Contributions to Surface Charge

In SEs and MIECs of interest the contributions to surface charges come mainly from mobile ions that exist in large concentrations rather than from electrons or holes, when they are the minority charge carriers. These ions can accumulate or be depleted near the surface forming a charged layer there (the core in Eig. 3a) [54, 55]. The position of the core may vary to be in between the first and second atomic layer, within the first atomic layer or on the first atomic layer. The opposite ionic charge left behind in the bulk is distributed nearby. For a core centered at (in Fig. 3), the opposite... 

The Triple T.aver Model and the Stern Model. The ions most intimately associated with the surface are assigned to the innermost plane where they contribute to the charge Oq and experience the potential tI>q These ions are generally referred to as primary potential determining ions. For oxide surfaces, the ions H+ and 0H are usually assigned to this innermost plane. In Stern s original model, the surface of a metal electrode was considered, and the charge cjq was due to electrons. 

Zhang, H. Zhang, X.-N. (1992) Contribution of iron and aluminum oxides to electrokinetic characteristics of variable charge soils in relation to surface charge. Pedosphere 2 31-42 Zhang, J. Buffle, J. (1995) Kinetics of hematite aggregation by polyacrylic acid Importance of charge neutralization. J. Colloid Interface Sci. 174 500-509... 

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... 

It is important to note that whilst only those electrons at the Fermi level can contribute to tunneling, all the electrons below the Fermi level contribute to the charge density. The STM therefore measures the electronic charge density at the Fermi level outside the surface (put another way — it images the spatial locations of the molecular orbitals) rather than the true positions of the atoms in the surface. The imaging of Si(100) surfaces provides a simple example of this difference and will be discussed later in the chapter. Whilst this electronic charge density at the Fermi level is directly related to the positions of the atoms on the surface, the theory relating these is rather complex and remains the subject of intensive debate. 

Tipping, E., Woof, C., and Harley, M.A. (1991) Humic substances in acid surface waters modelling aluminium binding, contribution to ionic charge-balance and control of pH. Wat. Res. 25, 425 135. 

Across real surfaces and interfaces, the dielectric response varies smoothly with location. For a planar interface normal to a direction z, we can speak of a continuously changing s(z). More pertinent to the interaction of bodies in solutions, solutes will distribute nonuniformly in the vicinity of a material interface. If that interface is charged and the medium is a salt solution, then positive and negative ions will be pushed and pulled into the different distributions of an electrostatic double layer. We know that solutes visibly change the index of refraction that determines the optical-frequency contribution to the charge-fluctuation force. The nonuniform distribution of solutes thereby creates a non-uniform e(z) near the interfaces of a solution with suspended colloids or macromolecules. Conversely, the distribution of solutes can be expected to be perturbed by the very charge-fluctuation forces that they perturb through an e(z).5... 

The zinc oxide electrode is a particularly simple example of a semiconductor electrode, because its large energy gap (3. 3 ev) makes the minority-carrier contribution to space charge negligible in the dark and because the fast surface state effects are negligible,. This latter fact has been demonstrated by data of the sort shown in Fig. 3 (3). 

Finally, clays such as the smectites almost invariably have a net negative structural charge because of isomorphous substitution of cations of lower charge than would be present in a balanced structure. In kaolinite, the amphoteric nature of the hydrated aluminum and silica surface contributes more to surface charge than does substitution. As a result of either substitution or surface dissociation, a region of counter ions (exchangeable and... 

We now consider the case of wide capillaries (large ira). For p(r) then the one-dimensional variant of the Poisson equation, p(r) = - e eld i/r / dz ) may be substituted, where z is the distance from the surface. Further, as only a very thin layer close to the surface contributes to the charge transport (the bulk has... 

Contact electrification of insulative materials, predominantly in film form, has been studied in many laboratories. In this paper, electric field dependent charging of polymeric and polymer-carbon black powders in contact with a metallic electrode has been studied. Results show the charging behavior to be strongly dependent on the composition of the powder surface. Carbon black loading, type of carbon black and degree of dispersion are methods used to alter the powder surface. The field dependent contribution to the charge exchange dominates over the zero field values. 

A schematic description of the surface/solution interface is given in Figure 1. Immediately at the surface, in the 0 plane, are specifically adsorbed hydrogen and hydroxide ions that experience the potential f/o and contribute to the charge ao- At the inner Helmholtz plane, or p... 

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