Colloidal silica bearing thin polyacrylate coat: A facile inorganic modifier of acrylic emulsions for fabricating hybrid films with least aggregation of silica nanoparticles

Novel nano-composite emulsions consisting of colloidal silica particles covered with thin polyacrylate coat (PreEm) were successfully prepared with the aid of a nonionic surfactant having a low cloud point (T-cp = 40 degrees C). This nonionic surfactant first deposited on the surface of colloidal silica particles above its T-cp to provide the sites for adsorption and the following polymerization of acrylic monomer. Scanning transmission electron microscopy of the colloidal particles obtained after the polymerization indicated the presence of very thin coat layer of polyacrylate (c.a., 1-3 nm nm in thickness) around silica nanoparticles. These PreEm particles were readily incorporated into the ordinary acrylic emulsions (AcEm) to obtain silica/ polyacrylate mixed emulsions (PreEm/AcEm). It was revealed that the mixed emulsions can give transparent coating films at a silica/polyacrylate ratio below 150/100 in which the colloidal particles were distributed in the polymer matrix without aggregation. This morphology was in sharp contrast with the particle aggregation morphologies shown by the films obtained from the naked colloidal silica-AcEm mixed emulsion and the conventional nanocomposite emulsion consisting of silica particles covered with thick polyacrylate coat. The PreEm/ AcEm films exhibited increased hardness with increasing the silica contents to 150%. These data supported the effectiveness of PreEm in controlling the properties of silica-polyacrylate hybrid films.