Surface polymerization of aniline on silica gel

The surface polymerization of aniline producing polyaniline nanofilms on surfaces in contact with the reaction mixture has been investigated. The hypothesis that aniline polymerization is heterogeneously catalyzed by the surfaces has been tested. This concept is applicable to planar surfaces and also to surfaces provided by microparticles. The introduction of silica gel, a substrate with a large specific surface area, led to the acceleration of polyaniline formation. The effect of silica gel concentration, particle size, and porosity is discussed, and the courses of polymerization in the presence of porous and compact spheres are compared. It can be concluded that the initiation of aniline polymerization is promoted by adsorption of oligomeric intermediates at the surface. The surface polymerization, giving rise to polyaniline coatings, is thus preferred to precipitation polymerization in the aqueous phase that produces a polyaniline precipitate. The coating of the silica gel surface with polyaniline was not complete, as demonstrated by X-ray photoelectron spectroscopy. The infrared spectrum of the polyaniline coating on silica gel has been compared with that of the PANI film deposited on silicon.