Metal diffusion in polymers

Various investigations, involving surface spectroscopy, electron microscopy, ion scattering, direct radiotracer measurements, and Monte Carlo simulations have contributed considerably to our understanding of metal diffusion in polymers. A strong correlation has been established between the reactivity of a metal and its diffusion behavior. Reactive metals like Cr and Ti form relatively sharp interfaces with polymers. While these metals do not seem to exhibit significant mobility in polymers, metals of low reactivity such as Cu, Ag and Au proved to be quite mobile. Noble metal diffusivities are yet many orders of magnitude smaller than diffusivities of gas molecules of comparable size. This points to a marked metal-polymer interaction even for weakly interacting metals. Diffusion of mobile metal atoms into polymers is strongly impeded through their tendency to aggregate. As a consequence no significant diffusion into polymers is expected from a continuous metal film. Pronounced diffusion was only observed during metal deposition at very low rates and elevated temperatures, where a large fraction of isolated metal atoms is able to diffuse into the polymer before being trapped by other atoms at or near the surface.