MOLECULAR-DYNAMICS SIMULATION OF THE STRUCTURAL DEVELOPMENT IN SOL-GEL PROCESS FOR SILICA SYSTEMS

The mechanism of the gel formation process has been studied using mole cular dynamics (MD) simulation. Two characteristic systems considered are silicic acid, Si(OH)(4), and monomethoxy silicic acid, Si(OMe)(OH) (3), which are regarded as differing from each other in the extent of hydrolysis. The interatomic potential used is that of Feuston and Garo falini [B.P. Feuston, S.H. Garofalini, J. Phys. Chem., 94 (1990) 5351- 5356.], except for a slight modification about methoxy groups. Microsc opic features of the structural development are discussed. There is a slow cluster growth during the early stage, a rapid cluster growth fol lows this due to cluster-cluster aggregation, and the network structur e becomes denser with time through the repeated bond-formation and bon d-breaking. Finally, the trend of phase separation is observed. The pr esence of the methoxy groups interferes with the aggregation and the f ormation of the dense network structure. Having some problems to be ex amined about set temperature, system size and dilution effect, MD simu lation has proved effective for understanding the structural developme nt in sol-gel process for silica systems. (C) 1998 Elsevier Science B. V.