Surface potential difference

B. Volta Potentials, Surface Potential Differences, and the Thermionic Work Function... 

Adsorption of a dipolar substance at the w/a and w/o interfaces changes surface tension and modifies the surface potential of water (Fig. 11). As seen in Fig. 11, the change in compensation voltage due to adsorption is the surface potential difference, usually called the surface potential or better the adsorption potential and often indicated unnecessarily by AV. ... 

Every liquid interface is usually electrified by ion separation, dipole orientation, or both (Section II). It is convenient to distinguish two groups of immiscible liquid-liquid interfaces water-polar solvent, such as nitrobenzene and 1,2-dichloroethane, and water-nonpolar solvent, e.g., octane or decane interfaces. For the second group it is impossible to investigate the interphase electrochemical equilibria and the Galvani potentials, whereas it is normal practice for the first group (Section III). On the other hand, these systems are very important as parts of the voltaic cells. They make it possible to measure the surface potential differences and the adsorption potentials (Section IV). 

As seen in this sketch, the change of compensation voltage A.E, due to adsorption is the surface potential difference, usually called shortly surface potential, or better the adsorption potential... 

The argument just presented can be extended to the differences of the various potentials. The outer potential difference A f can be measured (Klein and Lange Appendix 6.1) the surface potential difference A% cannot and therefore the inner potential differences d< ) = d y + Ax also cannot be experimentally obtained. 

Second, the inner potential difference across a double layer, d(J), was defined. It was determined that this inner potential can be resolved into two contributions. One of them, the outer potential difference or A jJ, emerged from the chaiges in the electrode and/or in the solution, and was found to be a measurable quantity. The other potential, the surface potential difference or A%, was due to the oriented dipoles existing on one... 

The presence of adsorbophilic counter ions on the surface reduces the surface potential difference since C charges partially counterbalance the opposite charges of the adsorbed H ions. The surface potential has to be calculated according to the following expression ... 

This issue is related to the surface potential difference between water and its vapor. Ax, and to the electrical double layer at the surface caused by the preferred orientation of the water dipoles. Parfenyuk (2002) has recently reviewed the values of Ax proposed by many authors, ranging from —1.1 to +0.5 V. His experiments involved an electrochemical cell and a non-aqueous solvent S ... 

It was a long way to go before the genesis of the surface potential differences caused by action potentials deep in the thorax was understood. It was the work of Einthoven and the lead concept that paved the way. It was Burger and van Milaan who introduced the lead vector, making it possible to find the direction to go. Richard McFee replaced the lead vector by the lead field, defined as the electric field set up in the body by a unit current applied to the pick up electrode pair. Otto Schmitt reintroduced the old Helmholtz concept about reciprocity and introduced the concept of transfer impedance already known from the use of four-electrode technique. And it was David Geselowitz who finally put it in the elegant mathematical form. A certain similarity with the Faraday—Maxwell intellectual process runs in our minds. 

Surface potential difference. Absorbed layers of contamination on metallic surfaces can be detected by measurement of variations in the amount of energy required for an electron to leave the surface. The Fokker Contamination Tester developed from this principle is claimed to be very useful in the optimization of various surface treatment processes and routine quality control activities (6). 

There also appears a fundamental force component which is proportional to the surface potential difference between the sample and the tip. We scan the tip over the surface typically at the rate of 0.1 Hz/line, while the tip-surface distance is controlled to give a constant F2a- The actual SMM system consists of a commercial AFM (Nanoscope, Digital Instruments) and a double-lock-in amplifier to selectively detect the oscillating electric force signals. We used AFM cantilevers with sharpened tips purchased from Olympus (OMCL-RC-800-PSA) with a spring constant of k=037 N/m. The AC voltage was 3 Vpp at 7.2 kHz, which should be chosen well below the resonance frequency of the cantilever. The resultant oscillation was about 2 nm or so at the closest approach of the tip to the surface. The lateral resolution was 10 nm with the potential sensitively of 1 mV. 

Fig. 39. (i) Variation in (a) Electrode potential (b) transmittance, and (c) surface potential difference of a Pd (7 nm) capped Sm (50 nm) film as a function of hydrogen concentration x = [H]/[Sm] determined from galvanosta-tic loading experiments. The proposed phase diagram is also depicted, (ii) Variation in (a) Electrode potential (b) transmittance, and (c) surface potential difference as a function of time on spontaneous discharge (Kumar and... 

Y., Fuyuki, T., Okuda, M. and Yamashita, I. (2007) Surface potential difference of biomineralized inorganic nanodot by Kelvin probe force microscopy. Japanese Journal of Applied Physics, 46, 5647-51. 

In order to arrive at the potential difference between the interiors of the two adjacent phases, the layer of partially oriented dipoles which develops at the phase boundary must not be overlooked. The work which must be done for a unit charge to cross a dipole layer can formally be assigned to a surface potential difference Ax- This voltage Ax must then be added to the Volta potential Ai//, which only includes charge separations at various locations in a vacuum, in order to get the total potential difference between the electrode interior and the interior of the adjacent electrolyte solution ... 

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