Aqueous Suspensions of Highly Disperse Silica and Germania/Silica

Highly disperse germania has been synthesized on the surface of fumed silica by the chemical vapor deposition (CVD) technique. Aqueous suspensions both of unmodified fumed silica and of the obtained germania/silica (GS) samples have been studied by electrophoresis, photon correlation spectroscopy, nuclear magnetic resonance (1H NMR), and quantum chemical semiempirical AM1-SM1 methods. For suspensions of GS samples, electrophoretic mobility, isoelectric point (IEP), particle size distribution, average effective diameter (Def), and free energy changes (DeltaG) of interfacial water were found to depend nonlinearly on the concentration of germania (CGeO2). At small concentrations, the structure of the synthesized germania is clustered rather than layered. For the last samples, maximum reduction of the free energy for interfacial water and larger values of IEP and Def in comparison with GS at high CGeO2 or unmodified silica have been observed. In suspensions, the particle size distributions for silica and GS are uni-, bi-, and trimodal and depend on pH and CGeO2. Values of polydispersity (P) are very rarely smaller than 0.05 and are usually between 0.25 and 0.70, which points to the wide size distribution. The solvation energy of the charged and uncharged GS clusters calculated by AM1-SM1 method decreases with increasing germania concentration. Copyright 1998 Academic Press.