Dispersions of particles are either stable or unstable, depending on whether the particles remain dispersed or have a tendency to form aggregates. The stability or otherwise of colloidal particles can often be described in terms of a balance between electrical repulsion and van der Waals attraction, an approach which was pioneered by Deryagin and Landau1 and Verwey and Overbeek2, and is now usually referred to as ‘DLVO theory’. The electrical repulsion between charged particles in dilute electrolyte solutions can be sufficient to prevent very close approach of the particles so that van der Waals attraction is not significant. By reducing the charge on the particles, or by increasing the ionic strength of the solution, the electrical repulsion can be reduced, which allows particles to approach close enough for van der Waals attraction to operate, and for aggregation to occur. The aggregation of colloidal particles is known either as ‘coagulation’ or ‘flocculation’. These terms are sometimes used interchangeably, but some authors use the different terms to imply different mechanisms of aggregation. We shall return to this question below.
KeywordsCharge Neutralization Cationic Polymer Adsorbed Polymer Anionic Polymer Silver Iodide
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