(587a) Probing the Mechanism of Silica Polymerization at Ambient Temperatures Using Molecular Simulations

Understanding the mechanism of silica formation is an important step in understanding the formation of various porous silica materials as well as zeolites. The study of silica formation from silicic acid polymerization using molecular simulations could provide the mechanistic insights and interpretation to experimental observations. However, the current potential models are unable to study the silicic acid polymerization at ambient temperature and corresponding experimental densities. To facilitate the polymerization study at experimental conditions, a new model has been developed based on assembly of silica tetrahedra. The simplicity of the model allows the study of large system sizes in reasonable computation times. Polymerization was studied with the model using reactive ensemble Monte Carlo simulations. The evolution of the Qn distribution during the simulations is in remarkable agreement with that seen in experiments. The analysis of simulation trajectory provides a mechanistic insight of the polymerization reaction. The polymerization starts with oligomerization forming small size units, followed by ring formation. These small oligomers with rings further aggregate causing cluster aggregation and finally cross linking within the large cluster. These different stages are explained by the analysis of cluster size and ring size distributions. The new model and methods provide a very promising approach to the study of silica polymerization in a variety of contexts.