Free radical-induced grafting from plasma polymers for the synthesis of thin barrier coatings

Plasma polymer films (PPF) are attracting a great deal of attention for application in various fields due to several remarkable properties, such as good adhesion to different substrates, improved mechanical/chemical stability and a high surface reactivity. This reactivity, associated with the presence of free radicals and originating from the PPF growth mechanism based on many fragmentation and recombination reactions, is often, however, a potential source of trouble. Oxidation of the PPF promptly begins in aerobic conditions via reactions of surface free radicals with oxygen molecules and causes a deterioration of its intrinsic properties in the surface region leaving a nonspecifically functionalized surface in the long-term. Recently a novel approach to functionalize plasma polymer films through the grafting reaction initiated from free radicals trapped on the PPF surface was developed. The present work investigates the potential to employ such an approach in a corrosion protection context. Characterization methods, including Electrochemical Impedance Spectroscopy (EIS) tests, demonstrate that the controlled consumption of surface free radicals via polymer grafting, instead of oxidation, has a beneficial effect on the corrosion protection behavior of the PPF layer deposited on clad 2024 aluminum alloy.