Colloidal solutions DLVO theory

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... 

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 DLVO theory [1,2], which describes the interaction in colloidal dispersions, is widely used now when studying behavior of colloidal systems. According to the theory, the pair interaction potential of a couple of macroscopic particles is calculated on the basis of additivity of the repulsive and attractive components. For truly electrostatic systems, a repulsive part is due to the electrostatic interaction of likely charged macroscopic objects. If colloidal particles are immersed into an electrolyte solution, this repulsive, Coulombic interaction is shielded by counterions, which are forming the diffuse layer around particles. A significant interaction occurs only when two double layers are sufficiently overlapping during approach of those particles. 

Figure 2.3a is purely a sketch. The exact interaction potential between n-butylammonium-substituted clay plates (or other charged colloidal particles) in solution must incorporate many effects, such as the size of the small ions and the molecular degrees of freedom of the solvent, that are beyond the scope of either the coulombic attraction theory or DLVO theory. However, whatever the complicated functional dependence, the curve must comprise two states of equal thermodynamic potential. Somehow, the valleys in VT, the total potential, must be of equal depth. As discussed previously, in Figure 2.3b we see that the DLVO theory can never account for this experimentally proved phenomenon. 

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). 

The influence of the cations and anions has been discussed separately with the solution properties and reactions in the main focus. It has, however, been known over 100 years that anions play a crucial role for the stabilization and coagulation of colloids. More recently, the contribution of anions on the stabilization of particles, biocolloids, and bubbles has received renewed attention. - In these papers, it has been pointed out that there exists a collaborative interaction between cations and anions upon adsorption of one of the complexes from solution. At high concentrations this effect renders the simple indifferent ions specific and selective to each other. It is also seen as a dependency on the acid-base pair chosen for the regulation of the pH. This effect certainly needs to be added as an extension to (correction of) the DLVO theory. However, as shown in this paper, it is just as probable that the anion and cation collaborate during the adsorption and formation of gels and precipitates at the surface. The presence of such mixed phases has been confirmed experimentally, e.g., during the formation of hydroxoapatite in silica gel layers. ... 

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. 

DLVO theory has often been applied to gain insight into the stability of colloidal systems. For colloidal montmorillonite with a particle radius of R = 200 x 10 m in an aqueous NaCl solution, the electrical double layer repulsion can be approximated as... 

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 ... 

The particles synthesized by precipitation form solution could consist of aggregates of much finer primary particles [17-19, 127-132]. With DLVO theory for colloid... 

The Derjarguin, Landau, Verwey, Overbeck (DLVO) theory [23-25] has established the potential energy-distance relationship between two particles as a function of the characteristics of both the particles and the suspending solution. In natural systems, this approach requires compilation [26-28] of the major key physicochemical parameters that characterize the colloid material, including (a) colloid shapes... 

The interaction forces and potentials between two charged surfaces in an electrolyte are fundamental to the analysis of colloidal systems and are associated with the formation of electrical double layers (EDLs) in vicinity of the solid surfaces. The charged surfaces typically interact across a solution that contains a reservoir of ions, as a consequence of the dissociation of the electrolyte that is already present. In colloid and interfacial sciences, the EDL interaction potential, coupled with the van der Waals interaction potential, leads to the fimdamental understanding of inter-siuface interaction mechanisms, based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [1]. In practice, the considerable variations in the EDL interaction, brought about by the variations in electrolytic concentration of the dispersing medium, pH of the medium, and the siuface chemistry, lead to a diverse natiue of the colloidal behavior. A fundamental understanding of the physics of EDL interactions, therefore, is of prime importance in... 

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