Molecular Modeling of Self-assembling Hybrid Materials (PhD Thesis)

TL;DR

This thesis uses lattice Monte Carlo simulations to explore the phase behavior and structure formation in self-assembling hybrid materials involving organic templates and inorganic precursors, revealing conditions for ordered mesoporous structures.

Contribution

It introduces a comprehensive simulation approach to predict the phase behavior and structural features of hybrid materials with different inorganic precursors and surfactant types.

Findings

Ordered structures depend on precursor solubility and surfactant concentration.

Bridging hydrophilic precursors enable a wider range of ordered phases.

Simulation results align with quasi-chemical theory predictions.

Abstract

Lattice Monte Carlo simulations are used to study the phase behavior of self-assembling ordered mesoporous materials formed by an organic template with amphiphilic properties and an inorganic precursor in a model solvent. Three classes of inorganic precursors have been modeled: terminal (R-Si-(OEt)3) and bridging ((EtO)3-Si-R-Si-(OEt)3)) organosilica precursors (OSPs), along with pure silica precursors (Si-(OEt)4). Each class has been studied by analyzing its solubility in the solvent and the solvophobicity of the inorganic group. At high surfactant concentrations, periodic ordered structures, such as hexagonally-ordered cylinders or lamellas, can be obtained depending on the OSPs used. Ordered structures were obtained in a wider range of conditions when bridging hydrophilic OSPs have been used, because a higher surfactant concentration was reached in the phase where the material was formed. Terminal and bridging OSPs produced ordered structures only when the organic group is solvophilic. In this case, a partial solubility between the precursor and the solvent or a lower temperature favored the formation of ordered phases. With particular interest, we have analyzed the range of conditions leaving to the formation of cylindrical structures, which have been evaluated according to the pore size distribution, the pore wall thickness, the distribution and the accessibility of the functional organic groups around the pores. The phase behavior has been also evaluated by applying the quasi-chemical theory, which cannot predict the formation of ordered structures, but confirmed the results of simulations when no ordered structures were observed. The study of the phase and aggregation behavior of two different surfactants, one modeled by a linear chain of head segments and the other modeled by a branched-head, permitted us to evaluate some structural differences of the materials obtained.