Nanocomposite silica/polyamine films prepared by a reactive layer-by-layer deposition

Composite material nanofilms of controlled thickness constituted by ceramics and polymers find more and more applications to improve the properties and functionalities of material surfaces. In this paper we present a new way to deposit such composite coatings by alternated contacts of a surface with a polyamine solution (either poly(allylamine), poly(ethyleneimine), poly-L-lysine, or poly(diallydimethylammonium)chloride and silicic acid. The experiments are mainly realized by spraying of solutions onto the surface. The polyamines deposited in the first spraying step catalyze silica formation upon further spraying of a silicic acid-containing solution. The film thickness increases linearly with the number of deposition steps, the thickness increment being of the order of a few nanometers per silicic acid/polyamine layer. Infrared spectroscopy in the total attenuated reflection mode reveals spectra that are close to those of pure silica particles. The film morphology is further investigated by means of atomic force microscopy and environmental scanning electron microscopy. This reactive layer-by-layer deposition constitutes a new way to build, in an easy way, nanocomposite coatings with precise control of their thickness.