Low-frequency dynamics of liquid crystals
Department of Physics and Astronomy, The University of Edinburgh, Edinburgh, EH9 3JZ, Scotland, United Kingdom
2 Institute of High Temperature and High Pressure Physics, Sichuan Union University - Chengdu 610065, Sichuan, P. R. China
Accepted: 3 March 1997
The nature of low-frequency (0 to 200 cm-1) dynamics of liquid crystal molecules is explored using a combination of high-resolution Raman spectroscopy and first principles computer simulations implemented on a parallel computer. The frequencies and displacement patterns associated with these vibrations have been determined by diagonalisation of a dynamical matrix. Results indicate that in the prototypical nematogen 5CB, complex internal modes have frequencies comparable to those of lattice modes in the low-temperature solid polymorphs. We expect this result is not specific to 5CB and that such behaviour is common to many liquid-crystal systems. Such low-frequency modes may be related to the conformational changes which have been observed to occur near liquid crystalline phase transitions. In smectic 8CB, very low-frequency features (near 10 cm-1) in the Raman spectrum are observed and are attributed to interlayer interactions in the smectic phase.
PACS: 64.70.Md – Transitions in liquid crystals / 78.30.-j – Infrared and Raman spectra / 31.15.Ar – Ab initio calculations
© EDP Sciences, 1997