(767c) Modeling Silica Polymerization in the Context of Self-Assembly of Ordered Porous Materials

Chien, S. C., University of Massachusetts
Auerbach, S. M., University of Massachusetts
Monson, P. A., University of Massachusetts Amherst

Ordered porous materials such as zeolites have a huge variety of applications in the chemical industry.  The long range ordered pores of the structure make these materials widely used in catalysis, separation, biotechnology, and also microelectronics. Various structures have been fabricated, though there is no clear understanding of the mechanisms due to the limitations of characterization techniques. The objective of our modeling work is to have better understanding of tailoring and controlling of ordered porous materials.

In this study, the reactive ensemble Monte Carlo method is implemented, which provides a feasible way to study silica polymerization at ambient temperature. The simulation is based on the molecular model of a flexible, corner-sharing tetrahedron. The silica is viewed as having a hard sphere core in the center of the tetrahedron with the four corners occupied by four hydroxyl groups. This flexible tetrahedron is maintained via harmonic springs between the oxygen atoms. The model also contains three-body Si-O-Si potentials on bridging oxygens. In previous work our group successfully simulated silica polymerization in low pH solution [1]. To extend this work over a pH spectrum, a square-well potential has been used to describe the hydrophobicity of the silica in the solution, and the association/dissociation of anionic silica and templates.  The combination of the square-well potential and reactive ensemble Monte Carlo is used to model silica polymerization over a broad pH range. 

From the outcome of this work, we have mimicked the core-shell structure of nanoparticles implicated in the nucleation and growth of zeolites. We also investigate atomic-level structural aspects of all the components in the system as well as the effects of the templates during the polymerization process.

[1] Ateeque Malani, Peter A. Monson, and Scott M. Auerbach, J. Phys. Chem. C 115, 15988-16000 (2011)