Electrostatic repulsive energy, electrically

The total energy of interaction ( VT ) is obtained from the summation between the electrostatic repulsive energy (i.e., the electrical double layer) and the attractive energy (i.e., van der Waals forces) ... 

Electrostatic Repulsive Forces. As the distance between two approaching particles decreases, their electrical double layers begin to overlap. As a first approximation, the potential energy of the two overlapping double layers is additive, which is a repulsive term since the process increases total energy. Electrostatic repulsion can also be considered as an osmotic force, due to the compression of ions between particles and the tendency of water to flow in to counteract the increased ion concentration. 

In a qualitative way, colloids are stable when they are electrically charged (we will not consider here the stability of hydrophilic colloids - gelatine, starch, proteins, macromolecules, biocolloids - where stability may be enhanced by steric arrangements and the affinity of organic functional groups to water). In a physical model of colloid stability particle repulsion due to electrostatic interaction is counteracted by attraction due to van der Waal interaction. The repulsion energy depends on the surface potential and its decrease in the diffuse part of the double layer the decay of the potential with distance is a function of the ionic strength (Fig. 3.2c and Fig. 

The secondary electroviscous effect is often interpreted in terms of an increase in the effective collision diameter of the particles due to electrostatic repulsive forces (i.e., the particles begin to feel the presence of other particles even at larger interparticle separations because of electrical double layer). A consequence of this is that the excluded volume is greater than that for uncharged particles, and the electrostatic particle-particle interactions in a flowing dispersion give an additional source of energy dissipation. 

A quantitative treatment of the effects of electrolytes on colloid stability has been independently developed by Deryagen and Landau and by Verwey and Over-beek (DLVO), who considered the additive of the interaction forces, mainly electrostatic repulsive and van der Waals attractive forces as the particles approach each other. Repulsive forces between particles arise from the overlapping of the diffuse layer in the electrical double layer of two approaching particles. No simple analytical expression can be given for these repulsive interaction forces. Under certain assumptions, the surface potential is small and remains constant the thickness of the double layer is large and the overlap of the electrical double layer is small. The repulsive energy (VR) between two spherical particles of equal size can be calculated by ... 

Flocculation is the result of van der Waals attraction that is universal for all disperse systems. The van der Waals attraction was described previously and, as shown in Figure 10.6, it is inversely proportional to the droplet-droplet distance of separation h it also depends on the effective Hamaker constant A of the emulsion system. One way to overcome the van der Waals attractions is by electrostatic stabiUsation using ionic surfactants this results in the formation of electrical double layers that introduce a repulsive energy that overcomes the attractive energy. Emulsions... 

Electrostatic Repulsion. The electrostatic energy of repulsion (Vr) between like charge surfaces arises from the overlap of the electrical double layers on the two particles. The range of interaction is of the order... 

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