Seed polymerization of tetraethyl ortho-silicate in the presence of rod-like colloidal particles of anionic palygorskite and cationic ?-FeO(OH)

Abstract

Kinetic analyses were made of the seed polymerization of tetraethyl ortho-silicate (TEOS) in the presence of rod-like colloidal particles of palygorskite and cationic β-FeO(OH) by turbidity and dynamic light-scattering measurements. Transmission electron microscopic measurements supported the formation of core-shell particles. The seed polymerization of TEOS took place exclusively on the surfaces of palygorskite. The main cause of the observation is due to the fact that the main component of palygorskite is SiO2 and the affinity between palygorskite and TEOS is high, though the electrostatic repulsion between them is not favorable for shell formation. The shell formation of silica on a β-FeO(OH) particle also proceeded. The electrostatic attraction forces between the anionic polar TEOS monomers and cationic β-FeO(OH) particles played an important role in shell formation. These results are consistent with a polymerization mechanism consisting of the formation of small preliminary particles followed by their coalescence on the surfaces of the seeds to give the final large particles coated with silica layers.