Surface potential measurements

Fig. IV-6. Vibrating electrode method for measuring surface potentials. (From Ref 1.)...

The variation of the observed surface potential with palladium content is shown in Fig. 24. No chemisorption was detected on pure silver but CO adsorbed rather slowly on the Ag-rich alloys and the measured surface potential increased with increasing Pd content. The surface potential in-... 

It is noted that the molecular interaction parameter described by Eq. 52 of the improved model is a function of the surfactant concentration. Surprisingly, the dependence is rather significant (Eig. 9) and has been neglected in the conventional theories that use as a fitting parameter independent of the surfactant concentration. Obviously, the resultant force acting in the inner Helmholtz plane of the double layer is attractive and strongly influences the adsorption of the surfactants and binding of the counterions. Note that surface potential f s is the contribution due to the adsorption only, while the experimentally measured surface potential also includes the surface potential of the solvent (water). The effect of the electrical potential of the solvent on adsorption is included in the adsorption constants Ki and K2. 

In xerographic measurements, as illustrated in Fig. 5.3, the sample is corona-charged to a voltage Vq and then exposed to a short wavelength (absorption depth S L) step illumination. At the end of the illumination, there is a measurable surface potential, termed the residual potential V because of the bulk trapped charges. If positive charging is used, then is due to trapped holes in the bulk of the specimen. 

One can assume that the saturated residual potential, at the end of a large number of cycles, decays. As thermal release proceeds, holes are emitted and swept out from the specimen, resulting in a decrease in the measured surface potential. The decay rate of the saturated potential is strongly temperature dependent due to thermal release from deep mobility gap centers, located approximately 0.9 eV above for holes. The discharge of the saturated potential due to electron trapping occurs much more slowly. The reason is that the energy depth of electron traps from is about 1.2 eV, which is greater than that of hole traps from E. ... 

For the films under examination, the residual voltage (a measurable surface potential at the end of the illumination) increases with the Sb content (Fig. 7.5). 

Hughes, Rideal, and others1 constructed an instrument on a very small scale for measuring surface potentials on 0 1 c.c. of heavy water this has no means of cleaning the surface. 

The method first used for measuring surface potentials of solutions is often known as the method of flowing junctions It was used by Bichat and Blondlot.2 Kenrick,2 and more recently by Frumkin.4... 

There are cases, however, including the very common one of an air-water surface, where no ions can possibly pass the boundary thermodynamical equilibrium cannot therefore be set up between the water and air, and adsorption potentials (the surface potentials of Chapters II and III) are permanent. The usual method for measuring surface potentials with a radioactive air-electrode does not appreciably disturb the adsorption potentials the gaseous ions are very few and are attracted into the water by image forces so that no double layer, compensating the double layer in the water due to the dipoles of the molecules in the surface film, can build up in the air. 

Figure 20.2 (a) Measured surface potential U x) (solid line) as obtained with an AFM Kelvin probe at U- = -30 V, for different gate voltages Uq, as annotated, and fit to a smooth interpolation formula (dashed) (b) output characteristics with (solid line) and without (dashed line) light from the laser diode in the AFM. 

Nevertheless, there have been many attempts to measure surface potential in order to correlate the surface charge of cells and their function. These methods include ... 

After the charging the initial surface potential Vq of the samples was measured by the vibrating electrode method with compensation (Reedyk et al.). The measured surface potential values are presented in Table 2. The results obtained show that the charging time to 30 minutes does not influence the surface potential of the PP films. 

A/3 is the Debye screening length of the outer (inner) monovalent electrolyte, b° and 6 are the distances between the neutral mechanical surface of the bilayer and the corresponding membrane interfaces. Using Eq. (6.9) we can estimate fpup or Dip experimentally measured surface potential... 

In conclusion, both cations and anions are located at the interface and contribute to the measured surface potential and charges. The high charge density found at the interfacial double layer is balanced by the ion distribution in the bulk to maintain overall electroneutrality. 

When trying to establish the ECG as a prognostic utility, the huge amount of existing physiological data must be supported by quantitative formulation of the relationship between the measurable surface potentials and the intracardiac... 

Contact Angle Measurements Surface Potential Measurements... 

It is not easy to directly measure the surface potential of small particles. Even if it was possible, because of statistical reasons the measurement cannot be made on only one particle. One way to measure surface potential of small... 

The apparent value of the equilibrium of Ca /Na exchange should decrease if the reaction about an increase of the measured surface potential with the amount of bound Ca ions. This increase in potential is the consequence of the reversal of the charges of the sites in the region t and eventually of the sign of the potential (j) in (6). The details concerning the H.P. A. spreading solvent and techniques used in the present study are described in Part 1 [29]. 

The titration curve of Figure 4 satisfies the Henderson-Hasselbach equation and our Equation (15). The slopes of the lines representing vs F or vs a are practically equal to the theoretical value of /2.3 kT= 17.8 V predicted by (9) and (15). The conclusion expressed by the second Equation (14) is verified e.g. the excess electrostatic partial free energy of an anionic site may then be taken as equal to ze4>Q where is the potential at the charged sites. It may be related also to the measured surface potential of the monolayer even when the distribution of the counterions is ignored. This is not allowed for polyelectrolytes membranes, solutions or gels for which neither the distribution of the fixed charged sites nor the potential shift be measured. 

On Figure 3 the supposed biological pH dependent shift is compared to the measured surface potential of our H.P.A. monolayer. It may be concluded that the conducting... 

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