
What causes static electricity? Until a few years ago, scientists were confident that they understood static electricity and exactly how it worked. The explanation went like this... Just like the ancient Greeks, we tend to think static electricity comes from rubbing things. So if you live in a home with nylon carpets and metal doorknobs, you'll soon learn that your body builds up a static charge when you walk across the floor, which can discharge when you touch a doorknob, giving you a tiny electric shock. In most school experiments, we also learn about static by rubbing things. You've probably tried that trick where you rub a balloon on your clothes to make it stick? You might conclude from this that static electricity is somehow connected to friction—that it's the very act of rubbing something vigorously that produces a buildup of electrical energy (in the same way that friction can produce heat and even fire). The triboelectric effect It's not the rubbing that's important but the fact that we're bringing two different materials into contact. Rubbing two things together vigorously simply brings them into contact again and again—and it's this that produces the static electricity through a phenomenon known as triboelectricity (or the triboelectric effect). All materials are built from atoms, which have a positive central core (the nucleus) surrounded by a kind of fuzzy "cloud" of electrons, which are the really exciting bits. Now some atoms have a more powerful pull on electrons than others; a great deal of chemistry stems from that fact. If we put two different materials in contact, and one attracts electrons more than the other, it's possible for electrons to be pulled from one of the materials to the other. When we separate the materials, the electrons effectively jump ship to the material that attracts them most strongly. As a result, one of the materials has gained some extra electrons (and becomes negatively charged) while the other material has lost some electrons (and becomes positively charged). Hey presto, we have static electricity! When we rub things together again and again, we increase the chances that more atoms will take part in this electron-swap, and that's why a static charge builds up. Photo: How the triboelectric effect explains static electricity: 1. Ebonite (hard vulcanized rubber—shown here as a black rod) and wool (shown as gray) normally have no electric charge. 2) Put them in contact and the ebonite attracts electrons from the wool. 3) Separate them and the electrons remain on the ebonite, making it negatively charged and leaving the wool with a lack of electrons (or a positive charge). Rubbing the two substances together increases the contact between them and makes it more likely that electrons will migrate from the wool to the ebonite. The negative charge on the ebonite is exactly the same size as the positive charge on the wool; in other words, no net charge is created. The triboelectric series If you experiment with different materials, you find some gain positive charges when they're rubbed and some gain negative charges; some materials also gain more charge than others. It turns out that we can rank materials in order according to the charge they gain, giving us a kind of league table of materials running from positive to negative. Different books and web pages show slightly different lists, but they all broadly run from minerals (positive) through such things as wood and paper (neutral) to plastics (negative). Don't worry too much about the exact order of the list; it's going to vary for all kinds of reasons (the kind of glass or the additives in the latex, for example). ++++++++ POSITIVE ++++++++



+ Air

+ Skin

+ Leather

+ Asbestos

+ Glass

+ Mica

+ Quartz

+ Nylon

+ Wool

+ Fur

+ Lead

+ Silk

+ Aluminum

0 Paper

0 Cotton

0 Steel

0 Wood

− Amber

− Latex

− Hard rubber

− Nickel

− Copper

− Brass

− Silver

− Gold

− Platinum

− Polyester

− Polystyrene

− Neoprene

− Saran ("cling film")

− Polyethylene

− Polypropylene

− Polyvinylchloride (PVC)

− Selenium

− Teflon

− Silicone rubber

− Ebonite (very hard vulcanized rubber)



−−−−−−−−NEGATIVE−−−−−−−− This list is called the triboelectric series. The further apart two materials are in the series, the more static electricity will build up when you rub them together. If two materials are very close in the series, it's hard to get them to build up any charge at all no matter how hard you rub them. That would seem to confirm that static electricity isn't about rubbing, per se, but about the nature of the materials we bring into contact.

Rethinking static electricity What you've just read is the traditional, widely accepted explanation of static electricity—and you'll still find it described that way in most school books. But in 2011, scientists reported some important new discoveries that seemed to suggest much more was going on. Instead of being purely a matter of physics, and a simple transfer of charged electrons from one material to another, it seemed static electricity could also be caused by chemistry (movement of ions and other essentially chemical processes). And it could also happen through a swapping of small amounts of actual material (a bit of balloon shifting to your pullover or vice versa). Where we used to think of static as a simple "pile" of negative or positive charge (electrons or a lack of them), on closer inspection, it now appears to be a "mosaic" of both positive and negative charges that add up to an overall charge (positive or negative). This research is very new, and still evolving, but it seems clear that our traditional explanation of static electricity is an oversimplified version of what's really happening, even if we've faithfully believed it for over 2000 years! Artwork: Top: The traditional theory sees a static charge on a balloon as an even spread of charged particles across its surface. Bottom: According to the latest thinking, a static charge is actually a random "mosaic" of much bigger charges, which can be both positive and negative, and which add up to an overall charge. In this case, there's much more negative charge than positive (yellow than red), so our balloon has an overall negative charge. Further reading Simple introductions What You Learned About Static Electricity Is Wrong by John Timmer. Wired, June 25, 2011.

A Shocking New Understanding of Static Electricity by Douglas Main. Popular Mechanics, June 29, 2011. More complex articles The Mosaic of Surface Charge in Contact Electrification by H. T. Baytekin, A. Z. Patashinski, M. Branicki, B. Baytekin, S. Soh, and B. A. Grzybowski. Science, July 15, 2011, Vol. 333, Issue 6040, pp.308–312.

Antioxidants dispel static electricity by Richard Van Noorden. Nature, September 19, 2013.

What Creates Static Electricity? by Meurig W. Williams. American Scientist, Volume 100, July/August 2012, pp.316–323.

What use is static electricity? Now static electricity is all very interesting, but what possible use is it? You can't make toast from a lightning bolt and you can't charge your cellphone simply by rubbing its case on your pullover. You might think static is one of those fascinating but ultimately quite useless bits of science that has no practical applications—but you'd be wrong: static electricity is used in all kinds of everyday technology! Laser printers and photocopiers use static electricity to build up ink on a drum and transfer it to paper. Crop spraying also relies on static electricity to help herbicides stick to the foliage of plants and distribute themselves evenly over the leaves. Factory paint-spraying robots use a similar trick to ensure that paint droplets are attracted to metal car bodies and not the machinery around them. In many power plants and chemical factories, static electricity is used in smokestacks to scrub away pollution (read more in our article on electrostatic smoke precipitators). Photo: How can you stop air pollution spewing out from smokestacks? One way is to give a static electric charge to smoke, then funnel it through a grid of metal plates with an opposite charge, so the dirty soot particles are removed. That's how "scrubbers" (electrostatic smoke precipitators) work, such as the ones installed in these smokestacks at the McNeil biomass power plant in Burlington, VT. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL). Of course, static electricity has its drawbacks too. It can cause sparks and explosions in fuel depots and stray static is a real nuisance if you're working with electronic components. That's why engineers and chemists have developed all kinds of anti-static technologies (from simple wires to ingenious, slightly conducting paints and coatings) that prevent static buildup in sensitive places. While you're reading these words, you can be sure that someone, somewhere is trying to find a new way to harness static electricity or a better way to stop it causing problems. Static electricity may be stationary, but it's never standing still!





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