Coating process and stability of metal-polyphenol film

Supramolecular metal-organic thin films coated on material surfaces have attracted considerable interest in chemistry and materials science. Tannic acid (TA), a natural polyphenol product, has been recently demonstrated to be able to crosslink through coordination with Fe3+ ions, thus providing a novel metal-organic system to build nano-scale coating on various substrates. However, the coating process of Fe3+-TA film and the experimental parameters that influence the stability of the film are not well elucidated. In this study, we explored the effects of experimental parameters (order of reagents addition, addition of alkali and surface wettability of the substrates) on the stability of the Fe3+-TA film, and further inferred the mechanism of the coating process, using quartz and silicon as model substrates. The results showed that the Fe3+-TA films prepared in reverse order of reagent addition exhibited totally different growth profiles during the film formation process. The addition of alkali solution had very little impact on the film thickness, but changed the structure and morphology of the film and dramatically improved its stability. Moreover, low-wettable surface facilitates the formation of stable Fe3+-TA film. By the analysis of the chemical compositions, the mechanisms of the formation of these films were specified. This study provides a better understanding of the coating process of the Fe3+-TA film, which would benefit to develop the stable Fe3+-TA system with desirable properties for specific applications. (C) 2015 Elsevier B.V. All rights reserved.