The talented gecko can walk up a glass wall or hang from the ceiling by only one toe. The little lizard owes its gravity-defying powers to carpets of microscopic hairs, called setae, covering its feet. These hairs, when in close contact with a surface, induce intermolecular attractive forces called van der Waals forces between themselves and the surface (SN: 7/15/00, p. 47: Available to subscribers at Gecko toes tap intermolecular bonds).
Materials scientists have now created synthetic gecko foot hairs that stick to surfaces 200 times as strongly as the setae do. To make this superstrong adhesive, Ali Dhinojwala of the University of Akron in Ohio and his colleagues grew a forest of carbon nanotubes on glass. Next, they poured a liquid chemical onto the glass. The chemical solidified into a polymer matrix around the base of the tubes. The team then peeled the resulting polymer-nanotube “rug” off the glass.
Using an atomic-force microscope, Dhinojwala and his colleagues measured just how powerfully adhesive their synthetic invention was, compared with gecko setae. They report the result in the July Chemical Communications.
Previous efforts to imitate gecko feet used tiny rods made from polyimide, a plastic (SN: 6/07/03, p. 356: Caught on Tape: Gecko-inspired adhesive is superstrong). Unfortunately, says Dhinojwala, the plastic rods “are not mechanically strong, and they try to clump together.” He attributes the carbon nanotubes’ extraordinary adhesion to both van der Waals forces and to their strength and flexibility under strain.
Carbon-nanotube carpets could eventually serve as dry adhesives in applications where moisture would be a problem, such as in electronics, Dhinojwala says.