Diffuse double layer theory electrostatic force

This model is based on the Gouy-Chapman theory (diffuse double-layer theory). The theory states that in the area of the boundary layer between solid and aqueous phase, independently of the surface charge, increased concentrations of cations and anions within a diffuse layer exists because of electrostatic forces. In contrast to the constant-capacitance model, the electrical potential does not change up to a certain distance from the phase boundaries and is not immediately declining in a linear manner (Fig. 14 a). Diffusion counteracts these forces, leading to dilution with increasing distance from the boundary. This relation can be described physically by the Poisson-Boltzmann equation. 

Electrostatic stabilization is of importance in solution synthesis as another way to stabilize dispersions.1 1 Colloidal particles almost always have charged surfaces that tend to repel each other. One of the most common charging processes is the adsorption of charged species on the surface of the particle. To maintain electroneutrality, a diffuse cloud of counter ions forms in the fluid around the suspended particle. This phenomenon is described by the diffuse double-layer theory. When the diffuse ion clouds of particles interpenetrate, the particles tend to repel each other electrostatically. The electrostatic repulsive forces are opposed by attractive van der Waals forces that are always present between particles in suspension. The description of the potentials created by these two opposing forces is known as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The DLVO theory predicts... 

The situation is still more complex in the presence of surfactants. Recently, a self-consistent electrostatic theory has been presented to predict disjoining pressure isotherms of aqueous thin-liquid films, surface tension, and potentials of air bubbles immersed in electrolyte solutions with nonionic surfactants [53], The proposed model combines specific adsorption of hydroxide ions at the interface with image charge and dispersion forces on ions in the diffuse double layer. These two additional ion interaction free energies are incorporated into the Boltzmann equation, and a simple model for the specific adsorption of the hydroxide ions is used for achieving the description of the ion distribution. Then, by combining this distribution with the Poisson equation for the electrostatic potential, an MPB nonlinear differential equation appears. 

The layer of counterions surrounding a charged particle is called the diffuse double layer and the concentration of counterions in the diffuse double layer is a function of the distance from the particle surface. When a charged particle moves with respect to the surrounding liquid, that is, electrophoresis, there is a plane of shear between the two phases and the electric potential at the plane of shear is called the zeta potential, f. This is the experimentally measured quantity computed from electrokinetic motion of particles. However, even if the zeta potential is not exactly the surface potential, o it is the value used for surface potential in calculations of electrostatic stabilization in the DLVO theory. Because the zeta potential determines the net interparticle forces in electrostatically stabilized systems... 

Many properties of disperse systems are related to the distribution of charges in the vicinity of the interface due to the adsorption of electrolytes. The adsorption of molecules is driven by the van der Waals attraction, while the driving force for the adsorption of electrolytes is the longer-range electrostatic (Coulomb) interaction. Because of this, the adsorption layers in the latter case are less compact than in the case of molecular adsorption (i.e., they are somewhat extended into the bulk of the solution), and the discontinuity surface acquires noticeable, and sometimes even macroscopic thickness. This diffuse nature of the ionized adsorption layer is responsible for such important features of disperse systems as the appearance of electrokinetic phenomena (see Chapter V) and colloid stability (Chapters VII, VIII). Another peculiar feature of the adsorption phenomena in electrolyte solutions is the competitive nature of the adsorption in addition to the solvent there are at least two types of ions (even three or four, if one considers the dissociation of the solvent) present in the system. Competition between these ions predetermines the structure of the discontinuity surface in such systems -i.e. the formation of spatial charge distribution, which is referred to as the electrical double layer (EDL). The structure and theory of the electrical double layer is described in detail in textbooks on electrochemistry. Below we will primarily focus on those features of the EDL, which are important in colloid... 

Electrostatic and Diffusion Theories. The electrostatic theory states that electrostatic forces in the form of an electrical double layer are present at the adhesive-adher-end interface. These forces account for resistance to separation. The electrostatic theory of adhesion is not generally applicable for common production assembly, but it does apply to the adhesion of particulates (e.g., dust) on plastic film. 

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