Contact charging definition

This complexity explains why definitive, quantitative verification of ionic contact charging has proved to be so elusive. Nevertheless, a body of convincing evidence for the role of ions in the charging process now exists for special categories of polymers with ionic features in their compositions. 

Other relevant information normally held as appendix or schedule to the SLA include user and suppher contact details, definition of fixed costs, charge-out rates, and penalty payments as appropriate. Contractual terms and conditions might also be included if not managed as a separate document. Escalation management processes should be documented and understood. 

The meaning of a complex formation constant is not as clear-cut as one can wish. The behavior of aqua ions which may be either definite species such as Ni(H60)6" or vague representations of the standard solute in dilute solution has already been discussed. One then must discuss the question When is a ligand bound to a central atom Certainly, this problem does not occur for most complexes of multidentate ligands, but weak complexes are not in an easy position. Prue (89) correctly emphasized that without any specific attraction between two molecules, for purely topological reasons, one would find a complexity constant of 0.2 liter/mole from contact charge-transfer spectra in typical conditions. If one finds a smaller formation constant, the two molecules repel each other... 

Inspection of the resistivity values shows a definite trend, or correlation, with charging behavior. Thus, one may estimate that contact charging drops off for powders below about 10 ohm-cm, while contact charging becomes predominant above about lO . 

At any interface between two different phases there will be a redistribution of charge in each phase at the interface with a consequent loss of its electroneutrality, although the interface as a whole remains electrically neutral. (Bockris considers an interface to be sharp and definite to within an atomic layer, whereas an interphase is less sharply defined and may extend from at least two molecular diameters to tens of thousands of nanometres the interphase may be regarded as the region between the two phases in which the properties have not yet reached those of the bulk of either phase .) In the simplest case the interface between a metal and a solution could be visualised as a line of excess electrons at the surface of the metal and an equal number of positive charges in the solution that are in contact with the metal (Fig. 20.2). Thus although each phase has an excess charge the interface as a whole is electrically neutral. 

In addition to electric charge between particles other factors are in some cases operative in preventing actual contact, thus the medium may be strongly adsorbed by the surface, and the thin film may not readily be displaced on collision of the two neutral particles, in other cases a tough elastic film may be formed, possessing definite mechanical strength and necessitating a violent impact to ensure rupture. 

An ion adsorbed on the surface of a suspension will draw near to it an ion of opposite sign in the solution these ions in the double layer are thus hound and can only escape if their kinetic energy exceeds a definite critical value W. If the chemically adsorbed ions have a valency % and n is the valency of the opposite charged ions in the liquid of dielectric constant K in contact with the solid and separated from the former by a distance x, we obtain... 

Almost by definition, an electronic device has at least two contacts. Here we consider a single one therefore, it is assumed that the bulk conductivity of the material and the distance between contacts are large enough, so that over most of that distance the material s energy levels are not influenced by the contacts. This is not true in the case of space-charge-limited currents [215], especially in double injection, a situation that may occur in CP LEDs (see Section V.C). 

According to this definition, the intrinsic energy barrier (pi represents the minimum energy required for the charge injection from the metal into the polymer molecule, which is a constant for a given polymer and metal pair. On the other hand, the contact-dependent component A

metal/polymer interface, which is morphology dependent. 

In nearly pure water, where all solute ions or molecules contact only water molecules, a, = m,-, and the activity coefficients of all solutes equal unity. As salt concentrations increase, however, individual aqueous species must move closer together and are, therefore, more and more likely to come in contact. Because the interaction between adjacent ions is largely Coulombic, it is also proportional to the charge of the ions involved. These effects are embodied in the definition of ionic strength (/) which is given by... 

---