Nematic order parameter as determined from dielectric relaxation data and other methods

Urban, S.; Gestblom, Bo; Kuczyński, W.; Pawlus, S.; Würflinger, A.

doi:10.1039/b211457g

Cited by 36 publications

(29 citation statements)

References 28 publications

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“…As it is seen, the P 2 values for 8OCFPB and 8OCPFB obtained from the optical spectroscopy are significantly greater than those calcu-lated from the retardation factor. Such a result was also obtained earlier for 8CB [24], and it is common for a lot of liquid crystals for which some different methods yielded distinct values of P 2 [30,31]. It is also evident that, on contrary to the dielectric method, the position of the fluorine atom in the investigated molecules influences the values of P 2 determined from the optical absorption.…”

Section: Order Parametersupporting

confidence: 81%

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

et al. 2011

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Dielectric relaxation study of nematogenic 4-n-alkyl-4 -cyanobiphenyls (nCB, n = 5, 6), 4-(trans-4 -n-alkylcyclohexyl)isothiocyanatobenzenes (nCHBT, n = 6, 8), 4-cyanophenyl-4 -n-alkylbenzoates (nCPB, n = 6, 8), 4-cyano-3-fluorophenyl-4 -n-octyloxybenzoate (8OCFPB), and 4-cyanophenyl-4 -n-octyloxy-3 -fluorobenzoate (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier-Saupe-Martin model of molecular diffusion in nematics, the orientational order parameter P 2 was determined from dielectric relaxation times and retardation factor. The values of P 2 calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional effect and the orientational order in the nematic phase were discussed.

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Section: Order Parametersupporting

confidence: 81%

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

et al. 2011

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“…Indeed, the vast majority of the dielectric studies suggest Arrhenius temperature dependence of the dielectric relaxation time and Debye spectrum of dielectric loss both above and below the IN transition temperature T IN (see Figure 1). 21,25,26 Deviations from the Arrhenius law, resulting in Vogel-Fulcher or power-law temperature dependence of the dielectric relaxation time, are very weak and can be observed only in the derivative of the linear dielectric response 27,28 or from a nonlinear dielectric response. 27 Given the Arrhenius dielectric relaxation of nematogens, the issue of non-Arrhenius reaction rates seen in experiment 10,11 remains open.…”

Section: Introductionmentioning

confidence: 99%

Dynamical Arrest of Electron Transfer in Liquid Crystalline Solvents

Kapko

Matyushov

2006

J. Phys. Chem. B

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We argue that electron transfer reactions in slowly relaxing solvents proceed in the nonergodic regime, making the reaction activation barrier strongly dependent on the solvent dynamics. For typical dielectric relaxation times of polar nematics, electron transfer reactions in the subnanosecond time scale fall into nonergodic regime in which nuclear solvation energies entering the activation barrier are significantly lower than their thermodynamic values. The transition from isotropic to nematic phase results in weak discontinuities of the solvation energies at the transition point and the appearance of solvation anisotropy weakening with increasing solute size. The theory is applied to analyze experimental kinetic data for the electron transfer kinetics in the isotropic phase of 5CB liquid crystalline solvent. We predict that the energy gap law of electron transfer reactions in slowly relaxing solvents is characterized by regions of fast change of the rate at points where the reaction switches between the ergodic and nonergodic regimes. The dependence of the rate on the donoracceptor separation may also be affected in a way of producing low values for the exponential falloff parameter.

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“…We have shown recently [10,11] that for substances with large positive dielectric anisotropy the Maier and Meier equation [12], as well as the approach by Coffey et al [13,14] based on the retardation factor, can give valuable information on the order parameter S(T ) = P 2 (cos 2 θ) as a function of temperature and pressure (θ is the angle between the long molecular axis and the director n). The above-mentioned procedures were applied to the present substances.…”

Section: Discussionmentioning

confidence: 99%

Dielectric and X-ray Studies of Eleventh and Twelfth Members of Two Isothiocyanato Mesogenic Compounds

et al. 2006

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Results of the dielectric and X-ray studies of the long-alkyl-chain members (n = 11, 12) of two homologous series: nBT (4-n-alkyl--4 -isothiocyanato-biphenyl) and nCHBT (4-trans-4 -n-alkyl-cyclohexyl--isothiocyanato-benzene) in their liquid crystalline phases are presented. These compounds exhibit different polymorphisms: the nematic phase for nCHBTs and the smectic E and smectic A phases for nBTs. The dielectric measurements were performed in a wide frequency range of 1 kHz-3 GHz. The layer thickness in the smectic E and smectic A phases and the orthorhombic unit cell parameters of the smectic E phase were determined using the small angle X-ray diffraction method. In the smectic E phase the layer-thickness-to-molecular-length ratios are found to be close to 1. The corresponding ratios observed for the smectic A phase of nBTs are considerably higher (≈ 1.24), which indicates that an alternating head-to-tail arrangement of molecules in the layers is favored. The rotational dynamics of molecules in the smectic E phases is discussed in relation to their packing in a unit cell.

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Nematic order parameter as determined from dielectric relaxation data and other methods

Cited by 36 publications

References 28 publications

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

Dynamical Arrest of Electron Transfer in Liquid Crystalline Solvents

Dielectric and X-ray Studies of Eleventh and Twelfth Members of Two Isothiocyanato Mesogenic Compounds

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