One-Step Dipping Method for Covalently Grafting Polymer Films onto a Si Surface from Aqueous Media

A facile and one-pot dipping method was proposed in this article for the first time to prepare vinylic polymer films on a silicon (Si) surface. This novel process was conducted in acidic aqueous media containing 4-nitrobenzene diazonium (NBD) tetrafluoroborate, hydrofluoric acid (HF), and vinylic monomers at room temperature in the open air and without any apparatus requirement. The formation of the polyvinyl film was confirmed by corroborating evidence from ellipsometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) analysis. The results revealed that both polymers of poorly water soluble methyl methacrylate (MMA) and water-soluble acrylic acid (AA) monomers were covalently grafted onto the Si surface via this simple process. The polyvinyl film was composed of polynitrophenyl (PNP) and polyvinyl, where PNP was doped into polyvinyl chains throughout the entire film. From a mechanistic point of view, the simple dipping method took advantage of the ability of the NBD cation to be spontaneously reduced at the Si surface at open circuit potential, providing aryl radicals. These radicals can be covalently bonded to the Si surface to form the PNP primer layer. Although the PNP sublayer was thinner and difficult to detect, it was necessary to graft polyvinyl chains. Furthermore, the aryl radicals were used to initiate the polymerization of vinylic monomers. The radical-terminated polyvinyl chains formed in the solution were then added to the aromatic rings of the primer layer to form the expected polyvinyl film.