Diffusion in Coatings - pdf
Charlie Wand1, Simon Gibbon2,3 and Flor Siperstein1
1 Department of Chemical Engineering and Analytical Science, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
2 AkzoNobel Research & Development, Northallerton, North Yorkshire, DL7 7BJ, UK
3Department of Materials, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
The infrastructure of our modern society relies on large scale metal structures, which have a very large embedded carbon dioxide footprint. Protective organic coatings are key to sustainability as they extend the life of assets in aerospace, automotive, and freight by providing protection against corrosion. It has been considered that polymer coatings provide corrosion protection by forming a barrier to prevent mass transfer between the metal surface and the surroundings. However, it has been shown that water can permeate through these coatings and reach the metal surface [1]. Therefore the mechanism for corrosion protection is significantly more complex than originally assumed, with the transport of species through the coating playing a significant factor in corrosion protection properties of the coating.
Here we perform atomistic molecular dynamics simulations to investigate the diffusion of water through an epoxy-amine coating and investigate the effect of temperature, cross-linking (cure), and moisture content on the diffusion of water through the organic coating. We find that water diffusion is via a polymer-assisted hopping mechanism between isolated free volume nanoscale pores and that the polymer mobility is the determining factor for the speed of water diffusion [2].
[1] C. Grave, I. Mcewan, and R. A. Pethrick, Influence of Stoichiometric Ratio on Water Absorption in Epoxy Resins, J. Appl. Polym. Sci. 69, (1998).
[2] C. R. Wand, S. Gibbon, and F. R. Siperstein, A Computational Study of Water Diffusion through an Epoxy-Amine Thermoset Polymer, Prep. (n.d.).