Electro‐optic effects in nematic liquid crystals

Experimental results on the electro-optic effects in nematic liquid crystals are presented. A hexagonal grid pattern is observed with (ac + dc) field at a critical frequency f(c) (168 Hz). The time required for the formation of the grid pattern with applied field is estimated

Thermotropic Liquid-Crystalline Phases in Binary Mixtures of Nonmesogenic Compounds

DSC and optical microscopic studies show that the mixtures of two nonmesogenic compounds, viz., cetyl alcohol and orthophosphoric acid, exhibit polymorphic smectic mesophases at different temperatures. With the help of phase diagrams of this binary mixture, the phase behavior is discussed. The X-ray studies at different temperatures of the system reveal that the molecular area of the polar head at high temperature is twice the molecular area of the crystallized aliphatic chains at lower temperature. Electroconductivity and birefringence measurements have been done and the results are consistent with the above observations. Spectroscopic studies like NMR (H-1 and P-31) and mass spectral analysis clearly establish that the system is a simple mixture exhibiting polymorphism

Optical Behaviour of Cholesteryl-2-Propyn-l-yl Carbonate

The paper discusses the study of phase behaviour of cholesteryl-2-propyn-1-yl carbonate (cpc) by DSC, optical microscopy and X-ray diffraction methods. The optical anisotropy and local order parameters are estimated using the measured density and refractive index data. The local order parameter corresponds to the untwisted nematic structure in the cholesteric phase. It is found that the optical anisotropy arising from the chain length is significant when compared to the core contribution

Order Parameter of Mixtures of Nematic Compounds

The orientational order parameters of the binary mixtures of three nematic compounds are calculated using the measured densities and refractive indices. The order parameter values are found to be in good agreement with the Maier-Saupe theoretical values

Mesomorphic Behaviour of Binary Mixtures of Two Non‐Mesogenic Compounds

Mixtures of two non-mesogenic compounds viz., stearyl alcohol (SA) and orthophosphoric acid (H3PO4) are found to exhibit lyotropic (non-aqueous) mesophases. The phase transition temperatures for different concentrations of SA in H3PO4 are determined using DSC. The phase diagram of binary mixture is illustrated. The different phases observed in these mixtures are identified using X-ray diffraction and optical microscopy techniques

Thermotropic Liquid Crystalline Phases in Binary Mixture of Nonmesogenic Compounds

The binary mixture of two nonmesogenic compounds viz., Tetradecyl Trimethyl Ammonium Bromide (TTAB) and Orthophosphoric acid (H3PO4) exhibits very interesting liquid crystalline smectic phases at large range of concentrations and temperature. The mixture with lower and higher concentrations of TTAB exhibits Sm A, Sm D, Sm B, and Sm E phases, sequentially when the specimen is cooled from its isotropic phase. Different liquid crystalline phases observed in the mixture were studied using DSC, X-ray, and Optical microscopic techniques. The temperature variation of optical anisotropy has also been discussed. Helfrich potential and elastic moduli have been estimated in the smectic phase using Helfrich model