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

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Abstract
Electrical conductivities parallel and perpendicular to the long axis of the molecules (respectively σ|| and σ⊥) are presented for the nematic and smectic (A and B) phases of various compounds having a low ratent heat of transition smectic A ↔ 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 σ|| becomes equal to σ⊥ a few degrees above the smectic A-nematic transition, while σ|| is at least five times smaller than σ⊥, in the smectic A phase. Furthermore σ⊥ increases anomalously with decreasing temperature, which is observed also for the dye diffusion coefficient normal to the molecular axis. In the second group σ|| differs only slightly from σ⊥. The different behaviour of the conductivity in this group is probably related to the fact that the smectic A layers comprise two molecules

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