1. Introduction to colloid science and rheology 2. Hydrodynamic effects 3. Brownian hard spheres 4. Stable colloidal suspensions 5. Non-spherical particles 6. Weakly flocculated suspensions 7. Thixotropy 8. Shear thickening 9. Rheometry of suspensions 10. Suspensions in viscoelastic media 11. Advanced topics.

Colloidal Suspension Rheology

Mesoscale periodic structures have been fabricated via directed assembly of colloidal inks. Concentrated colloidal gels with tailored viscoelastic properties were designed to form self-supporting f...

Colloidal inks for directed assembly of 3-D periodic structures

The transport and fate of fine grained cohesive sediments in estuarine and coastal waters is influenced by the settling velocity of the sediment, which in turn is affected by flocculation effects. The flocculation processes depend on the physico-chemical properties of the sediment and the water, and on several physical mechanisms, of which turbulence is a major one. In the present paper the effects of turbulence are further analyzed. The floes are treated as self-similar fractal entities. As a result, the settling velocity is shown not to scale with the diameter D squared, as predicted by Stokes' law, but with Dnf-1 , where nf is the fractal dimension. Based on a collision frequency function and a floe breakup formulation, a simple flocculation model is proposed that can be solved analytically for uniform conditions. The flocculation and floe breakup coefficients were obtained from experiments described in literature. It is shown that the maximal attainable floe size and settling velocity are determined t...

A simple model for turbulence induced flocculation of cohesive sediment

On the flocculation and settling velocity of estuarine mud

We review the sequences of structural states that can be induced in colloidal suspensions by the application of flow. Structure formation during flow is strongly affected by the delicate balance among interparticle forces, Brownian motion and hydrodynamic interactions. The resulting non-equilibrium microstructure is in turn a principal determinant of the suspension rheology. Colloidal suspensions with near hard-sphere interactions develop an anisotropic, amorphous structure at low dimensionless shear rates. At high rates, clustering due to strong hydrodynamic forces leads to shear thickening rheology. Application of steady-shear flow to suspensions with repulsive interactions induces a rich sequence of transitions to one-, two-and three-dimensional order. Oscillatory-shear flow generates metastable ordering in suspensions with equilibrium liquid structure. On the other hand, short-range attractive interactions can lead to a fluid-to-gel transition under quiescent suspensions. Application of flow leads to orientation, breakup, densification and spatial reorganization of aggregates. Using a non-Newtonian suspending medium leads to additional possibilities for organization. We examine the extent to which theory and simulation have yielded mechanistic understanding of the microstructural transitions that have been observed.

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Flow-induced structure in colloidal suspensions

The structure and properties of flocculated suspensions were investigated experimentally using small-angle light scattering. Experiments monitoring the breakup resulting from uniform shear of flocculated 0.14 μm diameter polystyrene latices minimized kinetic effects, isolating the instantaneous breakup modeled in existing theories. The average number of particles per floc, 〈N〉, and mean radius of gyration cubed, 〈Rg2〉3/2, varied as γx, with x = −0.878 and −1.06, respectively. This shear dependence is weaker than predicted by the existing models. Comparison of the two relationships yields 〈N〉 ∝ 〈Rg2〉D/2, where the observed fractal dimensionality D = 2.48 indicates a nonuniform structure in conflict with the uniform porosity assumed in the models. Other methods for determining the fractal dimensionality yielded D = 1.6, 2.2, and 2.5, depending on the shear history of the samples. The effect of increasing electrolyte concentration was a slight weakening of the flocs for [NaCl] < 0.04 M followed by a significant strengthening above 0.04 M; DLVO theory successfully correlated this trend.

Richard C Sonntag

Papers

Structure and breakup of flocs subjected to fluid stresses: I. Shear experiments

Structure and breakup of flocs subjected to fluid stresses: II. Theory

Elastic properties of flocculated networks

Structure and breakup of flocs subjected to fluid stresses: III. Converging flow