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Structural insights into the twist-bend nematic phase from the integration of 2H-NMR data and modelling: CB7CB and CB6OCB as case studies

Structural insights into the twist-bend nematic phase from the integration of 2H-NMR data and modelling: CB7CB and CB6OCB as case studies
Structural insights into the twist-bend nematic phase from the integration of 2H-NMR data and modelling: CB7CB and CB6OCB as case studies

The appearance of some special features in 2H-NMR spectra, which could not be explained by the conventional nematic order, was crucial for the discovery of the twist-bend nematic (NTB) phase. Such features reflect the order and symmetry of the local environment of a probe and in principle their analysis can provide quantitative insights into the structural parameters of the phase. We have developed a methodology for the analysis of experimental data, different from the approaches that are normally used for two main reasons: (i) the structural features of the NTB phase, specifically its local polarity, biaxiality and chirality, are consistently taken into account; (ii) the molecular features are introduced in a detailed way, through molecular modelling. We have applied this methodology to analyse 2H-NMR quadrupolar splittings for two representative systems, CB7CB and CB6OCB. The integration of theory, computational modelling and experiment allows us to extract quantitative information from the experimental data and to predict various properties, even not directly probed by measurements. We discuss how the molecular differences between CB7CB and CB6OCB translate into a different phase behaviour and we address issues concerning the distinguishing features of the NTB phase, such as the definition of a local tilted director.

H-NMR, conical angle, heliconical structure, liquid crystal dimers, molecular bend angle, molecular modelling, theory-experiment integration, Twist-bend nematic
0267-8292
2361-2375
Greco, Cristina
73a46655-54d5-4fae-bb0a-504c785611b4
Ferrarini, Alberta
acc78879-863d-4473-8c96-722d207871ca
Luckhurst, Geoffrey R.
3deaf900-9562-4589-ab5e-3b1fc6fce1a9
Timimi, Bakir A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Zimmermann, Herbert
5f846fc9-2d85-4743-88f0-20bd420a62a4
Greco, Cristina
73a46655-54d5-4fae-bb0a-504c785611b4
Ferrarini, Alberta
acc78879-863d-4473-8c96-722d207871ca
Luckhurst, Geoffrey R.
3deaf900-9562-4589-ab5e-3b1fc6fce1a9
Timimi, Bakir A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Zimmermann, Herbert
5f846fc9-2d85-4743-88f0-20bd420a62a4

Greco, Cristina, Ferrarini, Alberta, Luckhurst, Geoffrey R., Timimi, Bakir A. and Zimmermann, Herbert (2018) Structural insights into the twist-bend nematic phase from the integration of 2H-NMR data and modelling: CB7CB and CB6OCB as case studies. Liquid Crystals, 45 (13-15), 2361-2375. (doi:10.1080/02678292.2018.1516304). (In Press)

Record type: Article

Abstract

The appearance of some special features in 2H-NMR spectra, which could not be explained by the conventional nematic order, was crucial for the discovery of the twist-bend nematic (NTB) phase. Such features reflect the order and symmetry of the local environment of a probe and in principle their analysis can provide quantitative insights into the structural parameters of the phase. We have developed a methodology for the analysis of experimental data, different from the approaches that are normally used for two main reasons: (i) the structural features of the NTB phase, specifically its local polarity, biaxiality and chirality, are consistently taken into account; (ii) the molecular features are introduced in a detailed way, through molecular modelling. We have applied this methodology to analyse 2H-NMR quadrupolar splittings for two representative systems, CB7CB and CB6OCB. The integration of theory, computational modelling and experiment allows us to extract quantitative information from the experimental data and to predict various properties, even not directly probed by measurements. We discuss how the molecular differences between CB7CB and CB6OCB translate into a different phase behaviour and we address issues concerning the distinguishing features of the NTB phase, such as the definition of a local tilted director.

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More information

Accepted/In Press date: 2018
Keywords: H-NMR, conical angle, heliconical structure, liquid crystal dimers, molecular bend angle, molecular modelling, theory-experiment integration, Twist-bend nematic

Identifiers

Local EPrints ID: 428084
URI: http://eprints.soton.ac.uk/id/eprint/428084
ISSN: 0267-8292
PURE UUID: 8ec7418c-f593-4cd4-8f4b-3eb06db09e11

Catalogue record

Date deposited: 08 Feb 2019 17:30
Last modified: 07 Oct 2020 00:29

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Contributors

Author: Cristina Greco
Author: Alberta Ferrarini
Author: Geoffrey R. Luckhurst
Author: Bakir A. Timimi
Author: Herbert Zimmermann

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