Interfadal structure

In the active state, the dissolution of metals proceeds through the anodic transfer of metal ions across the compact electric double layer at the interface between the bare metal and the aqueous solution. In the passive state, the formation of a thin passive oxide film causes the interfadal structure to change from a simple metal/solution interface to a three-phase structure composed of the metal/fUm interface, a thin film layer, and the film/solution interface [Sato, 1976, 1990]. The rate of metal dissolution in the passive state, then, is controlled by the transfer rate of metal ions across the film/solution interface (the dissolution rate of a passive semiconductor oxide film) this rate is a function of the potential across the film/solution interface. Since the potential across the film/solution interface is constant in the stationary state of the passive oxide film (in the state of band edge level pinning), the rate of the film dissolution is independent of the electrode potential in the range of potential of the passive state. In the transpassive state, however, the potential across the film/solution interface becomes dependent on the electrode potential (in the state of Fermi level pinning), and the dissolution of the thin transpassive film depends on the electrode potential as described in Sec. 11.4.2. 

As outlined in the Introduction, a couple of suggested pathways have been proposed for the first electron transfer step (a) dissociative chemisorption of O2 (rds) probably accompanied by e-transfer and followed by proton transfer (b) simultaneous proton and electron transfer to a weakly adsorbed O2 molecule. We have recently shown through CPMD [21,69] and DFT [75] results that both pathways may take place under different conditions of the interfadal structure i.e., proton transfer may be involved in the first reduction step depending on the relative location of the O2 molecule with respect to the surface and to the proton, on the degree of proton hydration, and on the surface charge which is dependent on the electrode potential. Moreover, it was shown that proton transfer may precede or follow the first electron transfer, but in most cases the final product of the first step is an adsorbed HOO. ... 

We have reviewed here the simplest, isothermal version of CDLG models for two-phase fluid dynamics on the microscopic scale. Applications of these models for studying interfacial dynamics in liquid-vapor and liquid-liquid systems in microcapillaries were discussed. The main advantage of our approach is that it models the exphcit dependence of the interfadal structure and dynamics on molecular interactions, including surfactant effects. However, an off-lattice model of microscopic MF dynamics may be required for incorporating viscoelastic and chain-connectivity effects in complex fluids. Isothermal CDLG MF dynamics is based on the same local conservation laws for species and momenta that serve as a foundation for mechanics, hydrodynamics and irreversible thermodynamics. As in hydrodynamics and irreversible thermodynamics, the isothermal version of CDLG model ean be... 

An understanding of the molecular level behavior is necessary because the electrochemical models depend critically on the interfadal structure of the ionic liquid adjacent to the electrode. Thus, we used MD simulations to investigate the electrical double-layer structure in a model of a [BmimjPFe IL at different negatively charged surfaces. 

Phase separation involves the formation of interfaces between domains with different compositions, whilst compatibilization affects the interfadal structure and composition. Both of these processes can be investigated efficiently by using ellipsometry which, as a surface-sensitive optical technique, fits in well with the geometry of the interfaces. One major advantage of ellipsometry [16] is that it is easy to operate, especially when compared to NR which, despite having an excellent depth of resolution (ca. 0.2 nm), requires deuterated samples and large-scale apparatus. 

Fig. 2.2 Schematic of electrode processes at IL/electrode interface (left) and interfadal structure (right) for the electrochemical sensors at IL modified electrodes...

There are many published examples in which the coupling of two different materials leads to an increase in the photocatalytic activity. Many of them concern coupling and junctions between different nanopartides, considering also different topologies, like coupled and capped systems [72]. Tentative explanations based on possible heterojunction band profiles are given. However, in-depth analysis of the hetero junction band alignment, the physical structure of the junction, the role of (possible) interfadal traps and of spedfic catalytic properties of the material is still lacking. Some recently published models and concepts based on (nano)junction between different materials are briefly reviewed here. 

In general, the contact adsorption of deh3drated anions changes the interfacial lattice structure of adsorbed water molecules, thereby changing the interfadal property. For example, the clean surfaces of metallic gold and silver, which are hydrophobic, become hydrophilic with the contact adsorption of dehydrated halogen anions. 

Gallagher, KJ. Feifknecht,W. Marmweiler, U. (1968) Mechanism of oxidation of magnetite to Y-Fe20j. Nature 217 1118-1121 Gallias, J.L. (1998) Microstructure of the interfacial transition zone around corroded reinforcements. In Katz, A. Benier, M. Alexander, M. Arliguie, G. (eds.) The interfadal transition zone in cementitions composites. E.F.N. Spon, London, 171-178 Galvez, N. Barron,V. Torrent, J. (1999) Preparation and properties of hematite with structural phosphorus. Clays Clay Miner. 47 375-385... 

The next two chapters are devoted to ultrafast radiationless transitions. In Chapter 5, the generalized linear response theory is used to treat the non-equilibrium dynamics of molecular systems. This method, based on the density matrix method, can also be used to calculate the transient spectroscopic signals that are often monitored experimentally. As an application of the method, the authors present the study of the interfadal photo-induced electron transfer in dye-sensitized solar cell as observed by transient absorption spectroscopy. Chapter 6 uses the density matrix method to discuss important processes that occur in the bacterial photosynthetic reaction center, which has congested electronic structure within 200-1500cm 1 and weak interactions between these electronic states. Therefore, this biological system is an ideal system to examine theoretical models (memory effect, coherence effect, vibrational relaxation, etc.) and techniques (generalized linear response theory, Forster-Dexter theory, Marcus theory, internal conversion theory, etc.) for treating ultrafast radiationless transition phenomena. 

Beyond covalent connections within protein and lipid molecules, weak noncovalent interactions between large molecules govern properties of cellular structure and interfadal adhesion in biology. These bonds and structures have limited lifetimes and so will fail under any level of force if pulled on for the right length of time. As such, the strength of interaction is the level of force most likely to disrupt a bond on a particular time scale. 

The structure of the liquid- liquid interfadal layer depends on the difference in polarity between the two liquids (Kaeble, 1971). Asymmetric molecules of some liquids display a molecular orientation on the interface which is indicative of their structure. Thus, interfacial tension at the octane-water interlace is SO.S nm/m whereas at the octanol-water interne it is only 8.8 nm/m. Reduction of inter dal tension in the latter case points to the orientation of octanol hydroxyl groups toward water, in other words to the structure and polarity of the interfadal layer. Because of such an orientation, the stimulus for adsorption of other asymmetric molecules on the interface is decreased. A similar pattern is typical of the homologous series of lower attcy] acrylates at the interface with water the carbonyl groups of their asymmetrical molecules are oriented toward water this orientation is more eSective the higher the polarization of the carbonyl, i.e the smaller the alkyl. Interfadal tension decreases in the same order from 27.2 nm/m for hexyl acrylate (Yeliseyeva et at, 1978) to 8 nm/m for methyl acrylate (datum from our laboratory by A, Vasilenko). 

Equation (4.3) shows that the magnitude of the surfactant parameter fixes only the fimction of the interfadal curvatures, (1 + HZ + KZ2/3), rather than the curvatures of the interface themselves. In other words, the interfacial geometry - the structure of the surfactant aggregate - is not fixed by the surfactant parameter alone. Both the mean and Gaussian cur atures can be varied cooperatively without altering the value of the surfactant parameter. Nevertheless, the surfactant parameter does furnish a local constraint upon the curvatures of the interface. 

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