Geckos, it would seem, can just about stick to anything.
Well, researchers at the University of Akron decided to see what kind of surfaces geckos can cling to, and Teflon, or Polytetrafluoroethylene PTFE as engineers prefer to call it, was one of their tests. Their answer was surprising: geckos cannot cling to dry PTFE (wet PTFE is another matter altogether). Some people say that PTFE is the only dry surface that a gecko cannot cling to but why?
Geckos are able to cling to so many slick surfaces through the action of van der Waals forces combined with thousands of tiny hair-like structures on the bottom of their feet. Van der Waals forces are actually molecular attractions that operate over extremely small distances. They occur because of fluctuations in charge distributions between neighboring molecules. The thousands of tiny foot hairs on a gecko end in even more microscopic hair-like structures. These structures are tiny enough and in abundance enough make normally insignificant van der Waals forces their superpower: they can cling to almost frictionless surfaces with ease through molecular attraction.
Now for a new fact: did you know PTFE was engineering specifically to resist adhesion by van der Waals forces? PTFE is composed of carbon and fluorine atoms. Of all the elements known to date, fluorine has the highest electronegativity. This causes PTFE to repel other atoms that come near it. More specifically, it works against van der Waals forces. Furthermore, the molecular structure of Teflon is such that the fluorine atoms surround the carbon atoms. It repels any atoms that try to come near the carbon atoms, giving PTFE its outstanding chemical inertness.
So, it would seem that the very mechanisms that prevent geckos from walking up dry PTFE provide its most attractive characteristics: extremely low friction and high chemical resistivity. So, when you are looking for a low-friction option for a bearing or seal, dont forget the bane of a geckos life: PTFE.
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