Effect of electrolyte concentration and redox centre oxidation state on the layer mass of osmium-containing poly(4-vinylpyridine) films

Abstract

A quantitative analysis of the mass changes observed when an [Os(bipy)₂(PVP)₁₀Cl]Cl polymer is exposed to perchloric acid electrolytes of different concentrations is reported, together with the mass changes observed as a result of redox switching of the Os^II/III redox couple. The rigidity of the polymer under the conditions used is confirmed using admittance spectroscopy. The results obtained are discussed with reference to the structure of the polymer and the effect of osmotic pressure. The equilibrium mass changes observed show that ion and solvent transfer are greatly electrolyte dependent. From the mass changes observed as a function of the HClO₄ concentration, a pK_a value of 2.5 has been estimated for the immobilised film. Within the concentration range 0.01–1.0 mol dm^–3 HClO₄, electroneutrality is maintained during redox switching by counter-ion movement, but at very low HClO₄ concentrations (0.001 mol dm^–3) the mass changes observed are indicative of a mixed transport of co-ions and counter-ions. At concentrations greater than 1.0 mol dm^–3 permselectivity breaks down with transfer of salt occurring during oxidation.