Experimental Confirmation of Angular Dependence of Rayleigh Line Spectral Width in Nematic Liquid Crystals

We compared calculated results with experimental data on the scattering angular dependence of the relaxation time corresponding to the Rayleigh line spectral width obtained by using a homeotropically- and homogeneously-aligned cell to check the validity of the Orsays formulas for the dynamic behavior of the director modes and the accuracy of scattering measurements. However, to increase the strength of the scattered intensity, we tilted the cell, thus changing the angle φ' between the incident light and the director over a range of -30°≤φ'≤30° and 60°≤φ'≤120°, while keeping the director in the scattering plane. All measurements were made using the homodyne technique. The obtained experimental data were within an accuracy of 0.1% for the refractive index, 5% for the elastic constant ratio and 3% for the relaxation time. Experimental results indicate that the Leslie viscosity coefficients µ 1 and µ 3 of MBBA are very small in comparison with the four other coefficients. By using the twist elastic constant K 2 , other Leslie viscosity coefficients can be given as µ 2 / K 2 =-26×10 9 , µ 4 / K 2 =20×10 9 , µ 5 / K 2 =16×10 9 and µ 6 / K 2 =-10×10 9 in kgm -1 s -1 /N at a temperature T - T NI =-21°C (nematic-isotropic transition temperature T NI =46.2°C). Temperature variations in the relaxation time for splay, twist and bend deformation are also described.