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Double Stem model

Gouy-Chapman and Stem Models of the Double Layer... [Pg.1178]

Fig. 6.67. Helmholtz-Perrin, Gouy-Chapman, and Stem models of the double layer. Fig. 6.67. Helmholtz-Perrin, Gouy-Chapman, and Stem models of the double layer.
The contribution of the metal to the double layer was discussed in Sections 6.6.7 to 6.6.9. However, we have said little about the ions in solution adsorbed on the electrode and how they affect the properties of the double layer. For example, when presenting the Stem model of the double layer (Section 6.6.6), we talked about ions sticking to the electrode. How does an interface look with ions stuck on the metal What is the distance of closest approach Are hydrated ions held on a hydrated electrode i.e., is an electrode covered with a sheet of water molecules Or are ions stripped of their solvent sheaths and in intimate contact with a bare electrode What are the forces that influence the sticking of ions to electrodes ... [Pg.199]

Cantwell and co-workers submitted the second genuine electrostatic model the theory is reviewed in Reference 29 and described as a surface adsorption, diffuse layer ion exchange double layer model. The description of the electrical double layer adopted the Stem-Gouy-Chapman (SGC) version of the theory [30]. The role of the diffuse part of the double layer in enhancing retention was emphasized by assigning a stoichiometric constant for the exchange of the solute ion between the bulk of the mobile phase and the diffuse layer. However, the impact of the diffuse layer on organic ion retention was danonstrated to be residual [19],... [Pg.36]

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]

Stem model (of the double layer), 195 Stoichiometric number, 149 Strip microelectrode, 453 Supporting electrolyte, 208, 351 Surface concentration, 131 Surface excess, 225, 229 Surface excess of anions, 256 Surface excess, relative, 236... [Pg.313]

Figure 6.18. Potential decay In the electrical double layer at three salt concentrations as calculated with the PB equation (solid curves) and with the multilayer Stem model at various lattice spaclngs (symbols, as indicated in the legend). Figure 6.18. Potential decay In the electrical double layer at three salt concentrations as calculated with the PB equation (solid curves) and with the multilayer Stem model at various lattice spaclngs (symbols, as indicated in the legend).
The results are given in Figures 14.lid and 14.lie. The semiquantitative agreement between experimental data and calculated data is obvious. The surface charge estimated can be converted into a surface potential on the basis of the diffuse double-layer model from which a stability could be calculated. Alternatively, a Stem model approach may be used, incorporating a distance of closest approach of outer-sphere ions (Section 9.5). [Pg.844]

Figure 10. Electrical double layer models. Top right (a) typical type of potential vs. composition plot for a charged surface compared to (b) constant capacitance model. Top left Two double-layer models, (a) diffuse double layer, (b) part parallel plate capacitor and part diffuse layer.. Bottom left Stem layer model. Incorporation of adsorbed ions to surface. From Hiemenz and Rajagopalan (1997) Bottom right Comparison of Gouy-Chapman and Stem-Grahame models of the electrical double layer. From Davis and Kent (1990). Figure 10. Electrical double layer models. Top right (a) typical type of potential vs. composition plot for a charged surface compared to (b) constant capacitance model. Top left Two double-layer models, (a) diffuse double layer, (b) part parallel plate capacitor and part diffuse layer.. Bottom left Stem layer model. Incorporation of adsorbed ions to surface. From Hiemenz and Rajagopalan (1997) Bottom right Comparison of Gouy-Chapman and Stem-Grahame models of the electrical double layer. From Davis and Kent (1990).
The existing double electrical layer can be described by the Stem model... [Pg.54]

FIGURE 2-3 Stem model of the electrical double layer, (a) Distributioin of counterions in the vicinity of the charged surface, (b) Variation of electrical potential with distance from the charged surface. [Pg.37]

Stem improved the Gouy-Chapman theory of the DDL by assuming that some ions are tightly retained immediately next to colloid surfaces in a layer of specifically adsorbed or Stem- layer cations. The double layer is diffuse beyond this layer. A satisfactory approximation of the Stem model can be made by assuming that the specifically adsorbed ions quantitatively reduce the surface density of the colloid. The diffuse portion of the double layer then is assumed to develop on a colloid surface of correspondingly reduced charge density. Sample Stem-modification calculations for a series of monovalent cations are shown in Fig. 8.10, Relatively few of the... [Pg.228]

Explain in your own words the differences between the Helmholtz, Guoy-Chapman, and Stem models of (he double layer. [Pg.236]

The simplest model for the electrical double layer is the Helmholtz condenser. A distribution of counterions in the bulk phase described by a Boltzmann distribution agree with the Gouy-Chapman theory. On the basis of a Langmuir isotherm Stem (1924) derived a generalisation of the double layer models given by Helmholtz and Gouy. Grahame (1955) extended this model with the possibility of adsorption of hydrated and dehydrated ions. This leads to a built-up of an inner and an outer Helmholtz double layer. Fig. 2.14. shows schematically the model of specific adsorption of ions and dipoles. [Pg.54]

A distinction is often made between the plane where the centres of charge of the partially dehydrated specifically adsorbed ions reside, the inner Helmholtz plane, and Stem plane at distance d, which is also called the outer Helmholtz plane. The double layer model consists of an inner and outer Helmholtz layer and a diffuse layer. This is often called the triple layer model. [Pg.60]

Changing from z=2 to z=4 the power of the function decreases according to Eq. (7.85). A more quantitative interpretation of experimental data by this theory would be sensible after the location of counterions in the Stem layer could be taken into account. Interpretation of experiments using the numerical solution of the transport problem is the other alternative provided again a considerable improvement of the involved electric double layer model. [Pg.265]

Figure 3. Highly schematic view of the electrical double layer (EDL) at a metal oxide/aqueous solution interface showing (1) hydrated cations specifically adsorbed as inner-sphere complexes on the negatively charged mineral surface (pH > pHpzc of the metal oxide) (2) hydrated anions specifically and non-specifically adsorbed as outer-sphere complexes (3) the various planes associated with the Gouy-Chapman-Grahame-Stem model of the EDL and (4) the variation in water structure and dielectric constant (s) of water as a function of distance from the interface, (from Brown and Parks 2001, with permission)... Figure 3. Highly schematic view of the electrical double layer (EDL) at a metal oxide/aqueous solution interface showing (1) hydrated cations specifically adsorbed as inner-sphere complexes on the negatively charged mineral surface (pH > pHpzc of the metal oxide) (2) hydrated anions specifically and non-specifically adsorbed as outer-sphere complexes (3) the various planes associated with the Gouy-Chapman-Grahame-Stem model of the EDL and (4) the variation in water structure and dielectric constant (s) of water as a function of distance from the interface, (from Brown and Parks 2001, with permission)...
Analytical models of double layer structures originated roughly a century ago, based on the theoretical work of Helmholtz, Gouy, Chapman, and Stem. In Figure 26, these idealized double-layer models are compared. The Helmholtz model (Fig. 26a) treats the interfacial region as equivalent to a parallel-plate capacitor, with one plate containing the... [Pg.256]

Figure 26. Schematics of the electrical double layer at a solid-liquid interface, (a) the Helmholtz model, (b) the Gouy-Chapman model, and (c) the Stem model. Figure 26. Schematics of the electrical double layer at a solid-liquid interface, (a) the Helmholtz model, (b) the Gouy-Chapman model, and (c) the Stem model.
A schematic representation of the inner region of the double layer model is shown in Fig. 1. Figure lb describes the distribution of counterions and the potential profile /(a ) from a positively charged surface. The potential decay is caused by the presence of counterions in the solution side (mobile phase) of the double layer. The inner Helmholtz plane (IHP) or the inner Stem plane (ISP) is the plane through the centers of ions that are chemically adsorbed (if any) on the solid surface. The outer Helmholtz plane (OHP) or the outer Stem plane (OSP) is the plane of closest approach of hydrated ions (which do not adsorb chemically) in the diffuse layer. Therefore, the plane that corresponds to x = 0 in Eq. (4) coincides with the OHP in the GCSG model. The doublelayer charge and potential are defined in such a way that ao and /o, op and Tp, and <5d and /rf are the charge densities and mean potentials of the surface plane, the Stem layer (IHP), and the diffuse layer, respectively (Fig. 1). [Pg.161]

The method developed here for the description of chemical equilibria including adsorption on charged surfaces was applied to interpret phosphate adsorption on iron oxide (9), and to study electrical double-layer properties in simple electrolytes (6), and adsorption of metal ions on iron oxide (10). The mathematical formulation was combined with a procedure for determining constants from experimental data in a comparison of four different models for the surface/solution interface a constant-capacitance double-layer model, a diffuse double-layer model, the triplelayer model described here, and the Stem model (11). The reader is referred to the Literature Cited for an elaboration on the applications. [Pg.41]


See other pages where Double Stem model is mentioned: [Pg.138]    [Pg.106]    [Pg.105]    [Pg.105]    [Pg.49]    [Pg.49]    [Pg.53]    [Pg.34]    [Pg.535]    [Pg.47]    [Pg.47]    [Pg.314]    [Pg.398]    [Pg.513]    [Pg.755]    [Pg.209]    [Pg.1853]    [Pg.476]    [Pg.257]    [Pg.261]    [Pg.626]    [Pg.460]    [Pg.71]   
See also in sourсe #XX -- [ Pg.118 , Pg.119 , Pg.120 ]




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