Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N U and NTB, studied by NMR spectroscopy

C. T. Imrie; D. A. Paterson; J. M.D. Storey; C. Chamignon; M. Lelli; J. W. Emsley; G. R. Luckhurst

doi:10.1103/PhysRevE.102.042706

Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N U and NTB, studied by NMR spectroscopy

C. T. Imrie, D. A. Paterson, J. M.D. Storey, C. Chamignon, M. Lelli^* (Corresponding Author), J. W. Emsley^* (Corresponding Author), G. R. Luckhurst^* (Corresponding Author)

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

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Abstract

Both H1 and C13 NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, NTB, and uniaxial nematic, NU, before entering the isotropic phase. The H1 spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, TCrNTB, and then TNUI when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The H1 and C13 NMR spectra in the paranematic phase are used to measure the critical temperature T∗ below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.

Original language	English
Article number	042706
Number of pages	16
Journal	Physical Review E
Volume	102
Issue number	4
Early online date	28 Oct 2020
DOIs	https://doi.org/10.1103/PhysRevE.102.042706
Publication status	Published - 31 Oct 2020

Bibliographical note

Acknowledgements
We thank Dr. A. Jákli for communicating to us recently that a calibration error in the work reported in Ref. [6] is responsible for the discrepancy between their results and ours. We are grateful to the IR-RMN project for enabling access to the 1000-MHz spectrometer in the Centre de Résonance Magnétique Nucléaire à Très Hauts Champs de Lyon. Very helpful discussions are acknowledged with Dr. I. Dozov of Laboratoire de Physique des Solides, UMR 8502 CNRSUniversité Paris-Sud, Orsay, France, and Dr. C. Meyer of PSC, Université de Picardie Jules Verne, Amien, France. We also wish to thank Dr. B. A. Timimi of the School of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, UK, for valuable discussions of the thermodynamic theory by Prof. Rosenblatt. M.L. acknowledges Fondazione CR Firenze for funding support.

Keywords

HIGH-RESOLUTION NMR
PRETRANSITIONAL BEHAVIOR
MOLECULES
SPECTRA
ORDER
REGION
PULSE

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title = "Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N U and NTB, studied by NMR spectroscopy",

abstract = "Both H1 and C13 NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, NTB, and uniaxial nematic, NU, before entering the isotropic phase. The H1 spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, TCrNTB, and then TNUI when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The H1 and C13 NMR spectra in the paranematic phase are used to measure the critical temperature T∗ below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.",

keywords = "HIGH-RESOLUTION NMR, PRETRANSITIONAL BEHAVIOR, MOLECULES, SPECTRA, ORDER, REGION, PULSE",

author = "Imrie, {C. T.} and Paterson, {D. A.} and Storey, {J. M.D.} and C. Chamignon and M. Lelli and Emsley, {J. W.} and Luckhurst, {G. R.}",

note = "Acknowledgements We thank Dr. A. J{\'a}kli for communicating to us recently that a calibration error in the work reported in Ref. [6] is responsible for the discrepancy between their results and ours. We are grateful to the IR-RMN project for enabling access to the 1000-MHz spectrometer in the Centre de R{\'e}sonance Magn{\'e}tique Nucl{\'e}aire {\`a} Tr{\`e}s Hauts Champs de Lyon. Very helpful discussions are acknowledged with Dr. I. Dozov of Laboratoire de Physique des Solides, UMR 8502 CNRSUniversit{\'e} Paris-Sud, Orsay, France, and Dr. C. Meyer of PSC, Universit{\'e} de Picardie Jules Verne, Amien, France. We also wish to thank Dr. B. A. Timimi of the School of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, UK, for valuable discussions of the thermodynamic theory by Prof. Rosenblatt. M.L. acknowledges Fondazione CR Firenze for funding support.",

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T1 - Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N U and NTB, studied by NMR spectroscopy

AU - Imrie, C. T.

AU - Paterson, D. A.

AU - Storey, J. M.D.

AU - Chamignon, C.

AU - Lelli, M.

AU - Emsley, J. W.

AU - Luckhurst, G. R.

N1 - Acknowledgements We thank Dr. A. Jákli for communicating to us recently that a calibration error in the work reported in Ref. [6] is responsible for the discrepancy between their results and ours. We are grateful to the IR-RMN project for enabling access to the 1000-MHz spectrometer in the Centre de Résonance Magnétique Nucléaire à Très Hauts Champs de Lyon. Very helpful discussions are acknowledged with Dr. I. Dozov of Laboratoire de Physique des Solides, UMR 8502 CNRSUniversité Paris-Sud, Orsay, France, and Dr. C. Meyer of PSC, Université de Picardie Jules Verne, Amien, France. We also wish to thank Dr. B. A. Timimi of the School of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, UK, for valuable discussions of the thermodynamic theory by Prof. Rosenblatt. M.L. acknowledges Fondazione CR Firenze for funding support.

PY - 2020/10/31

Y1 - 2020/10/31

N2 - Both H1 and C13 NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, NTB, and uniaxial nematic, NU, before entering the isotropic phase. The H1 spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, TCrNTB, and then TNUI when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The H1 and C13 NMR spectra in the paranematic phase are used to measure the critical temperature T∗ below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.

AB - Both H1 and C13 NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, NTB, and uniaxial nematic, NU, before entering the isotropic phase. The H1 spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, TCrNTB, and then TNUI when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The H1 and C13 NMR spectra in the paranematic phase are used to measure the critical temperature T∗ below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.

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KW - PRETRANSITIONAL BEHAVIOR

KW - MOLECULES

KW - SPECTRA

KW - ORDER

KW - REGION

KW - PULSE

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Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N U and NTB, studied by NMR spectroscopy

Abstract

Bibliographical note

Keywords

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