Electrostatic surface effects

This distance is called the Debye length. It measures the penetration depth of the electrostatic surface effects. 

Since the electrostatic potential sharply decreases with increasing distance from the polyelectrolyte cylinder, the degree of reactivity modification by functional groups fixed to the polyion is strongly dependent on the distance from the cylinder surface. Considerable electrostatic potential effects on the photoinduced forward and thermal back electron transfer reactions, which will be discussed in the following chapters, can be attributed to the functional chromophore groups directly attached to the polyelectrolyte back-bone through covalent bonds. 

Although the electrostatic field on the polyelectrolyte surface effectively impedes back ET, it is unable to retard very fast back ET or charge recombination of the primary ion pair within the photochemical cage. The overall quantum yield of photoinduced ET is actually controlled in most cases by the charge recombination. Hence, its retardation is the key problem for attaining high quantum yields in the photoinduced ET. 

CV measurements showed that the reversible eleetrode reaetion of the [Fe(CN)6]" redox eouple was suppressed to some extent by the treatment with the DNA. The addition of the anti-DNA antibody further suppressed the redox reaetion thus decreasing the magnitudes of the CV peak currents. This is most likely caused by a steric hindrance of the bulky protein, which binds to the DNA double strands on the electrode surface, to mainly reduce the effective area of the electrode. The electrostatic repulsive effect may also contribute to the electrode response, since the isoelectric point of mouse IgM is commonly in the range of 4.5 to 7.0. Figure 11 shows the relationship between the decrease in the anodic peak current (A/p ) and the antibody concentration. As seen in this figure, the electrode system responded to the anti-DNA antibody in the concentration range of 1 — 100 nM. For the case of the mouse IgM, which does not interact with double-stranded DNA, the present system gave almost no response. The sensor did not respond to other serum proteins as well (data not shown). 

Boundary conditions in the systems I have considered primarily ensure the maintenance of a state of nonequilibrium with respect to the environment their relation with the size and form of the reaction medium, with the chemical and transport processes, determines the nature and properties of the dissipative structures that occur. These boundary conditions are imposed once and for all and do not couple with surface effects or electrostatic interactions. Such a coupling is likely to be the source of self-organization processes also, but was not the object of my talk. 

As a spherical system increases in size, its volume grows as the cube of the radius while its surface grows as the square. Thus, in a truly macroscopic system, surface effects may play little role in the chemistry under study (there are, of course, exceptions to this). However, in a typical simulation, computational resources inevitably constrain the size of the system to be so small that surface effects may dominate tlie system properties. Put more succinctly, the modeling of a cluster may not tell one much about tlie behavior of a macroscopic system. This is particularly true when electrostatic interactions are important, since the energy associated witli tliese interactions has an r dependence. 

The details of the influence that electrostatic surface forces on the stability of foam films is discussed in Section 3.3. As already mentioned, the electrostatic disjoining pressure is determined (at constant electrolyte concentration) by the potential of the diffuse electric layer at the solution/air interface. This potential can be evaluated by the method of the equilibrium foam film (Section 3.3.2) which allows to study the nature of the charge, respectively, the potential. Most reliable results are derived from the dependence foam film thickness on pH of the surfactant solution at constant ionic strength. The effect of the solution pH is clearly pronounced the potential of the diffuse electric layer drops to zero at certain critical pH value. We have named it pH isoelectric (pH ). As already mentioned pH is an intrinsic parameter for each surfactant and is related to its electrochemical behaviour at the solution/air interface. Furthermore, it is possible to find conditions under which the electrostatic interactions in foam films could be eliminated when the ionic strength is not very high. 

A major difficulty with this analysis, however, is that the assumption AS t % 0 requires that the solvation environment of the transition state is unaffected by its proximity to the electrode surface (Sect. 3.4). Stated equivalently, it is often expected that the temperature-dependent work terms required to extract kscorr from k ob contain large components from short-range solvation and other factors in addition to the usual "electrostatic doublelayer effects (Sect. 2.4 and 4.6). As noted in Sect. 2.3, the situation is somewhat more straightforward for surface-attached reactants since then the effects of work terms at least partly disappear. This question underscores the inevitable difficulties involved in extracting quantitative information on electron-transfer barriers from rate measurements. 

A Donnan effect that prevents self-repulsion of the similarly charged adsorbed IPR ions at higher ionic strength, the higher surface concentration of the IPR ( LH in Equation 3.5) partially compensates for the decreased magnitude of the electrostatic surface potential due to the increased Scoi in Equation 3.5. 

The double layer theory describes the process of ion-exchange and ion-interaction chromatography from the point view of distributed electrostatic field effect on the charged analyte retention. Other approaches have a more stoichiometric character and describes the analyte retention on the basis of the formation of ionic pairs and their subsequent retention on the adsorbent surface. 

The subscript s denotes isolated ions on the surface. The intrinsic equilibrium constants (K are determined at zero charge and potential conditions, thereby eliminating the electrostatic field effects. 

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