Volume 57, Number 3, February 2002
|Page(s)||389 - 395|
|Section||Condensed matter: structure, mechanical and thermal properties|
|Published online||01 September 2002|
Rotational friction at the molecular level
Department of Chemical Engineering, University of Amsterdam
Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands, and
FOM-Institute for Atomic and Molecular Physics
Kruislaan 407, 1098 SJ Amsterdam, The Netherlands
Accepted: 13 November 2001
We use second-harmonic generation measurements to follow the reorientation of liquid-crystal molecules in the first few molecular layers in contact with a surface. These measurements reveal four molecular relaxation times differing by orders of magnitude arising from different dissipation processes taking place at the interface with a solid. The slowest processes are due to the direct interaction of molecules with the solid, while the others concern molecules located just above this surface layer. This position-dependent dynamics explains some of the discrepancies previously observed in measurements of the surface reorientation dynamics of liquid crystals.
PACS: 68.08.-p – Liquid-solid interfaces / 68.15.+e – Liquid thin films / 61.30.-v – Liquid crystals
© EDP Sciences, 2002
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