Chinese Acad Sci, Inst Coal Chem, State Key Lab Coal Convers, Taiyuan 030001, Peoples R China
; Chinese Acad Sci, Wuhan Inst Phys & Math, State Key Lab Magnet Resonance & Atom & Mol Phys, Wuhan 430071, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Lab Synchrotron Radiat, Beijing 100039, Peoples R China
In-situ Si-29 liquid-state nuclear magnetic resonance (NMR) was used to investigate the ammonia catalyzed hydrolysis and condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursor systems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that of TEOS in the single silane component precursor systems. Meanwhile, the hydrolysis rate constants of DDS in the mixed precursor systems were smaller than those of DDS in the single silane component precursor systems. The hydrolysis and condensation kinetics showed more compatible hydrolysis-condensation relative rates between TEOS and DDS, which remarkably affected the final microstructure of the resulting silica particles. Small angle X-ray scattering (SAXS) experiments showed a typical double fractal structure in the particulate networks.