Diffusion effective charge

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

Binary Electrolyte Mixtures When electrolytes are added to a solvent, they dissociate to a certain degree. It would appear that the solution contains at least three components solvent, anions, and cations, if the solution is to remain neutral in charge at each point (assuming the absence of any applied electric potential field), the anions and cations diffuse effectively as a single component, as for molecular diffusion. The diffusion or the anionic and cationic species in the solvent can thus be treated as a binary mixture. 

The most straightforward approach is to assume that the field charging and diffusion charging are independent processes i.e., particle charge can be presented as a sum of charges due to field (s ) and diffusion (sj) charging. Another simple approach to estimating the combined effect is... 

The aqueous diffusivities of charged permeants are equivalent to those of uncharged species in a medium of sufficiently high ionic strength. The product DF(r/R) is the effective diffusion coefficient for the pore. It is implicit in k that adsorption of the cations does not occur, so that the fixed surface charges on the wall of the pore are not neutralized. Adsorption is more likely to occur with multivalent cations than with univalent ones. 

Polar solvents stabilize and lower the enthalpies of charged reactants and charged transition states. The more diffuse the charge on the species, the less effective the stabilization by the polar solvent. 

Charge transport through organic polymeric systems shows some unusual features. When the time of flight experiments are performed in inorganic crystalline solids the charge carriers drift in a sheet without any dispersion (except for the normal diffusion effects). All the carriers exit the sample at a specific time Tt. However a similar experiment with polymer films shows a very dispersive transit (Fig. 5 a) which indicates that only a small fraction of the carriers exit the sample at t = Tt. 

Let us now ask how the currents are modified by the effects of space charge. Space charge is present whenever growth occurs by the diffusion of charged defect species. 

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