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Latha D.M.,Koneru Lakshmaiah College of Engineering | Pisipati V.G.K.M.,SSD Polymers | Prasad P.V.D.,SSD Polymers
Liquid Crystals | Year: 2013

Temperature gradient of refractive indices, dne/dT and dno/dT, of the isotropic mixtures of the liquid crystals of nO.m compounds, namely N-(p-n-butyloxybenzylidene)-p-n-hexyl aniline, 4O.6, and N-(p-n-hexyloxybenzylidene)-p-n-butyl aniline, 6O.4, are estimated using the refractive index data. The former one exhibits a second-order nematic-to-smectic-A (N-SmA) phase transition, while the later compound shows a first-order (N-SmA) phase transition. These two compounds exhibit high clearing temperatures, i.e. well above the room temperature. It is found that the two materials and the mixtures exhibiting second-order N-SmA transition show the crossover temperatures (TCO's) well below the room temperature while the mixtures showing first-order transition exhibiting TCO's well above the room temperature. © 2013 Copyright Taylor and Francis Group, LLC. Source


Pardhasaradhi P.,Koneru Lakshmaiah College of Engineering | Pisipati V.G.K.M.,Koneru Lakshmaiah College of Engineering | Prasad P.V.D.,SSD Polymers
Molecular Crystals and Liquid Crystals | Year: 2015

As a part of our systematic studies on liquid crystals of nO.m, n.Om, nO.Om and n.m homologous series, n-(p-n-alkoxy/alkylbenzylidene)-p-n-alkyl/alkoxy anilines, we present in this article the nature of phase transitions across isotropic-nematic exhibited by all the compounds mentioned below. Further, the orientational order parameter in the nematic phase of N-(p-n-propyl/propyloxy benzylidene)-p-n-alkoxy anilines, 3.Om and 3O.Om with m = 6-8 are estimated from the molecular polarizabilities calculated using the experimental refractive indices and density results. The molecular polarizabilities αe and αo are obtained for all the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. αe and αo calculated in this way are used to obtain Δα. The polarizability anisotropy in the perfect order (absolute K) is calculated theoretically using the δ-function model developed by Lippincott et al. and molecular vibration method. These enabled the calculation of the orientational order parameter S. The values of polarizability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence measurement and this value of S is compared with those obtained from field models. Copyright © Taylor & Francis Group, LLC. Source


Rao D.V.,S v University | Pardhasaradhi P.,Koneru Lakshmaiah College of Engineering | Pisipati V.G.K.M.,Koneru Lakshmaiah College of Engineering | Prasad P.V.D.,SSD Polymers
Phase Transitions | Year: 2015

Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1-T/Tc) β, effective geometry parameter g and Vuks scaling factor SC. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks method. © 2014 Taylor & Francis. Source

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