Molecular Orientational Order and NMR in the Uniaxial and Biaxial Phases

Bos, Philip J.; Pirš, J.; Ukleja, Paul; Doane, J. William; Neubert, Mary E.

doi:10.1080/15421407708084471

Cited by 50 publications

(11 citation statements)

References 12 publications

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“…The experimental result which need to be explained is the observation that the splittings corresponding to deuterons at different sites of the molecules are not proportional to one another when the temperature is varied. Two extreme explanations have been proposed to explain this result [1,2] : (i) the most probable conformation changes with temperature [2] and (ii) the most probable conformation does not change with temperature, but more than one order parameter is needed to describe the molecular orientational order [1]. Recently, explanation (ii) has become very popular among some researchers, based on the finding that for a number of uniaxial phases, if we call Avi, w;, evk the splittings corresponding to deuteron sites i, j, k on the molecules, then the ratio plot ev;'vk versus Ov'Ovk is a straight line within experimental accuracy [3,4].…”

Section: Classificationmentioning

confidence: 99%

Molecular conformational changes in the smectic C, smectic A and nematic phases of TBBA

Dianoux

Volino

1980

J. Phys. France

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2014 On discute de manière quantitative la dépendance en température de plusieurs rapports de splittings de DMR, dans les phases smectique C, smectique A et nématique de TBBA, à l'aide d'un modèle qui prend explicitement en compte les rotations internes et les changements de la conformation moléculaire la plus probable. On montre que dans toutes les phases, cette conformation n'est pas plane. La valeur de l'angle dièdre moyen entre quelques fragments moléculaires rigides est estimée et comparée à des valeurs théoriques. Dans l'Appendice, on présente une discussion du même problème à l'aide d'un modèle à deux paramètres d'ordre orientationnels. Abstract. 2014 The relative temperature dependence of several DMR splittings in the smectic C, smectic A and nematic phases of TBBA is discussed quantitatively in terms of internal rotations and changes of the most probable molecular conformation. It is shown that in these phases, the conformation is not planar. The mean dihedral angles between some rigid molecular fragments are estimated and compared with theoretical calculations. A discussion in terms of two order parameters is also made in the Appendix.

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Section: Classificationmentioning

confidence: 99%

Molecular conformational changes in the smectic C, smectic A and nematic phases of TBBA

Dianoux

Volino

1980

J. Phys. France

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“…The temperature dependences of S yy -S xx and S zz have been analysed in detail in previous studies [29,30,46,47]. However, these studies utilized liquid crystals for which the mean efg was almost certainly not zero.…”

Section: Biaxial Order Parametermentioning

confidence: 96%

A temperature dependence study of small solutes in zero electric field gradient nematic liquid crystal mixtures

Chandrakumar¹,

Burnell²

1997

Molecular Physics

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The temperature dependences of the proton nuclear magnetic resonance (NMR) spectra of the solutes 1,3,5-trichlorobenzene, metadichlorobenzene, orthodichlorobenzene, 1,3-bromochlorobenzene, benzene and 2-butyne have been studied in the special`zero electric ® eld gradient' mixtures 55 wt% 1132± N-(4-ethoxybenzylidene)-4 Â -n-butylaniline (EBBA) and 70 wt% (4-n-pentyl)-4 Â -cyanobiphenyl± EBBA. The order parameter matrices obtained for each solute from an analysis of the NMR spectra indicate that the solutes experience a similar anisotropic potential in both mixtures.

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“…Eq. (5) tells us that if we consider any three independent splittings Avi, Av,, Avk, a plot /Av,/Av,I versus lAvj/Avkl should be a straight line:' 1 Avi/Av, I = f I Avj/Avk I + (6) where f and y are conformational constants which depend on ai, j . k , bi.…”

Section: Analysis In Terms Of Two Order Parameters and The Question Omentioning

confidence: 97%

Temperature Dependence of DMR Splittings in Nematic PAA: A Quantitative Interpretation in Terms of Changes in the Molecular Conformation—Comparison with Other Models

Volino

Martins

Dianoux

1981

Molecular Crystals and Liquid Crystals

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It is shown that the deuterium magnetic resonance data of Emsley et al. (Mol. Phys. 37, 959 (1979)) on nematic PAA, can be quantitatively explained in terms of a single order parameter model which permits changes in the most probable conformation. The question of straight line plots of ratios of splittings introduced by Bos and Doane (Phys. Rev. Lett. 40, 1030 (1978)) in the framework of a two order parameter model, is discussed in detail. In the case of PAA, it is shown that the single order parameter model also predicts such plots, and a simple geometrical interpretation of this result is given for this particular case. Comments on other approaches to the same data are also made.

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Molecular Orientational Order and NMR in the Uniaxial and Biaxial Phases

Cited by 50 publications

References 12 publications

Molecular conformational changes in the smectic C, smectic A and nematic phases of TBBA

Molecular conformational changes in the smectic C, smectic A and nematic phases of TBBA

A temperature dependence study of small solutes in zero electric field gradient nematic liquid crystal mixtures

Temperature Dependence of DMR Splittings in Nematic PAA: A Quantitative Interpretation in Terms of Changes in the Molecular Conformation—Comparison with Other Models

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