(432e) Silicic Acid Polymerization: A Low Coordination Lattice Model Study

We have performed Monte Carlo simulations to study the polymerization of silicic acid in aqueous solutions using a new developed silicon-oxygen lattice model. In the model, each silicic acid molecule is represented as a tetrahedron on body centered cubic lattice with one silicon atom at the center and hydroxyl groups at the corners. At ambient temperatures, the covalent bond between Si and O atoms cannot be broken or reformed due to thermal fluctuations. Therefore, this model avoids moving Si or O atoms independently but treats each silicic acid tetrahedron as a building unit when implementing displacement or rotational movement. Condensation and hydrolysis reactions are also included in the model. This low-coordination lattice model is computationally simple and efficient for simulating silicic acid polymerization for long time-scales and large system-sizes. The model captures the basic kinetics of silica polymerization and provides structural evolution information about the silica particles formed. The agreement with experimental data for the evolution of the Qn distribution is qualitatively very good. The model and simulation method will provide the basis for studies of silica polymerization in the presence of templates to produce zeolite frameworks or ordered mesoporous materials.