To prepare large monodisperse silica particles, it is necessary to grow silica seeds without the formation of new silica particles.
Described in this paper are investigations of the characteristic Since Kolbe (5) discovered the formation of monodisperse aspects of formation of new particles during the growth of silica silica particles through the hydrolysis and condensation of seeds through the hydrolysis and condensation of tetraethylortetraethylorthosilicate (TEOS) in ethanol with ammonia as thosilicate. Experimental results indicated that with silica particles catalyst, many studies have been made on this reaction sysas seeds, under a given set of reaction conditions and total external tem (6-8). Some mechanisms were put forward. Phillips surface area of seeds, the smaller the seed particles, the fewer the suggested that the growth was limited by diffusion of subparnewly formed particles during seed growth. The larger the total ticles against a Coulomb potential of the growing spheres surface area of the seeds, the fewer the newly formed particles (9). Bogush and co-workers regarded the nucleation and during growth with the same diameter particles as seeds. The growth of silica particles as an aggregation process of small critical surface area of nucleation increases linearly with the diamsubparticles several nanometers in size (8). Matsoukas and eter of seeds. Addition of a small amount of NaCl to the breeding Gulari proposed that particle nucleation was the result of the solution can dramatically decrease the number of newly formed particles. From these experimental findings, it is believed that reaction between two hydrolyzed monomers, such that the under the conditions of formation of new particles, seed growth particles grew only by monomer addition (10). Van Blaadduring the early stage is controlled by diffusion of colloid-unstable eren and co-workers postulated that particle formation procondensed species carrying electric charges capable of overcoming ceeded through an aggregation process of siloxane substrucelectrostatic repulsion. ᭧ 1996 Academic Press, Inc.
tures, while growth proceeded through surface reaction-lim-Key Words: monodisperse; silica particles; growth of crystals; ited condensation of hydrolyzed monomers or small mechanism; tetraethylorthosilicate. oligomers (7). To date, none of the available mechanisms is able to explain all of the experimental facts (11).
In seeded growth experiments where no new particles are