BEND AND SPLAY ELASTIC-CONSTANTS OF DIHEPTYLAZOXYBENZENE

In this study we report the values of the bend (K3) and splay (K1) elastic constants of the nematic liquid crystal diheptylazoxybenzene, using a Freedericksz-transition technique. Both the bend and the splay constants were measured over a range of temperatures approaching the nematic-smectic-A (NA) transition. The ratios of K3/K1 follow the trend of increasing towards the NA transition, which makes the conditions favorable, in the homeotropic geometry, for striped instabilities to set in. The value of K3/K1 for our material is fairly small at higher temperatures when compared to similar materials, which is consistent with the decreasing of K3/K1 with an increasing alkyl-chain length. The bend critical exponent rho3 was determined to be 0.68 +/- 0.04, which is in close agreement with a prediction of de Gennes [Solid State Commun. 10, 753 (1972)]. The effect of the nematic range on this critical exponent is examined in terms of a critical-multicritical crossover.