Interfadal dipole

Fig. 6-13. Potential created at a contact interface between metal M and a<)ueoii8 solution S (a) before contact, (b) after contact, (c) charge-induced and dipole-induced potentials X = surface potential at free surfaces gdip = potential due to an interfadal dipole gun = potential due to an interfadal charge = potential across an interfadal compact layer.

The surface potential, Xm> due to the interfadal dipole of the electron tailing away from the metal surface is given as a function of the excess or defidt of metal electrons in Eqn. 5-27 ... 

In comparing Eqn. 5-39 with Eqn. 5-9 (4< >h = gia.+ M.d - s,dip), which is based on the classical double layer model, it appears that the sum of the first, second and third terms on the right hand side of Eqn. 5-39 corresponds to the sum of gbm due to the interfadal charge and gM,dii> due to the interfacial dipole on the metal side and the fourth term corresponds to gs.dip due to the interfadal dipole of adsorbed water molecules on the solution side. These equivalences give Eqns. 6-40 and 5-41 ... 

Fig. 6-26. For the hard sphere model on metal electrodes (a) interfacial dipole induced by adsorbed water molecules and (b) interfadal dipole induced by contact adsorption of partially ionized bromine atoms. - 6 = charge number of adsoihed particle (z ). [From Schmickler, 1993.]...

Equation 5-82 indicates that the potential AjtH across the compact layer depends linearly on the solution pH. This potential Atv includes both the potential due to the interfadal charge oh (= [-OHj (b)] — [-0 (a)]) and the potential 4 due to the interfadal dipole, 4 >h = 4o + as shown in Fig. 5-51. 

Fig, 6-61. Potential across a compact layer without adsorbed ions on semiconductor electrodes Oh = interfadal charge of dissociated hydroxyl group os = excess charge at OHP on the solution side d dip = potential of a compact layer due to interfadal dipole = potential of a compact layer due to interfadal charge. 

For most metal-oxide interfaces, however, the Fermi level does not coincide with Ezcp- A charge transfer takes place, which aligns the chemical potentials, and induces an interfadal dipole potential, which bends the bands. It is possible to estimate the self-consistent charge density in the vicinity of the interface, within a Thomas-Fermi approximation, if the MIGS density at mid-gap is taken equal to a single exponential function Af( zcp,z) = noexp(—z//p). The potential V z) due to the mean charge density p(z) is related to p(z) by Poisson s equation ... 

Molecules or groups of atoms (ions) behaving as permanent dipoles may have considerable inertia, so relaxation frequencies for orientation polarization may be expected to occur at relatively smaller frequencies, as in the radio-frequency range. Since the alternation of interfadal polarization requires a whole body of charge to be moved through a resistive material, the process maybe slow. The relaxation firequency for this mechanism is thus low, occurring at about 10 Hz. 

A short-term electrophoretic-type separation of water and hydrocarbon oil occurs in the external electric field in the vicinity of the electrode surface. Under even a moderate electric field the mass transport of small water dipoles with dielectric constant of 80 is much more facile than that of polymers with dielectric constant of 2. High local concentration of water dipoles may be created in the vicinity of the electrode interface as a result of water redistribution and percolation in an external electric field. Relatively high water conductivity and the facile nature of charge-transfer reactions carried out through water dipoles located in the interfadal region explain the dramatic decrease in the low-frequency impedance immediately following the water injection. Deposition of conductive layers of water on the electrode/lubricant interface and significant presence of water dipoles in the diffusion layer replace both specifically adsorbed and electroactive lubricant additive species at the lubricant-electrode... 

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