Hydrolysis of interfacial bonds in a metal/polymer electrical double layer

Abstract

Effect of water on the electrical double layer structure at a metal/polymer interface is studied with the use of scanning vibrating capacitor and electrochemical impedance spectroscopy. In the initial stage, the Volta potential of the contact changes well reversibly and rapidly, being proportional to the water vapor pressure, following its diffusion in the polymer ( ∆ V = A + B log (time) 1/2 ). Water dipoles at the metal/polymer interface orientate counter the field and compensate it. Drying of the contact restores the initial potential drop. In the first stage of exposure, water somewhat enhances the interfacial interaction, which manifests itself in increasing the potential drop, as well as the charge transfer resistance, and in decreasing the capacitance of the electrical double layer. As time passes, the interface hydrolyzes, its capacitance grows and the time of subsequently restoring the electrical double layer by drying increases. Kinetic dependences of the potential and capacitance, exhibit two segments, we ascribe to easily removable and strongly bonded water molecules solvating the interface, respectively. It is shown that metal-polymer interfacial bonds passivate the metal; however, the passivation can be broken down because of the hydrolysis and the interfacial moisture film formation.

Novel conducting polymer based composite coatings for corrosion protection of zinc

“…Another problem is that CPs applied on zinc lead to the formation of an insulating layer at CP/metal interface resulting in electronically decoupling (Fermi-level misalignment) between the CP and the metal, leading to a seemingly too low potential. Williams et al [18,19] and Nazarov and Thierry [20] also observed very low potentials when the coatings based on CPs were used on zinc, which can be explained by Fermi-level misalignment [17,21]. Consequently the CP is incapable of sensing the potential decrease occurring when the metal changes from passivity to active corrosion [15,17,21,22].…”