Gecko Science (Part 3) — Physics to the Rescue?Last time we talked about the mind-boggling fac

Gecko Science (Part 3) — Physics to the Rescue?Last time we talked about the mind-boggling facts of gecko stickiness (if you’ve missed it take a minute to catch up here: http://bit.ly/1RxD3vv).Now let’s get to what this “stickiness” really is.It turns out that to get wiser we need to take a leap into the atomic realm. It was discovered as early as 1932 that certain insects are able to adhere to surfaces by making use of a small layer of water, which works by exploiting the cohesive property of the polar H20 molecules: Inside a polar molecule like water electrons aren’t shared equally among atoms and atoms aren’t arranged perfectly symmetrically, creating ends that are more negative and ends that are more positive. This means that a polar molecule interacts strongly with itself (hence the high boiling point of water) but it also means that a neutral molecule that finds itself in the vicinity (let’s say the molecule of an insect leg) will experience a temporary polarization as their electrons get distorted, resulting in a mutual attraction.A number of frogs have been found to make use of this effect, as well as the occasional mammal (like the Australian Feathertail Glider). In plants, the carrying up of water through the xylem functions through the same mechanism.Be that as brilliant as it may, unless your habitat is naturally humid or you can secrete your own water, this adhesion is not always going to be available to you. There are, after all, dry desert geckos that stick very nicely all the same — so this cannot be all there is to the story.We’ve mentioned two molecular attractions already: the attraction between polar molecules, like in water, (called the Keesom force) and the interaction between polar and non-polar molecules (called the Deybe force). What about interactions between two non-polar molecules? Surely liquids that are non-polar don’t just fall apart — there must be a force keeping even the most un-interactive molecules together, right?There is. It’s called the London dispersion force and together the three make up the infamous van der Waals forces. Many textbooks consider the dispersion force to be the weakest of the set but this isn’t entirely fair: more often than not do many liquids (polar and non-polar alike) owe their intermolecular strength to these dispersion forces more so than to the other two combined.How does the dispersion force work?Quantum mechanics.In a nutshell: Due to the only vaguely determinable location of a particle like an electron, it’s not an unlikely event that at any one moment one side of an atom might count a slightly higher electron density than another side, becoming an infinitesimal bit more negative and giving the atom as a whole a very short but noticeable polarity. Then, when this polarity is picked up upon by a neighbouring atom or molecule we suddenly we have two temporarily polarized atoms and voilà.If you could stick by using only these forces then you could stick to pretty much any surface you’d like. All you’d need is a large surface area and to get really, really close — and that’s exactly what geckos have managed to do.How can we be sure? Well, the more loosely an atom holds on to its electrons, the more the electrons can “dance around” and the stronger the dispersion forces will be. So if we could construct some kind of material that is non-polar to start with and holds on so tightly to its electrons that polarization is next to impossible, then it seems that we could finally beat these clever creatures.As it turns out we already have done precisely that, except instead of using it to prank reptiles we’re using it to keep our fried eggs from sticking to our pans. It’s called Teflon, and you can rest assured, geckos find it impossible to get a grip!-DSPicture Credit: Bjørn Christian Tørrissen (Wikipedia: http://bit.ly/1T5UcSd)References:Main paper (Oxford Journals): http://bit.ly/22EkBJvhttp://stanford.io/1nPcNVMhttp://bit.ly/1RjaEfAhttp://bit.ly/11NXHWshttp://bit.ly/22EkKwGOn molecular forces and polarization:http://bit.ly/22vdTJ8http://bit.ly/1MBpLga -- source link

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