Surface charge arising from

Retention study. At surfactant concentrations below CMC, micelles do not exist and, as demonstrated by Knox (12), Deming (13) and our previous works (14-15), the degree of retention was directly related to the surface charge arising from the adsorbed surfactant With both the surfactants, the retention of neutral species (toluene and caffeine) slightly decreased. When an anionic surfactant was adsorbed, the retention of negatively charged solutes (benzoate and SOBS) fell dramatically whereas the retention of cationic solutes (BTAB and CPC) increased. The reverse occured with the cationic surfactant (14). The same kind of behavior was observed with pure aqueous mobile phases, 5-95% v/v methanol-water phases and 0.1 mol/L NaCl phases. 

A variation on the theme of specific-ion adsorption is encountered when a surface charge arises from the dissociation of a salt, say a sodium carboxylate (—COO" + Na ), to produce a negatively charged surface. If di- or trivalent ions are present in the solution, they may adsorb onto the surface in such a... 

Electrical Characteristics and the Electrical Double Layer. Electrical surface charges arise from charge imbalances due to imperfections in the crystal structure and preferential adsorption of counter or potential determining ions [22, 23]. At low surfactant concentrations the surface charge largely determines the surfactant adsorption. However, as the surfactant concentration increases other factors such as the tendency of the surfactant to aggregate, become significant. 

Therefore, we decided to remove the adsorbed emulsifier as completely as possible and to rely upon the sulfate endgroups to give the particle the required stability. This would give an ideal model colloid, i.e., monodisperse spheres of constant and known surface charge arising from chemically-bound strong-acid surface groups. 

By changing the electrolyte concentration we have shown that electrostatic repulsion is operative. If the surface charge arises from preferential adsorption of OH ions [43] it should be possible to destroy it by decreasing the pH ofthe bulk solution at constant (and rather low) ionic strength [5]. 

The isoelectric point is the pH at which the net surface charge is zero, i.e. the positive and negative charges arising from all sources are equal, i.e. 

Zero Point of Charge. We are operating on the assumption that pH-dependent surface charge arises predominantly from H+ adsorption by reactions of the hydroxylated surface similar to Reactions 1 and 3. Figure 4 shows schematic H+ adsorption isotherms illustrating the pH variation of surface charge and H+ adsorption density, Y/, associated with this source. Curve a represents the total amount of adsorption on a given amount of surface area. Curve b represents more surface. In both... 

Vcore(v) is the potential associated with the interaction between valence and core electrons and VexchangeC-v) is the exchange potential between valence electrons. The exchange potential accounts for the repulsive interaction between electrons of like spin (Pauli exclusion principle) and electrons of either spin (correlation interaction). Both of these potentials are experienced in the bulk as well as at the surface. Vdipoie(v) is specific to the surface and arises from charge redistribution at the asymmetric surface. 

Sp represents a site of fixed charge arising from isomorphous substitution r other structural defects. Because the intrinsic equilibrium constants for equations 30 and 31 reflect solute concentrations at the surface of the sorbent, vhich depend in turn on the surface potential, a coulombic term must be included in the mass law expression... 

Charged areas on the mineral surface that arise from unsatisfied bonds and isomorphic substitution help to retain polar molecules. In addition, the asymmetrical distribution of orbital electrons in O and OH groups produces local negative and positive (polar) areas. Both the charged and the polar surfaces actively adsorb polar molecules by hydrogen bonding and by van der Waals forces. 

The second term hx includes function F(P,a), which depends on ratio of conductivities, more precisely, from parameter / . The appearance of this part of the field can be explained in the following way. Under action of the primary electric field of the dipole surface charges arise in a medium with density ... 

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