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1H NMR study of molecular order and dynamics in CBC9CB Liquid Crystal

Aluculesei, Alina; Cachitas, Hugo; Carvalho, José; Vaca Chavez, Fabian; Figueirinhas, João L; Sebastião, Pedro José; Cruz, Carlos; Tamba, Maria Gabriela; Kohlemeir, Alexandra; Mehl, Georg H

Authors

Alina Aluculesei

Hugo Cachitas

José Carvalho

Fabian Vaca Chavez

João L Figueirinhas

Pedro José Sebastião

Carlos Cruz

Maria Gabriela Tamba

Alexandra Kohlemeir



Contributors

Abstract

Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78T and 7.04T, and relaxometry. The first relaxometry experiments for a very wide frequency domain (8kHz -300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF) , molecular self diffusions (SD), and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Lamor frequency, for the phases under investigation, allow for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths, and activation energies (in the case of thermally activated mechanisms). A clear difference between the structure of the N and the Ntb phases was detected from the results of spin-lattice relaxation through distinct temperature and frequency dependencies’ signatures of collective modes. Significant pre-transitional effects were observed in the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and experiments for comparable liquid crystalline systems.

Journal Article Type Article
Publication Date Jan 30, 2019
Journal Physical Chemistry Chemical Physics
Print ISSN 1463-9076
Electronic ISSN 1463-9084
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 21
Issue 8
Pages 4523-4537
APA6 Citation Aluculesei, A., Cachitas, H., Carvalho, J., Vaca Chavez, F., Figueirinhas, J. L., Sebastião, P. J., …Mehl, G. H. (2019). 1H NMR study of molecular order and dynamics in CBC9CB Liquid Crystal. Physical chemistry chemical physics : PCCP, 21(8), 4523-4537. https://doi.org/10.1039/c8cp06868b
DOI https://doi.org/10.1039/c8cp06868b
Keywords Physical and Theoretical Chemistry; General Physics and Astronomy
Publisher URL https://pubs.rsc.org/en/Content/ArticleLanding/2019/CP/C8CP06868B#!divAbstract
Additional Information This is the accepted manuscript of an article published in Physical chemistry chemical physics, 2019. The version of record is available at the DOI link in this record.

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