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Abstract
The refractive indices of p(p-ethoxyphenylazo) phenyl (EPAP) alkanoates, which are the nematic liquid crystals where the alkyl chain n is 5, 6, 7 and 11, were measured as a function of temperature at λ = 6328 Å using a wedge technique. The temperature variation of the orientational order parameter (S) is calculated at this wavelength using the Vuks model (with consideration of internal field) and by different methods excluding the internal field – Haller and Kuczynski models, and involving effective geometry parameter (αg). The intensity of light deflection in a uniaxial EPAP alkanoate with a particular molecular configuration and ordering by varying temperature is discussed. The temperature gradients of the ordinary (∂no /∂T) and extraordinary (∂ne /∂T) refractive indices are analysed. Due to a high clearing temperature with low molecular chain length, EPAP valerate exhibited low deviation of light with a large positive value of ∂no /∂T.
Acknowledgements
The authors are grateful for the financial assistance provided by UGC Major Research Project F: 34–12/2008 (SR) dated 30 December 2008, Project No. ERIP/ER/0703688/M/01/1134 dated 31 March 2010 of DRDO and for the UGC DRS Level III programme F.530/1/DRS/2009 (SAP–I), New Delhi, dated 9 February 2009.