2011. But not all static is a nuisance: Triboelectric charging, when controlled, is at work in products such as copiers and laser printers. Static electricity is the result of an imbalance between negative and positive charges in an object. Although not contributing to the question of the nature of the charge exchange species, these theories have had debatable success in addressing the driving force for charge exchange in terms of the “effective work functions” of insulators. 2011. For this exchange to happen, covalent bonds must be broken, with the formation of polymer fragment free radicals at both scission sites.
Contact charging between particles; some current understanding.
Integrating the separate pieces of the puzzle into a coherent overall picture will take multidisciplinary efforts. Although static electricity is a familiar subject, much still remains unknown about how and why such charges form. Electron transfer from the polyethylene radicals to the more electronegative Teflon radicals converts these free radicals to positive and negative polymer ions, respectively, which are known as amphiphiles. However, properly controlled and manipulated, it can also be a tremendous boon to modern life. It follows that electron, ion and material transfer mechanisms can possibly occur simultaneously, depending on the materials and conditions of contact. He stated: “Kodak was using trade secrets more often [than patents] … They would rather keep their inventions as trade secrets, because they did not want them to expire.” A curious comment indeed, considering the major contribution that Kodak patents made to Xerox technology, and especially because this remark was made in the presence of the workshop chairman, a retired Xerox senior executive who had been a physics manager at the corporation in the 1970s. Figure 3. When two objects are brought into contact and then separated, electrical charges are generated at the surfaces. The difficulty of making new discoveries. Triboelectric charging of compositionally identical materials also happens with particulate matter, as in dust storms and the industrial handling of fine particles. Could this mean that the mechanical forces between toner and carrier were too low for simultaneous transfer of polymer fragments? This activity resulted in a series of at least a dozen patents based directly on the Kodak design, filed between 1978 and 1985 and issued to Xerox between 1980 and 1987; I was co-inventor of several of these advances. Static electricity can be a bother when it shocks you unexpectedly, but during the winter months and when working with electronics, the static shocks can become frequent and painful and disastrous if a surprise shock ruins an electronic component. I used this phenomenon while at Xerox in the mid-1970s to investigate charge penetration depth. How does intellectual property support the creative process of invention? Static electricity can be a nuisance or even a danger. Figure 2. When two objects are brought into contact and then separated, electrical charges are generated at the surfaces. This new mechanism could also apply to symmetrical rubbing and pressing of identical polymers on the basis that small, unintentional degrees of asymmetry could result in sufficient asymmetric compositional transfer to result in charging. Could it be related to a Federal Trade Commission (FTC) complaint issued against Xerox in 1973 for alleged unfair competitive practices? Yet charging occurs when identical polymers are either pressed or rubbed together, symmetrically or asymmetrically. The surface science of xerography. Triboelectric charging was determined by cascading small (100 and 250 micrometer) beads, both bare metal and polymer coated, over inclined polymer films cast on aluminum plates, a method of established precision and reproducibility. The field is currently being revolutionized by the application of surface analysis—electrical, chemical and electrochemical. Scherer, F. M. 2010. Wuchty, S., B. F. Jones and B. Uzzi. It is well known that low-surface-energy additives in polymers will migrate to the surface if films are fabricated from solution so as to allow thermodynamic equilibration of the components. Competitive analysis is standard business practice, so one wonders at such selectivity in historical documentation. Chester Carlson spent many years (and endured much trial and tribulation) inventing the first xerographic apparatus (top ). It is becoming increasingly clear that more than one mechanism can occur simultaneously, and what happens may depend on the material compositions and conditions of the experiments in ways not yet known. After separation, the team found macroscopic domains or patterns, both positively and negatively charged, analogous to those reported by Grzybowski’s group. A technique called Kelvin force microscopy shows the transfer of nanoscopic clumps of polymers between surfaces after contact and separation. The toner is triboelectrically charged by mixing it with a carrier, forming what’s called a developer. Different theories have proposed either electrons or ions. But when at least one of the materials is an electrical insulator, there is no general understanding of what carries charges from one surface to the other. Evidence also exists for ion transfer (bottom, left ), where contact causes one member of a pair of positive and negative ions to relocate to the other surface, which can be a polymer or a metal.
Many different types of contact have been employed in innovative experimental designs, but apparently no efforts have been made to study this factor as a controlled primary variable. Click "American Scientist" to access home page. Williams, M. W. 2012.
But polymer-chain scission of a soft polymer such as PDMS can occur at lower temperatures in low-pressure, low-friction contacts on account of the polymer chains entangling at the interface, which break on separation. The increasing dominance of teams in production of knowledge. Charged toner particles are allowed to be attracted to the image pattern on the photoconductor, transferred to paper and fused to produce a copy. Xerox electrophotographic imaging technology had hit a ceiling in the 1970s for which their research laboratories had no solution, and it was rescued from this potentially disastrous business problem by adopting Kodak technology, conductive developer materials with positively charged toner. The surprising finding was that contact charging between two polymers relates to their topmost molecular layers, but between a metal and a polymer it relates to layers beneath the polymer surface. It would apply equally well to charging between materials of different compositions and, in this way, contributes to the understanding of the general material transfer mechanism. Recently, new research has demonstrated that charge exchange can also result from the physical transfer of tiny amounts of surface material from one substance to another. Carriers typically consist of beads 100 micrometers in diameter, which are partially coated with a polymer. Another motivation is pure research, whose objective is the understanding of natural phenomena and observable facts with no specific application or problem solving in mind. Baytekin, H. T., A. The use of polymers designed to have compositional inhomogeneity as a function of depth, such as those described in experiments earlier, would provide a sensitive test for this hypothesis because the transfer of materials with different compositions would be easily detected. I played a central role in the Kodak analyses and still have the original documentation, but surprisingly these developments are not included in any historical accounts of Xerox copier technology. Heat fixes the toner permanently onto the paper to create the final printout (f ). Galembeck’s team proposed this mechanism: High temperature at the frictional points of contact results in polymer plasticization and/or melting. Consensus prevailed, with the consequence that, when the first Kodak Ektaprint copier was introduced in 1975, Xerox was caught by surprise on several fronts.
In addition, recent developments have brought attention to the need for the application of mechanochemistry, which is central to the material transfer mechanism.
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