Particle contact charge

In the field of toner materials, the emphasis in the 1990s is on increasing developer life, particularly using color toners. The life of a typical black two-component developer is about 80—100 kilocycles per kilogram, whereas for color toners it is only about 10 kilocycles per kilogram (64). Also, there is a need for better control of triboelectrification of toner particles that would not only allow stable operation under all environmental conditions but also provide consistent, fast, and reproducible contact charging. 

Particles carrying charges of opposite polarity due to contact electrification will be attracted to opposite electrodes when passing through an electric field and thus can be separated from each other. 

So far the discussion has been limited to the case where the particle s charge is uniformly distributed. However, as discussed by researchers such as Goel and Spencer [89], and Hays [76,81], this might not be the case, especially if the particle is irregularly shaped. This can occur, as argued by Hays, if asperities on the particle prevent much of the surface area from contacting a neighboring... 

It is clear that the presence of electrostatic charges, whether due to contact charging, fractoemissions, or some other mechanism, will affect particle adhesion. However, to date there has been no satisfactory attempt made at properly integrating electrostatic forces into partiele adhesion theory. 

It should also be noted that in those methods in which charged particles are deposited on an electrode under the influence of an electrostatic field, there exists the possibility of reverse contact charging of the particle if the particle is sufficiently conductive. Such contact charging can cause the particle to oscillate between the electrodes, carrying current from one to the other. This phenomenon has often been observed in connection with electrostatic printing and has been specifically reported by Cho (C2). Such a transfer of particles would result in a transfer of charge to the electrodes far in excess... 

C2. Cho, A. Y. H., Contact charging of micron-sized particles in intense electric fields, J. Appl. Phys. 35, 2561 (1964). 

The most common form of gas sensor is based on a porous, sintered ceramic as shown schematically in Fig. 4.46. As adsorption occurs over the surface of the semiconductor grains, the barriers to charge transport develop, especially at the grain boundaries and at particle contact areas (the neck regions). 

Fig. 2 Model concept of the contact charging of polymer grains, a Contact between an electron pair donator domain (empty dots) of the particle 1 and an electron pair acceptor domain (grey dots) of the particle 2. Charge transfers (e-) are taking place. After separation the two particles (b), a positively charged ( ) and a negative charged ( ) domain, remain on the particles surface...

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