Aqueous suspension of fumed oxides: particle size distribution and zeta potential

Comparative analysis of the results of the investigations, which were performed by means of photon correlation spectroscopy (PCS) and electrophoresis, of aqueous suspensions of individual fumed oxides (SiO2, TiO2, Al2O3), binary X/SiO2 (X=TiO2, Al2O3, GeO2, C) and ternary Al2O3/SiO2/TiO2, fumed oxides modified by organic and organosilicon compounds or interacting with dissolved polymers, surfactants, etc., allows us to deeper understand the dependencies of structural and other characteristics of the dispersions on features of primary particles, their morphology, the nature of the surfaces of unmodified and modified individual and mixed oxides varied due to the synthetic techniques and the concentrations of the oxide phases or modifiers, concentrations of oxides in the liquid media, adsorption of soluble polymers, influence of surfactants, polyelectrolytes, inert electrolytes, etc. Some results related to chemically similar oxides but prepared by using other synthetic methods or data obtained by means of other experimental methods, e.g. DRS, TSD, NMR, etc., were used only in minor amounts in order to elucidate some aspects of the aqueous suspensions of fumed oxides studied by using PCS and electrophoresis methods. The main reasons of non-linear dependencies of the particle size distributions (PSD) and ζ potential on the concentration of fumed oxides in the aqueous suspensions, on the amounts of the guest X phases in X/SiO2 or the modifiers, on the pH values, etc., can be (a) a large polydispersity of PSD of both unmodified and modified fumed oxides linked with a four-stepwise structural hierarchy of fumed oxide particles, which can keep (or rearrange) in the suspensions despite different pretreatments of initial silica, X/SiO2 or their dispersions; and (b) a significant non-uniformity of the surfaces of mixed oxides due to features of the grafted or dopant phase distribution on/in the matrix depending on the guest oxide concentrations and the synthetic techniques.