Colloids, lyophobic, DLVO theory

Verwey, E. J. W., and Overbeek, J. Th. G., Theory of the Stability of Lyophobic Colloids, Elsevier, Amsterdam, Netherlands, 1948. (Another classic reference, by two of the originators of the DLVO theory of colloidal interactions.)... 

The DLVO theory, which was developed independently by Derjaguin and Landau and by Verwey and Overbeek to analyze quantitatively the influence of electrostatic forces on the stability of lyophobic colloidal particles, has been adapted to describe the influence of similar forces on the flocculation and stability of simple model emulsions stabilized by ionic emulsifiers. The charge on the surface of emulsion droplets arises from ionization of the hydrophilic part of the adsorbed surfactant and gives rise to electrical double layers. Theoretical equations, which were originally developed to deal with monodispersed inorganic solids of diameters less than 1 pm, have to be extensively modified when applied to even the simplest of emulsions, because the adsorbed emulsifier is of finite thickness and droplets, unlike solids, can deform and coalesce. Washington has pointed out that in lipid emulsions, an additional repulsive force not considered by the theory due to the solvent at close distances is also important. 

The basic idea of the DLVO theory is that the stability of lyophobic colloids in aqueous systems is determined by the combination of van der Waals attraction and electrostatic repulsion and that the two are exactly additive. In other words, the total interaction free energy VT would at any value of h... 

The DLVO theory has been very successful in predicting (in) stability against aggregation for many, especially inorganic, systems. Although developed for lyophobic colloids, the theory can often be usefully applied to lyophilic colloids these are often found in biogenic systems, including most foods. However, some complications and other interaction forces may come into play. 

The above is only a very brief account of the DLVO theory, since its full development involves rather elaborate mathematics and some necessary approximations which arc probably of limited validity. Nevertheless, the general principles upon which it is based are valuable guides to an understanding of lyophobic colloids. 

Properties of clays and clayey rocks, and also the processes in them depend on a number of factors. Then the mathematical simulation of the properties and processes, as one of the methods of their examination, is a rather difficult problem. Physically it is clear that the speciflc properties of clay rocks (low permeability, plasticity in moist condition) are caused by the existence of clay minerals in their composition, and these properties are a manifestation of surface capacities, which exist between particles of the clay minerals, which are included in the composition of clays. The most useful conception of the activity of surface capacities is the conception of disjoining pressure between colloid particles, Mitchell (1976). In this work we provide a description of the physical and mechanical clay properties and transport processes in them. The description is based on methods of theory of filtration consolidation. Nikolaevskiy (1996), and also on the theory of stability of lyophobic colloids (theory of Deijaguin-Landau-Verwey-Overbeeck, or DLVO theory), which uses the conception of disjoining pressure. 

The DLVO theory, named after its founders Derjaguin, Landau, Verwey, and Overbeek, provides a quantitative description of the stability of lyophobic colloids. 

Finally, it is emphasized again that the DLVO theory predicts the stability of lyophobic colloids. It addresses the question, whether aggregation occurs in the primary minimum. However, as it does not include short-range interactions, the DLVO theory cannot be used to describe the behavior of the particles in the aggregates. 

DLVO Theory. Derjaguin and Landau (64,65) and Verwey and Overbeek (66) developed a quantitative theory for the stability of lyophobic colloids, referred to as DLVO theory. It was known from experiment that classical colloids (Agl, Au)... 

The destabilisation of colloidal systems can also be described with the DLVO (Deryagin-Landau-Verwey-Overbeek) theory. This theory has been proposed for lyophobic colloidal systems but can also be applied qualitatively to lyophilic colloidal systems. If the potential energy is plotted as a function of the distance of two particles, a curve is obtained as shown in Fig. 18.8. 

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