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Molecular dynamics in perfluoro-n-eicosane. II. Components of disorder

Albrecht, T. and Elben, H. and Jäger, R. and Kimmig, M. and Steiner, R. and Strobl, G. and Stühn, B. and Schwickert, H. and Ritter, C. (1991):
Molecular dynamics in perfluoro-n-eicosane. II. Components of disorder.
95, In: Journal of Chemical Physics, (4), pp. 2807-2816, [Article]

Abstract

The defect structure in the rhombohedral modification R of perfluoro-n-eicosane has been analyzed in a temperature-dependent x-ray and neutron scattering study. The analysis was based on an evaluation of Bragg-reflection intensities and of the diffuse scattering. Different components of disorder were detected and characterized. At the transition from the low temperature phase to modification R, rotation of the molecules about their long axes sets in. As shown by the azimuthal distribution of the diffuse scattering, rotations occur cooperatively with correlations between neighbors. The Debye-Waller factors measured for the layer reflections are indicative for a moderate roughening of the interfaces due to a restricted longitudinal diffusive motion. Molecules are perturbed by the formation of helix reversal defects. Evaluation of the diffuse scattering yields the associated finite azimuthal correlation length. There is also evidence for a continuous slow untwisting of the helix. With increasing temperature, it approaches the all-trans form.

Item Type: Article
Erschienen: 1991
Creators: Albrecht, T. and Elben, H. and Jäger, R. and Kimmig, M. and Steiner, R. and Strobl, G. and Stühn, B. and Schwickert, H. and Ritter, C.
Title: Molecular dynamics in perfluoro-n-eicosane. II. Components of disorder
Language: English
Abstract:

The defect structure in the rhombohedral modification R of perfluoro-n-eicosane has been analyzed in a temperature-dependent x-ray and neutron scattering study. The analysis was based on an evaluation of Bragg-reflection intensities and of the diffuse scattering. Different components of disorder were detected and characterized. At the transition from the low temperature phase to modification R, rotation of the molecules about their long axes sets in. As shown by the azimuthal distribution of the diffuse scattering, rotations occur cooperatively with correlations between neighbors. The Debye-Waller factors measured for the layer reflections are indicative for a moderate roughening of the interfaces due to a restricted longitudinal diffusive motion. Molecules are perturbed by the formation of helix reversal defects. Evaluation of the diffuse scattering yields the associated finite azimuthal correlation length. There is also evidence for a continuous slow untwisting of the helix. With increasing temperature, it approaches the all-trans form.

Journal or Publication Title: Journal of Chemical Physics
Volume: 95
Number: 4
Divisions: 05 Department of Physics
05 Department of Physics > Institute for condensed matter physics
Date Deposited: 26 Feb 2010 13:35
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