Colloidal crystallization of monodisperse and polymer-modified colloidal silica in organic solvents

The formation of colloidal crystals from polymer-modified silica in organic solvent was studied. The colloidal crystallization of poly(maleic anhydride-styrene)-, polystyrene- and poly(methyl methacrylate)-modified silica took place in organic solvents, which were good solvents for the grafted polymer. It is, however, observed that there is a matching or a mismatching between the grafted polymer and solvent for the crystallization. The critical volume fraction (φo) of the silica particles for the colloidal crystallization depended on the modified polymer, the extent of grafting, and molecular weight of the polymer. From the fact that φo in the crystallization of poly(malic anhydride-styrene)-modified silica in acetonitrile decreased with the addition of a salt, NH4PF6, the crystallization occurred in the organic solvents due to the electrostatic repulsion between the particles, as well as those in aqueous solution. The neighboring inter-sphere spaces agreed well with the calculated values, which were obtained by the assumption of the close packing under electrostatic repulsion between the particles. It is suggested that the grafted polymer contributes to the enhancement of the elecrostatic interaction through electric double layer between the particles in the colloidal crystallization in organic solvent.