Determination of the Frank Elastic Constant Ratios in Nematic Liquid Crystals (nCB) by Observing Angular Dependence of Rayleigh Light Scattering Intensity

Abstract

The Frank elastic constant ratios, K ₁₂ and K ₃₂ in a homologous series of nCB (n = 5 − 8) were determined as a function of temperature by observing the angular dependence of Rayleigh light scattering intensity. The temperature dependence of K ₁₂ exhibits an odd-even effect. Both K _l2 and K ₃₂ obtained are clearly smaller than the reported values by means of other methods, e.g., the Frederiks transition method. However, our K ₃₁ indirectly deduced from K ₃₂/K ₁₂ shows good agreement with that by others. Characteristic temperature dependences due to the appearance of the pretransitional ordering were observed in 8CB which has the smeclic A phase below the nematic phase; K ₁₂ significantly diverges and K ₁₂ shows a sudden descent as a smectic A is approached. On the basis of these experimental results, we claim that the Rayleigh light scattering is the most adequate method of determining the Frank constant ratios.