Polyaniline-silica composite conductive capsules and hollow spheres

In this paper, we report on the preparation of monodisperse polyaniline (PANi)-silica composite capsules and hollow spheres on monodisperse core-gel-shell template particles. An extension of the previously reported inward growth method was used. The samples were self-stabilized without external additives. The core-gel-shell particles were prepared by the inward sulfonation of monodisperse polystyrene particles. The introduced sulfonic acid and sulfone groups are responsible for the gel properties. The gel-shell thickness and core size were synchronously controlled over the whole particle radius range. After aniline (ANi) monomer was preferentially absorbed in the sulfonated polystyrene shell, PANi was formed by polymerization. PANi was doped in situ with a sulfonic acid group to give the capsules a high conductivity. PANi hollow spheres were derived after the polystyrene cores were dissolved: their cavity size and shell thickness were synchronously controlled by using different core-gel-shell particles. The PANi-silica composite capsules and hollow spheres were therefore prepared by a sol-gel process using tetraethylorthosilicate in the conducting shell. The PANi shell became more robust while maintaining the same conductivity level. Morphological results indicate that the PANi and silica formed a bicontinuous network. Fourier-transform infrared (FTIR) spectra revealed that the hydrogen bonding in the PANi-gel shell was enhanced after the silica phase was incorporated, which could explain the high conductivity level after the silica phase was added. In a converse procedure, silica capsules and hollow spheres were prepared by a sol-gel process that incorporated tetraethylorthosilicate into the core-gel-shell templates, which was followed by the absorption and polymerization of aniline in the silica shell thus forming PANi-silica composite capsules and hollow spheres. The silica capsules and hollow spheres thereby became conductive.