DLVO theory application

Uvw values for the three curves are calculated from Eq. (3.76) at three different values of Kyw As it can be seen from the figure, the depth and position of minima on the curves strongly depend on Kvw value. The analysis indicates that the best agreement between the calculated and experimental results is reached at Kvw 3.5-10 21 J. This clearly and quantitatively characterises the competition between Tlei and rivw which justifies the DLVO-theory application to explaining the stability of liophobic colloids. Two other Kvw values have been reported in [155,161] 21 O 21 J for an equilibrium film and 6 10"21 J for a thinning film at KC1 concentration 0.1 mol dm 3. On that basis an average Kvw value equal to 41 O 21 J has been proposed for films from aqueous solutions [29,73,155,161]. It is close to the theoretically calculated in [159,160] Kvw = 3-10 21 J (this result was obtained employing a similar method and solution composition). 

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

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. 

Kruyt, H. R. (Ed.), Colloid Science. Vol. 1. Irreversible Systems, Elsevier, Amsterdam, Netherlands, 1952. (Graduate and undergraduate levels. A classic reference on colloids. Chapters 6-8, by Professor J. Th. G. Overbeek, present the classical DLVO theory of colloidal forces and their application to kinetics of coagulation.)... 

The stability of dispersions in aqueous media can often be described by the DLVO theory, which contains the double-layer repulsion and the van der Waals attraction. In some applications other effects are important, which are not considered in DLVO theory. At short range and for hydrophilic particles the hydration repulsion prevents aggregation. Hydrophobic particles, in contrast, tend to aggregate due to the hydrophobic force. 

The role of electrostatic repulsion in the stability of suspensions of particles in non-aqueous media is not yet clear. In order to attempt to apply theories such as the DLVO theory (to be introduced in Section 5.2) one must know the electrical potential at the surface, the Hamaker constant, and the ionic strength to be used for the non-aqueous medium these are difficult to estimate. The ionic strength will be low so the electric double layer will be thick, the electric potential will vary slowly with separation distance, and so will the net electric potential as the double layers overlap. For this reason the repulsion between particles can be expected to be weak. A summary of work on the applicability or lack of applicability of DLVO theory to non-aqueous media has been given by Morrison [268],... 

The applicability of DLVO theory is restricted partly because the primary potential energy minima are somewhat shallow. Another factor is the tendency of adsorbed... 

In fact, the SFA was initially developed for practically probing the DLVO theory, and DLVO forces were successfully measured in electrolyte solutions and colloidal systems [4,22]. However, the applications of the apparatus were not restricted to this. Detailed and accurate information was obtained on thickness and refractive index profiles of thin films [6], simple liquid molecular structuring... 

The application of DLVO-theory to explain the experimental TI(/i) isotherms in the range of small thickness values, in particular for NBF, is even more inconsistent, since in this case it is necessary to account for the short-range interaction forces and other physical concepts are required. That is why we believe that the approach according to which the NBF represents an ordered bilayer system with strongly expressed short-range molecular interactions is the most promising (see Section 3.4.1 and 3.4.4). 

Application of DLVO Theory. Some of the concepts and expressions of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory of colloid stabihty have been described in Chapter 1, or can be found in many different textbooks 4, 5). The application of DLVO theory to oil-in-water colloids with special reference to the stability of bitumen-in-water emulsions will be discussed here. 

To confirm the applicability of DLVO theory, coagulation tests were performed on the production samples. The results, shown photographically... 

However, the theory of Section II in this chapter gives the exact criterion that diffusion theory for the encounter rate is valid when a in Eq. (2.33) is large than unity. For potentials without barriers the factor IF(0)/IF(oo) is close to unity, and the criterion for applicability of the diffusion theory is that the mean free path Dj/C8kT/nfi) be much smaller than the particle size (1 + b)/4-However, for large barriers the criterion is similar to that of Verwey and Overbeek, except that SR is the half-width of the potential barrier at an energy of only kT/2 below the maximum. This is much less than the full width of the barrier, and for reasonable values of the parameters in aqueous solution it can be shown that DLVO theory breaks down for equal-size particles with R, > 150 nm. However, when hydrodynamic interaction between particles is introduced in the formula for in terms of and it is concluded ... 

Chang, Y.I. and Chang, P.-K. The role of hydration force on the stability of the suspension of Saccharomyces cerevisiae — application of the extended DLVO theory. Colloids Surfaces A, 211, 67, 2002. 

DLVO Theory and the Stability of Electrostatically Stabilized Dispersions in OiH Critics of electrostatic stabilization in non-aqueous liquids point out that 1) the low dielectric constant leads to much weaker repulsion between charged particles than in water and 2) the low ionic concentration in solution leads to enormous Debye lengths, resulting in weaker forces of repulsion than found in aqueous systems. (8) These charges are best answered by the full application of DLVO theory. The energy of... 

Application. To apply the DLVO theory in practice, several pieces of information have to be collected. Particle size (distribution) and shape can generally be experimentally determined. Hamaker constants often are to be found in the literature or can be calculated from Lifshits theory. The surface potential can be approximated by the zeta potential obtained in electrophoretic experiments. The ionic strength is generally known (or can be calculated) from the composition of the salt solution. All the other variables needed are generally tabulated in handbooks. This then allows calculation of V(h). To arrive at an aggregation rate, more information is needed this is discussed in Section 13.2. 

Early theories of colloidal dispersions, such as the DLVO theory (Chapter 9) and Einstein s theory of viscosity (Chapter 8). were, of necessity, limited in their applicability to very dilute dispersions. They gave general guidance, however, in the search for att understanding of more concentrated dispersions and formed the basis from which more recent progress has evolved. 

Application of DLVO Theory. Our approach to determine the contribution of double-layer interaction and van der Waals potentials to AGads involves comparing differences in the magnitudes of AGads found on the same solid but with different solution conditions, to potentials (U), or theoretical free energy components, evaluated from the DLVO-Lifshitz theory of colloid stability. 

Given the appropriate potential energy diagrams from the DLVO theory, the stability ratio may be calculated by graphical or numerical integration and then compared with experimental values of W=kyk, the ratio of the experimental rate constants for rapid and slow flocculation. Such a comparison is a severe test of the applicability of theory to experiment, and the observed deviations, although often not appreciable, reflect the assumptions and approximations which are necessary in the calculation of the potential energy terms. An advanced treatment of these issues will be found in Russel et al.- . 

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