Estimation of order parameter from different models in symmetric dimeric liquid crystals

The birefringence measurements with the temperature are carried out employing the wedge technique at the wavelength λ = 5893Å on symmetric dimeric liquid crystalline compounds of α,ω-bis(4-alkylanilinebenzylidene-4′-oxy) alkanes which are popularly known as m.OnO.m's with m = 3, 4 and 5 and spacer length n = 8, 9 and 10. The studied compounds are mono variant with long range of nematic phase. The birefringence data δn = (n e -n o ) along with the density results are employed to estimate the molecular polarisabilty anisotropy, δα = (α e -α o ) assuming a particular local field (due to Vuks and Neugebauer) the nematic molecule experiences and the order parameter S is estimated from δα and Δα, i.e., polarisabilty anisotropy which is estimated employing different methods. Further, S can also be obtained from Kuczynski model and also using the effective geometry parameter, α g . Further, it is observed that from our analysis the S value obtained from Δn and α g are identical. The results are analysed and compared with the data available in the literature.