DIFFUSION OF METALS IN POLYMERS

First information on metal diffusion in polymers resulted from surface spectroscopies which mainly provided insight into chemical interactio ns of metals at polymer surfaces and into their growth mode. Medium en ergy ion scattering, electron microscopy, atomic force microscopy, and second-harmonic generation revealed a strong tendency of metals of lo w and intermediate reactivity to form clusters when deposited onto pol ymers. The interplay of diffusion and aggregation was also studied by Monte Carlo simulations. Metal diffusivities were obtained from radiot racer and Rutherford backscattering measurements. The available result s show that reactive metals do not have any long-range mobility and ar e effective diffusion barriers. In contrast, isolated atoms of less re active metals diffuse deep into polymers at elevated temperatures. How ever, the very pronounced aggregation tendency of these metals effecti vely impedes diffusion unless they are deposited at rates of the order of monolayers per minute or lower. Nevertheless, traces of noble meta ls always diffuse into polymers during the early stages of metal depos ition, whereas no significant diffusion occurs from a continuous metal film. Even noble metal diffusivities are many orders of magnitude sma ller than diffusivities of non-reactive gas molecules and largely deco upled from polymer dynamics. This is attributed to a pronounced reduct ion in the local chain mobility near metal atoms, e.g., by temporary m etal-atom-induced crosslinking. (C) 1998 Elsevier Science S.A.