Double layer extension

The double-layer extension depends on electrolyte concentration and valency of the counterions,... 

The double-layer extension increases with a decrease in electrolyte concentration. 

When charged colloidal particles in a dispersion approach each other such that the double layers begin to overlap (when the particle separation becomes less than twice the double layer extension), then repulsion will occur. The individual double layers can no longer develop unrestrictedly, as the limited space does not allow complete potential decay [5]. 

The double layer extension increases with decreases in electrolyte concentration. Stem [9] introduced the concept of the nondifiuse part of the double layer for specifically adsorbed ions, the remainder being diffuse in nature. The potential... 

When charged coUoidal particles in a dispersion approach each other such that the double layer begins to overlap (when particle separation becomes less than twice the double layer extension), then repulsion will occur. The individual double layers can no longer develop unrestrictedly, as the limited space does not allow complete potential decay [3]. This is illustrated in Figure 10.8 for two flat plates, and shows clearly shows that when the separation distance h between the emulsion droplets become less than twice the doubly layer extension, the potential at the mid plane between the surfaces is not equal to zero (which would be the case if h were more than twice the double layer extension) plates. 

The double layer extension decreases with increase of electrolyte concentration. This means that the repulsion decreases with increase of electrolyte concentration, as is illustrated in Figure 10.9. 

For crystalline particles which are large in comparison with the double layer extension, the effect of the interaction will practically be restricted to the crystal faces which axe brought in opjposite positions during a particle encounter. The effect upon crystal faces not facing each other may be neglected as a first approximation. 

On the other hand, when the particles are small in comparison with the double layer extension, so that, in a particle encounter, one particle may be enclosed by the double layer of the second and vice versa, the model of interacting spheres is more adequate. Moreover, the influence of the particle dimensions can be gathered more easily from the case of spheres than from the infinitely large fl t plates, where particle dimensions have to be introduced in a more or less arbitrary way. 

When two droplets approach to a distance h that is smaller than the double layer extension, double layer overlap occurs and this leads to repulsion (the double layers cannot be fully developed) [5]. The double layer extension depends on electrolyte concentration and valency (the lower the electrolyte concentration and the lower the valency the more extended the double layer is). 

The data tabulated below for 1 1 electrolyte (e.g. KCl) show that the double layer extension increases with decreasing electrolyte concentration. 

The double layer extension is determined by the electrolyte concentration and the valency of the counter ions, as given by the reciprocal of the Debye-Huckel parameter (1 /k) - referred to as the thickness of the double layer,... 

Electrical double layers are produced when using ionic surfactants. On adsorption of these molecules on particles or droplets a surface charge is produced from the head group of the ionic surfactant. This surface charge is compensated by unequal distribution of counterions (opposite in charge to the surface) and co-ions (same sign as the surface) which extend to some distance from the surface. This forms the basis of the diffuse double layer proposed by Gouy and Chapman [73]. The double layer extension depends on electrolyte concentration and valency of the counterions,... 

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