Electrostatic forces zeta potential

The electrostatic repulsive forces are a function of particle kinetic energy (/ T), ionic strength, zeta potential, and separation distance. The van der Waals attractive forces are a function of the Hamaker constant and separation distance. 

The second parameter influencing the movement of all solutes in free-zone electrophoresis is the electroosmotic flow. It can be described as a bulk hydraulic flow of liquid in the capillary driven by the applied electric field. It is a consequence of the surface charge of the inner capillary wall. In buffer-filled capillaries, an electrical double layer is established on the inner wall due to electrostatic forces. The double layer can be quantitatively described by the zeta-potential f, and it consists of a rigid Stern layer and a movable diffuse layer. The EOF results from the movement of the diffuse layer of electrolyte ions in the vicinity of the capillary wall under the force of the electric field applied. Because of the solvated state of the layer forming ions, their movement drags the whole bulk of solution. 

A foaming agent, such as crude cresol or pine oil (soap is unsuitable, as it lowers 0 too much), is added to the suspension of ground ore and collector oil in water and the pH is adjusted to give the particles low zeta potentials and, therefore, minimise electrostatic repulsions. Air is forced through a fine sieve at the bottom of the vessel. The particles of metal ore become attached to the air bubbles, which carry them to the surface (Figure 6.7), where they collect as a metal-rich foam which can be skimmed off. 

The largest adhesion force of alumina particles in DI water was attributed to a stronger electrostatic attraction between alumina particles and copper surface in DI water owing to their opposite signs of zeta potentials. The smallest adhesion force of alumina particles in the citric acid slurry was attributed to the... 

The charges are electric, so they possess electrostatic potential. As indicated on the right-hand side of Figure 12.3, this potential is greatest at the surface and decreases to zero at the bulk of the solution. The potential at a distance from the surface at the location of the shear plane is called the zeta potential. Zeta potential meters are calibrated to read the value of this potential. The greater this potential, the greater is the force of repulsion and the more stable the colloid. 

Dielectric Constant Magnitudes of all electrostatic interactions in a medium are determined by the dielectric constant of that medium. Thus all charge-related parameters (e.g., zeta potential, isoelectric point, electrochemical forces.) are affected by the dielectric constant (see Chapters 4-7). 

The effects of various electrolytes are usually compared in terms of the flocculation values, or minimal concentrations (expressed in millimoles per liter), required to bring about coagulation. Flocculation values for nonspecific electrolytes can be interpreted in terms of electrostatic repulsion and van der Waals attraction. The van der Waals attractive forces vary with size and shape of the particles, but roughly speaking the force is appreciable between colloidal particles at distances of the order of magnitude of their own radii. The significant feature is that flocculation occurs before the zeta potential reaches zero, that is, when it reaches a small critical value. 

The study of Lafrance and Mazet [549] not only provided further confirmation of the beneficial effect of cations (Na ) but also clarified its mechanism by analyzing the effect of sodium salt concentration on the zeta potential of a commercial powdered activated carbon (see Section I V.B. 1). The reported uptakes of a commercial. sodium humate remained <100 mg/g (at 10 mg/L). In the study of Annesini et al. [556], even at humic acid concentrations of 20 mg/L the uptake did not exceed 10 mg/g. These uptakes should be contrasted with those reported recently by Newcombe and Drikas [566] and illustrated in Fig. 23 at low pH, when electrostatic repulsive forces (see Section IV.B. 1) are eliminated, the uptake at comparable concentrations can be as high as 200-300 mg/g. 

The physical stability of a colloidal system is determined by the balance between the repulsive and attractive forces which is described quantitatively by the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. The electrostatic repulsive force is dependent on the degree of double-layer overlap and the attractive force is provided by the van der Waals interaction the magnitude of both are a function of the separation between the particles. It has long been realized that the zeta potential is a good indicator of the magnitude of the repulsive interaction between colloidal particles. Measurement of zeta potential has therefore been commonly used to assess the stability of colloidal systems. 

When the electrostatic stabilization of the emulsion is considered, the electrolytes (monovalent and divalent) added to the mixture are the major destabilizing species. The zeta potential of the emulsion particles is a function of the concentration and type of electrolytes present. Two types of emulsion particle-electrolyte (ions) interaction are proposed non-specific and specific adsorption.f H non-specific adsorption the ions are bound to the emulsion particle only by electrical double-layer interactions with the charged surface. As the electrolyte concentration is increased, the zeta potential asymptotes to zero. As the electrostatic repulsion decreases, a point can be found where the attractive van der Waals force is equal to the repulsive electrostatic force and flocculation of the emulsion occurs (Fig. 9A). This point is called the critical flocculation concentration (CFC). 

It is very important to note the lower is the zeta potential, the greater the flocculation. As it increases, charge also increases. As charge increases, electrostatic repulsion (Coulombic force) increases and hence flocculation decreases in the system under investigation. The amount of detergent required to reverse the charge is in the order LPC >CTAB >CPC >CPB (Table III). 

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