A quantum molecular dynamics simulation study of the initial hydrolysis step in sol-gel process

The dynamic behavior of the hydrolysis reaction of Si(OCH₃)₄ under neutral, basic, and acidic conditions was investigated, for the first time, at the atomic level with short time intervals using a novel tight-binding quantum chemical molecular dynamics program "Colors". The initial parameters required for the computation were determined completely on the basis of the first principles density functional calculations using Amsterdam density functional program. The simulation results of this study clearly indicate that a flank-side attack mechanism is favored, in all the three cases, for the hydrolysis process, and pentacoordinate silicon intermediates are easy pathways for the displacement of -OCH₃ by -OH on silicon. Moreover, the presence of the acid or the base as catalyst promotes the hydrolysis by rapid formation of Si-OH bond in comparison to the hydrolysis under neutral condition. Furthermore, in the case of the latter condition, it was observed that the proton oscillates between -OH and -OCH₃ before it migrates to the latter group.