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being sensory organs for spiders to helping adhesion for geckos The setae on the feet of these creatures are made of keratin, a structural protein, and end in smaller structures—spatulae The spatulae on the bottom of geckos’ feet interact with the surface through van der Waals forces Van der Waal forces are intermolecular attractions
Objectives: To understand how weak van der Waals force can lead to enormous, reversible adhesion Readings: K Autumn, American Scientist, 94 124 2006 and Tian, et al PNAS 2006 103, 51, 19320 Multimedia : K Autumn, Discovery Channel movie COLLOIDS AND INTERPARTICLE FORCES -Definitions; Colloids, colloidal dispersion, colloidal inks
the secrets of how geckos use millions of tiny foot-hairs to adhere to even molecularly smooth surfaces We tested the two currently competing hypotheses (2, 3) of adhesion mechanisms in gecko setae: (i) thin-film capillary forces (or other mechanisms relying on hydrophilicity) and (ii) van der Waals forces First, we tested
(2002) showing how the van der Waals force (London dispersion force) explains the stickiness of the gecko setae The data of the experiments together are shown in Fig 1c, d Also shown in Fig 1 is the predicted outcome of the experiment based on either a capillary force or a van der Walls force model for the stickiness of the gecko
A single spatula attaches to the surface by Van der Waals forces The Van der Waals interaction between the individual spatulae and the surface of the substrate are the reason that gecko adhesion is material independent The Van der Waals force is the sum of attractive or repulsive forces between molecules other than those due to covalent bonds