Sunday, February 06, 2011
Triboelectricity and enduring mysteries of physics
This past week I hosted Seth Putterman for a physics colloquium here at Rice, and one of the things he talked about is some of his group's work related to triboelectricity, or the generation of charge separation by friction/rubbing. When you think about it, it's quite amazing that we have no first-principles explanation of a phenomenon we're all shown literally as children (rub a balloon on your hair and it builds up enough "static" charge that it will stick to a plaster wall, unless you live in a very humid place like Houston). The amount of charge that may be moved is on the order of 1012 electrons per square cm, and the resulting potential differences can measure in the tens of kilovolts (!), leading to remarkable observations like the generation of x-rays from peeling tape, or UV and x-ray emission from a mercury meniscus moving along a glass surface. In fact, there's still some disagreement about whether the charge moving in some triboelectric experiments is electrons or ions! Wild stuff.
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Hi Doug,
Start with the complexity of uniform bulk materials. Add extreme nonlinear continuum mechanics. Throw in multiple different fractal-like surfaces. Shock waves. Fracture. Dielectric breakdown and plasma physics. All on the microscale. I'm not betting on any breakthroughs in triboelectrics in my lifetime! A famous physicist I knew spent a couple of decades trying and I think failing to learn anything at all about why ice particles charge up in a storm.
It's symptomatic of where we are in 21st century physics - hard work in all directions! Still interesting though.
Hi Dave - I know what you mean. Still, basic frictional charge transfer shouldn't be that bad, right? Teflon is a very stable fluoropolymer, and I can imagine rubbing it on glass with an applied (average) pressure well within the realm of linear elasticity, while shearing it across the surface at a speed way below the speed of sound in either material, also generating shear stresses well within the realm of linear elasticity. So, no (macroscale) shock waves, no (macroscale) fracture, no (macroscale) nonlinearities, and yet there is still charge transfer. It definitely makes me curious (though not at a level where I'm going to redirect my research program :-) ).
To me, they mystery isn't the x-rays from peeling tape. It is the HUGE amount of x-rays. The power density is crazy high. That's truly wierd.
I'm not betting on any breakthroughs in triboelectrics in my lifetime! A famous physicist
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