This is a hot topic-was the subject of a prestigious article in the June 8 issue of nature (www.nature.com). People are looking into geckos to try to figure out adhesion (no less than Pierre Gilles DeGennes-Nobel prize winner-is trying to tackle adhesion)Turns out that the gecko has split ends on their feet which help.
Personally, I like the fact that geckos and tree frogs can both scale the aquarium, but for different reasons (tree frogs can have the capillary forces from wet big toes)
So chemists like me try to duplicate nature-I guess that is the natural order of things.
Please note that the moderator of this forum has asked posters to include a link to the article which they are discussing. ** REMINDER: PLEASE CITE LINK **
I don’t know if the Nature article can be found at their web site, but a summary of the findings (along with some colourful photographs) can be found at the Scientific American site.
I thought it had to do with the micro-fiber/filaments on the geckos feet that created a static charge? I suppose the idea of a micro-vacuum is as plausible, but the static thing is what I had heard.
If our body weight precludes us from climbing walls like a gecko, why do our fingers share the same properties of “stickiness” that their feet do? What purpose does this serve in humans?
Uhm, it does enable us to climb trees and pick up things. Imagine trying to hold a club (or a screwdriver) or food if your hands had little or no friction. Get your hand all soapy and slick, then try to shave.
Just a point of clarification… Our fingers do not stick to glass slides using the same forces as geckos. Geckos are able to use Van der Waals forces b/c their toes are coated with very tiny ‘hairs’ that are able to make intimate contact with the surface molecules of wherever they happen to be. In contrast, at the same scale the tips of our fingers look the newborn Rockies- we simply can’t get our skin molecules close enough (it has nothing to do with weight). Glass slides, bits of paper, whatever are able to cling to our fingers due to the surface action of the natural oils/grime coating our skin.
Gonz wrote: “Just a point of clarification… Our fingers do not stick to glass slides using the same forces as geckos.”
Yes, they do, it’s just that Van der Waals are not the ONLY forces at work. I didn’t say the ONLY force, any more than you said that there is ZERO actual contact between your fingertip and the glass. Neither extreme is correct. Look at it this way: if the only thing holding geckoes up was Van der Waals forces, how could they cling to anything OTHER than glass? If there was no contact of your fingers to the glass, how could you generate any friction at all?
Everything is a combination of different forces, forgive me for trying to cut corners and give simple explanations when I can’t quantify exactly how much adhesion is based on one type of force versus another.
OK one more time…I admit that forces other than pure Van der Waals may be used when Geckos adhere to rough surfaces, but they are the primary means of adhesion. Geckos create neither a vacuum or adhesive film in order to cling, so I suppose that the filaments cold provide simple friction. However, the filaments provide the nanoscale contact with any surface – glass or not (btw at the size scale we’re discussing, glass does not appear smooth).
The same forces cannot operate in our finger. Van der Waals forces only operate over incredibly small distances (angstroms)- distances MUCH shorter than that achieved by the skin/glass connection. In fact if you can consider molecular/atomic forces to operate at all at that distance, they would most probably be weak repulsive. The same forces I’m sure many of you are currently experiencing.
On a cool side note- although the scientists figured out how the geckos stuck, they can only offer theories on how they get ‘unstuck.’