The influence of surface heterogeneity and solution composition on the colloid stability of SiO2 and TiO2 dispersions
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(Published version)
Date
2003
Authors
Snoswell, David Robert Evan
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thesis
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Abstract
Hydrophobic colloidal suspensions are common in nature and industry. DLVO theory has been used to model the interactions between colloidal particles for decades, however the origin of long-ranged attractive forces observed between hydrophobic colloids remains the subject of much debate. In an effort to understand these forces and improve the prediction of colloidal stability, the colloidal stability of synthetic silica and titania was studied at various concentrations of dissolved gas, KCl electrolyte and pH.The colloidal stability of synthetic silica spheres with clean, methylated and dehydroxylated surfaces were studied at different concentrations of dissolved gas and KCl electrolyte at a fixed pH of 4.2. A classic stability ratio/electrolyte concentration analysis showed that hydrophobic, methylated particles undergo faster rates of aggregation with increasing concentrations of dissolved carbon dioxide. Similar data for hydrophilic particles and dehydroxylated particles showed no change as a function of dissolved carbon dioxide concentration. Zeta potential data behave similarly, showing a strong influence of dissolved gas only for methylated particles. The results are interpreted in terms of DLVO theory, with the surface-to-surface interaction dominated by the presence of very small, protruding bubbles.An analysis of surface forces in the presence of protruding bubbles indicates that the bubbles significantly reduce the effective interaction radius. The concept of an effective interaction radius is explored further in a study of silica and titania aggregation. The analysis of these data demonstrates that a single effective interaction radius may be used for a particle system at various pH conditions, resulting in improved accuracy of aggregation rate predictions in the slow aggregation regime. The correlation between surface roughness and gradient of the stability curve depends on the Debye length and surface roughness, but not the particle size.Using the model parameters obtained for silica and titania, including their effective interaction radii, solutions conditions for the selective aggregation of titania in a binary suspension of silica and titania were chosen. Experiments performed under these conditions confirm the selective aggregation of titania from the mixed suspension, and demonstrate that high efficiency submicron particle separation can be performed.
School/Discipline
University of South Australia Ian Wark Research Institute
Ian Wark Research Institute
Ian Wark Research Institute
Dissertation Note
Thesis (PhD)--University of South Australia, 2003
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Copyright 2003 David Robert Evan Snoswell
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eng
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506 0#$fstar $2Unrestricted online access