Electrostatic repulsive force

However, in subsequent studies [23-25,88-90] it was demonstrated that in reality the particle deposition is not a purely geometric effect, and the maximum surface coverage depends on several parameters, such as transport of particles to the surface, external forces, particle-surface and particle-particle interactions such as repulsive electrostatic forces [25], polydispersity of the particles [89], and ionic strength of the colloidal solution [23,88,90]. Using different kinds of particles and substrates, values of the maximum surface coverage varied by as much as a factor of 10 between the different studies. 

A special case of coagulation is the "quasi crystal" formation by unit layers of mont-morillonite bearing exchangeable Ca2+ cations (cf. Fig. 3.10). As Sposito (1989) points out, "one can imagine that the competition between the repulsive electrostatic forces and the attractive van der Waals force will, along with random thermal motions, largely determine the behavior of two siloxane surfaces approaching each other to a distance of separation >10 nm. However, at a separation distance of... 

The repulsive, electrostatic forces of sialic acids contribute to the rigidity of the cell surface, as was shown hy an increase in the defor-mability of sarcoma cells after enzymic removal of sialic acid residues.424 Enzymic release of sialic acids from the zona pellucida of rabbit ovum lessens the rigidity of this cell, and spermatozoa can no longer penetrate it.425 Glycoproteins on the surface of sea-urchin eggs... 

The pHPZC of ferric hydroxide surfaces is about 8 [127], so aqueous Pb2+ should be electrostatically repelled from these surfaces at pH values less than 8. However, as seen in Figure 7.6(a), the Pb2+ present in this aqueous solution is sorbed essentially completely to ferric hydroxide surfaces at pH 6. This behavior suggests that Pb2+ forms direct chemical bonds to these surfaces in order to overcome the repulsive electrostatic forces below the pHpzc of ferric hydroxide. This conclusion based on macroscopic uptake data has been confirmed by direct spectroscopic observation using X-ray absorption fine structure (XAFS) spectroscopy under in situ conditions (i.e., with aqueous solution in contact with a-FeOOH surfaces at ambient temperature and pressure) [133,134]. These studies showed that the aquated Pb(II) ion forms dominantly inner-sphere, bidentate complexes on a-FeOOH surfaces. 

More generally, it is widely recognized that it is the establishment of repulsive electrostatic forces stronger than attractive van der Waals forces that is the main effective mechanism preventing aggregation of biopolymer molecules and colloidal particles in stable aqueous systems. 

FIGURE 7.1 A covalent H-H bond is the net result of attractive and repulsive electrostatic forces. The nucleus-electron attractions (blue arrows) are greater than the nucleus-nucleus and electron-electron repulsions (red arrows), resulting in a net attractive force that holds the atoms together to form an H2 molecule. 

Thomas JK (1967) Pulse radiolysis of aqueous solutions of methyl iodide and methyl bromide. The reactions of iodine atoms and methyl radicals in water. J Phys Chem 71 1919-1925 Tsang W, Hampson RF (1986) Chemical kinetic data base for combustion chemistry, part I. Methane and related compounds. J Phys Chem Ref Data 15 1086-1279 UlanskiP, von Sonntag C (1999) The OFI-radical-induced chain reactions of methanol with hydrogen peroxide and with peroxodisulfate. J Chem Soc Perkin Trans 2 165-168 Ulanski P, Bothe E, Hildenbrand K, von Sonntag C, Rosiak JM (1997) The influence of repulsive electrostatic forces on the lifetimes of polyfacrylic acid) radicals in aqueous solution. Nukleonika 42 425-436... 

Figure 2 Electrostatic stabilization of metal nanoparticles. Repulsive electrostatic forces outweigh attractive van der Waals forces...

In addition, if the spheres are in water, there will be a repulsive electrostatic force between them. Under usual conditions of stability, this force is quite strong and its range is on the order of the sphere s radii. It is easy to see that the location of this repulsive wall with respect to the thickness 5 of the adsorbed layers will determine the type of binding which will be possible. If the wall is within the adsorbed layer ((7. 5)> unsaturated spheres will experience a short range attraction and... 

First, bacterial adhesion (usually gram-positive cocci and filamentous bacteria) occurs primarily through a Ca + complex formation between carboxyl (COO ) and phosphate (HPOs ) groups of bacterial surface and acquired pelhcle, although van der Waals forces and repulsive electrostatic forces are also present. Some specific bacterial surface proteins also serve as adhesins for specific receptors on acquired peUicle. Pellicle-integrated immunoglobulins also bind bacteria specifically. 

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). 

In the application of surface complexation models to clay minerals or to soils dominant in clays, the assumption is often made that metal ion adsorption occurs primarily on the aluminol and silanol groups of clay edges. The effect of the permanent charge sites on the adsorption process may not be considered. This simplification may be inappropriate, particularly for metal and metalloid anions, since repulsive electrostatic forces emanating from clay faces may spill over and affect the adsorption process on clay edges (Secor and Radke, 1985). 

The forces acting on a colloidal system include gravitational, diffusion, viscous, inertial, attractive Van der Waals, and electrical repulsive forces. Because most of these forces are functions of the particle size, it is important to know both particles size and size distribution. The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory describes colloid stability on the basis of pair interaction, considering only attractive van der Waals forces and repulsive electrostatic forces (Molina-Bolfvar and Ortega-Vinuesa, 1999). The total potential energy of interaction, Ujc, between two particles is defined as ... 

For ionic solids, in which both attractive and repulsive electrostatic forces as well as short-range repulsive forces complicate the description of the overall energy, the Bom-Lande equation has been shown to provide an adequate estimate of lattice energy, /. ... 

Stability is based. The attractive van der Waals force depends on the size of and the distance between two bodies. The repulsive electrostatic force originates from the surface charge of the colloidal particles. Apart from this, structural forces (e.g., hydrogen bonding) can stabilize or destabilize colloidal particles depending on the nature of the particles, and adsorption of polymer material at the sulfur-solvent interface can cause steric stabilization. 

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