Control of mesostructured silica particle morphology

The formation of mesostructured silica was investigated using acidic condit ions with tetraethoxysilane (TEOS) as the silica precursor and cetyltrimeth ylammonium bromide (CTAB) as the structure directing agent. A synthesis mix ture of composition 2.2TEOS : 1.1CTAB : 75HCl ∶ 1000H(2)O gave a well ordered material exhibiting a range of particle shapes from extended rope- like structures of hexagonal cross-section to gyroid structures. Addition o f monomethyltriethoxysilane (MTES) or tetrahydrofuran (THF) to the synthesi s mixture gave rise to spherical particles. Studies of particle development showed initial growth of gel-like particles within which the mesostructure developed. A new model is proposed for the formation of mesostructured pre cipitates in which (1) growth of inorganic oligomers gives rise to a thermo dynamically unstable mixture, (2) phase separation occurs giving droplets o f a second liquid (or liquid crystal) phase rich in oligomer and surfactant , (3) the droplets are colloidally stabilized, (4) microphase separation oc curs within the droplets, giving rise to a mesostructure and (5) further po lymerization fixes the mesostructure.