Bend and Splay Elastic Constants of Some Discotic Nematic Compounds

AbstractThe dielectric constants and the elastic coefficients for splay and bend of the discotic nematic phase of three homologous hexakis-((4-alkylphenyl)ethynyl)benzenes and of 1,2,3,5,6,7-hexakis((4-nonyl-phenyl)ethynyl)naphthalene have been determined by studying the electric field induced bend deformation using a capacitance method. For all compounds a negative dielectric anisotropy was found. The bend elastic constants are between 1*10−12N and 4*10−12N which is in the same order of magnitude as for nematic phases consisting of rod-like molecules. An inverse behaviour to that generally expected for rod-like molecules is found for the homologues of the benzene series: K1 is larger than K3 and the ratio K1/K3 decreases slightly with temperature as well as with increasing alkyl chain length.