Static electricity: How does that work?

staticcling.jpg

Much like magnets, the inner workings of static electricity appear simple. This is, it turns out, misleading. So misleading, in fact, that scientists were fooled.

Back in grade school, you probably learned that static electricity happened when you rub two different objects together (like a balloon and your hair). In the process, one object loses its electrons, becoming positively charged, and the other object gains electrons, making it negatively charged. Once that happens, the positive object and the negative object will be attracted to one another—your hair will reach out for the balloon, the balloon will stick to your head.

But a recent paper is showing that this explanation doesn't quite explain everything about static electricity. There's a short, very visual, take on what's really going on at the Starts With a Bang blog. I'm going to quote the longer, more detailed perspective of Ars Technica's John Timmer:

... it wasn't until last year that some of the authors of the new paper published a surprising result: contact electrification (as this phenomenon is known among its technically oriented fans) can occur between two sheets of the same substance, even when they're simply allowed to lie flat against each other. "According to the conventional view of contact electrification," they note, "this should not happen since the chemical potentials of the two surfaces/materials are identical and there is apparently no thermodynamic force to drive charge transfer."

One possible explanation for this is that a material's surface, instead of being uniform from the static perspective, is a mosaic of charge-donating and charge-receiving areas. To find out, they performed contact electrification using insulators (polycarbonate and other polymers), a semiconductor (silicon), and a conductor (aluminum). The charged surfaces were then scanned at very high resolution using Kelvin force microscopy, a variant of atomic force microscopy that is able to read the amount of charge in a surface.

Surface before static charging (top) and after (below). Science The Kelvin force microscopy scans showed that the resulting surfaces were mosaics, with areas of positive and negative charges on the order of a micrometer or less across. All materials they tested, no matter what overall charge they had picked up, showed this mosaic pattern. The charges will dissipate over time, and the authors found that this process doesn't seem to occur by transferring electrons between neighboring areas of different charge--instead of blurring into the surroundings, peaks and valleys of charge remain distinct, but slowly decrease in size.

... So, what causes these charges to build up? It's not, apparently, the transfer of electrons between the surfaces. Detailed spectroscopy of one of the polymers (PDMS) suggests that chemical reactions may be involved, as many oxidized derivatives of the polymer were detected. In addition, there is evidence that some material is transferred from one surface to another.

Via Jennifer Ouellette

Image: Fun With Static #3, a Creative Commons Attribution Share-Alike (2.0) image from jemsweb's photostream

10

  1. Interesting to read, but more interesting to read the comments on the WIRED article you linked to. There is a professed scientist in the comments who takes issue with the author’s interpretation of the scientific paper. To quote one of his comments (and forgive the caps…his lab PC’s keyboard is broken):

    “JUST BECAUSE WIRED MAGAZINE HAS A LARGE INTERNET VOICE DOESN’T MEAN THEY GET TO PROCLAIM AND MISLEAD PEOPLE BY SAYING THAT ELECTROSTATICS IS “WRONG”. THE AUTHORS OF THE ORIGINAL WORK ARE NOT REALLY MAKING THIS CLAIM. AND DO YOU KNOW WHY? BECAUSE THEY KNOW ELECTROSTATICS IS ENTIRELY A CONTINUUM/BULK THEORY…IT IS ACTUALLY NOT SOMETHING THAT WAS EVER MEANT TO SCALE DOWN TO DISCRETE QUANTUM ION, ATOM, MOLECULES, ETC, AT LEAST NOT ALL THAT WELL. FOR INSTANCE, THE CONCEPT OF A DIELECTRIC CONSTANT, OR ANY OTHER CONSTANT DESCRIBING A BULK PROPERTY IN E&M IS NOT AT ALL CONSTANT WHEN YOU GET ON THE SCALE OF THE THINGS PRESENTED IN THIS WORK. THIS IS BECAUSE ALL OF ELECTROSTATICS WAS INVENTED WELL BEFORE THE ADVENT OF THE ATOMIC FORCE MICROSCOPE. SAYING THAT IT IS WRONG IS THEREFORE MISSING THE POINT OF THE E&M COMPLETELY. IT DOES WHAT IT DOES, AND IT DOES IT QUITE WELL, IN FACT E&M IS SO GOOD AT DESCRIBING SO MANY THINGS, IT IS ONE OF THE MOST SUCCESSFUL WAYS OF FRAMING WHAT WE OBSERVE.”

    I don’t know enough about the topic to judge, but I thought his comments were interesting. Especially his annoyance at magazines like WIRED who interpret science like this without the proper background to understand it – using loaded headlines like “What you learned is WRONG!” to draw eyeballs and sell ads. And those of us who don’t know any better won’t complain, and get some wrong information to boot.

  2. Um….do scientists never do laundry or something? Because all the housewives in America knew that two pieces of the same stuff will stick together.

    Thanks for catching up guys! Please try cleaning out your own fridges every now and then. Maybe you’ll find new ecosystems or something.

  3. This is interesting, and news to a lot of people, but the people who study semiconductors and materials science already knew that surfaces are physically and electrically complicated. Of course, it’s cool that scanning kelvin probe microscopy lets you see it more directly (some papers report being able to measure individual dopant atoms in silicon).

    The things you learn in school are always incomplete. This doesn’t usually get conveyed by teachers, but it is universally true. If it weren’t, there would be no need for new research. It’s true in graduate level classes as well as 1st grade (though less so, of course).

    Take the flattest surface you can possibly create. It’s still not flat. There are atomic-height steps due to the crystallinity of the material, and to defects (like dislocations) in the crystal structure. In fact, it is nearly impossible to produce a defect-free crystal. Once you produce a surface, stuff lands on it. Dust particles from a few nanometers to tens of microns across will stick to anything, and are more than large enough to gather charge.

  4. So misleading, in fact, that scientists were fooled. Back in grade school, you probably learned that static electricity happened when you rub two different objects together (like a balloon and your hair).

    And reading this, it looks like in most cases that is still true, with the same mechanism that was envisioned. Is not knowing about a different effect the same as being fooled?

  5. Well I think something the article is trying to point out is what the really basic understanding of static electricity is vs. how we see it in the everyday world.

    Lightening was always explained as a static electrical activity. Which in a real basic term makes since, electrons are flowing from one place to another because of charge imbalance. Same thing goes for a static shock. Like when you rub your socks on carpet in the winter and get zapped by the door knob. Obviously electrons are flowing from one place to another.

    But you don’t see that same thing happen when you “charge” a balloon and stick it to a wall. The charge in/on the balloon does not move to the wall. There is no zap. I think what the paper is trying to convey is that there really has been little to no actual charge applied to the balloon. You are really just rearranging the charge clusters that already exist on the balloon surface, creating areas of more +/- charge.

    Next up Gravity! How the fuck does it work?!

  6. This is *one study* which suggests that some of what we learned in the past might be wrong. It’s hardly exhaustive, and certainly complicates the picture. Neither friction nor static charge have ever been well understood, and very few ever pursued serios answers. Most of what we “know” was inductively arrived at (based on inability to research) by generations of very experienced people. They might not have been all THAT wrong.

    Great that it’s being investigated, and that tools have arrived that will allow us – hopefully in the near future – to more fully understand these phenomena based in real research. The study raises a lot of great questions. BUT we shouldn’t just throw away what we’ve learned in the past, because much of it *might still hold up* as time goes by.

  7. So is it helpful/accurate to see static electricity, as it’s describe here, as something akin to Velcro? Just looking for another visual way of understanding this.

Comments are closed.