The effects of non-DVLO forces in colloidal aggregation

Detailed knowledge of the stability of colloidal dispersions and the growth process it undergoes after de-stabilization is of great importance. It is manifested, for example, in (1) the shelf life of drug suspensions, dispersed paints and inks, ceramics, etc., (2) the structure of porous media used in oil recovery, catalysis, water treatment, and chromatography, (3) the structure of such entities as snowflakes, quartz, etc, and (4) the physical and chemical properties that the dispersion or aggregate exhibits. When the dispersion becomes unstable, the structure of the resulting cluster is inherently related to the dynamics of the aggregation. The traditional approach in understanding both colloidal stability and aggregation has been the Derjaguin-Landau-Verwey-Overbeeck (DLVO) theory, the determination of the interaction energy between two colloidal particles as a function of their center-to-center separation. While DLVO theory has been applied to accurately describe the stability and the irreversible aggregation of electrostatically-stabilized colloids, the same cannot be said in many circumstances where steric or hydration forces dominate. The objective of this work is to examine the effect of non-DLVO forces on the kinetics and the morphology of aggregate formation.; Investigations into these effects in theory and experiment are carried out. First, the use of viscosity-enhancing/crosslinkable polymers in a dispersed phase is examined to assist in the collection of particles in a solid-liquid separation process. Agglomerate structure which is important in resisting hydrodynamic effects is found to be dependent on a variety of factors. The following two case studies investigated the de-stabilization of sterically-stabilized particles in non-aqueous media. We show that the aggregation in such systems is reversible and that its rate and structure may be tuned by carefully controlling solvency conditions. In the final case study, hydration forces in high salt media are believed to unexpectedly reduce the aggregation rate of colloids resulting in compact aggregate structure found to resemble those formed in very low salt concentrations.