Electrochemical behaviour of hexacyanoferrate(II)/(III) and ferrocene/ferricinium in lyotropic liquid crystals of polyoxyethylene (10) cetylether (Brij 56)

Abstract

The conductivity of a lyotropic liquid crystal medium (LLC) consisting of 50:50 wt% Brij 56® and 0.5 M aqueous KCl was found to be five times lower than the purely aqueous solution. Electrochemical properties of potassium hexacyanoferrate(II/III) and ferrocene/ferricinium in the LLC were examined by cyclic voltammetry and chronoamperometry on platinum foil and microdisk electrodes. The hexacyanoferrate showed reversible redox behaviour under diffusion control with a diffusion coefficient of 0.5 – 1.0 × 10–6 cm2s–1, up to 14 times lower than in water. Ferricinium reduction, while complicated in water by precipitation of ferrocene, showed solution behaviour and normal diffusion control in the liquid crystal. Effective diffusion coefficients of ferrocene and ferrocinium in the lyotropic liquid crystal were found to be further reduced to 4 – 5 × 10–8 cm2s–1. The lower diffusion coefficients compared with those in liquid solvents were attributed to restricted mobility and channel size effects in the LLC. The results are relevant to the design of electrochemical syntheses using LLC as nanostructured templates or as amphiphilic solvents