Adsorption Potentials of Surface-Active Electrolytes

ADSORPTION POTENTIALS OF SURFACE-ACTIVE ELECTROLYTES 

Equations (25) to (29) concern the case of neutral adsorbates, where there is no ionic double layer to contribute to the surface potential. In the case of charged (i.e., ionic) adsorbates, the measured potential consists of two terms. The first term is due to dipoles oriented at the interface, which may be described by the above formulas, and the second term presents the potential of the ionic double layer at the interface from the aqueous 

The g (ion) is the electrical potential drop between the film of adsorbed long-chain ions and the bulk of aqueous solution. is the reciprocal value of and expresses the surface area per ion. 

The physical meaning of the g (ion) potential depends on the accepted model of an ionic double layer. The proposed models correspond to the Gouy-Chapman diffuse layer, with or without allowance for the Stem modification and/or the penetration of small counter-ions above the plane of the ionic heads of the adsorbed large ions. The experimental data obtained for the adsorption of dodecyl trimethylammonium bromide and sodium dodecyl sulfate strongly support the Haydon and Taylor mode According to this model, there is a considerable space between the ionic heads and the surface boundary between, for instance, water and heptane. The presence in this space of small inorganic ions forms an additional diffuse layer that partly compensates for the diffuse layer potential between the ionic heads and the bulk solution. Thus, the Eq. (31) may be considered as a linear combination of two linear functions, one of which [A% - g (dip)] crosses the zero point of the coordinates (A% and 1/A are equal to zero), and the other has an intercept on the potential axis. This, of course, implies that the orientation of the apparent dipole moments of the long-chain ions is independent of A. 

The measurement of change in the surface potentials of aqueous solutions of electrolytes caused hy adsorption of ionophore (e.g., crown ether) monolayers seems to he a convenient and promising method to ascertain selectivity and the effective dipole moments of the ionophore-ion complexes created at the water surface. 

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XIII. ADSORPTION POTENTIALS OF SURFACE-ACTIVE ELECTROLYTES... 

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