Specific Coulomb interactions

Calculations based on non-specific coulombic interactions between the micelle and its counterions gave reasonable values of a, which were insensitive to the concentration of added salt (Gunnarsson et al., 1980). Although these calculations do not explain the observed specificity of ion binding, they suggest that such hydrophilic ions as OH- and F- may not in fact enter the Stern layer, as is generally assumed. Instead they may cluster close to the micelle surface in the diffuse layer. 

The double layer can be divided into two regions the compact double layer that includes the area between the electrode and the plane of closest approach, and the diffuse double layer extending from the plane of closest approach to the bulk of the solution. The compact double layer is also referred to as the Helmholtz double layer or inner double layer [1]. In an outer or diffuse layer the force holding the ions in the interphase is the non-specific Coulombic interaction between the charge on the electrode q (together with that on the inner layer and the charge on the ions [4]. In the inner layer there may or may not be adsorbed ions held partly by Coulombic and partly by specific forces. Potential 02 at the plane of closest approach (separating the inner and outer layers) depends on the electrode potential and concentration of the electrolyte [1]. Potential 0 in the diffuse double layer decreases almost exponentially with distance x from the plane of closest approach, and it can be written [1] ... 

The energy of solvation can be further broken down into terms that are a function of the bulk solvent and terms that are specifically associated with the first solvation shell. The bulk solvent contribution is primarily the result of dielectric shielding of electrostatic charge interactions. In the simplest form, this can be included in electrostatic interactions by including a dielectric constant k, as in the following Coulombic interaction equation ... 

The outer Helmholtz plane (OHP) refers to the distance of closest approach of non specifically adsorbed ions, generally cations. The interactions of the ions of the OHP with the surface are not specific and have the character of longer range coulombic interactions. Cations that populate the outer Helmholtz plane are usually solvated and are generally larger in size than the anions. 

To conclude this section let us note that already, with this very simple model, we find a variety of behaviors. There is a clear effect of the asymmetry of the ions. We have obtained a simple description of the role of the major constituents of the phenomena—coulombic interaction, ideal entropy, and specific interaction. In the Lie group invariant (78) Coulombic attraction leads to the term -cr /2. Ideal entropy yields a contribution proportional to the kinetic pressure 2 g +g ) and the specific part yields a contribution which retains the bilinear form a g +a g g + a g. At high charge densities the asymptotic behavior is determined by the opposition of the coulombic and specific non-coulombic contributions. At low charge densities the entropic contribution is important and, in the case of a totally symmetric electrolyte, the effect of the specific non-coulombic interaction is cancelled so that the behavior of the system is determined by coulombic and entropic contributions. 

Non-Newtonian flow may result if the monolayer array consists of molecules that interact by specific Coulombic or dipole interactions to form floating islands , which in turn may interact by van der Waals forces around their peripheries (Joly, 1956). Non-Newtonian flow may also be a property of collapsed films. The resulting differences in viscosity over a range of flow rates may then reflect film-component segregation or partial monolayer collapse. 

The effects that proximal positively charged groups can have on the DEA process were the primary focus in Ref. [5]. Specifically, we considered the Coulomb stabilization that one or more nearby positive groups (e.g., simulating the protonated Lys sites in the molecule shown in Fig. 1) can have on the nascent a anion. As an example of the effects of Coulomb interactions, in Fig. 3 we show the MeS-SMe neutral and MeS-SMe a anion potentials as in Fig. 2 but calculated in the presence of two +1 charges each 30 or 10 A from the midpoint... 

As a consequence, the summation over all occupied orbitals counts once again the 1-2 Coulomb interaction confined within the valence space, specifically, the dT2 dr term already found in (3.8), and adds the new integral... 

Ion bridging is a specific type of Coulombic interaction involving the simultaneous binding of polyvalent cations (e.g., Ca, Fe, Cu ) to two different anionic functional groups on biopolymer molecules. This type of ionic interaction is commonly involved in associative self-assembly of biopolymers. As a consequence it is also an important contributory factor in the flocculation (via bridging or depletion) of colloidal particles or emulsion droplets in aqueous media containing adsorbed or non-adsorbed biopolymers (Dickinson and McClements, 1995). 

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