Triboelectric charging measurement

A second adverse effect of van der Waals adhesion is a tendency of carrier and photoconductor surfaces to become coated with a thin film of toner residue—a film which progressively impairs the efficiency of toner charging and photoreceptor performance. Salaneck et al. (57) have reported that material transfer amounting to as little as 1 atom/10 surface sites is measurable as a shift in "triboelectric" charging behavior ... 

Figure 11. Correlation of triboelectric charging with electronegativity, as measured by Hammet sigma function. (Reproduced from Ref. 66. Copyright 1975, American Chemical Society.)...

Figure 1. Cascade device for measurement of triboelectric charging (20,...

The measurement of triboelectric charge generation is well known for its variability where relative humidity, surface contamination or abrasion, tress configuration, and other variables have to be strictly controlled. Even with the combing of up to five replicate tresses and five successive determinations, Lunn and Evans report a 95% confidence interval of 15%. The apparatus that Lunn and Evans used is shown in Figure 28. The insulated tress is combed with a hand-held insulated test comb, and after the appropriate number of strokes, the tress is released into a Faraday cage connected to an electrometer. The whole setup is enclosed in a box in which temperature and humidity are controlled. 

The measurement of the electrical properties of highly resistive polymers presents a number of problems. The surface conductivity is often greater than the bulk value and is increased by absorbed impurities. The latter is also affected by impurities. The presence of localized-defect states in the energy gap means that contact with metals is accompanied by charge transfer to the polymer in the absence of an applied field. The triboelectric charge appears to be relatively insensitive to sample purity or preparation and even to polymer structure. This indicates that the important defects are structural, with a density that is almost sample independent. The work function of the metal affects the charge transfer, but large experimental uncertainty renders precise functional fits unreliable. 

A number of researchers have explored the use of triboelectric effects in measuring the properties of the pneumatic conveying systems [12, 13, 14]. Usually the researcher would like to eliminate these charges, but under controlled conditions they can be used to an advantage. Klinzing, et al. [15] have used a field probe that is both nonintrusive and effective in picking up the field variations in the flow of charged particles. 

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