Adsorption of ionics

The potentials of zero charge considered in this chapter are those in the absence of specific adsorption of ionic as well as nonionic species. There has been no attempt to review the enormous amount of data on the effect of specific adsorption on Ea+j, except for the few cases where extrapolation back to zero specific adsorption has been used as a more accurate way to determine <7-o- However, specific adsorption is difficult to relate quantitatively to the structure of interfacial water as well as to the effect of the metal. 

The specific adsorption, which in the case of ITIES is usually the adsorption of ionic pairs [8], contributes to the Galvani potential, as well as changes the zero charge of this interface. 

Thermodynamics of adsorption at liquid interfaces has been well established [22-24]. Of particular interest in view of biochemical and pharmaceutical applications is the adsorption of ionic substances, as many of biologically active compounds are ionic under the physiological conditions. For studying the adsorption of ionic components at the liquid-liquid interface, the polarized liquid-liquid interface is advantageous in that the adsorption of ionic components can be examined by strictly controlling the electrical state of the interface, which is in contrast to the adsorption studies at the air-water or nonpolar oil-water interfaces [25]. 

In the case of the adsorption at a liquid-liquid interface, the adsorption is possible from both sides of the interface and hence the adsorption of an adsorbate at the interface is not independent of its partitioning between the two phases. This link between the adsorption and partition is unique to liquid-liquid interfaces and is of particular importance in the case of the adsorption of ionic components, since both adsorption and partition of ionic components strongly depend on the phase-boundary potential [23]. 

Interfacial adsorption of ionic solute can be controlled by an external electrical potential [29]. 

Bors J, Dultz S, Riebe B (2000) Organophilic bentonites as adsorbents for radionuclides I. Adsorption of ionic fission products. Appl Clay Sci 16 1-13... 

Hydrophobic polar surfaces, adsorption of ionic surfactants on, 24 140-141 Hydrophobic precipitated silica, 22 399 Hydrophobic solvents, 16 413 Hydrophobic surfaces, 1 584-585... 

The adsorption of ionic polyelectrolytes by mineral fillers, fibres and fines is an essential first step in many chemical modification... 

As mentioned earlier the possibility of the adsorption of ionic species of the supporting electrolyte will complicate the equation of state of the surface, but the general ideas discussed so far remain valid. 

The Helmholtz-von Smoluchowski equation indicates that under constant composition of the electrolyte solution, the EOF depends on the magnitude of the zeta potential, which is determined by various factors inhuencing the formation of the electric double layer, discussed above. Each of these factors depends on several variables, such as pH, specihc adsorption of ionic species in the compact region of the double layer, ionic strength, and temperature. 

Adsorption of Ionic Surfactants in Presence of Inorganic Electrolytes. .. 34... 

The deviations from the Szyszkowski-Langmuir adsorption theory have led to the proposal of a munber of models for the equihbrium adsorption of surfactants at the gas-Uquid interface. The aim of this paper is to critically analyze the theories and assess their applicabihty to the adsorption of both ionic and nonionic surfactants at the gas-hquid interface. The thermodynamic approach of Butler [14] and the Lucassen-Reynders dividing surface [15] will be used to describe the adsorption layer state and adsorption isotherm as a function of partial molecular area for adsorbed nonionic surfactants. The traditional approach with the Gibbs dividing surface and Gibbs adsorption isotherm, and the Gouy-Chapman electrical double layer electrostatics will be used to describe the adsorption of ionic surfactants and ionic-nonionic surfactant mixtures. The fimdamental modeling of the adsorption processes and the molecular interactions in the adsorption layers will be developed to predict the parameters of the proposed models and improve the adsorption models for ionic surfactants. Finally, experimental data for surface tension will be used to validate the proposed adsorption models. 

Regression analysis developed on the basis of the proposed model described by Eqs. 36 and 38-40 has been applied for the adsorption of ionic surfactants. The regression analysis minimizes the revised chi-square,... 

The adsorption of ionic surfactants creates an adsorption layer of surfactant ions, a Stern layer of counterions and a diffusive layer distributed by the electric field of the charged surface. Every layer has its own contribution to surface tension. For example, the adsorption of dodecyl sulfate (DS") ions from the sodium dodecyl sulfate solution is described by the modified Frumkin isotherm as... 

Once (stable) nuclei have formed, there are several ways in which they can increase in size. One is a continuation of the process of embryo growth discussed earlier adsorption of ionic species from the solution onto the nucleus. Crystal... 

However, when adsorption of ionic species takes place on solid electrodes, it is difficult to decide what particular characteristic—surface heterogeneity, transfer of charge, lateral interactions, displacement of adsorbed solvent, size of the ions, etc.—is dominant in the process or which one can be neglected. Nonetheless, would it not be possible to include all these effects in a single isotherm It is possible, although not easy. In the following sections we will introduce the development of one isotherm for ionic adsorption where many of these distinctive characteristics of ionic adsorption are considered. 

This is the equation, the isotherm, we were seeking. It is a generalized isotherm for the adsorption of ionic species on a heterogeneous surface. It considers the adsorption reaction as a substitution process, with the possibility of transfer of charge between the ion and the electrode and also lateral interactions among adsorbed species. 

While initial aging did cause some loss in volume resistivity, it was no more severe in unstabilized than in stabilized compositions. The most startling effect was the marked increase in volume resistivity under severe aging conditions. This may be due to volatilization loss of DOP or cross-linking of polyvinyl chloride, both of which could reduce migration of ionic impurities, or it may involve adsorption of ionic impurities by the dark-colored, conjugated, polyene structure which forms by loss of hydrogen chloride. In any case it deserves further study. 

Lajtar, L., J. Narkiewicz-Michalek, W. Rudzinski, and S. Partyka. 1993. A new theoretical approach to adsorption of ionic surfactants at water/oxide interfaces Effects of oxide surface heterogeneity, Langmuir 9, 3174-3190. 

The adsorption of ionic or polar surfactants on charged or polar surfaces involves coulombic (ion-surface charge interaction), ion-dipole, and/or dipole-dipole interaction. For example, a negatively charged silica surface (at a pH above the isoelectric point of the surface, i.e., pH >2-3)... 

The increase in temperature increases adsorption of non-ionic surfactants on solid surfaces since the solubility of non-ionic surfactants in water decreases with increased temperature. On the other hand, increasing temperature decreases the adsorption of ionic surfactants on solid surfaces because the solubility of ionic surfactant increases with increased temperature. Furthermore, the presence of electrolytes increases the adsorption of ionic surfactants if the solid surface has the same charge as the surfactant head groups. 

Hua, X.Y. and Rosen, M.J. (1982) Calculation of the coefficient in the Gibbs equation for the adsorption of ionic surfactants from aqueous binary mixtures with nonionic surfactants. /. Colloid Interface Sci., 87, 469. 

Equation (4.44) is the Gibbs energy for the adsorption of surfactant at the interface. Equation (4.44) is applied to systems containing a nonionic surfactant as well as generalized for the consideration of adsorption of ionic substances in order to maintain electroneutrality at the interface ... 

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