What is static electricity

It quickly became evident from analysis of the Kodak developer that their image quality resulted from the use of a conductive developer with positively charged toners as opposed to the insulating developers with negative toners in use by Xerox. Clearly Kodak had shown the scientific prowess of their chemists relative to those at Xerox!

The skills needed to design electrophotographic developer materials are the same as those needed to begin the process of understanding triboelectric charging of polymers—skills based on chemistry, a major strength at Kodak but a relative weakness at Xerox.

Yet in spite of this Kodak advantage, the field was later more than evened by Xerox through an unusual set of circumstances.

Figure 4. A copier makes use of static electricity, as shown in this sideview schematic. A photoconductive drum or belt is negatively charged a , and a light discharges those areas that will not be part of the printed image b.

Positively charged toner is attracted to the negatively charged surface of the drum c , and then transferred onto paper d and e. Heat fixes the toner permanently onto the paper to create the final printout f. The difference in copy quality was of such magnitude that Xerox immediately realized the need to use the Kodak technology.

Xerox physicists fervently studied how superior image quality resulted from the use of conductive developers. A team of chemists was established to produce and test toners containing a large number of different quaternary ammonium salts in conductive developers. This activity resulted in a series of at least a dozen patents based directly on the Kodak design, filed between and and issued to Xerox between and ; I was co-inventor of several of these advances.

Remarkably, Kodak never challenged these patents. Xerox chose to settle the case instead of undertaking litigation. Scherer, then FTC chief economist? Xerox electrophotographic imaging technology had hit a ceiling in the s 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.

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. Indeed, one of the authors of one Xerox history had personally studied conductive developers and published his results elsewhere in Competitive analysis is standard business practice, so one wonders at such selectivity in historical documentation.

As a consequence of the Kodak-Xerox events, Xerox had found a solution to their imaging problems—and motivation for basic research in triboelectricity at Xerox was lost. Triboelectricity was classified as a problem in solid-state physics because contact charging between two metals had been well understood in terms of the physics of electron transfer. For metal-polymer contacts, researchers had found linear relationships between the density of charge created on a polymer and metal work functions, which was presented as evidence for an electron transfer mechanism.

It was later reported that this relationship is not always present, but this discrepancy was attributed to the difficulty of obtaining reproducible results due to the many variables involved and the possibility of more than one simultaneous mechanism. Figure 5. Current research shows that triboelectric charges happen by three different mechanisms, some or all of which may take place simultaneously.

The first established mechanism is electron transfer top , where an electron from a metal tunnels into the bulk of a polymer after they come into contact and are separated. 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. New data now point to material transfer as a mechanism of charge exchange between two polymers bottom, right.

A physical clump of material rubs onto each opposing surface, and this material has a mosaic pattern of domains of positive and negative polymer-fragment ions that sum to an overall difference in charge between the two surfaces.

For charging between two insulators, physicists developed theories based on the assumption of an electron transfer mechanism. This concept is of questionable validity because there are no available free electrons in insulators. But such theories have been more successful in accounting for the limit of charge exchange in terms of the electric field generated by the charges in some cases. In other circumstances, charge buildup is limited when the ambient electric field becomes large enough to exceed the dielectric strength of the surrounding air, pulling apart the electrons from the air molecules and turning it from an insulator to a conductor, thus leaking current away from the material.

Eventually a concession was made by a Xerox chemist who reviewed models for the electronic structure of organic polymers, with a focus on those having highly ordered groups with rigid, periodic arrays of atoms, some having nearly metallic properties. It was two decades after the Kodak discovery of toner charge control agents that researchers used this design approach, an example of the chemistry concept of mobile ions, to produce evidence for an ion transfer mechanism for triboelectric charging.

A mobile ion has freedom to transfer from one surface to another, because it has a counterion of opposite charge that is either significantly larger and has less mobility, or is attached to a polymer and has no freedom to transfer. With molecules and polymers containing a mobile ion, the mechanism of charge exchange has indeed been related to the transfer of this ion, both to the sign of charging and to its magnitude. But the driving force for this mechanism remains elusive.

Charge exchange of equal magnitude also can happen when polymers do not contain mobile ions, so an additional mechanism must be at work. In , McCarty and Whitesides found an answer with their hydroxide ion hypothesis, in which water molecules within the thin water layer between polymers dissociate, with preferential adsorption of the resulting hydroxide OH — ions to one surface. Electrokinetic evidence supported their hypothesis.

But experiments in by Bartosz Grzybowski and his group at Northwestern University, designed to verify this hypothesis, have shown that charge exchange can take place between two nonionic polymers in the total absence of water, thus implicating a mechanism entirely different from both the proposed hydroxide ion hypothesis and ion transfer in general.

However, their result does not preclude the hydroxide ion mechanism in the presence of water, perhaps representing another situation in which more than one mechanism can apply simultaneously. Figure 6. A technique called Kelvin force microscopy shows the transfer of nanoscopic clumps of polymers between surfaces after contact and separation.

Before contact a , the material is relatively smooth. Contact with a polymer of the same composition b and of a different makeup c yields different transfer patterns. From H. Baytekin et al. Illustration adapted by Barbara Aulicino. Major advances in understanding the methods of charge transfer have been reported in the past few years, and in all of them charging results from the application of a significant amount of mechanical force between two polymers, specifically in pressing, rubbing and shearing contacts.

The field is currently being revolutionized by the application of surface analysis—electrical, chemical and electrochemical. It has long been known that contact of a polymer with another material can result in the transfer of some of the polymer from one surface to another; it was also established that, on a macroscopic scale, a triboelectrically charged surface may have both positive and negative regions.

This kind of charge exchange was unexpected. For centuries, it had been assumed that, in such contact charging, one surface charges to become uniformly positive and the other uniformly negative. The group found that, although each surface develops a net charge of either positive or negative polarity, each surface also supports a random mosaic of oppositely charged regions in nanoscopic dimensions.

The net charge on each surface is the arithmetic sum of the positively and negatively charged domains. This finding means that more charges are being exchanged than previously assumed. Charging is not an event affecting one in 10, surface groups, but more of the order of one charge in surface groups.

Various types of spectroscopy and chemical analysis of the surfaces revealed oxidized species, believed to be responsible for the charging. Pressing two polymers together, followed by separation, causes small clumps of materials to transfer between the surfaces. For this exchange to happen, covalent bonds must be broken, with the formation of polymer fragment free radicals at both scission sites. Free radicals are atoms or molecules having unpaired electrons, which cause them to be highly chemically reactive, and it is believed that they react with ambient oxygen and water to form the charged species.

In , Fernando Galembeck and his coworkers at the University of Campinas in Brazil took this material transfer mechanism a step further. Teflon and polyethylene were sheared together—pressed and twisted against one another. Materials extracted from the surfaces with solvents were identified as polymer ions.

The Teflon residues were predominantly negatively charged, and the polyethylene residues were primarily positively charged. 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.

Charged macroscopic domains form due to a combination of two factors: Amphiphiles at interfaces are known to sort themselves into arrays when they are in the type of polar environment created by the ions, and Teflon and polyethylene are immiscible.

A comparison of the work of Galembeck and Grzybowski illustrates the complex interaction between polymer properties and the nature of the contact in affecting the charge exchange mechanism. The contribution of each of the factors Galembeck identified in the material transfer mechanism depends on the viscoelastic, topographical, chemical and other properties of the specific polymers used, and also on the nature of the contact.

For example, the ease of bond scission would differ between polydimethylsiloxane PDMS , a polymer having a silicon-oxygen backbone, employed by Grzybowski, and the carbon backbone—based polymers used by Galembeck.

The degree of melting, or plasticization, can be expected to be less in light, low-friction contacts than in shear or vigorous rubbing contacts, on account of the lower temperatures involved, in addition to being affected by inherent polymer properties such as glass transition temperature where the material changes its flow properties without any change in molecular structure.

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.

Such entanglements are enhanced in silicon-oxygen backbone polymers by the presence of oligomers fragments of polymers and cyclic oligomers where the fragments have a ring structure. These substances exist in dynamic equilibrium; they are modified constantly due to the continual opening and closing of silicon-oxygen bonds, but have no net change. In the material transfer mechanism the driving force for creation of the charges is the input of mechanical energy during the contact of the polymers.

Research advances have also been made recently for rubbing contacts between two polymers. In , Chong-yang Liu and Allen Bard at the University of Texas at Austin, and independently Toribio Otero at the Polytechnic University of Cartagena in Spain, proposed an electron transfer mechanism on the basis that, after separation, the surfaces were able to induce several electrochemical reactions that can only be caused by electrons. Their interpretation was challenged in by Silvia Piperno and her colleagues at the Weizmann Institute of Science in Israel, who proposed an ion transfer mechanism based on the transfer of material containing polar species.

Also in rubbing contacts between two polymers, bipolar charging patterns were reported in by Nikolaus Knorr of the Sony Materials Science Laboratory in Stuttgart, Germany. Triboelectric charging results from contact between surfaces, but precisely what is meant by each of these terms is not defined or understood as they relate to charging.

My interest has focused on these questions: How are triboelectric charging mechanisms related to the depth of a polymer surface the charge penetration depth , and how does this depth vary as a function of the nature of the contacts? 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.

Some of the current, though, can travel through the body and damage the nervous system, according to the National Weather Service. Additionally, the concussion from the blast can cause traumatic internal injuries and permanent hearing loss, and the bright flash can cause temporary or permanent vision damage. As an example of the tremendous energy released in a lightning strike, Marsh told Live Science about his personal observation of a large oak tree that was literally split in half by high-pressure steam created by a lightning strike.

If you can hear thunder, generally, you are already within striking range, according to the University of Florida. If you are outdoors when a storm approaches, you should immediately seek shelter in a building or vehicle and avoid touching any metal.

If you cannot get inside, move away from tall objects such as trees, towers or hilltops, squat down, and if possible, balance on the balls of your feet making as little contact with the ground as possible, according to Brigham Young University.

While static electricity can be a nuisance or even a danger, as in the case of static cling or static shock, in other cases it can be quite useful. For instance, static charges can be induced by electrical current. One example of this is a capacitor , so named because it has the capacity to store electric charge, analogous to how a spring stores mechanical energy. A voltage applied to capacitor creates a charge difference between the plates.

If the capacitor is charged and the voltage is switched off, it can retain the charge for some time. This can be useful, as in the case of supercapacitors , which can replace rechargeable batteries in some applications, but it can also be dangerous.

Electronic equipment such as older CRT computer monitors and television sets contain large capacitors that can retain a charge with up to 25, volts, which can cause injury or death even after the device has been turned off for several days. Another way to create a useful static charge is with mechanical strain. In piezoelectric materials , electrons can literally be squeezed out of place and forced to move from the region that is under strain.

The voltage due to the resulting charge imbalance can then be harnessed to do work. One application is energy harvesting, whereby low-power devices can operate on energy produced by environmental vibrations. Another application is for crystal microphones. Sound waves in the air can deflect a diaphragm connected to a piezoelectric member that converts the sound waves to an electrical signal.

In the inverse operation, the electric signal can cause a piezoelectric transducer in a loudspeaker to move, thus reproducing the sound. Localized static charges can also be affected by an intense light.

This is the principle behind photocopiers and laser printers. In photocopiers, the light may come from a projected image of a sheet of paper; in laser printers, the image is traced onto the drum by a scanning laser beam.

A positive ion has a missing electron. So, it can easily accept an electron from a negative static charge:. What is Static Electricity? In both cases there is an electron available to neutralise a positive charge. Was this article helpful?