Dipole image force

Carnie and Chan and Blum and Henderson have calculated the capacitance for an idealized model of an electrified interface using the mean spherical approximation (MSA). The interface is considered to consist of a solution of charged hard spheres in a solvent of hard spheres with embedded point dipoles, while the electrode is considered to be a uniformly charged hard wall whose dielectric constant is equal to that of the electrolyte (so that image forces need not be considered). 

In addition to the nonelectrostatic adsorptive force, there is an image force between a dipole and a metal, which will be present whenever charged or dipolar particles in a medium of one dielectric constant are near a region of another dielectric constant. If the metal is treated as an ideal conductor, the image-force contribution to the energy of a dipole in the electrolyte is proportional to p2j z3, where z is the distance of the dipole from the plane boundary of the metal (considered ideal, with no surface structure), and to 1 + cos2 0. This ideal term is, of course, the same for all metals. If... 

For neutral dipolar molecules, the value of B depends on the dipole moment itself, and the value of y is 3/2 or, in the presence of image forces, 5/2. The former of these has been verified experimentally for the adsorption of such molecules as 2-chloropyridine on mercury. 

Fig. 6.43. The two stages of getting the inner, or < >, potential (a) The work done to bring a unit of positive test charge from infinity to a point just outside the range of the image forces defines the outer, or j/, potential, (b) The charge on the solution is then removed, and the solution is wrapped in an oriented-dipole layer. The work done to transport the test charge across the oriented-dipole layer defines the surface, or, %, potential. Thus, the total work to bring the test charge from infinity to a point just inside the solution is given by s = /s + xs.

Define the following terms used in Section 6.7 (a) image forces, (b) image dipole, (c) dispersion forces, (e) chemical forces, (f) saturated dielectric, (g) water monomers and water dimers, (h) configurational entropy, (i) libration entropy, and (j) vibrational entropy. (Gamboa-Aldeco)... 

Consider the deviations of 0max from the pzc quantitatively. Can you associate them with the probable orientation of the adsorbed organic molecules on the surface Or perhaps on image potentials formed by dipoles of the organic with the metal Perform simple calculations to determine whether breakdown of the first approximation assumption of zero interaction of the organic molecule with the field, or image forces, explains the deviation of Vmax of the organic molecule from the pzc. (Bockris)... 

When a dipole molecule is adsorbed on the surface of a metal or on other conducting surfaces (charcoal), the attraction may be described by the image force. The energy of interaction is given by... 

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. 

If we neglect image forces, the interaction of two such dipoles can be represented by means of a force F, that is given by... 

The work function is defined as the minimum work that is required to extract an electron from within the sample to a position just outside the sample (far enough to avoid contributions from image forces). It is comprised of the chemical work and the electrostatic work necessary for transporting the charged electron through the dipole layer at the surface ... 

The locus (typically 10 cm distance from the surface) is characterized by the following Image forces as well as effects of the dipole layer are negligible, but the volta-potential is fully perceived. 

When an atom or molecule approaches a surface, the electrons in the particle - due to quantum fluctuations - set up a dipole, which induces an image dipole in the polarizable solid. Since this image dipole has the opposite sign and is correlated with fluctuations in the particle, the resulting force is attractive. In the following we construct a simple model to elucidate the phenomenon. 

Balachandran [23] analyzed the role of electrostatic forces in the adhesion between sohd particles and surfaces. According to the available information this role is not completely clear, the results are contradictory. Electrostatic forces can be significant in the case of polymer and semi-conductor particles. These forces have four main types Coulomb, image charge, space charge and dipole forces. 

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