M. S. Madhava

Birefringence of some nematic compounds.

Abstract This paper reports the refractive index and density data and discusses the orientational order parameters in the case of the following eight nematic compounds, viz., (1)p(p-ethoxyphenylazo) phenyl valerate, (2) p(p-ethoxyphenylazo)phenyl hexanoate, (3) p(p-ethoxyphenylazo)phenyl heptanoate, (4) p(p-ethoxyphenylazo)phenyl undecylenate, (5) 4,4′-bis(hexyloxy)azoxybenzene, (6) 4,4′-bis(heptyloxy)azoxybenzene, (7) anisylidene-p-aminophenyl acetate, and (8) anisylidene-p-aminophenyl butyrate.

Optical Effects and Molecular Ordering in Spherulites

Abstract The optical behaviour of spherulite textures exhibited by mixtures of cholesteryl acetate and cholesteryl ethyl carbonate is investigated. The observed optical effects arise due to a helicoidal arrangement of the molecules along the radial directions of the spherulites, the long axes of the molecules being oriented transverse to the radial directions. The helicoidal nature of the structure is strikingly demonstrated by two sensitive interference experiments wherein sinusoidal interference fringes are observed. The observed results are in agreement with the theory developed for the interference effects.

Optical Behaviour of Spherulite Textures of Cholesteryl Acetate Doped with Cetyl Alcohol

Abstract Optical diffraction rings are observed in the solid phase with spherulite textures of cholesteryl acetate and cholesteryl acetate doped with varying amounts of cetyl alcohol, the rings being intense and sharp in the case of the latter. The diffracted light is polarized with its vibration direction transverse to the radial direction of the spherulite. When observed under the polarizing microscope, the textures exhibit fine circular rings corresponding to the periodic nature of the structure along each radial direction. It emerges from the observed results that in the spherulites, along each radial direction the molecules are arranged in a helicoidal structure. In the case of the doped samples, the cetyl alcohol molecules endow the structure with a more uniform pitch for the helicoidal arrangement about each radial direction. The spherulite textures of doped samples are found to be metastable and they undergo a slow transformation to a fibrillar crystalline texture, the domains of which give rise t...

Refractive Indices, Lorentz Field Factors, Order Parameters In Pure and Binary Nematic Mixtures

Using the small angle prism technique refractive indices are measured at different temperatures in the nematic phase of (i) two nematogenic compounds, viz., hexylbenzoic acid (HBA) and diheptyl azoxybenzene (DHAB), and (ii) binary mixtures of HBA and octylbenzoic acid(OBA) (Mixture-I), and DHAB and nonylbenzoic acid (NBA) (Mixture-II). From the measured refractive index data and employing Neugebauer relations, anisotropy of Lorentz field factors and orientational order parameter have been estimated. The higher order parameter ?P4? has also been computed using the Humphries-James-Luckhurst model and is compared with that of Maier-Saupe model.

Order parameter and distribution functions for nematogenic OBA and NBA

Abstract Using refractive index and density data for nematogenic compounds Octyl benzoic acid (OBA) and Nonyl benzoic acid (NBA), orientational order and hence distribution function has been determined. From this, the higher order parameter has been estimated for these two compounds. The physical interpretation of these parameters and has been given in terms of statistical quantities like variance and kurtosis.

Orientational distribution function in nematic liquid crystals by x-rays: Fourier method

The existing methods for the determination of the orientational distribution functionf(β) in the nematic liquid crystals using X-rays have been reviewed. A simple Fourier method which givesf(β) in terms of the measured intensity is analysed. Using this distribution function, the accuracy with which the order parameters could be evaluated is discussed and the results show the elegance of the Fourier method used here.

Lamellar Mesophase(G) in Mixtures of Stearyl Alcohol and Dimethyl Sulfoxide

The mixts. of stearyl alc. and DMSO exhibit lamellar mesophase (G) with a double layer of mols. sepd. by DMSO layers. A phase diagram for this binary mixt. is also given. [on SciFinder(R)]

Refractive Indices, Densities and Optical Anisotropy of Cholesteryl Oleate

Abstract Density and refractive index data of cholesteryl oleate in the smectic, cholesteric and isotropic phases are reported and the effective principal polarizabilities in the cholesteric and smectic phases are calculated. There is a systematic decrease in the effective optical anisotropy with increase in temperature owing to the decrease in orientational order.

Refractive Index, Density and Distribution Function in Nematic Mixtures

Abstract Using refractive index and density data for the nematogenic mixtures Octyl benzoic acid (OBA) and Nonyl benzoic acid (NBA), orientational order and hence the distribution function has been determined. From this higher order parameter has been computed.

Optical properties of spherulites of cholesteryl-do-decyl carbonate

We report here some very interesting optical textures exhibited by a pure cholesterogenic compound viz., Cholesteryl-do-decyl carbonate. It also exhibits ringed spherulitic texture when crystallized at different temperatures. The observed ring spacing is found to increase with the increase of crystallization temperature and we were also able to determine Avaramis constants by studying the growth rate of these spherulites. Light scattering and optical diffraction studies have been carried out using optical textures exhibited by the sample. The local order parameters corresponding to untwisted nematic structure in the cholesteric layer has been estimated at various temperatures in the cholesteric phase using the measured refractive index and density data.