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

Publisher Website
Google Scholar
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.