Size change of silica nanoparticles induced by non-alcoholic solvent addition during sol-gel reaction

The effect of solvent addition on particle size was investigated for silica nanoparticles synthesized by sol-gel reaction. In order to prepare solvent mixtures having a wide range of solvent polarity, non-alcoholic organic solvents with various dielectric constants were selected, such as toluene, N-methylformamide, chlorobenzene, methyl isobutyl ketone, and N,N-dimethylacetamide, which are firstly tested in this study as cosolvents for controlling the particle size of sol-gel silica. The role of the solvent dielectric constant during the sol-gel reaction is further clarified by experimental observation of increased particle size with low dielectric constant solvents (toluene, chlorobenzene, and methyl isobutyl ketone), and decreased particle size with high dielectric constant solvent (N-methylformamide and N,N-dimethylacetamide). Contradictory observations of particle size change according to water content are discussed in terms of its two competing roles-as a high-dielectric constant solvent and a hydrolysis reactant.