How do anti-static sprays work? Where do the electrons go to or come from to neutralise a charged surface?
鈥� The short answer is anti-static spray consists of an electrically conducting polymer dissolved in a solvent of de-ionised water and alcohol. When sprayed on a surface, the solvent evaporates, leaving the polymer as an invisibly thin conducting film, preventing the build up of excess charge.
This question opens up a fascinating topic, with many potential threads. Static normally builds up on an insulator, where charges cannot move, or on a conductor insulated from earth. Most people have seen the dust that builds up on television screens, particularly of the increasingly obsolete cathode-ray-tube type. Electrons fired at the phosphor-based screen make the rear of the screen negatively charged. This induces a positive charge on the front of the screen, which attracts negatively charged dust or fluff. Even when the TV is off, the fluff stays put, held there by its inherent stickiness.
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Attracting dust in this way is regarded as a nuisance to be cured by anti-static spray. However, just over a decade ago, researchers at the University of Southampton, UK, put this nuisance to good use in a cockroach trap. There are two things you need to know about cockroaches: they are positively charged and can climb vertical planes of glass by secreting a thin film of fluid, which acts as an adhesive, from their feet.
鈥淐ockroaches are positively charged and climb planes of glass by secreting fluid from their feet鈥�
The trap makes use of a highly desirable pheromone to lure a hapless insect across a sloping surface that is coated in an anti-static, or negatively charged, powder. The roach鈥檚 positively charged feet become coated in the powder, destroying its ability to gain traction on the sloping surface. Gravity ushers it into a well, from which there is no escape. Who dislikes static now?
Mike Follows, Willenhall, West Midlands, UK
鈥� When two high-resistance surfaces, such as hair and a plastic comb, rub together, surface electrons are transferred from one surface to another, making one positively charged (lacking electrons) and the other negatively charged (with extra electrons). The surfaces have a high electrical resistance so the electrons do not move and stay where they landed, producing static electricity. Anti-static sprays make the surfaces more conducting, so, although electrons may be dragged by the rubbing from one surface to another, they do not stay there, because the surface now allows them to flow away.
Keith Ross, Villembits, France