A straightforward procedure for the synthesis of silica@polyaniline core-shell nanoparticles

The synthesis of core-shell silica@polyaniline nanoparticles is of interest for many applications including electrorheology and inkjet printing. Formation of such structures by simple adsorption of aniline onto silica surfaces followed by polymerization is rather difficult. Chemical grafting of alkoxysilane monomers on silica surfaces followed by polymerization has been used to prepare silica@polyaniline microspheres but has never been applied to silica nanoparticles. Here, we report an efficient method to prepare silica@polyaniline nanoparticles of different sizes. This study goes far beyond the simple synthetic procedure. It also evidences a general law that can be applied by all to anticipate the efficient encapsulation of silica nanoparticles by polyaniline. Here, silica nanoparticles of different sizes (90-300 nm) were firstly synthesized by Stober process and then functionalized with N-[3-(Trimethoxysilyl) propyl] aniline. The last step implied the room temperature polymerization of aniline in the presence of these functionalized-silica nanoparticles using ammonium persulfate as oxidant. Several sets of particles were prepared using different amounts of aniline monomers resulting in different polyaniline thicknesses. SEM, TEM, IR, TGA and XPS were then used to characterize thoroughly these core-shell particles. The highlight of this paper is that efficient encapsulation of silica particles by polyaniline occurred if, and only if, the ratio between the polyaniline thickness and the particle diameter was close to 10%. Higher ratio led to the presence of isolated polyaniline granules while lower ratio resulted in uncompleted encapsulation.