On the Formation Mechanism of Pluronic-Templated Mesostructured Silica

The synthesis of mesostructured silica formed at mildly acidic conditions using the nonionic surfactant Pluronic P123 has been studied with the aim of showing the importance of the degree of condensation of the silica source. The experimental investigation employed was in situ small-angle X-ray scattering (SAXS) in combination with an advanced model. The results are further supported by dynamic light scattering (DLS) and transmission electron microscope (TEM) analyses. Tetraethyl orthosilicate (TEOS) has been used as silica source, using a two step procedure involving a prehydrolysis of the TEOS, so that the degree of condensation of the silica at the start of the reaction could be varied. The results obtained demonstrated that, by controlling the degree of condensation of the silica at the start of the synthesis, it is possible to control the formation rate and the degree of order of the final material. The findings are summarized in a formation mechanism comprising three steps: Entropy driven surfactant-silica attraction that results in cylindrical silica containing micelles, particle formation induced by micelle−micelle association caused by the surfactant-silica interaction, and finally rearrangement of the internal particle structure into a hexagonal arrangement that also affects the morphology of the entire particle, creating elongated particles.