Dependence of surface potential

At oxide surfaces, the surface activities of H+ and OH are not fixed in a similar way. Then the variation in surface potential with solution activity of H+ depends on the chemical and electrostatic properties of the interface. For the many oxides that are insulators, it is much more difficult to obtain a measurement of the surface-solution potential differences than it is for conductors such as Agl. Thus there is uncertainty whether the dependence of surface potential on pH is approximately Nernstian or significantly sub-Nernstian. 

Our modeling approach was first used to describe the EDL properties of well-characterized, crystalline oxides ( 1). It was shown that the model accounts for many of the experimentally observed phenomena reported in the literature, e.g. the effect of supporting electrolyte on the development of surface charge, estimates of differential capacity for oxide surfaces, and measurements of diffuse layer potential. It is important to note that a Nernstian dependence of surface potential (iIJq) as a function of pH was not assumed. The interfacial potentials (4>q9 4> 9 in Figure 1) are... 

The surface potential vs. area curves obtained on sodium chloride solutions of different concentrations are independent of salt concentration for areas per head group less than 20 A2. A dependence of surface potential on salt concentration is observed as soon as the area per head group becomes greater than that corresponding to a close packed monolayer. 

With these site-binding constants being determined, the value of sphalerite in electrolyte solutions can be calculated as a function of pH, and the results are shown in Fig. 3 by solid lines (only three NaCl concentrations are shown for clarity). The excellent fit of the prediction with the experimental results is illustrated by all the points lying on the predicted curve. These results testify to the significant improvement achieved by our hybrid TLM over the conventional TLM which cannot predict accurately both pH and ionic strength dependence of surface potentials. The improvement is due in part to allowing the variations of differential capacitance across the diffuse double layer, given by Eq. (4), in contrast to the conventional TLM, in which the capacitance of the outer Helmholtz layer is assumed to be independent of electrolyte concentrations. 

The dependence of surface potential and reaction rate on the NADH concentration are similar (Fig. 11), and the potential shift in the given system is proportional to the oxidation rate of NADH. The obtained result agrees well with the theoretical model of a heterogeneous catalytic reaction proposed earlier [23-25], according to which the potential shift at the interface between immiscible liquids relative to the supporting electrolyte is directly proportional to the rate of the heterogeneous electron-exchange reaction. 

And the substitution of (8.D.12) into Gui-Chapman equation gives the analytical dependence of surface potential (p and surface charge density a upon packed density of water molecules in the surface layer 1/5 , dissociation constant of water and concentration of dissolved salt C ... 

The empirical potentials for the molecules were obtained on the assumption of single attraction centers. This assumption is probably good for H2, fair for CH4 and N2, and very poor for Cl2. Even for molecules such as CH4 which are relatively spherical in shape, the fact that some atoms are near the outer surface rather than the center has an important effect. The closest interatomic distances are emphasized by the i 6 dependence of the potential. This point has been considered by several authors who worked out examples showing the net intermolecular potential for several models. 

Liquid alloys of Hg with a variety of metals (amalgams) constitute particularly complex systems in view of the potential dependence of surface composition. A detailed study of In and T1 amalgams, with... 

Figure 12. (a) Dependence of the potential of zero charge, Eaw0, on the crystallographic orientation for the metals Cu, Ag, and Au, which crystallize in the fee system. From Ref. 32, updated, (b) (pg. 155) Correlation between Eam0 of single-crystal faces of Cu, Ag, and Au, and the density of broken bonds on the surface of fee metals. From Ref. 32, updated. 

Because of the influence of potential gradients, the work function depends on the position of the point to which the electron is transferred. As in the definition of surface potential, a point a) situated in the vacuum just outside the metal is regarded as the terminal point of transfer. It is assumed, moreover, that when the transfer has been completed, the velocity of the electron is close to zero (i.e., no kinetic energy is imparted on it). 

The work function of charged particles found for a particular conductor depends not only on its bulk properties (its chemical nature), which govern parameter but also on the state of its surface layer, which influences the parameter (a) xhis has the particular effect that for different single-crystal faces of any given metal, the electron work functions have different values. This experimental fact is one of the pieces of evidence for the existence of surface potentials. The work function also depends on the adsorption of foreign species, since this influences the value of... 

Studies of the adsorption of surface active electrolytes at the oil-water interface provide a convenient method for testing electrical double layer theory and for determining the state of water and ions in the neighborhood of an interface. The change in the surface amount of the large ions modifies the surface charge density. For instance, the surface ionic area of 100 per ion corresponds to 16, /rC/cm. The measurement of the concentration dependence of the changes of surface potential were also applied to find the critical concentration of formation of the micellar solution [18]. 

Fig. 4.4 The dependence of the potential difference in the diffuse layer on the difference E — Epzc (the rational potential) for various concentrations of the surface inactive electrolyte KF. (According to R. Parsons)... 

Figure 2.4 (a) The dependence of the potential as a function of the distance from the electrode surface, taking into account the presence of adsorbed water dipoles, (b) The interface in (a) represented in terms of two capacitors. CD is the dipole capacitance ( = Ef.0/[a - rMj0] and CM is the original Helmholtz capacitance ( - Ee0/r jO). 

The net charge of the particles are not directly available in practice. Furthermore we prefer to speak in terms of surface potential generated by these charges because this parameter depends only on the nature of the... 

Fig. 13. Dependence of surface charge ((-potential) of Si3N4, Y203, A1203 powders on pH [241]...

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