Electrical double layer of ions

AC Impedance of Contaminated Specimens. The ACIS of the contaminated sample under DC bias at 100% RH is consistent with a corroding system (15) in which a fixed number of aqueous pathways have formed, resulting in a constant area of metallization exposed to the electrolyte. In this case, the parallel capacitance corresponds to an electrical double layer of ions on the metallization. The capacitance of the contaminated sample is > 100 times larger than that of the clean sample at 100% RH due to the relatively larger concentrations of ions and water at the IC surface, which overwhelms the oxide capacitance described earlier. The reduction in the parallel resistance with increasing bias arises from the voltage dependent charge transfer process (i.e. electrochemical reaction). 

Much use has been made of micellar systems in the study of photophysical processes, such as in excited-state quenching by energy transfer or electron transfer (see Refs. 214-218 for examples). In the latter case, ions are involved, and their selective exclusion from the Stem and electrical double layer of charged micelles (see Ref. 219) can have dramatic effects, and ones of potential imfKntance in solar energy conversion systems. 

Fig. 8. Electrical double layer of a sohd particle and placement of the plane of shear and 2eta potential. = Wall potential, = Stern potential (potential at the plane formed by joining the centers of ions of closest approach to the sohd wall), ] = zeta potential (potential at the shearing surface or plane when the particle and surrounding Hquid move against one another). The particle and surrounding ionic medium satisfy the principle of electroneutrafity.

Ion incorporation has two important aspects a) due to the transport of ions from solution to the adsorbed protein layer, contributions to enthalpy and entropy are usually negative b) in the case of charge redistribution in the electrical double layer, the ion contribution to the enthalpic forces depends on the protein-surface charge difference, pH, and solution ionic content. Its entropic contribution is positive. 

The surface potential results in a concentration of the counter-ions and a depletion of the co-ions in the aqueous phase close to the charged surface, which results in the so-called electrical double layer. The ion concentrations in the aqueous phase at a given distance x from the charged surface are given by ... 

In this chapter some aspects of the present state of the concept of ion association in the theory of electrolyte solutions will be reviewed. For simplification our consideration will be restricted to a symmetrical electrolyte. It will be demonstrated that the concept of ion association is useful not only to describe such properties as osmotic and activity coefficients, electroconductivity and dielectric constant of nonaqueous electrolyte solutions, which traditionally are explained using the ion association ideas, but also for the treatment of electrolyte contributions to the intramolecular electron transfer in weakly polar solvents [21, 22] and for the interpretation of specific anomalous properties of electrical double layer in low temperature region [23, 24], The majority of these properties can be described within the McMillan-Mayer or ion approach when the solvent is considered as a dielectric continuum and only ions are treated explicitly. However, the description of dielectric properties also requires the solvent molecules being explicitly taken into account which can be done at the Born-Oppenheimer or ion-molecular approach. This approach also leads to the correct description of different solvation effects. We should also note that effects of ion association require a different treatment of the thermodynamic and electrical properties. For the thermodynamic properties such as the osmotic and activity coefficients or the adsorption coefficient of electrical double layer, the ion pairs give a direct contribution and these properties are described correctly in the framework of AMSA theory. Since the ion pairs have no free electric charges, they give polarization effects only for such electrical properties as electroconductivity, dielectric constant or capacitance of electrical double layer. Hence, to describe the electrical properties, it is more convenient to modify MSA-MAL approach by including the ion pairs as new polar entities. 

Figure 1 2-3 The electrical double layer of a colloid consists of a layer of charge adsorbed on the surface of the particle (the primary adsorption layer) and a layer of opposite charge (the counter-ion layer) in the solution surrounding the particle. Increasing the electrolyte concentration has the effect of decreasing the volume of the counter-ion layer, thereby increasing the chances for coagulation.

The sorption mechanism includes diffusion motion, facilitating the penetration of molecules and ions to the active surface of colloids, their release into the medium and mutual exchanges. The diffusion is manifested during the motion of ions in the electric double layer of colloids as well as during the motion of ions and molecules to the surface of plant and microbial cells. 

Near each plane an electrical double layer of thickness Id is formed. If the distance between planes is such that the double layers are superimposed, there is interaction between the planes. Due to symmetry, the minimum value of the potential distribution between the planes is achieved at the symmetry axis of the planes (x = hl2), where d(j)/dx = 0, that is, the electric field is absent. At the axis, there is an excess of ions of the same sign as the charge on the planes, which results in increase of osmotic pressure trying to force the planes apart. 

Simonova, T.S. and Shilov, V.N., Influence of the mobilities of the ions in the compact part of the electric double layer of spherical particles on the electrophoresis and electric conductivity of disperse... 

FIGURE IIM The Helmholtz layer is an electric double layer of charged metal ions (M ) and anions (A ) facing each other at the electrode-electrolyte inteiface. 

This definition is theoretically adequate, but may give rise to confusion when measurements are to be interpreted. In electrolyte solutions and the solution side of electrical double layers, the ions are the carriers of charge. However, in ions, charge is always linked to matter so that transport of the charge can only be achieved by simultaneously transporting matter. Consequently, the total work of ion transport includes an electrical and a chemical contribution. 

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