Deijaguin-Landau-Verwey-Overbeek theory

Fig. 1 Interactions between nanoparticles, (a) Traditional forces for colloidal stabilization (e.g., electrostatic, van der Waals, steric) that occur when particles are dispersed in aqueous media, (b) The van der Waals forces are attractive whereas the electrostatic forces are repulsive ovta- a typical length scale. The Deijaguin-Landau-Verwey-Overbeek theory in colloid science considers the sum of these forces. Reprinted with permission from [80]. Copyright 2011 EIscvIct...

The stability of colloidal dispersions is often described quantitatively via the DLVO (Deijaguin-Landau-Verwey-Overbeek) theory which accounts in a simple additive way for both the (usually) attractive van der Waals (vdW) energies, V,, and the (typically) repulsive electric/electrostatic or double-layer energies, Vr ... 

Ruckenstein and Schiby derived4 an expression for the electrochemical potential, which accounted for the hydration of ions and their finite volume. The modified Poisson-Boltzmann equation thus obtained was used to calculate the force between charged surfaces immersed in an electrolyte. It was shown that at low separation distances and high surface charges, the modified equation predicts an additional repulsion in excess to the traditional double layer theory of Deijaguin—Landau—Verwey—Overbeek. 

According to Deijaguin-Landau-Verwey-Overbeek (DLVO) theory, a cornerstone of modem colloid science, two types of forces exist between colloidal particles suspended in a dielectric medium electrostatic forces, which result from an unscreened surface charge on the particle, and London-van der Waals attractive forces, which are universal in nature. The colloidal stability and rheology of oxide suspensions, in the absence of steric additives, can be largely understood by combining these two forces (assumption of additivity). 

From the brief sketch of the Deijaguin, Landau, Verwey, Overbeek (DLVO)-theory the following three important practical conclusions, suitable for foams and emulsions, can be drawn ... 

TTHE MOST IMPORTANT FORCES ACTING BETWEEN MEMBRANE SURFACES are van der Waals, electrostatic, and hydration. The first two forces are explained by the Deijaguin-Landau-Verwey-Overbeek (DLVO) theory (I) the existence of the hydration force was anticipated before it was measured (2). The van der Waals force is always attractive and displays a power law distance dependence, whereas the electrostatic and hydration forces are repulsive and exponentially decay with distance. The electrostatic force describes the interaction between charged membrane surfaces when the separation between surfaces is above 10 molecular solvent diameters. The hydration force acts between charged and uncharged membrane surfaces and at distances below 10 molecular solvent diameters its value dominates the values of van der Waals and electrostatic forces (3). The term hydration reflects the belief that the force is due to the structure of water between the surfaces. Electrostatic and hydration forces are similar in some respects both are exponential and repulsive and their theoretical description involves coupling electrostatic concepts and ideas borrowed from statistical mechanics. Although the nature of the electrostatic force is solidly established, this is not the case for the hydration force. To illustrate the role the electrostatic... 

For example, it is well known that the silica hydrosols are stable at their point of zero charge (pzc) and that they also coagulate in alkaline solutions, in which their electrical smface charge is high and should therefore increase their stabUity. Such behavior is very unusual indeed, and this question arises immediately Why does the Deijaguin-Landau-Verwey-Overbeek (DLVO) theory seem to be unable to cope with the silica hydrosols while it explains satisfactorily, at least to the best of our knowledge, the behavior of all other colloidal systems ... 

Direct adhesion of particles to fibres can be explained with Deijaguin—Landau— Verwey—Overbeek (DLVO)" " theory for soft cell particles,and the adhesion of cell particles to the fibres may be quantified by using the attachment rate coefficient, att which is related to the collision efficiency, rj, and the sticking efficiency, , as follows... 

Having reviewed the properties of single adsorption monolayers, we proceed with the couples of interacting monolayers the thin liquid films. First, we present the thermodynamics of thin films, and then we describe the molecular theory of the surface forces acting in the thin films. We do not restrict ourselves to the conventional DLVO (Deijaguin, Landau, Verwey, Overbeek) forces [2,3], but consider also the variety of the more recently discovered non-DLVO surface forces [4]. The importance of the micelle-micelle interaction for the mechanism of micelle growth is also discussed. 

This is the well-known empirical Schulze-Hardy rule of coagulation concentration, which has been confirmed experimentally in many colloidal systems. The above theory of dispersion and coagulation of colloidal particles, based on the repulsive interaction between two diffuse layers and on the attractive interaction owing to the van der Waals-London force, is called the Deijaguin-Landau-Verwey-Overbeek (D.L.V.O.) theory. 

FIGURE 9.5 Comparison between the Deijaguin-Landau theory [9] and the Verwey-Overbeek theory [10]. These two theories give the same result. 

Because of the drastic energy increase involved in the emulsification process, the resulting emulsion is not thermodynamically stable and the deemulsification process must be either slowed down to get stable goods or accelerated in separation operations. This chapter will focus on stabilizing emulsions. This stabilization can be explained using two different concepts the interfadai film using the hydrophilic-lipophilic balance (HLB) method and the Deijaguin, Landau, Verwey, and Overbeek (DLVO) theory. 

Now, if we think that the increase of the interfacial area involved in the emulsification process is of a 10 order of magnitude and that even the most efficient surface-active agent can reduce the interfacial tension by a factor of 5-10, we cannot understand why emulsifiers can stabilize the emulsions on the base of surface-tension calculations. In order to answer this question, the modem theory of Deijaguin, Landau, Verwey, and Overbeek (DLVO) will be used, but from a qualitative point of view because this chapter is devoted to the formulation job. 

The classical quantitative calculations of interaction forces in thin liquid films were made during the second world war hy Deijaguin Landau (1941) and in a monograph by Verwey Overbeek (1948). This theory for thin liquid films is therefore known as the Derjaguin, Landau, Verwey and Overbeek theory (DLVO). 

The physicochemical forces between colloidal particles are described by the DLVO theory (DLVO refers to Deijaguin and Landau, and Verwey and Overbeek). This theory predicts the potential between spherical particles due to attractive London forces and repulsive forces due to electrical double layers. This potential can be attractive, or both repulsive and attractive. Two minima may be observed The primary minimum characterizes particles that are in close contact and are difficult to disperse, whereas the secondary minimum relates to looser dispersible particles. For more details, see Schowalter (1984). Undoubtedly, real cases may be far more complex Many particles may be present, particles are not always the same size, and particles are rarely spherical. However, the fundamental physics of the problem is similar. The incorporation of all these aspects into a simulation involving tens of thousands of aggregates is daunting and models have resorted to idealized descriptions. 

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

The first quantitative theory of interactions in thin liquid films and dispersions is the DLVO theory called after the names of the authors Deijaguin and Landau and Verwey and Overbeek. In... 

Here we consider the total interaction between two charged particles in suspension, surroimded by their counterions and added electrolyte. This is the celebrated DLVO theory, derived independently by Deijaguin and Landau and by Verwey and Overbeek [41]. By combining the van der Waals interaction (equation (C2.6.4fi with the repulsion due to the electric double layers (equation (C2.6.1011. we obtain... 

On the basis of work done in the years just before World War II, Deijaguin and Landau [26] were able to explain in 1941 many of the complex phenomena involved in aggregative stability on the basis of forces of interaction between colloidal particles, namely the van der Waals-London forces of attraction and the electrostatic forces of repulsion. In the meantime, as a result of theoretical investigations and calculations performed in the years 1940-1944 and without the benefit of much of the literature that appeared during the war years, Verwey and Overbeek [7] formulated a theory of stability of lyophobic colloids and published it as a book in 1948. Because their... 

A quantitative theory of interactions in thin liquid films and dispersions was proposed by Deijaguin and Landau [313] and Verwey and Overbeek [3]. In this theory, called DLVO after the authors names, the total interaction is supposed to be a superposition of van der Waals and double-layer interactions. In other words, the total disjoining pressure, II, and the particle-particle interaction energy, U, are presented in the forms... 

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