Organic molecule-modulated phase evolution of inorganic mesostructures

The involvement of alkane in the P123-TEOS-NH4F-H3O+ synthesis system alters the phase behavior of the complex emulsion system dramatically. Changing one of the reaction parameters (such as the initial reaction temperature, IRT) will result in diverse solution mesostructures. With subsequent condensation of silicate species, interesting inorganic materials with various mesostructures are obtained. The present work is aimed at understanding the phase evolution behavior of this complex alkane (C6-C12)-P123-TEOS-NH4F-H3O+ emulsion system, with emphasis on the influence of alkane chain number (ACN) and IRT. HREM (high-resolution electron microscopy), XRD (X-ray diffraction), nitrogen sorption, FFEM (freeze-fracture electron microscope), and interfacial tension techniques have been used to investigate the phase behavior of the emulsion system and the structure of the inorganic products. A linear relationship between the phase-transformation temperature (PTT) and ACN has been established, which could be attributed to the modification of alkane with respect to the hydrophobic-hydrophilic properties of the complex emulsion system. Moreover, the right combination of reaction temperature, ACNs, and thus-induced swelling of hydrophobic PPO blocks as well as the modification of hydrophilicity of PEO brushes by silicate oligmers is the driving force in altering the packing parameter/geometry of the copolymers surfactant (P123) aggregates. This leads to the diverse structures of the obtained mesoporous silicas. A temperature-induced phase-transformation mechanism has also been proposed and discussed.