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College Park, Maryland      June 6 - 10 , 2004

T3-B4 (4:45 PM): Intramolecular Diffusive Motion in Alkane Monolayers Studied by High-Resolution Quasielastic Neutron Scattering and Molecular Dynamics Simulations

H. Taub (Department of Physics and Astronomy and University of Missouri Research Reactor, University of Missouri-Columbia, Columbia, Missouri 65211), F.Y. Hansen (Department of Chemistry, Technical University of Denmark, IK 207 DTU, DK-2800 Lyngby, Denmark), L. Criswell (Department of Physics and Astronomy and University of Missouri Research Reactor, University of Missouri-Columbia, Columbia, Missouri 65211), D. Fuhrmann (Department of Physics and Astronomy and University of Missouri Research Reactor, University of Missouri-Columbia, Columbia, Missouri 65211; Infineon Technologies, Memory Products, Balanstr. 73, D-81541 Munich, Germany), K.W. Herwig (Spallation Neutron Source, Oak Ridge National Laboratory), A. Diama, H. Mo (Department of Physics and Astronomy and University of Missouri Research Reactor, University of Missouri-Columbia, Columbia, Missouri 65211), R.M. Dimeo, D.A. Neumann (NIST Center for Neutron Research), U.G. Volkmann (Facultad de Física, Pontificia Universidad Católica de Chile, Santiago 22, Chile)

Monolayers of intermediate-length alkane molecules such as tetracosane (n-C24H50 or C24) serve as prototypes for studying the interfacial dynamics of more complex polymers, including bilayer lipid membranes. Molecular dynamics simulations of a C24 monolayer adsorbed on a graphite basal-plane surface show that there are diffusive motions associated with the creation and annihilation of gauche defects occurring on a time scale in the range 0.1 ns to 4 ns. We present evidence that these relatively slow motions are observable by high-energy-resolution quasielastic neutron scattering (QNS) thus demonstrating QNS as a technique, complementary to nuclear magnetic resonance, for studying conformational dynamics on a nanosecond time scale in molecular monolayers.1,2

1. F.Y. Hansen et al., Phys. Rev. Lett. 92, 046103 (2004).
2. This work was supported by the NSF under Grant Nos. DMR-9802476 and DMR-0109057, by the Chilean government under FONDECYT Grant No. 1010548, and by the U.S. Department of Energy through grant DE-FG02-01ER45912. The neutron scattering facilities in this work are supported in part by the National Science Foundation under Agreement No. DMR-0086210.

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