Control of Polymer Layer Thickness in Coating of Monodispersed Colloidal Silica

Two methods for the polymer coating of monodispersed colloidal silica and for the control of layer thickness by radical polymerization were examined. Consecutive radical polymerization of styrene on the prepolymer-coated silica by periodic addition of 2,2′-azobis(isobutyronitrile) in ethanolic solution induced the aggregation of the composite particles. The radical polymerization in the surface hydrophobic layer, formed by the reaction of surface silanol with a silane coupling agent on the colloidal silica, gave monodispersed composite particles having surface polymer layers, the thickness of which was dependent on the molecular size and polarity of the silane modifier. It is suggested that the polymer coating layer is controllable in the range of about two times to five times the modifier size.