Improved stability of thin insulating poly(o-aminophenol) films in aqueous solutions through an efficient strategy for electrosynthesis under neutral pH conditions: Electrochemical and XPS investigation

The stability of non-conducting poly(o-aminophenol) films (PoAP), electrosynthesized on Pt substrates by cyclic voltammetry and chronoamperometry, was investigated through electrochemical tests, evaluating changes in permeability to potassium ferricyanide upon prolonged immersion in water solutions. PoAP growth potentiodynamically evidenced poorer stability despite the similar chemical composition, thickness and morphology as detected by XPS and AFM. The prolonged dipping in water caused a post synthesis oxidation of part of iminic functionalities to carbonyls and the removal of polymeric chains weakly bound. Such a removal was estimated by QCM to be about the 43% of the mass deposited by cyclic voltammetry and about the 12% of the mass deposited by chronoamperometry. Potentiostatic deposition was then selected and implemented to achieve an enhanced stability suitable for film practical application. The novel deposition procedure herein proposed is composed of three successive stages: film potentiostatic deposition for 40 min, immersion in water for 1 h, further potentiostatic deposition for 20 min. The major packing efficiency, testified by the higher degree of platinum covering, was responsible for the notable long-term stability. Film compactness was attributed to the intensification of inter-chain hydrogen bonds, mainly between aminic groups, mediated by water molecules trapped inside the polymer at a high extent. The notable stability, verified in pure water as well as in concentrated saline solutions, and the presence of carbonyl terminal groups on the outermost surface, evidenced by Angular Resolved XPS, encourage a future employment of PoAP as a sensor for biomolecules capture and as anticorrosive coating.