Surface potential maximum

In a recent study of the computed electrostatic potentials and related quantities on the molecular surfaces of 13 trinitroaromatic derivatives [77], we noted two rough trends both the local polarity n and the surface potential maximum above the ring, Vs,max. tend to increase as the impact sensitivity increases. Accordingly we used a statistical analysis program [85] to investigate whether an acceptable quantitative relationship could be developed. We found that the sensitivity I150 could indeed be represented in terms of n and Vs,max(ring) our best expression was [77],... 

The repulsion between oil droplets will be more effective in preventing flocculation Ae greater the thickness of the diffuse layer and the greater the value of 0. the surface potential. These two quantities depend oppositely on the electrolyte concentration, however. The total surface potential should increase with electrolyte concentration, since the absolute excess of anions over cations in the oil phase should increase. On the other hand, the half-thickness of the double layer decreases with increasing electrolyte concentration. The plot of emulsion stability versus electrolyte concentration may thus go through a maximum. 

This energy maximum is calculated from the electric surface potential. An approximation of this surface potential is the zeta potential, which is experimentally deterrnined with commercial instmments. For o/w emulsions with low electrolyte content in the aqueous phase, a zeta potential of 40 mV is sufficient to bring the energy maximum to this level. 

In order to establish safe values for velocity-diameter product, various studies have been made to determine the minimum liquid surface potential that will result in an incendive discharge in the presence of a grounded electrode. Studies reviewed in [8] showed that for credible charging conditions, liquids must be negatively charged to yield incendive bmsh discharges. The consensus has been that to avoid incendive discharges the maximum liquid... 

This formula is useful in the design calculation to determine the electrode size for a maximum allowable surface potential variation during the experiments. 

Reactants AB+ + CD are considered to associate to form a weakly bonded intermediate complex, AB+ CD, the ground vibrational state of which has a barrier to the formation of the more strongly bound form, ABCD+. The reactants, of course, have access to both of these isomeric forms, although the presence of the barrier will affect the rate of unimolecular isomerization between them. Note that the minimum energy barrier may not be accessed in a particular interaction of AB+ with CD since the dynamics, i.e. initial trajectories and the detailed nature of the potential surface, control the reaction coordinate followed. Even in the absence (left hand dashed line in Figure 1) of a formal barrier (i.e. of a local potential maximum), the intermediate will resonate between the conformations having AB+ CD or ABCD+ character. These complexes only have the possibilities of unimolecular decomposition back to AB+ + CD or collisional stabilization. In the stabilization process,... 

Figure 3. Vertical cross-section showing equipotential contours inside a conductive cylindrical silo containing a symmetric conical heap of uniformly charged solids. The electrostatic potential maximum exists on the center line somewhat below the powder surface, while the maximum electric field intensity occurs near the wall just above the powder.

Sachtler and Dorgelo (74) measured the change in photoelectric work function when Na and Ha were adsorbed on evaporated films of Ni and Ta. These films were deposited under a vacuum of 10 mm. Hg, and the maximum surface potentials observed were 0.1 v. for the system Ni + Ha, —0.44 V. for Ta + Ha, and —0.38 v. for Ta + Na. On the other hand, the adsorption of Ha on a Ni surface prepared under less satisfactory experimental conditions decreased the work function (7S). As a result of this work, some doubt arises as to whether the positive S.P. values reported for the adsorption of Ha on various metals, particularly Pt (68), refer to clean surfaces. 

Langmuir and Kingdon (93) used the diode method in conjunction with thermionic experiments to study the adsorption of alkali metals and O2 on a W anode. The arrangement of the electrodes in the diode is shown in Fig. 18a. Their results were not very accurate for the adsorption of Cs and Th, the maximum surface potentials were +2.8 and +1.4 v., respectively, but the value for 62 was only —0.8 v. The technique was greatly improved by... 

To determine the 7r-A isotherms of dissolving films, two extrapolation methods were employed (29) either log tt at constant AT, or log AT at constant ir was plotted as a function of /1, where t is elapsed time. Extrapolation to t = 0 yields values of A or ir to within dr 5% for rapidly desorbing films. Palmitic acid at pH 9.2 was an exception its desorption rate was so rapid that the error in A was d= 10%. All the experiments were performed at 23° d= 0.5 °C. the maximum temperature variation during a single run was < 0.2 °C. The surface potential, AV, was monitored and found not to drift by more than 10 mv. during a single run. Reproducibility was d= 10 mv. 

The AV-A results for NH4OH substrates exhibit a unique behavior not seen with the other basic subsolutions. At 60 sq. A. per molecule, the AV values are negative and remain so with compression up to 40 sq. A. per molecule. Beyond this point, the curves rise sharply toward positive surface potentials at maximum compression, potentials of +75 mv. are recorded for stearic acid. Montagne reports +40 mv. for stearic acid films at maximum compression over NH4OH solutions at pH 11 (41). 

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