(231a) Modeling Synthesis of Mesoporous Silica Materials with Hybrid MD/MC Simulations

Mesoporous materials have been extensively studied because of their potential applications in catalysis and separations of molecules that are too large to fit into micropores. Additionally, ordered mesoporous materials have also been applied in biotechnology as bioadsorbents and biocatalysts, and as drug delivery vehicles. These materials differ from the zeolites in that the atomic level structure is amorphous rather than crystalline, but the pore network is ordered at longer length scales. Better understanding of the formation mechanism for mesoporous materials is a key to controlling and tailoring materials for specific applications. These kinds of materials, such as MCM-41, are usually fabricated via the templated sol-gel synthesis route by adding different surfactants into the system. In general, there is a broad agreement that silica and surfactant species cooperate during mesoscale structure formation [1]. However, the detailed mechanism for mesoscale order formation in this hypothetical mechanism remains uncertain.

Several studies have been carried out to investigate surfactant-inorganic oxide-solvent systems [2,3,4,5]. A previous molecular dynamics (MD) study has shown that addition of silica monomer promotes the sphere-to-rod transition in alkyltrimethylammonium surfactants-silica-solvent system [6]. It is also suggested that the interaction between silicates and surfactants plays an important role in micelle aggregation and in the formation of hexagonal arrays. In our latest study, we investigate the formation of different mesophases, such as lamellar and gyroid structure, by MD simulation. We herein further introduce a hybrid molecular dynamics/Monte Carlo (MD/MC) approach, in which the interplay of the self-assembly of the porous structure and silica polymerization in the early stages of mesoporous materials formation can be explored. The MD/MC hybrid approach uses a coarse-grained (CG) model to represent the species in our simulation, and the reactive ensemble Monte Carlo is performed to sample silica polymerization [7]. We will also present a detailed investigation on the interaction between surfactants and silicate using this hybrid approach. This study can provide a new insight into the formation process of mesoporous materials on the atomic level.

[1]  Beck, J. S., Vartuli, J. C., Roth, W. J., Leonowicz, M. E., Kresge, C. T., Schmitt, K. D., Chu, C. T. W., Olson, D. H., Sheppard, E. W., McCullen, S. B., Higgins, J. B., and Schlenker, J. L., J. Am. Chem. Soc. 114 (1992) 10834

[2] Siperstein, F. R., and Gubbins, K. E., Langmuir 19 (2003) 2049

[3] Patti, A., Mackie, A. D., and Siperstein, F. R., J. Mater. Chem., 19 (2009) 7848

[4] Jorge, M.; Gomes, J. R. B.; Cordeiro, M. N. D. S; Seaton, N. A., J. Am. Chem. Soc., 129 (2007) 15414

[5] Jorge, M.; Gomes, J. R. B.; Cordeiro, M. N. D. S; Seaton, N. A., J. Phys. Chem. B, 113 (2009) 708

[6]  Pérez-Sánchez, G., Gomes, J. R. B., and Jorge, M., Langmuir 29 (2013) 2387

[7] Malani, A., Auerbach, S. M., and Monson, P. A., J. Phys. Chem. C 115 (2011) 15988