Concrete Formation of Organic Thin Film on Metal via Reduction of Aryl Diazonium Salt

Abstract

In this study, surface modification with organic thin layer concretely adhered to commercially available zinc coated steel surfaces was achieved with diazonium induced grafting process. Unlike electrically induced grafting process requiring extremely anhydrous condition, the diazonium induced grafting process works at room temperature, atmospheric pressure, in aqueous medium and without any external energy source. This process relies on the chemical reduction of diazonium salts by reducing agents in absence or presence of a vinylic monomer. Typically, aryl diazonium salts are reduced by reducing agent to give aryl radicals leading (i) to the formation of a grafted polyphenylene-like film on the substrate surface and (ii) to the initiation of the radical polymerization of the vinylic monomer in solution. The resulting radical-terminated oligomer chains formed in solution are then able to react with ortho site of the polyphenylene primer layer. Herein, a number of polymer thin-films, i.e. poly (acrylonitrile) (PAN), poly (methyl methacrylate), PMMA, poly (acrylic acid) (PAA) and polynitrophenylene (PNP) were successfully grafted on the steel substrates. Accordingly, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and contact angle were used to investigate grafted organic layers. Furthermore, lap shear test was conducted to evaluate the grafted organic layer can be used as an adhesion primer to plastic, i.e. polyamide 6 (PA6), and the durability of these joins after exposing to 92˚C hot water.