Measuring surface charge densities

Fig. 7.4 Block diagram of a method of measuring surface charge density with a guarded probe connected to a negative-feedback electrometer.

FIG. 4 Comparison between the predicted, using triple-layer and hybrid triple-layer models, and measured surface charge density and zeta potential of boehmiie in KNO3... 

This is used to measure charge, surface charge density, volumetric charge density or charge-to-mass ratio. It comprises an all-metal container, such as... 

The capacitance is a readily measured interfacial property and it gives qualitative information on the adsorption of species at the electrode surface. Since the surface charge density, q, is a function of the potential and of coverage, the measured capacitance may be expressed as the sum of a true (high frequency) capacitance and an adsorption pseudocapacitance, i.e. q f(E,6) and hence... 

Because the second harmonic response is sensitive to the polarizability of the interface, it is sensitive to the adsorption and desorption of surface species and is capable of quantifying surface species concentrations. Furthermore, SHG can be used to quantify surface order and determine surface symmetry by measuring the anisotropic polarization dependence of the second harmonic response. SHG can also be used to determine important molecular-level and electrochemical quantities such as molecular orientation and surface charge density. 

Studies of the adsorption of surface active electrolytes at the oil-water interface provide a convenient method for testing electrical double layer theory and for determining the state of water and ions in the neighborhood of an interface. The change in the surface amount of the large ions modifies the surface charge density. For instance, the surface ionic area of 100 per ion corresponds to 16, /rC/cm. The measurement of the concentration dependence of the changes of surface potential were also applied to find the critical concentration of formation of the micellar solution [18]. 

Of the quantities connected with the electrical double layer, the interfacial tension y, the potential of the electrocapillary maximum Epzc, the differential capacity C of the double layer and the surface charge density q(m) can be measured directly. The latter quantity can be measured only in extremely pure solutions. The great majority of measurements has been carried out at mercury electrodes. 

Figure 3.4 Distribution of the electronic density in the jellium model the metal occupies the region x < 0. The unmarked curve is for an uncharged surface, the other two curves are for the indicated surface-charge densities. The distance along the x axis is measured in atomic units (a.u.), where 1 a.u. of length = 0.529 A.

If the interfacial tension 7 can be measured, the surface charge density can be obtained by differentiation, which yields the Lippmann equation ... 

The surface potential, y, cannot be measured directly. It can be estimated however, e.g., with the help of Eq. (3.8a) from the surface charge density. Discuss the assumptions involved in applying such a calculation. 

W. S. Chow and J. Barber, Salt dependent changes of 9-aminoacridine as a measure of charge-densities of membrane surfaces, J. Biochem. Biophys. Methods 3, 173-185 (1980). 

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