Orientational order in three nO.m liquid crystalline compounds

Abstract

Refractive index and density measurements have been carried out on three nO.m liquid crystalline compounds, namely, 4O.2, 4O.3 and 1O.10 belonging to the N-(p-n-alkoxybenzylidene)-p-n-alkylaniline series. From the data, the orientational order parameter has been estimated using Vuks and Neugebauer local field models. Furthermore, the orientational order parameter has been calculated directly from refractive index data employing the Vuks scaling factor method, Neugebauer f(B) parameter, effective geometry parameter and a method proposed by Kuczyński et al. It is observed that order parameter values estimated from different methods agree well near the nematic–isotropic transition and diverge as the nematic phase attains equilibrium. The temperature gradient of refractive indices and the nematic crossover temperatures have also been estimated for these compounds. The results obtained are compared and discussed.

Keywords:

• nO.m series
• nematic
• orientational order parameter
• birefringence
• density
• crossover temperature

Acknowledgements

The authors acknowledge M/s SSD Polymers, Machilipatanam, for providing the facilities for refractive index and density measurements. The authors thank Prof. V.G.K.M. Pisipati and Dr P.V. Datta Prasad for fruitful discussions. Author M.K. Usha acknowledges the Department of Science and Technology (DST), New Delhi, for the award of an INSPIRE fellowship. N. Vinutha is grateful to the University Grants Commission (UGC), New Delhi, for the award of an RFSMS fellowship.

Additional information

Funding

D. Revannasiddaiah is thankful to the UGC for financial support under the Major Research Project Scheme [F.No. 41–882/2012 (SR)] and UPE project.