Fabrication of tetraethyl orthosilicate/ethanol-water surfactant-free microemulsions and their applications in self-templating synthesis of monodispersed silica colloidal spheres.

Surfactant-free microemulsions (SFMEs) composed of tetraethyl orthosilicate (TEOS), ethanol, and water have been successfully fabricated by visual titration and electrical conductivity methods. Three types of SFMEs, water in TEOS (W/O), bicontinuous (BC) and TEOS in water (O/W), were identified by dynamic light scattering and transmission electron microscopy with negative-staining methods. We demonstrated that there are significant differences in the properties of silica products synthesized with different types of SFMEs, and monodispersed silica colloidal spheres (MSCSs) can only be synthesized in the O/W type SFMEs. Moreover, we found that the particle size of MSCSs is closely related to the size of oil droplets. Cooling the O/W type SFMEs in the early reaction stages, results in the larger MSCSs with different condensation degrees. Furthermore, if the cooling temperature decreased to -20 °C, ring-like spheres could be observed. Based on our results and observations, a self-templating growth mechanism was proposed to explain the formation of silica spheres.