Modelling the self-assembly of silica-based mesoporous materials

Abstract

Periodic Mesoporous Silicas (PMS) are one of the prime examples of templated porous materials-there is a clear connection between the porous network structure and the supramolecular assemblies formed by surfactant templates. This opens the door for a high degree of control over the material properties by tuning the synthesis conditions, and has led to their application in a wide range of fields, from gas separation and catalysis to drug delivery. However, such control has not yet come to full fruition, largely because a detailed understanding of the synthesis mechanism of these materials remains elusive. In this context, molecular modelling studies of the self-assembly of silica/surfactant mesophases have arisen at the turn of the century. In this paper, we present a comprehensive review of simulation studies devoted to the synthesis of PMS materials and their hybrid organic-inorganic counterparts. As those studies span a wide range of time and length scales, a holistic view of the field affords some interesting new insight into the synthesis mechanisms. We expect simulation studies of this complex but fascinating topic to increase significantly as computer architectures become increasingly powerful, and we present our view to the future of this field of research.

The role of charge-matching in nanoporous materials formation

“…The discovery of templated periodic mesoporous silica (PMS) in the early 1990's, of which MCM-41 is the archetypal example [1], heralded a new era in material science research. This revolutionary approach, whereby the porous structure of the material is determined by cooperative self-assembly of silicates and surfactant molecules (originally cationic ammonium compounds) in solution [2][3][4], allowed scientists to apply soft-matter physics principles to the synthesis of solid-state materials, enabling an unprecedented degree of control over the properties of the final material [5] and leading to a wide range of practical applications [6].…”

“…The main bottleneck hindering further progress in this field is the lack of in-depth understanding of the underlying mechanism of amine-templated silica synthesis [4,8]. In this paper, we shed new light on this issue through a combination of experimental studies and multi-scale modelling, focussing on HMS [9] as the first example of synthetic aminetemplated silica material.…”

“…Parameters of a coarse-grained model of the system, based on the MARTINI approach [26], were then calibrated so that micelle density profiles and other structural properties matched those of the atomistic simulations. This approach has been successfully validated and applied to elucidate the self-assembly mechanism in the synthesis of PMS materials [23,[27][28][29][30] as well as of their organosilica derivatives [4,31]. Details of the model parameterisation and validation procedure for HMS precursor solutions, including a diagram of the mapping scheme ( Figure S5) and a table with the final set of parameters (Table S7), are provided in Supporting Information.…”

Engineering self-assembly

“…Their contribution ranges from studies of surfactant template aggregation in solution [5], to exploration of the complex free energy landscape in zeolite synthesis [6], to examination of the role played by peptide molecules in biomineralisation processes [7]. The paper by Jorge et al [8] presents a detailed review of modelling efforts to understand how the different processing steps lead to the final structure of silica-based mesoporous materials. Finally, Bernardes et al [9] demonstrate how atomistic simulations can be used to help interpret experimental data, clarifying the role of molecular correlations in the emergence of ordered domains in ionic liquids.…”

“…Here, with one exception [9], all papers apply some form of coarse-graining in their simulations. It is common to represent colloids [1,2] and nanoparticles [3,4] as single interaction sites instead of describing them in atomistic detail, whereas surfactants [5,8] and biomolecules [7] are usually modelled as a collection of beads, thus preserving some of their structure and flexibility. Although this reduction of the number of interaction sites may sometimes appear quite drastic, it is often a direct consequence of the need to sample large time and length scales in order to probe the self-assembly mechanism.…”