Lithium carbonate and lithium oxalate were incorporated as leachable corrosion inhibitors in model organic coatings for the protection of AA2024-T3. The coated samples were artificially damaged with a scribe. It was found that the lithium-salts are able to leach from the organic coating and form a protective layer in the scribe on AA2024-T3 under neutral salt spray conditions. The present paper shows the first observation and analysis of these corrosion protective layers, generated from lithium-salt loaded organic coatings. The scribed areas were examined by scanning and transmission electron microscopy before and after neutral salt spray exposure (ASTM-B117). The protective layers typically consist of three different layered regions, including a relatively dense layer near the alloy substrate, a porous middle layer and a flake-shaped outer layer, with lithium uniformly distributed throughout all three layers. Scanning electron microscopy and white light interferometry surface roughness measurements demonstrate that the formation of the layer occurs rapidly and, therefore provides an effective inhibition mechanism. Based on the observation of this work, a mechanism is proposed for the formation of these protective layers.

The surface properties of polymeric materials are generally determined by the chemical groups present at their surface. For low surface energy polymeric films the preferential location of the low surface energy chemical groups at the surface is crucial for the low-adhesion properties which are of high interest for various engineering fields. Controlling the surface segregation of such chemical groups would allow maintaining the materials properties at high performance level all through its service lifetime. In this work we used a combined experimental–simulation approach to study the surface segregation and the bulk distribution of low surface energy polymeric dangling chains, chemically bonded to a cross-linked poly(urethane) network. The surface properties of the cross-linked polymeric films, prepared with different experimental parameters, were investigated by contact angle (CA) measurements and X-ray photoelectron spectroscopy (XPS). A dissipative particle dynamics (DPD) method was used to model the distribution of the low surface energy dangling chains, at the surface and in the bulk of the cross-linked systems, equivalent to the ones prepared experimentally. The combined results show with excellent agreement the segregation of the low surface energy polymeric dangling chains toward the air–polymer interface. The influence of different experimental parameters, such as fluorine concentration and dangling chains molecular mobility, on the surface segregation is discussed. DPD simulations revealed further details of the polymeric films structure: the formation of a depletion zone beneath the top surface and the presence of highly dynamic clusters of the polymeric dangling chains in the bulk of the network, but not at its surface.

No abstract

No abstract

A numerical method to simulate reactions in a cross-linked polymer is developed and applied to the photodegradation process of polyester-urethane clearcoats during artificial exposure in a Weather-Ometer. This coarse-grained simulation method, which is based on a kinetic Monte Carlo scheme, is verified with experimental data on the depth-resolved changes in optical properties and chemical composition that have been previously determined. By modelling the depth-dependency of physical processes that occur in the coating, such as the absorption of photons and the diffusion of oxygen, the experimentally observed evolution of depth gradients in chemical composition can be well described by the simulation. A sensitivity analysis of individual simulation input parameters with respect to a set of resulting observables is performed and the results provide insight into the influence of specific reaction mechanisms on the overall degradation process and help to distinguish essential from less important processes. The values of input parameters that result in the most accurate simulation of the experimental data are determined with an optimisation procedure. In this way, the numerical values of several kinetic and physical parameters that are difficult to determine directly in an experimental way, such as various reaction rate constants, can be obtained from the simulations.

No abstract

No abstract

No abstract