MEASUREMENTS OF TRANSPORT PROPERTIES IN THE NEMATIC AND SMECTIC PHASES OF VARIOUS COMPOUNDS

Electrical conductivities parallel and perpendicular to the long axis of the molecules (respectively all and a,) are presented for the nematic and smectic (A and B) phases of various compounds having a low latent heat of transition smectic At, nematic. All the materials show pretransitional effects in their nematic phase. The study of conductivity in smectics A has led us to distinguish two groups of materials. In the first one 011 becomes equal to a, a few degrees above the smectic A-nematic transition, while all is at least five times smaller than a, in the smectic A phase. Furthermore a, increases anomalously with decreasing temperature, which is observed also for the dye diffusion coefficient normal to the molecular axis. In the second group a11 differs only slightly from a,. The different behaviour of the conductivity in this group is probably related to the fact that the smectic A layers comprise two molecules.