IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Applied Surface Analysis Thursday Sessions
       Session AS-ThA

Paper AS-ThA2
Polymer-metal Interfaces: The Influence of a Metallic Surface on the Interphase Formation Mechanisms

Thursday, November 1, 2001, 2:20 pm, Room 134

Session: Adhesion and Corrosion
Presenter: A.A. Roche, INSA de Lyon, France
Authors: A.A. Roche, INSA de Lyon, France
M.-G. Barthés-Labrousse, CNRS, France
J. Bouchet, INSA de Lyon, France
F. Debontridder, CNRS, France
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Epoxy-diamine networks are extensively used as adhesives or paints in many industrial applications. It will be shown in this paper that studies carried out starting from the adsorption of simple diamine molecules to the application of an epoxy-diamine mixture onto oxidized metallic surfaces can lead to a better understanding of the chemistry inducing the interphase formation and to the adhesion mechanisms of epoxy systems on metallic substrates. Results obtained following deposition of either pure diamines or mixtures of epoxy and diamines onto gold and aluminum surfaces will be presented. When mixtures of epoxy-diamine are applied onto gold coated substrates, the properties obtained for the coating are the same as the bulk network ones. When the precursors are applied on oxidized or hydroxylated metallic substrates and subsequently cured, an interphase is created between the substrate and the polymer, which has chemical, physical and mechanical properties quite different from the bulk polymer ones. For example, when mixtures of epoxy-diamine are applied onto aluminum surfaces, the glass transition temperature, the reaction rate between amine and epoxy, the interphase thickness, the residual stresses within the interphase and the Young’s modulus of the interphase all depend on the amine nature (aromatic, aliphatic or cycloaliphatic), the stoichiometric ratio, the processing conditions (time and temperature), the organic layer thicknesses and the metallic surface treatment nature. Characterization of the metallic surfaces (XPS, IRRAS, GXRD) shows that, whatever may be the surface treatment of the metallic substrates, adsorption of the diamine monomer onto the metallic hydroxylated surface leads to both Lewis (bonding between the metallic surface cationic sites and the diamine nitrogen atom) and Brønsted (bonding between the hydroxyl groups and protonated amine function) acid-base interactions. The change in the ratio between Brønsted and Lewis type interactions can be ascribed to the differences in hydroxylation of the superficial oxide layer. Besides, coating spectroscopy data (FTIR, FTNIR, DSC, DMTA, H+ and C13 NMR, SEC, ICP and POM) suggest that diamine monomers dissolve the metallic hydroxylated oxide layer. Then, the metallic ions diffuse through the liquid organic layer to form a complex by coordination with diamine monomers (chelate or ligand). When metal-amine complexes are mixed within the DGEBA monomer a phase separation is induced during the curing cycle, leading to the formation of a new network. Furthermore, when the organo-metallic complex concentration is higher than the solubility product, these complexes crystallize as sharp needles. They align themselves parallel to the metallic oxidized surface and act as oriented short fibers in an organic matrix thus leading to an increase of its mechanical properties.