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Abstract: Lattice Monte Carlo simulations are used to study the phase behavior ofself-assembling ordered mesoporous materials formed by an organic template withamphiphilic properties and an inorganic precursor in a model solvent. Threeclasses of inorganic precursors have been modeled: terminal R-Si-OEt3 andbridging EtO3-Si-R-Si-OEt3 organosilica precursors OSPs, along withpure silica precursors Si-OEt4. Each class has been studied by analyzingits solubility in the solvent and the solvophobicity of the inorganic group. Athigh surfactant concentrations, periodic ordered structures, such ashexagonally-ordered cylinders or lamellas, can be obtained depending on theOSPs used. Ordered structures were obtained in a wider range of conditions whenbridging hydrophilic OSPs have been used, because a higher surfactantconcentration was reached in the phase where the material was formed. Terminaland bridging OSPs produced ordered structures only when the organic group issolvophilic. In this case, a partial solubility between the precursor and thesolvent or a lower temperature favored the formation of ordered phases. Withparticular interest, we have analyzed the range of conditions leaving to theformation of cylindrical structures, which have been evaluated according to thepore size distribution, the pore wall thickness, the distribution and theaccessibility of the functional organic groups around the pores. The phasebehavior has been also evaluated by applying the quasi-chemical theory, whichcannot predict the formation of ordered structures, but confirmed the resultsof simulations when no ordered structures were observed. The study of the phaseand aggregation behavior of two different surfactants, one modeled by a linearchain of head segments and the other modeled by a branched-head, permitted usto evaluate some structural differences of the materials obtained.

Author: Alessandro Patti


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