Electrostatic properties, flocculation

Apparently, polymer conformation plays an important role in flocculation caused predominantly by bridging. This effect of polymer conformation on the dispersion properties has been confirmed by many observations where significantly different dispersion behavior is obtained with identical adsorption density and electrostatic property. There have been substantial efforts both theoretically and experimentally to develop relationships between the stability and the polymer conformation... 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

In principle, it should be possible to predict the critical conditions for flocculation and the rheological properties of the flocculated gel from the effective interparticle potential W (D), where D is the distance or gap separating the surfaces of neighboring particles. Typically, W(D) is estimated by adding together contributions from hard-core steric interactions, van der Waals interactions, electrostatic interactions, and possibly other interactions such as those from absorbed, grafted, or dissolved chains, or from thin (so-called Stem) layers of adsorbed ions, along with their hydration shells (Israelachvili 1991 Russel et al. 1989 Adamson and Cast 1997). 

Imagine a suspension of colloidal particles in water. What causes stability, and what, imder changing solution conditions like addition of salt causes flocculation (precipitation of the suspension) Two opposing forces were considered to operate between two such particles. The one, attractive, is the quantum mechanical van der Waals force and treats an intervening liquid as if it has bulk liquid properties up to the interfaces of the particles (theme (i)). The other, repulsive, due to charges formed by dissociation of ionisable surface groups, is electrostatic in origin, and depends on salt concentration. 

The second part is devoted to adsorption of polyelectrolytes at interfaces and to flocculation and stabilization of particles in adsorbing polymer solutions. A recent theory of the electrostatic adsorption barrier, some typical experimental results, and new approaches for studying the kinetics of polyelectrolyte adsorption are presented in the first chapter of this part. In the following chapters, results are collected on the electrical and hydrodynamic properties of colloid-polyelectrolyte surface layers, giving information on the structure of adsorbed layers and their influence on the interactions between colloidal particles examples and mechanisms are analyzed of polyelectrolyte-induced stabilization and fragmentation of colloidal aggregates ... 

The effect of water-soluble polymers on the properties of dilute lamellar dispersions was studied and the primary effect was found to be due to the exclusion of polymer from the water layers. This exclusion results in an osmotic compression of the water layers and a reduction in the vesicle diameter, phase volume, and dispersion viscosity. Depletion flocculation leads to fusion and morphological changes in the dispersion. Polyelectrolytes screen the electrostatic repulsion between bilayers and vesicles and this effect is superimposed on the osmotic compression. There was no apparent direct interaction between the polymmrs and the bilayers observed. 

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