Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by<sup>13</sup>C NMR

Balakrishnan, N. S.; Bayle, J. P.; Ho, Mei-Sing; Pham, Son C.; Fung, B. M.

doi:10.1080/02678299308027675

Cited by 11 publications

(3 citation statements)

References 22 publications

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“…Because most successful applications of the Landau-de Gennes theory have concentrated in this small temperature range and have set y = 1, we assume that this condition describes well the temperature dependence in the vicinity of the isotropic to nematic phase transition. Therefore, we will use equation (15) for the temperature dependence of A with y = 1 in the three types of temperature dependence of B and C discussed below.…”

Section: A = a ( T -T * ) Ymentioning

confidence: 99%

“…As the ordering tensor and the observed chemical shift are directly related, equations (36) and (37) may be combined. If we neglect the elastic terms in equation (35) and use equation (15) for the temperature dependence of A, the following approximation is obtained where (39) and Biso is the asymptotic value of the chemical shift in the isotropic phase. The solid curves in figures 4 and 5 show that the experimental data can be fitted very well with equation (38).…”

Section: Pretransitional Behaviourmentioning

confidence: 99%

“…The order parameters for both rings were determined by C-13 nuclear magnetic resonance (NMR) spectroscopy, combining the SLFNAS (separated local field spec- troscopy/variable angle spinning) technique with chemical shift data [9,11,[13][14][15][16]. Because the C-13 chemical shifts can be measured accurately as a function of temperature, it is possible to obtain a precise determination of the order parameter for a large number of temperatures.…”

Section: Mbba C H 3 E N and C H~c H~c H Z C H~mentioning

confidence: 99%

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On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

1995

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Based on the ideas of Landau-de Gennes theory applied to nematic liquid crystals, several forms for the variation of the order parameter as a function of temperature are investigated over a wide nematic range. These functional forms are used to fit the experimental order parameters, determined through the use of C-13 NMR, for 4-methoxybenzylidene-4'-butylaniline (MBBA) and 4-n-pentyl-4'-cyanobiphenyl (5CB), and the physical significance of the parameters is discussed. A comparison of the results shows that the functional form which fits the experimental data best is similar to the Haller equation, a useful relation which is usually regarded as empirical. In this case, the coefficients resulting from a semi-empirical approach based on the Landau-de Gennes treatment may be thought of as quantifying the importance of the structure and rigidity of the liquid crystal in determining the temperature dependence of the order parameter for that liquid crystal. In the process, we have also examined the pretransitional behaviour in the C-13 NMR chemical shifts of liquid crystals observed within a few tenths of a degree above the nematic to isotropic transition temperature. IntroductionMany interesting properties and important applications of nematic liquid crystals result from their anisotropic orientational ordering, which can be quantified through the use of the order parameter. The variation of the order parameter as a function of temperature has been the subject of much interest, and several approaches have been used to describe the temperature dependence of the order parameter. For example, the Maier-Saupe mean-field theory [ 1,2] predicts that the order parameter of nematic liquid crystals is a universal function of temperature, which is not observed experimentally. Other variations of mean-field theory do allow for differences between liquid crystals, but do not always predict experimentally observed results [3]. The Landau-de Gennes theory has also been used to derive the temperature dependence of the order parameter from a low-order polynomial which approximates the free energy density of the nematic liquid

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Section: A = a ( T -T * ) Ymentioning

confidence: 99%

Section: Pretransitional Behaviourmentioning

confidence: 99%

Section: Mbba C H 3 E N and C H~c H~c H Z C H~mentioning

confidence: 99%

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On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

1995

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Liquid Crystalline Samples: Carbon-13 NMR

Fung¹

2007

Encyclopedia of Magnetic Resonance

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Coherent Averaging and Correlation of Anisotropic Spin Interactions in Oriented Molecules

Marjańska

Havlin

Sakellariou

2003

NMR of Ordered Liquids

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Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by¹³C NMR

Cited by 11 publications

References 22 publications

On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

Liquid Crystalline Samples: Carbon-13 NMR

Coherent Averaging and Correlation of Anisotropic Spin Interactions in Oriented Molecules

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Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by13C NMR

Cited by 11 publications

References 22 publications

On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

Liquid Crystalline Samples: Carbon-13 NMR

Coherent Averaging and Correlation of Anisotropic Spin Interactions in Oriented Molecules

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Product

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Determination of the orientational ordering of 4′-cyanophenyl-4-alkylbenzoates by¹³C NMR