Modified Verwey-Niessen model

FIGURE 32.3 Modified Verwey-Niessen model of an ITIES with an inner layer (shaded area) separating two space-charge regions. 

The Gouy-Chapman theory for metal-solution interfaces predicts interfacial capacities which are too high for more concentrated electrolyte solutions. It has therefore been amended by introducing an ion-free layer, the so-called Helmholtz layer, in contract with the metal surface. Although the resulting model has been somewhat discredited [30], it has been transferred to liquid-liquid interfaces [31] by postulating a double layer of solvent molecules into which the ions cannot penetrate (see Fig. 17) this is known as the modified Verwey-Niessen model. Since the interfacial capacity of liquid-liquid interfaces is... 

III. MICROSCOPIC MODELS A. Modified Verwey-Niessen Model (MVN)... 

Homogeneous kinetics may be considerably more MVN (modified Verwey-Niessen) model - Verwey-comphcated than the simple first-order reactions de- Niessen model... 

Enhancement of Capacitance. The agreement between (modified) Verwey-Niessen models and experiment is less satisfactory for lower-polarity organic media (e.g., DCE, as opposed to NB) and for lower electrolyte concentrations [13]. What is the physical origin of the higher experimental capacitances seen for these conditions As noted by Schmickler and co-workers [59], this enhancement of capacitance at the ITIES relative to the classical model stands in contrast to the response of electrode-electrolyte interface, where the capacitance is often found to be lower than the Gouy-Chapman function. 

These deviations were first explained by the presence of a compact, ion-free layer at the interface this is known as the modified Verwey-Niessen model. Obviously, the presence of an ion-free layer can only reduce the capacity, so the theory had to be modified further. For a few systems a consistent interpretation of the experimental capacity was achieved [78-80] by combining this model with the soolled modified Poisson-Boltzmann (MPB) theory [81], which attempts to correct the GC theory by accounting for the finite size of the ions and for image effects, while the solvent is still treated as a dielectric continuum. The combined model has an adjustable parameter, so it is difficult to judge whether the agreement with experimental data is significant. The existence... 

Figure 17.3.3 The modified Verwey-Niessen model and potential distribution. (Reprinted with permission from (20). Copyright 1977 Elsevier Science).

The description of the ion transfer process is closely related to the structure of the electrical double layer at the ITIES [50]. The most widely used approach is the combination of the BV equation and the modified Verwey-Niessen (MVN) model. In the MVN model, the electrical double layer at the ITIES is composed of two diffuse layers and one ion-free or inner layer (Fig. 8). The positions delimiting the inner layer are denoted by X2 and X2, and represent the positions of closest approach of the transferring ion to the ITIES from the organic and aqueous side, respectively. The total Galvani potential drop across the interfacial region, AgCp = cj) — [Pg.545]

This paper was a landmark not only from an experimental point of view but also because the authors proposed an interfacial model which pictures the interface as a compact layer of orientated dipole molecules separating the two diffuse layers. Nowadays, this model is often referred to as the modified Verwey-Niessen (MVN) model. Another very interesting conclusion of this work is that the potential drop across the compact layer was found to be negligible. A very similar experimental approach was followed by Buck et who obtained similar results for a tetraalkylammonium series ranging from tetramethyl- to tetrahexylammonium. In particular,... 

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