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On orientational order in nematic and twist-bend nematic phases: a 2 H-NMR study of binary mixtures of the odd dimer,1″,9″-bis(4-cyanobiphenyl-4′-yl) nonane, (CB9CB), and the monomer, 4-pentyl-4′-cyanobiphenyl, (5CB-d 2 )

On orientational order in nematic and twist-bend nematic phases: a 2 H-NMR study of binary mixtures of the odd dimer,1″,9″-bis(4-cyanobiphenyl-4′-yl) nonane, (CB9CB), and the monomer, 4-pentyl-4′-cyanobiphenyl, (5CB-d 2 )
On orientational order in nematic and twist-bend nematic phases: a 2 H-NMR study of binary mixtures of the odd dimer,1″,9″-bis(4-cyanobiphenyl-4′-yl) nonane, (CB9CB), and the monomer, 4-pentyl-4′-cyanobiphenyl, (5CB-d 2 )
In this article, we explore those factors that influence the orientational order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dimer and a related monomer thus enabling its behaviour to be controlled continuously, through its composition rather than chemical structure. Earlier studies have revealed that as the temperature is lowered in the nematic phase, the orientational order frequently passes through a maximum prior to the formation of the NTB phase. A confirmative indication of this unusual behaviour is that the Haller function cannot fit this dependence over the entire nematic range; such behaviour is intriguing. In the NTB phase, the measured order parameter is often insensitive to decreasing temperature for systems with strong NTB–N transitions often associated with a narrow nematic range. For those mesogens with longer nematic ranges and hence weaker NTB–N transitions, the order parameter decreases more markedly with temperature. As expected for the weak transitions, the behaviour of the order parameter is observed to be essentially continuous across the transition. Associated with the orientational order in the NTB phase is the conical angle and an off-diagonal element of the Saupe ordering matrix.
pretransitional behavior, conical angle, Haller function, Saupe ordering matrix, transitional entropy, nematic range, chiral quadrupolar splitting, gay-berne
1366-5855
1913-1928
Luckhurst, Geoffrey
3deaf900-9562-4589-ab5e-3b1fc6fce1a9
Timimi, Bakir A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Wells, Neil J.
86312185-007b-495b-86da-4e2e5b9b8025
Zimmermann, Herbert
5f846fc9-2d85-4743-88f0-20bd420a62a4
Luckhurst, Geoffrey
3deaf900-9562-4589-ab5e-3b1fc6fce1a9
Timimi, Bakir A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Wells, Neil J.
86312185-007b-495b-86da-4e2e5b9b8025
Zimmermann, Herbert
5f846fc9-2d85-4743-88f0-20bd420a62a4

Luckhurst, Geoffrey, Timimi, Bakir A., Wells, Neil J. and Zimmermann, Herbert (2019) On orientational order in nematic and twist-bend nematic phases: a 2 H-NMR study of binary mixtures of the odd dimer,1″,9″-bis(4-cyanobiphenyl-4′-yl) nonane, (CB9CB), and the monomer, 4-pentyl-4′-cyanobiphenyl, (5CB-d 2 ). Liquid Crystals, 45 (13-15), 1913-1928. (doi:10.1080/02678292.2018.1533597).

Record type: Article

Abstract

In this article, we explore those factors that influence the orientational order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dimer and a related monomer thus enabling its behaviour to be controlled continuously, through its composition rather than chemical structure. Earlier studies have revealed that as the temperature is lowered in the nematic phase, the orientational order frequently passes through a maximum prior to the formation of the NTB phase. A confirmative indication of this unusual behaviour is that the Haller function cannot fit this dependence over the entire nematic range; such behaviour is intriguing. In the NTB phase, the measured order parameter is often insensitive to decreasing temperature for systems with strong NTB–N transitions often associated with a narrow nematic range. For those mesogens with longer nematic ranges and hence weaker NTB–N transitions, the order parameter decreases more markedly with temperature. As expected for the weak transitions, the behaviour of the order parameter is observed to be essentially continuous across the transition. Associated with the orientational order in the NTB phase is the conical angle and an off-diagonal element of the Saupe ordering matrix.

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TLCT-2018-0263 (Rev) Text On orientational order.._ - Accepted Manuscript
Restricted to Repository staff only until 6 January 2020.
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Accepted/In Press date: 6 January 2019
e-pub ahead of print date: 6 January 2019
Keywords: pretransitional behavior, conical angle, Haller function, Saupe ordering matrix, transitional entropy, nematic range, chiral quadrupolar splitting, gay-berne

Identifiers

Local EPrints ID: 428373
URI: https://eprints.soton.ac.uk/id/eprint/428373
ISSN: 1366-5855
PURE UUID: a100045a-92c2-46c4-b8fb-d3e5b8c78d3b
ORCID for Neil J. Wells: ORCID iD orcid.org/0000-0002-4607-5791

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Date deposited: 22 Feb 2019 17:30
Last modified: 20 Jul 2019 01:12

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