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. 

Electrostatic-Separation Machines The first electrostatic machines to be used commercially employed the principle of contact elec trification. These were free-fall devices incorporating large vertical plates between which an electrostatic field was maintained. Tribo-elec tric separation (contact charging) has experienced an increase in apphcations due to advances in mechanical self-cleaning and electrical design as well as the development of efficient precharging techniques. 

Efforts to quantify the magnitude and polarity of contact charging have had hmited success, because minute variations in the types and concentrations of contaminants exert a large influence on charge sep-... 

The double layer can be formed by contact (triboelectric) charging of one surface of the nonconductor, while the opposite surface is in contact with a conductor, e.g., a nonconductive coating on a metal chute or a plastic-lined, metalpipe for powders. A less frequent cause is contact-charging of one surface, while air ions are supplied to the opposite surface. 

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. 

The ethylenediamine derivative [31] possesses higher promoting activities than other diamines. This phenomenon may be ascribed to the copromoting effect of the two amino groups on the decomposition of persulfate through a CCT (contact charge transfer complex) formation. So we proposed the initiation mechanism via CCT as the intimate ion pair and deprotonation via CTS (cyclic transition state) as follows ... 

This association has its counterpart that was also variously described as an encounter complex, a nonbonded electron donor-acceptor (EDA) complex, a precursor complex, and a contact charge-transfer complex.10 For electrically charged species such as anion/cation pairs (which are relevant to ion-pair annihilation), the pre-equilibrium association results in contact ion pairs (CIP)7 (equation 3)... 

A relatively strong organization of an electron donor by an acceptor is typically indicated by experimental values of KEUA or KC f> > 10 M-1. For intermediate values of the formation constant, i.e., 1 < KE A < 10 m, the donor/acceptor organization is considered to be weak.17 Finally, at the limit of very weak donor/acceptor organizations with KEDA 1, the lifetime of the EDA complex can be on the order of a molecular collision these are referred to as contact charge-transfer complexes.18... 

Onodera, K., Furusawa, C.-I., Kojima, M., Tsuchiya, M., Aihara, S., Akaba, R., Sakuragi, H. and Tokumaru, K. (1985). Mechanistic considerations on photoreaction of organic compounds via excitation of contact charge transfer complexes with oxygen. 

Rest, A.J., Salisbury, K. and Sodeau, J.R. (1977). Contact charge transfer interactions between aromatic molecules and oxygen in gas matrixes at 10 K. J. Chem. Soc. Faraday Trans. 2 Mol. Chem. Phys. 73, 265-273... 

Hashimoto, S. and Akimoto, H. (1986). Visible light photooxygenation of 2,3-dimethyl-2-butene at the contact charge-transfer band in the cryogenic oxygen matrix. J. Phys. Chem. 90, 529-532... 

Vasenkov, S. and Frei, H. (1997). UV-visible absorption spectroscopy and photochemistry of an alkene-02 contact charge-transfer system in large NaY crystals. J. Phys. Chem. B 101, 4539 1543... 

Takeya, H., Kuriyama, Y. and Kojima, M. (1998). Photooxygenation of stilbenes in zeolite by excitation of their contact charge transfer complexes with oxygen. Tetrahedron Lett. 39, 5967-5970... 

From the above, it would be expected that, except for metal-metal contacts, charging can be very sensitive to the method of contacting and to the surface condition (or state of contamination) of the material. This is, in general, borne out by the seeming contradiction of available data, which are based on widely different methods of contacting and degrees of cleanliness. 

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). 

P4. Peterson, J. W., Contact charging between a borosilicate glass and nickel, J. Appl. Rhys. 25, 501 (1954). 

Nitrobenzene (NB) is such a weak acceptor that it is not capable of initiating polymerization of VCZ in the dark. Nitrobenzene has been used as a solvent for polymerization of VCZ in several instances. However, from a spectroscopic study of VCZ-NB mixture, the formation of a CT complex is confirmed (33). Although no new absorption peak is observed when VCZ and NB are mixed in benzene solution, a shift of absorption of NB is clearly detected. This CT complex is the contact charge transfer type as shown in Fig. 4. 

Fig. 4. Contact charge transfer complexes of nitrobenzene with VCZ and poly VCZ measurements of optical density at 437 mp. at room temperature Optical length 1 cm VCZ, -o- Poly VCZ in nitrobenzene, [NB] + [VCZ] = 0.3 M in benzene...

The charge transfer interaction between AN and IBVE is confirmed by electronic spectroscopy. As with the VCZ-NB system, the charge transfer interaction is observed as a shift of specific absorptions of the components. The complex is again of contact charge transfer type. 

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