path of atoms or molecules is relatively long compared to the pore or channel through which they move, so that wall collisions become more frequent than those between particles. This model holds for pores between 2 and 50 nanometers, but what happens during flow in smaller channels? Holt et al. (p. 1034, see the cover and the Perspective by Sholl and Johnson) fabricated membranes using double- and multiwalled carbon nanotubes to form the pores. For gases, flow rates were an order of magnitude greater than those predicted by Knudsen diffusion, and water flow rates greatly exceeded values calculated from hydrodynamics. The authors argue that the enhanced transport is caused by the smoothness of the inner nanotube surfaces, in agreement with results from computer simulations.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
