Formation and Characterization of Monodisperse, Spherical Organo‐Silica Powders from Organo‐Alkoxysilane‐Water System

Monodisperse, spherical organo‐silica powders were synthesized from an immiscible mixture of an aqueous NH 4 OH solution and organo‐alkoxysilanes, such as phenyl‐trimethoxysilane (PTMS), methyltrimethoxysilane (MTMS), and methyltriethoxysilane (MTES). When the organo‐alkoxysilanes were added to the aqueous NH 4 OH solution with stirring, organo‐alkoxysilane/water macroemulsions were formed because of the immiscibility of the aqueous NH 4 OH solution and the organo‐alkoxysilane. In the emulsion, organo‐alkoxysilane droplets dissolved into the water phase through the droplet‐water interface, and the organo‐silica powder was formed by the hydrolysis and condensation of the organo‐alkoxysilane. The powders were obtained reproducibly under broad concentrations of organo‐alkoxysilanes; 0.3‐1.5 mol/L for PTMS, 0.3‐0.6 mol/L for MTMS, and MTES, with concentrations of ammonia between 0.0625 and 2.0 mol/L. According to the analysis of the solid‐state MAS 29 Si NMR and the 13 C NMR analysis, the organo‐silica powder did not contain any residual alkoxy groups, only carbon sources from nonhydrolyzable R groups: phenyl groups in PTMS, and methyl groups in MTMS and MTES.