Interfacial energy and strength of multiwalled-carbon-nanotube-based dry adhesive

Vertically aligned multiwalled carbon nanotube (MWCNT) arrays can mimic the hairs on a gecko's foot and act as a dry adhesive. We demonstrate the van der Waals interactions originated dry adhesion between MWCNT array surfaces and various target surfaces over millimeter-sized contact areas. The adhesive strengths were measured over 10 N/cm(2) in the normal direction and about 8 N/cm2 in the shear direction with glass surface: The adhesion strength over repeated cycles is limited by the relatively poor adhesion of MWCNTs to their growth substrate, which was improved significantly by adding molybdenum to the catalyst underlayer. We also measured the interfacial work of adhesion as a fundamental adhesion property at the interface. Our measured values of a few tens of mJ/m, which falls in the range of typical van der Waals interactions energies, provide a direct proof of the van der Waals dry adhesion mechanism. Furthermore, in contrast to other dry adhesives, we show that MWCNT adhesives are electrically and thermally conducting, which makes them a unique interfacial material. (c) 2006 American Vacuum Society.