DC CONDUCTIVITY IN SMECTIC-A PHASES - A BREAKDOWN OF KOHLRAUSCH LAW

We have combined the two cations N-hexadecylpyridinium and the dicyclo hexyl-18-crown-6 complex of sodium with the three anions bromide, p-to luenesulphonate and tetraphenylborate, into six different salts, and m easured their conductivity in the smectic A liquid crystal, S3. This a llows us to extract mobilities for the five individual ions. It is fou nd that the mobility of different ions within a smectic A layer is det ermined by the cross section the ion presents in the direction of move ment, and the law of independent movements of ions is valid. For the m obility perpendicular to the smectic A layers the mobility is critical ly dependent on the quality of the homoetropic alignment. This quality will be determined by the history and alignment conditions of the sam ple, as well as any impurities present. The movement of the individual ions can thus no longer be treated independently of other ions or und issociated salt that are present in the sample.