Thèse de doctorat de l ’ École Polytechnique

In this work, three surface functionalization processes have been studied: the spontaneous grafting fromdiazonium salts, the chemically induced grafting from diazonium salts and the chemically induced graftingfrom diazonium salts in presence of vinylic monomers (which is Graftfast). These processes work at roomtemperature, atmospheric pressure, in aqueous medium and without any external energy source (“green”chemistry). They lead to the formation of organic films (in particular polymer films in the case of theGraftfast process), stable, strongly grafted and with a controlled thickness (chemically activated processes).Contrary to diazonium salt electrografting methods, the reaction can occur on any type of substrate frominsulators to conductors including nanomaterials. The so-modified surface can show new properties (forinstance water-repellency or protection against corrosion) which is of a major interest in some industrial fields.The main objective of this work was to understand the grafting mechanism of those processes, especially ofthe Graftfast process, by studying the chemical composition of the films, their structure as well as thecomposition of the reactive solution. As for classical radical chain polymerization, the mechanism can be splitin three steps: initiation, propagation, termination. The polymerization is initiated by aryl radicals in solutioncoming from the chemical reduction of the diazonium salts (outer-sphere or inner-sphere mechanism accordingto the reducing agent used). In parallel, aryl radicals can graft to the surface of the substrate and form anessential polyphenylene primer-layer. The propagation stops when the growing polymer chains react on thearomatic rings already grafted on the substrate (termination step). It results an aryl groups/polymers mixedstructure of the films. The Graftfast process has been notably tested with a view to improve the dispersion ofnano-objects in water in the framework of a preliminary study on sunscreens containing TiO2 nanoparticles.