Equations and boundary conditions describing one-dimensional steady

Equations and Boundary Conditions Describing One-Dimensional Steady Transport of Adsorbing Ions 

At first, the equations of convective diffusion for a system of three ions has to be considered. Under the condition (7.9), the diffuse layer is approximately electrically neutral  

Besides, under condition (7.11), the charge of the monolayer is approximately equal to the uncompensated charge of the diffuse layer, i.e. the adsorption layer as a whole is electrically neutral. This means the density of the electric current I is approximately equal to zero  

Let us consider first a system consisting only of surface active anions and inorganic cations. Using Eqs (7.12) and (7.13), and the formulas for the ion fluxes, the electric field strength E can be expressed in terms of the concentration gradient c. In this case j is given by 

This result can be qualitatively explained in the following way. Since the density of the electric current in the diffusion layer is approximately equal to zero, densities of the fluxes of surfactant anions and inorganic cations must be equal to each another. Since D D, an electric field should arise at this stage that accelerates organic anions and retard cations. Therefore, the total flux of surfactant anions is greater than their pure diffusion flux, and D. 

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