Properties of molten carboxylates. Part 8.—A.c. impedance of mesophases of some even chain length lead(II) n-alkanoates

Abstract

Measurements have been made of the conductance of lead(II) n-alkanoates of even carbon chain length from hexanoate to octadecanoate inclusive in the liquid crystalline region. Phase transitions are reproduced in agreement with previous d.t.a. studies. There is only a small change in conductance on transition of the liquid to the V₂ phase and activation energies for these phases are similar to those in the liquid. The activation energies for conductance in the laminar G phases are chain length dependent indicating that the charge transporting species may contain the carboxylate group. Conductance and capacitance are frequency dependent in all phases. In the liquid and V₂ phases the effect of frequency on conductance is small and on capacitance large. It may be explained by the linearised space charge polarisation theory (LSCPT), if there are two charge carriers the discharge of the minor of which is blocked at the electrode whilst the other carrier is free. In the G phases the effect on conductance is large whilst that on capacitance relatively small. The data are inconsistent with the LSCPT and can not be fitted by a single relaxation time. Similar effects are observed for the solid phases and for solid sodium isovalerate. A model is proposed that may qualitatively explain the observations.