Vm. Gunko et al., AQUEOUS SUSPENSIONS OF HIGHLY DISPERSE SILICA AND GERMANIA SILICA/, Journal of colloid and interface science (Print), 205(1), 1998, pp. 106-120
Highly disperse germania has been synthesized on the surface of fumed
silica by the chemical vapor deposition (CVD) technique. Aqueous suspe
nsions both of unmodified fumed silica and of the obtained germania/si
lica (GS) samples have been studied by elec trophoresis, photon correl
ation spectroscopy, nuclear magnetic resonance (H-1 NMR), and quantum
chemical semiempirical AM1-SM1 methods. For suspensions of GS samples,
electrophoretic mobility, isoelectric point (IEP), particle size dist
ribution, average effective diameter (D-ef), and free energy changes (
Delta G) of interfacial water were found to depend nonlinearly on the
concentration of germania (C-GeO2), At small concentrations, the struc
ture of the synthesized germania is clustered rather than layered. For
the last samples, maximum reduction of the free energy for interfacia
l water and larger values of IEP and D-ef in comparison with GS at hig
h C-GeO2 or unmodified silica have been observed. In suspensions, the
particle size distributions for silica and GS are uni-, bi-, and trimo
dal and depend on pH and C-GeO2. 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 cha
rged and uncharged GS clusters calculated by AM1-SM1 method decreases
with increasing germania concentration. (C) 1998 Academic Press.