Formation and characterization of monodisperse, spherical organo-silica powders from organo-alkoxysilane-water system

Abstract

Monodisperse, spherical organo-silica powders were synthesized from an immiscible mixture of an aqueous NH4OH solution and organo-alkoxysilanes, such as phenyl-trimethoxysilane (PTMS), methyltrimethoxysilane (MTMS), and methyltriethoxysilane (MTES), When the organo-alkoxysilanes were added to the aqueous NH4OH solution with stirring, organo-alkoxysilane/water macroemulsions were formed because of the immiscibility of the aqueous NH4OH 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 Si-29 NMR and the C-13 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.