Forced Rayleigh Scattering in nCB's (n=5-9) with Methyl Red and Binary Mass Diffusion Constants

Binary mass diffusion constants of methyl red in n CB's ( n =5-9) were measured by forced Rayleigh scattering. It was found that the diffusion constants in n CB's with odd carbon atoms in the alkyl chain are larger than those with even ones. This odd-even effect could be explained by the molecular structural anisotropy, which is mainly governed by the alkyl chain length. The origin of the transient grating in liquid crystalline phases is attributed to the periodic structure of an order parameter. An anomalous increase in the diffraction efficiency was observed as the phase-transition temperature was approached. This phenomenon could be interpreted as a photostimulated change in the phase transition temperature proposed by Odulov et al .