Monday, August 09, 2010
Smart Materials and Structures Journal has a nice review article on "dry adhesives" - the microstructured surfaces that show unusual adhesive properties. These are synethic copies of natural structures such as are most commonly assigned to geckos, but also exist with other animals .
As with many, oh heck, most adhesives, van der Waals interactions are extremely important. But another aspect often overlooked initially when studying these feet is that the materials are also self-cleaning, or at least, they still work even when exposed to "dirt". The dirt moves to the spaces between the posts/pillars/setae (pick your favorite term) and is out of the way. 
The current state of the art is summarized in the article and it is open access (with registration) for the first 30 days, so if you are interested, grab the article while you have a chance.
 You see the same type of name-calling with superhydrophobic surfaces being assigned to the lotus plant even though many other plants show similar behavior. I see it in the lady's mantle growing in my wife's gardens - Minnesota is just a tad too cold for lotus plants.
 This same dirt absorbing mechanism is a big part for the success of Post-It notes - they can be used and reused many times before showing a significant loss of adhesion - try that with masking tape or some other tape, especially on a lightly soiled surface. Post-It adhesive is not just any old weak adhesive, but a specially structured adhesive.
Image provided by Bjørn Christian Tørrissen