Electrostatic image

Phenylenediamines are used in a variety of other appHcations, such as corrosion inhibitors, cross-linking agents for epoxy resins, toners for electrostatic image development (35), and to improve wrinkle resistance of cellulose acetate fibers (36). 

The electrophotographic system (102,103) involves two key physicochemical elements a photoreceptor and a toner. The minimum requirements of the process are (/) to charge a photoconductive photoreceptor uniformly (2) to illuminate selectively the photoreceptor to form a latent electrostatic image and (J) to develop the image by applying charged toner. These steps are illustrated in Figure 17. 

The abihty to accept and hold the electrostatic charge in the darkness. The photoconductive layer should support a surface charge density of approximately 0.5-2 x 10 C/cm. The charge also has to be uniformly distributed along the surface, otherwise nonuniformities can print out as spot defects. The appHed surface potential should be retained on the photoreceptor until the time when the latent electrostatic image is developed and transferred to paper or, if needed, to an intermediate belt or dmm. In other words, the "dark decay" or conductivity in the dark must be very low. The photoconductor materials must be insulators in the dark. 

Once the latent electrostatic image has been developed on the photoreceptor surface, it must be transferred to plain paper with no loss in clarity. 

Ishida, Y. K. Y Otsuka, K. I. M. (Orient Chemical Ind.). Electrostatic Image Toners. G. B. Patent Application... 

AHa for the Adsorption of Alkali Metals. If an alkali metal atom is located at an infinite distance from a metal surface at zero potential, then the heat of adsorption comprises the work done in (1) transferring an electron from the atom to the metal, and (2) bringing the positive ion to its equiUbrium distance from the metal surface (127). In the first step, the energy change is (e0 — el), where is the work function of the metal and I is the ionization potential of the alkali metal atom. In the second, the force of attraction on the positive ion at a distance d from the metal surface, i.e., the electrostatic image force, is e /4d hence, the heat Uberated is e /4do, where do is the equilibrium distance of the adsorbed ion from the metal surface. This distance is often assumed to be equal to the ionic radius, which is 1.83 A. for the Na ion. The initial heat of adsorption, therefore, is... 

A rapid survey of some of the more recent publications seems to point to DNA indeed being a very broad-gap semiconductor or insulator for lengths exceeding a few hundred base pairs. This conclusion was reached in references [74] and [75] on the basis of electrostatic imaging, in reference [77] using conducting atomic force microscopy on A-DNA, in [78] using 300-nm DNA strands both of poly(GG) and of A-DNA, and in [52] for A-DNA supported on mica. 

Therefore, as a general trend, Ts decreases when the energy gap between surface and bulk states is made weaker Figs. 3.1-3 provide a perfect illustration of the expression (3.26) for the bulk effect on the surface emission. A more detailed analysis of the bulk effect will be given below. However, this reduction of the surface radiative width may be interpreted classically as the destructive interference between the emission of the surface and that of its electrostatic image in the bulk.140 The bulk reflectivity amplitude rv(to) is quasi-metallic near resonance and at low temperatures. 

Development. This is obtained through the electrical attraction of a toner (thermoplastic pigment mixed with carbon black), whose fine particles carry electrical charges that are opposite in polarity to the latent electrostatic image charges. 

For a review of early work on electrostatic imaging, see Carlson (1965). For more recent work, see Mort (1989). 

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