Colloids Stability DLVO Theory

We need to understand under which conditions a colloidal system will remain dispersed (and under which it will become unstable). Knowing how colloidal particles interact with one another makes possible an appreciation of the experimental results for phase transitions in such systems as found in various industrial processes. It is also necessary to know under which conditions a given dispersion will become unstable (coagulation). For example, one needs to apply coagulation in wastewater treatment so that most of the solid particles in suspension can be removed. Any two particles coming close to each other, will produce different forces. 

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Combination of Ga and G at various h results in the energy-distance curve is illustrated in Figure 11.34, which forms the basis of the Deryaguin-Landau-Verwey-Overbeek theory colloid stability (DLVO theory) [38]. 

Another point of view concerning foam stability appeared in relation to the development of the general theory of stability of colloid systems (DLVO-theory). It has already been noted that this theory was verified for the first time with foam films [35]. This gave rise to the concept of foam stabilisation on the account of the electrostatic component of disjoining pressure [e.g. 24, 32, 36],... 

The potentials (7-1), (7-2), and (7-4a), when combined, form the basis of the celebrated DLVO (Derjaguin and Landau, 1941 Verwey and Overbeek, 1948) theory of colloid stability. This theory is useful in predicting the conditions of surface potential, ionic strength, and so on, under which flocculation will occur. But the theory has important limitations, in part because it only considers van der Waals, electrostatic, and hard-core interactions. 

The electrostatic interaction between diffuse layers of ions surrounding particles is one of the most thoroughly theoretically developed factors of colloid stability. The theory of electrostatic factor is, essentially, the basis for the quantitative description of coagulation by electrolytes. This theory was developed in the Soviet Union by B.V. Derjaguin and L.D. Landau in 1935 -1941, and independently by the Dutch scientists E.Verwey and T. Overbeek, and is presently known by the initial letters of their names as the DL VO theory [44,45]. The DLVO theory is based on comparison of molecular interaction between the dispersed particles in dispersion medium and the electrostatic interaction between diffuse layers of ions, with Brownian motion of particles taken into account (in the simplest version of theory this is done on a qualitative level). 

The DLVO theory [88,89], a landmark in the study of colloids, interprets stability as dependent on the competition between the long-range repulsion forces of similarly charged... 

At short interparticle distances, the van der Walls forces show that two metallic particles will be mutually attracted. In the absence of repulsive forces opposed to the van der Walls forces the colloidal metal particles will aggregate. Consequently, the use of a protective agent able to induce a repulsive force opposed to the van der Walls forces is necessary to provide stable nanoparticles in solution. The general stabihzation mechanisms of colloidal materials have been described in Derjaguin-Landau-Verway-Overbeck (DLVO) theory. [40,41] Stabilization of colloids is usually discussed... 

Comparison of the proposed dynamic stability theory for the critical capillary pressure shows acceptable agreement to experimental data on 100-/im permeability sandpacks at reservoir rates and with a commercial a-olefin sulfonate surfactant. The importance of the conjoining/disjoining pressure isotherm and its implications on surfactant formulation (i.e., chemical structure, concentration, and physical properties) is discussed in terms of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of classic colloid science. 

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

The stabilization mechanisms of colloidal materials have been described in Derjaguin-Landau-Verway-Overbeek (DLVO) theory [8, 9]. Colloids stabilization is usually discussed in terms of two main categories, namely charge stabilization and steric stabilization. 

The DLVO theory, a quantitative theory of colloid fastness based on electrostatic forces, was developed simultaneously by Deryaguin and Landau [75] and Verwey and Overbeek [76], These authors view the adsorptive layer as a charge carrier, caused by adsorption of ions, which establishes the same charge on all particles. The resulting Coulombic repulsion between these equally charged particles thus stabilizes the dispersion. This theory lends itself somewhat less to non-aqueous systems. 

The DLVO theory is thus found to be useful to predict and estimate colloidal stability behavior. Of course, in such systems with many variables, a simplified theory is to be expected to fit all kinds of systems. 

Derjaguin and Landau, and Verwey and Overbeek (1941-8) developed the DLVO theory of colloid stability. 

Missana, T. Adell, A. 2000. On the applicability of DLVO theory to the prediction of clay colloids stability. Journal of Colloid and Interface... 

The well-known DLVO theory of colloid stability (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the liquid—solid interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobility or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see COLLOIDS). 

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.)... 

Throughout most of this chapter the emphasis has been on the evaluation of zeta potentials from electrokinetic measurements. This emphasis is entirely fitting in view of the important role played by the potential in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. From a theoretical point of view, a fairly complete picture of the stability of dilute dispersions can be built up from a knowledge of potential, electrolyte content, Hamaker constants, and particle geometry, as we discuss in Chapter 13. From this perspective the fundamental importance of the f potential is evident. Below we present a brief list of some of the applications of electrokinetic measurements. 

Hunter, R. J., Foundations of Colloid Science, Vol. 2, Clarendon Press, Oxford, England, 1989. (Undergraduate and graduate levels. Along with Volume 1, these two volumes cover almost all the topics covered in the present chapter at a more advanced level. Volume 1 discusses DLVO theory and thermodynamic approaches to polymer-induced stability or instability and is at the undergraduate level. Volume 2 presents advanced topics (e.g., statistical mechanics of concentrated dispersions, rheology of dispersions, etc.).)... 

Two kinds of barriers are important for two-phase emulsions the electric double layer and stcrie repulsion from adsorbed polymers. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stability that is called DLVO, after its originators Deijaguin, Landau. Vervcy, and Overbeek. The theory provided substantial progress in the understanding of colloidal stability, and Its treatment dominated the colloid science literature lor several decades,... 

Proteins are both colloids and polymers. Therefore, attempts have been made to understand the phenomenon of protein aggregation with the help of models from the polymer and colloid fields such as DLVO theory, describing the stability of colloidal particles, or phase behavior and attraction-repulsion models from polymers (De Young, 1993). For faster progress, more phase diagrams for equilibrium protein precipitation, in both the crystalline and the non-crystalline state, as well as more data on observations of defined protein oligomers or polymers, are required. 

In 1965 Dunn and Taylor confirmed the theory for vinyl acetate polymerization (15), and proposed, in the light of the presumed importance of rapid coagulation during the earliest stages of reaction, that the "DLVO" theory for colloid stability (16) be applied. Fitch proposed a kinetic basis for a quantitative theory and observed that for observation of particle formation kinetics, "fast" reaction techniques must be used because "particle formation occurs in a matter of seconds or even less (17)". 

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