Charge density from electrocapillary curve

Kakiuchi and Senda [36] measured the electrocapillary curves of the ideally polarized water nitrobenzene interface by the drop time method using the electrolyte dropping electrode [37] at various concentrations of the aqueous (LiCl) and the organic solvent (tetrabutylammonium tetraphenylborate) electrolytes. An example of the electrocapillary curve for this system is shown in Fig. 2. The surface excess charge density Q, and the relative surface excess concentrations T " and rppg of the Li cation and the tetraphenylborate anion respectively, were evaluated from the surface tension data by using Eq. (21). The relative surface excess concentrations and of the d anion and the... 

These equations clearly show that the the slope of the electrocapillary curve of nonpolarized interface does not give the surface charge density but the relative surface excess of ionic components, as defined by Eq. (18) for case Ilb. In other words, the electrocapillary maximum potential does not correspond to the potential of zero charge . An approach to investigate the surface charge density and the double layer structure may be predicted as follows. When the values of the second terms of the right-hand sides of Eq. (18) (that is, the and Tnb values), are known or estimated on reasonable argument, Fd and F(so that by Eq. (19)) can be found from the slope... 

Using a drop time method for the determination of interfacial tension and a four-electrode potentiostat to polarize the interface, Kakiuchi and Senda measured electrocapillary curves for ideally polarized systems, in particular for the interface between an aqueous solution of lithium chloride and a solution in nitrobenzene of TBATPB. They showed that the surface charge density, Q, obtained by differentiation of the electrocapillary curve was equal to that calculated from the integration of the corresponding differential capacity versus potential curves. This demonstrated the validity of the Lippmann equation for the polarized ITIES ... 

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