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Primary adsorption layer

Positively charged primary adsorption layer on colloidal particle ----... [Pg.318]

Figure 1 2-3 The electrical double layer of a colloid consists of a layer of charge adsorbed on the surface of the particle (the primary adsorption layer) and a layer of opposite charge (the counter-ion layer) in the solution surrounding the particle. Increasing the electrolyte concentration has the effect of decreasing the volume of the counter-ion layer, thereby increasing the chances for coagulation. Figure 1 2-3 The electrical double layer of a colloid consists of a layer of charge adsorbed on the surface of the particle (the primary adsorption layer) and a layer of opposite charge (the counter-ion layer) in the solution surrounding the particle. Increasing the electrolyte concentration has the effect of decreasing the volume of the counter-ion layer, thereby increasing the chances for coagulation.
An even more effective way to coagulate a colloid is to increase the electrolyte concentration of the solution. If we add a suitable ionic compound to a colloidal suspension, the concentration of counter-ions increases in the vicinity of each particle. As a result, the volume of solution that contains sufficient counter-ions to balance the charge of the primary adsorption layer decreases. The net effect of adding an electrolyte is thus a shrinkage of the counter-ion layer, as shown in Figure 12-2b. The particles can then approach one another more closely and agglomerate. [Pg.320]

Primary adsorption layer Charged layer of ions on the surface of a solid, resulting from the attraction of lattice ions for ions of opposite charge in the solution. [Pg.1115]

Although rapid adsorption of cytochrome c at mercury electrodes is widely accepted based on diverse experimental results, " the structure of this primary adsorption layer remains a point of controversy. If the cytochrome c... [Pg.319]

The interaction of an electrolyte with an adsorbent may take one of several forms. Several of these are discussed, albeit briefly, in what follows. The electrolyte may be adsorbed in toto, in which case the situation is similar to that for molecular adsorption. It is more often true, however, that ions of one sign are held more strongly, with those of the opposite sign forming a diffuse or secondary layer. The surface may be polar, with a potential l/, so that primary adsorption can be treated in terms of the Stem model (Section V-3), or the adsorption of interest may involve exchange of ions in the diffuse layer. [Pg.412]

After formation of a primary deposit layer on foreign substrates, further layer growth will follow the laws of metal deposition on the metal itself. But when the current is interrapted even briefly, the surface of the metal already deposited will become passivated, and when the current is turned back on, difficulties will again arise in the formation of first nuclei, exactly as at the start of deposition on a foreign substrate (see Section 14.5.3). This passivation is caused by the adsorption of organic additives or contaminants from the solution. Careful prepurification of the solution can prolong the delay with which this passivation will develop. [Pg.311]

Besides the resuspension of particles, the perfect sink model also neglects the effect of deposited particles on incoming particles. To overcome these limitations, recent models [72, 97-99] assume that particles accumulate within a thin adsorption layer adjacent to the collector surface, and replace the perfect sink conditions with the boundary condition that particles cannot penetrate the collector. General continuity equations are formulated both for the mobile phase and for the immobilized particles in which the immobilization reaction term is decomposed in an accumulation and a removal term, respectively. Through such equations, one can keep track of the particles which arrive at the primary minimum distance and account for their normal and tangential motion. These equations were solved both approximately, and by numerical integration of the governing non-stationary transport equations. [Pg.211]

These examples show that adsorption of water molecules on platinum electrodes depends on the solution components. If the energy of the solute adsorption is higher than that of water molecules, water tends to adsorb on the top of the primary solute layer, which is directly bound to the platinum adsorption sites. If the interaction of organic molecules with platinum is weak, water adsorbs directly onto the electrode surface. In the... [Pg.34]

The surface of silica turns hydrophobic on treatment with organo-silicon chlorides. Water vapor adsorption isotherms measured by Stober (219) showed a very marked decrease in reversible adsorption. Less than 0.3 primary adsorption centers per 100 A remained in the surface after covering with the organosiloxane layer. Similar effects were observed in the adsorption of ammonia. About 2.2 silanol groups per 100 A had not reacted with the trimethylsilyl chloride. Nevertheless, the greater part of these had become unaccessible for water vapor. Apparently, they were hidden underneath a trimethylsilyl umbrella. ... [Pg.236]

Steric stabilization differs from electrostatic stabilization in not being a function of a net force, but of the thickness of an adsorbed layer. When < >, equals 5-10%, stabilizing and destabilizing forces extend beyond the length of the electrostatic, interparticle barrier (Cabane et al., 1989). At this distance, attraction and repulsion are inconsequential, and electrolytes therefore have little effect. Bergenstahl (1988) proposed that the steric stabilization of emulsions by gums in the presence of a surfactant involves adsorption of the gum on the surfactant to form a combined structure constituted by a primary surfactant layer covered by an adsorbed polymer layer. [Pg.65]

The surface after adsorption will be chained with a potential, as in Figure 9.14, so that primary adsorption can be treated in terms of a capacitor model called the Stem model [43]. The other type of adsorption that can occur involves an exchange of ions in the diffuse layer with those of the surface. In the case of ion exchange, the primary ions are chemically bound to the structure of the solid and exchanged between ions in the diffuse double layer. [Pg.389]

Bioactivity in adsorbers has been reported alternately as both advantageous and disadvantageous to the primary adsorption process. As a potential disadvantage, the depth and composition of the biofilm may adversely influence adsorption dynamics by blocking carbon pore openings or by retarding boundary layer... [Pg.486]

Interactions between proteins and polysaccharides give rise to various textures in food. Protein-stabilized emulsions can be made more stable by the addition of a polysaccharide. A complex of whey protein isolate and carboxymethylcellulose was found to possess superior emulsifying properties compared to those of the protein alone (Girard et al., 2002). The structure of emulsion interfaces formed by complexes of proteins and carbohydrates can be manipulated by the conditions of the preparation. The sequence of the addition of the biopolymers can alter the interfacial composition of emulsions. The ability to alter interfacial structure of emulsions is a lever which can be used to tailor the delivery of food components and nutrients (Dickinson, 2008). Polysaccharides can be used to control protein adsorption at an air-water interface (Ganzevles et al., 2006). The interface of simultaneously adsorbed films (from mixtures of proteins and polysaccharides) and sequentially adsorbed films (where the protein layer is adsorbed prior to addition of the polysaccharide) are different. The presence of the polysaccharide at the start of the adsorption process hinders the formation of a dense primary interfacial layer (Ganzelves et al., 2008). These observations demonstrate how the order of addition of components can influence interfacial structure. This has implications for foaming and emulsifying applications. [Pg.195]

Surface Adsorption. As we have already mentioned, the surface of the precipitate will have a primary adsorbed layer of the lattice ions in excess. This results in surface adsorption, the most common form of contamination. After the barium sulfate is completely precipitated, the lattice ion in excess will be barium, and this will form the primary layer. The counterion will be a foreign anion, say, a nitrate anion, two for each barium ion. The net effect then is an adsorbed layer of barium nitrate, an equihbrium-based process. These adsorbed layers can often be removed by washing, or they can be replaced by ions that are readily volatilized. Gelatinous precipitates are especially troublesome, though. Digestion reduces the surface area and the amount of adsorption. [Pg.319]

The results reported in this paper support the conclusion of Zis-man [2, 5] and others [1, 4], that films produced at comparatively short times contain both the polar solute and the nonpolar solvent, but that coadsorbed films are also formed at longer adsorption times. The proposed model describes the primary adsorbed layer next to the metal surface as consisting of nearly 100% adsorbed stearic acid at long adsorption times. [Pg.274]

In 1960, Blair [59] and Dodd [68] published key studies on water-in-crude oil emulsions and their films (see [1-6] for references). Using a Cenco surface film balance to study the water-oil interface, Blair showed that the principal source of stability arises from the formation of a condensed and viscous interfaciai film by adsorption of soluble material from the petroleum phase, such film presenting a barrier to coalescence of the dispersed droplets. This primary film may be augmented by secondary adsorption of large particles or micelles originally suspended in the petroleum. The classical picture of emulsion stabilization by an adsorbed monolayer yielding low interfaciai tension values does not seem to be an accurate one in this case. It appears that a primary adsorbed layer is initially formed, almost certainly comprised of asphaltenes, and a secondary layer superimposes on this primary layer and is likely comprised of asphaltenes, wax particles, and possibly... [Pg.144]

It is well described that materials in contact with biofluids are irmnediately coated with proteins. Protein adsorption is influenced by the underlying substrate surface properties including surface chemistry, charge, and free energy. After cell adhesion on top of this primary protein layer, the formation of secondary protein layers can take place due to nonspecific adsorption of ceU-secreted proteins (Fig. 4.27). [Pg.167]


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See also in sourсe #XX -- [ Pg.318 ]




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