Thermodynamic and static properties of liquid crystals

The measurement of vibrational Raman depolarization ratios has been used to study molecular orientational order in uniaxial single domain nematic and smectic liquid crystal samples. This technique is demonstrated to obtain the same microscopic order parameter 〈P2〉=1/2 〈3 cos2ϑ−1〉, where ϑ is the angle between a molecular long axis and the uniaxial direction, as other existing methods. In addition, the next higher moment of the orientational distribution function 〈P4〉=1/8 〈35 cos4 ϑ−30 cos2ϑ+3〉 has been measured for the first time. The physical basis, theoretical apparatus, and experimental methods necessary for the application of this technique are thoroughly detailed in this paper. Measurements are presented of the temperature dependence of 〈P2〉 and 〈P4〉 of N‐ (p′‐butoxybenzylidene) ‐p‐cyanoaniline (BBCA) dissolved in N‐ (p′‐methoxybenzylidene) ‐p‐cyanoaniline (MBBA) and of pure MBBA in the isotropic and nematic phases, and in the isotropic, nematic, smectic A, and smectic B phases of N‐ (p′‐butoxybenzyl...

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Polarized Raman Scattering Studies of Orientational Order in Uniaxial Liquid Crystalline Phases

Raman-scattering techniques have been used to obtain a new quantitative measure of orientational statistics of individual molecules in a nematic liquid crystal. A marked discrepancy is observed between these measurements and the predictions of existing theories of nematic ordering.

Raman Scattering from a Nematic Liquid Crystal: Orientational Statistics

The calculation of the principal polarizabilities of nematic compounds with reference to the two approaches using either the Vuks formulae or the Neugebauer's relations is discussed. The polarizabilities and internal field constants have been calculated from the birefringence data in the nematic phase of seven compounds viz., (i) p-azoxyanisole, (ii) p-azoxyphene-tole, (iii) anisaldazine, (iv) p-methoxybenzylidene p-butylaniline, (v) 4-n-butyl-4 ′-ethoxy-α-chlorostilbene, (vi) 4-n-octyl-4′-etnoxy-α-chlorostilbene and (vii) mixture of the isomers of 4-methoxy-4′-butylazoxybenzene. The results support the validity of the Neugebauer's relations rather than the Vuks formulae. The isotropic polahzability and the polarizability α‖ parallel to the long axis of the molecules are accounted for on the basis that, in the case of the conjugated bonds immediately on either side and in between the benzene rings, the respective bond polarizabilities have values which correspond to their double bond polarizabili...

Optical Anisotropy of Nematic Compounds

Refractive indices of a mixture of nematic liquid crystals as functions both of wavelength and applied voltages were measured. The measured results are compared with a theoretical calculation in which first the distributions of tilt angle of the molecules were computed by solving a reorientation equation, then, the effective refractive indices were computed from this distribution using an index ellipsoid. It is shown that the agreement between the experimental measurements and the calculated values are fairly good within the experimental error.

Wavelength and Voltage Dependences of Refractive Indices of Nematic Liquid Crystals

The refractive indices of anisaldazine, CH3OC6H4CH:NN:CHC4H4OCH3, have been measured in the crystalline, nematic and isotropic phases and the orientational order parameter in the mesophase has been evaluated by the application of the Vuks formula. The curve for the order parameter versus the relative temperature (Te-T) is nearly parallel with those for p-azoxyanisole and p-azoxyphenetole and lies approximately midway between them.

N. V. Madusudana

Papers

Orientational order in anisaldazine in the nametic phase