DC Conductivity in Smectic A Phases-A Breakdown of Kohlrausch's Law

Abstract

We have combined the two cations N-hexadecylpyridinium and the dicyclohexyl-18-crown-6 complex of sodium with the three anions bromide, p-toluenesulphonate and tetraphenylborate, into six different salts, and measured their conductivity in the smectic A liquid crystal, S3. This allows us to extract mobilities for the five individual ions.

It is found that the mobility of different ions within a smectic A layer is determined by the cross section the ion presents in the direction of movement, and the law of independent movements of ions is valid. For the mobility perpendicular to the smectic A layers the mobility is critically dependent on the quality of the homoetropic alignment. This quality will be determined by the history and alignment conditions of the sample, as well as any impurities present. The movement of the individual ions can thus no longer be treated independently of other ions or undissociated salt that are present in the sample.

Key Words:

• ionic conductivity
• smectic A