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

Comparative analysis of the results of the investigations, which were perfo rmed by means of photon correlation spectroscopy (PCS) and electrophoresis, of aqueous suspensions of individual fumed oxides (SiO2, TiO2, Al2O3), bin ary X/SiO2 (X = TiO2, Al2O3, GeO2, C) and ternary Al2O3/SiO2/TiO2, fumed ox ides modified by organic and organosilicon compounds or interacting with di ssolved polymers, surfactants, etc., allows us to deeper understand the dep endencies of structural and other characteristics of the dispersions on fea tures of primary particles, their morphology, the nature of the surfaces of unmodified and modified individual and mixed oxides varied due to the synt hetic techniques and the concentrations of the oxide phases or modifiers, c oncentrations 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 s ynthetic 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 elucid ate some aspects of the aqueous suspensions of fumed oxides studied by usin g PCS and electrophoresis methods. The main reasons of non-linear dependenc ies of the particle size distributions (PSD) and zeta potential on the conc entration 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 oxi des linked with a four-stepwise structural hierarchy of fumed oxide particl es, which can keep (or rearrange) in the suspensions despite different pret reatments of initial silica, X/SiO2 or their dispersions; and (b) a signifi cant 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 gues t oxide concentrations and the synthetic techniques. (C) 2001 Elsevier Scie nce B.V. All rights reserved.