Static Dielectric Studies of Some Nematogenic Compounds

Kumaraswamy, Sriram; Somashekar, R.; Madhava, M. S.; Revannasiddaiah, D.

doi:10.1080/10587259508030992

Cited by 7 publications

(4 citation statements)

References 6 publications

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“…Further, the average value of the dielectric permittivities " av in the N phase is found to be lower than that of its extrapolated isotropic value. This is in accordance with the theory and the results reported by the earlier investigators for strongly polar and non-polar liquid crystalline materials [28][29][30][31]. At the N-SmB transition, " 0 k goes down whereas " 0 ?…”

Section: Resultssupporting

confidence: 94%

“…The relaxation frequency of this mode shows strong temperature dependence and decreases with decrease in temperature for both cells. The decrease in relaxation frequency f R with decrease in temperature is presumably due to increase in viscosity of the sample on lowering the temperature and follows the Arrhenius behaviour [28] for both measurements as…”

Section: Phase Transitions 13mentioning

confidence: 95%

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Dielectric investigations in the nematic and hexatic smectic B phases of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

2009

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Temperature-dependent dielectric characterization of 4-hexyl-4 0 -[2-(4-isothiocyanatophenyl)ethyl]-1,1 0 -biphenyl (HIEB), which exhibits smectic B and nematic phases, has been carried out over the frequency range of 1 Hz to 10 MHz for homeotropic and planar alignment of sample molecules. This compound shows positive dielectric anisotropy (Á" ¼ " k À " ? 40) in the nematic (N) phase. One mode of dielectric relaxation showing Arrhenius behaviour has been detected in the hexatic smectic B (SmB) phase. Various electrical parameters, namely, dielectric anisotropy, relaxation frequency and activation energy, have been determined in the N and SmB phases.

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Section: Resultssupporting

confidence: 94%

Section: Phase Transitions 13mentioning

confidence: 95%

Dielectric investigations in the nematic and hexatic smectic B phases of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

2009

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“…A structure solution in P1 Å did not give a good a very small positive dielectric anisotropy and it has a combined gure of merit. The resulting E-map did not very small dipole moment [1], as compared with other reveal the complete structure nor could it be further mesogens. The dielectric constant along the preferred expanded by a diOE erence Fourier map after a few cycles direction (along the nematic director) is slightly greater of re nement.…”

Section: Introductionmentioning

confidence: 79%

Crystal structure of 4-n-nonylbenzoic acid

Lokanath¹,

Sridhar²,

Revannasiddaiah³

et al. 2000

Liquid Crystals

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The title compound, 4-n-nonylbenzoic acid, CH 3 (CH 2 ) 8 C 6 H 4 COOH (NBA), has been characterized thus: triclinic, P1, a = 13.514( 4) A Ã , b = 23.4672 (5) A Ã , c = 7.658 (3) A Ã , a = 90.914( 3)ß , b = 100.403( 3)ß , c = 77.781( 2)ß , V = 2334 (2) A Ã 3, Z = 2, and F.W = 745.06, D m = 1.161 g cmÕ 3, D c = 1.061 g cmÕ 3, F 000 = 816.00, l = 0.71069 A Ã , m = 0.6 cmÕ 1, goodness-of-t is 1.029, nal R1 = 0.063 and wR2 = 0.16. Introductionbe indexed with respect to a triclinic cell. Lorentz and The crystal structure studies of mesogens provide polarization corrections were applied. The structure was insight into the understanding of physical properties and solved using SHELXS-97 [3]. The structure solution phase transitions. In view of this a crystal structure did not yield any meaningful E-map in the space group study of 4-n-nonylbenzoic acid was undertaken. The P1 Å , even though the E-statistics showed better agreecompound melts into the nematic state at 97.7ß C and ments of zonal and all data with the centrosymmetric into the isotropic phase at 114.8ß C. The material exhibits system. A structure solution in P1 Å did not give a good a very small positive dielectric anisotropy and it has a combined gure of merit. The resulting E-map did not very small dipole moment [1], as compared with other reveal the complete structure nor could it be further mesogens. The dielectric constant along the preferred expanded by a diOE erence Fourier map after a few cycles direction (along the nematic director) is slightly greater of re nement. than that in the transverse direction. The small value of Subsequently the structure was solved in the nonthe dielectric constant is due to the absence of a strongly centric space group P1. The peak list from SHELXS-97 polar end group. The dipole moment contributed by the revealed all the phenyl rings and the side chains were COOH group is 1.7 D whereas the dielectric anisotropy revealed partially. The diOE erence Fourier map showed is in the range 0.15-0.38 D. The dipole moment of the the positions of all missing non-hydrogen atoms. The molecule is 0.40 D. 4-n-Nonyl benzoic acid in pure form structure was re ned by full matrix least-squares using is not used for electro-optic devices because of low SHELXL-97 [4], using 6002 unique re ections. The birefringence, but there is a continued interest in nematic hydrogen atoms were generated at chemically acceptable liquid crystals with low optical birefringence, as is evident positions and re ned with isotropic thermal parameters from the work of Dalmolen et al. [2]. assigned to them. 997 parameters were re ned using 5352 observed re ections with I > 2s(I) to R1 = 0.063 and wR2 = 0.16. In the nal diOE erence map Dr max = 0.191, ExperimentalDr min = Õ 0.203 e A Ã Õ 3, and goodness-of-t = 1.029. After Clear needle-shaped crystals of the title compound the completion of the structure, the coordinates were (Merck Ltd., England ) were obtained from a solution in checked for missing symmetry using BUNYIP [5 ]. No acetone. A crystal of approximate siz...

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“…From electric dipole moment molecular polarizability anisotropy were evaluated the size and the value of dielectric anisotropy. The dielectric anisotropy is low and positive in the absence of a dipole moment [3][4][5][6][7][8][9][10]. The present paper discusses the dipole structure of 4-4 0 Dipentylazoxy benzene and their dielectric properties.…”

Section: Introductionmentioning

confidence: 98%

Static Dielectric Studies in the Nematic Phase of a Nematogenic Compound

Gopalakrishna¹

2011

Molecular Crystals and Liquid Crystals

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Static dielectric permittivity in the nematic phase of a Nematogenic compound 4-4 0 Dipentylazoxy benzene had been measured at various temperatures using a sensitive LCR meter. Using these data, the dipole moment associated with the molecule is calculated. The validity of this approach is discussed by comparing the order parameter 'S' obtained from the Refractive index with the values of 'S' computed from the predictions of the mean field theories. Boardwijk's theory is applied here with appropriate molecular parameters to compute dipole-dipole correlation factor.

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Static Dielectric Studies of Some Nematogenic Compounds

Cited by 7 publications

References 6 publications

Dielectric investigations in the nematic and hexatic smectic B phases of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

Dielectric investigations in the nematic and hexatic smectic B phases of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl

Crystal structure of 4-n-nonylbenzoic acid

Static Dielectric Studies in the Nematic Phase of a Nematogenic Compound

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