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Director reorientation processes in a monodomain thin nematic liquid crystal film: a deuterium NMR spectroscopy study

Director reorientation processes in a monodomain thin nematic liquid crystal film: a deuterium NMR spectroscopy study
Director reorientation processes in a monodomain thin nematic liquid crystal film: a deuterium NMR spectroscopy study
Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4'-cyanobiphenyl (5CB), confined between two glass plates and subject to magnetic and electric fields. The nematic cell was held in the NMR probe head so that the electric field, whose direction is normal to the substrate surface, makes an angle of about 45° with the magnetic field. This experimental geometry avoids the degeneracy in the field-induced alignment pathway for the director found for larger angles. A series of deuterium NMR spectra, obtained using a quadrupolar echo sequence, was acquired as a function of time. When the electric field, whose intensity is controlled so that the director makes an angle with the magnetic field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to the magnetic field because ?(?)over tilde and ?(?)over tilde are both positive for 5CB. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the turn-off alignment processes as a function of time. The realignment pathway of the director was monitored by measuring ?(?)over tilde, the deuterium quadrupolar splitting. We have studied the time dependence of the director orientation for the turn-on and turn-off processes at different temperatures in the nematic phase. The temperature independence of ?(?)over tilde/?(?)over tilde is also discussed on the basis of experiment and theory. The diamagnetic anisotropy and the rotational viscosity coefficient were also determined as a function of temperature. The deuterium NMR spectra corresponding to the field-induced director dynamics were predicted by an analysis based on hydrodynamic theory.
orientational order, polymer, phase, dynamics, behavior
0021-9606
5899-5907
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Miyamoto, T.
bd635bfc-13ea-41bd-a687-e5466a9cdbd4
Sugimura, A.
ad404617-1e0f-445f-84d4-1f7efdf57909
Timimi, B.A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Miyamoto, T.
bd635bfc-13ea-41bd-a687-e5466a9cdbd4
Sugimura, A.
ad404617-1e0f-445f-84d4-1f7efdf57909
Timimi, B.A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca

Luckhurst, G.R., Miyamoto, T., Sugimura, A. and Timimi, B.A. (2002) Director reorientation processes in a monodomain thin nematic liquid crystal film: a deuterium NMR spectroscopy study. Journal of Chemical Physics, 117 (12), 5899-5907. (doi:10.1063/1.1495846).

Record type: Article

Abstract

Deuterium nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the director dynamics in the nematic liquid crystal, 4-pentyl-4'-cyanobiphenyl (5CB), confined between two glass plates and subject to magnetic and electric fields. The nematic cell was held in the NMR probe head so that the electric field, whose direction is normal to the substrate surface, makes an angle of about 45° with the magnetic field. This experimental geometry avoids the degeneracy in the field-induced alignment pathway for the director found for larger angles. A series of deuterium NMR spectra, obtained using a quadrupolar echo sequence, was acquired as a function of time. When the electric field, whose intensity is controlled so that the director makes an angle with the magnetic field is applied to the nematic film, the director moves from being parallel to the magnetic field to being at an angle with respect to the magnetic field because ?(?)over tilde and ?(?)over tilde are both positive for 5CB. After the electric field is switched off, the director relaxes back to being parallel to the magnetic field. Deuterium NMR spectra were recorded during the turn-on and the turn-off alignment processes as a function of time. The realignment pathway of the director was monitored by measuring ?(?)over tilde, the deuterium quadrupolar splitting. We have studied the time dependence of the director orientation for the turn-on and turn-off processes at different temperatures in the nematic phase. The temperature independence of ?(?)over tilde/?(?)over tilde is also discussed on the basis of experiment and theory. The diamagnetic anisotropy and the rotational viscosity coefficient were also determined as a function of temperature. The deuterium NMR spectra corresponding to the field-induced director dynamics were predicted by an analysis based on hydrodynamic theory.

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More information

Published date: 22 September 2002
Keywords: orientational order, polymer, phase, dynamics, behavior
Organisations: Chemistry

Identifiers

Local EPrints ID: 19811
URI: http://eprints.soton.ac.uk/id/eprint/19811
ISSN: 0021-9606
PURE UUID: 906855ff-997e-4ccd-b549-153c7d1016f2

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Date deposited: 21 Feb 2006
Last modified: 08 Jan 2022 12:51

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Contributors

Author: G.R. Luckhurst
Author: T. Miyamoto
Author: A. Sugimura
Author: B.A. Timimi

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