Electrochemical analysis of the adsorption and desorption behaviors of carboxylic acid and anhydride monomers onto zinc surfaces

The interfacial bondings formed between succinic acid and myristic acid, as well as succinic anhydride molecules with a set of differently treated zinc substrates have been investigated using infrared reflection absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The compounds were selected to model typically used carboxylic-based adhesives and coatings. Moreover, the adsorption kinetic has been evaluated by means of chronoamperometry (CA) and chronovoltammetry measurements. XPS results showed a relation between the amount of carboxylates formed by adsorption of succinic acid/myristic acid and the hydroxyl fraction presented on the surfaces as proved by a higher electron transfer in CA. On the other hand a set of oxidative/reductive interactions was detected during the adsorption of succinic anhydride, in turn proving a spontaneous ring opening and adsorption mechanism. A clear relationship between the amount of adsorbents and surface hydroxyls/carbonates was detected for the adsorption of succinic anhydride. The extent to which the formed carboxylates resisted negative potentials was also investigated by cyclic voltammetry (CV) in an aqueous solution. The coordinative bonding of a bifunctional carboxylic acid group to the oxide surface was found to be not stable in the presence of a negative potential, while a monofunctional carboxylic acid group could resist displacement by water for a prolonged period of time. On the other hand, a low double layer capacitance was obtained after the adsorption of succinic anhydride, which was related to a change in potential of zero charge (PZC) upon the adsorption.