The first direct observation of a chemically heterogeneous nanostructure within an epoxy resin is reported. Epoxy resins comprise the matrix component of many high performance composites, coatings and adhesives, yet the molecular network structure that underpins the performance of these industrially essential materials is not well understood. Internal nodular morphologies have repeatedly been reported for epoxy resins analysed using SEM or AFM, yet the origin of these features remains a contentious subject, and epoxies are still commonly assumed to be chemically homogeneous. Uniquely, in this contribution we use the recently developed AFM-IR technique to eliminate previous differences in interpretation, and establish that nodule features correspond to heterogeneous network connectivity within an epoxy phenolic formulation.

The long-term failure of seemingly intact corrosion resistant organic coatings is thought to occur via the development of ionic transport channels, which spontaneously evolve from hydrophilic regions on immersion, i.e., as a result of localized water uptake. To this end, we investigate water uptake characteristics for industrial epoxy-phenolic can coatings after immersion in deionized water and drying. Moisture sorption and the changing nature of polymer-water interactions are assessed using FTIR for dry and pre-soaked films. More water is found to be absorbed by the pre-soaked coatings on exposure to a humid environment, with a greater degree of hydrogen-bonding between the polymer and water. Furthermore, morphological changes are then correlated to localized water uptake using the AFM-IR technique. Nanoscale softened regions develop on soaking, and these are found to absorb a greater proportion of water from a humid environment.

An investigation into corrosion inhibition properties of a primer coating containing lithium carbonate as corrosion inhibitive pigment for AA2024 aluminum alloy was conducted. It was found that, during neutral salt spray exposure, a protective film of about 0.2 to 1.5 μm thickness formed within the area where an artificial defect was introduced by scribing through the coating to the base alloy. This film showed a multilayered structure consisting of a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. The thicknesses of the layers varied, as a consequence of the difference in the local concentration of lithium species leaching from the primer coating. The presence of the film in the scribed area significantly reduced corrosion of the alloy, with little consumption of the metal substrate within the scribed area during neutral salt spray exposure. Furthermore, the presence of the protective film resulted in a significant increase of impedance modulus, measured after the salt spray exposure.