Nature of interfacial interaction mechanisms between polyacrylic acid macromolecules and oxide metal surfaces

• Published in: Journal of materials science 1984-12, Vol.19 (12), p.4045-4056
• Main Authors: SUGAMA, T, KUKACKA, L. E, CARCIELLO, N
• Format: Article
• Language: English
• Subjects: Application fields; Applied sciences; Exact sciences and technology; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/bf00980770

The mechanism for the adhesion of polyacrylic acid (PAA) coatings to oxidized metal surfaces has been studied. The work entailed studies of the mechanical and chemical interactions occurring at the interfaces between PAA polyelectrolyte macromolecules and iron (III) orthophosphate dihydrate or zinc phosphate hydrate (hopeite) crystalline films that were deposited on the metal surfaces. With respect to mechanical interactions, it was determined that the surface topography of the highly crystallized hopeite layers consisted of an open microstructure. This resulted in enhanced wettability of the oxide film by the polyelectrolyte macromolecules, thereby increasing the mechanical interlocking bond forces. Studies of the interfacial chemical reactions indicated that the conformation changes in the PAA macromolecules related directly to the frequency of the magnitude of acid/base and divalent metallic ion cross-linking interactions between the proton-donating pendent COOH groups in PAA molecules and polar OH groups at hydrated oxide surface sites. Namely, the presence of numerous free nucleophilic ions existing on the deposited oxide film leads to a substantial increase in the coil-up and entanglement macromolecule density. These entangled complex macromolecules at the interfaces result in a decrease in the degree of chemisorption at the oxide film surfaces, whereas regularly oriented COOH groups produce strong interfacial chemisorption with the polar OH groups. Since the polyelectrolyte macromolecules have hydrophilic pendent COOH groups, the polymer structure which appears best for use as an adhesive and coating should have only enough hydrophilic COOH groups to occupy all available polar OH groups at the oxide metal surface sites. 27 ref.--AA