Novel approach to the study of the ion and solvent content of thin polymer films

Abstract

The admittance response of [Os(bpy) ₂ (PVP _x ) ₁₀ Cl] ⁺ crystal coatings, where x signifies the percentage of poly(4-vinylpyridine) (PVP) in PVP:styrene copolymers, is probed as a function of both the styrene content of the polymer backbone and the HClO ₄ bathing electrolyte concentration. Analysis of the admittance response of these coated crystals provides information about solvent uptake when the coatings are immersed in water and also about the changes in layer mass accompanying protonation of the unbound pyridine units in acidic solution. With increasing styrene content of the polymer backbone the requirement for anion and solvent ingress is proportionally reduced. For the polymers investigated, there is good correlation between the mass change observed in 0.5 m HClO ₄ and the mass change anticipated, assuming complete protonation of the polymer backbone. The apparent acid dissociation constant of the protonated pyridine units, pK _a ^app , for these polymers is 2.66±0.06, and is independent of the styrene content of the polymer backbone.