Materials
Innovations
NEW MATERIAL
One-sided velcro for
real life Spidermen
Velcro is often cited as an example of a 'biomimetic' material, ie one which
takes inspiration from nature by conscious mimicking of biological systems.
A new biomimetic technology developed at the University of Manchester can
be thought of as one-sided Velcro, inspired by the ability of lizards such as
geckos to run across smooth ceilings.
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Gecko has sticking power to support up to 400 times its own weight
Natural adhesive on its feet is clean and reusable
Works on all surfaces – wet or dry
Exploits physical phenomenon – van der Waals forces
How does it work?
• Soles of gecko’s feet have a billion tiny hairs clumped on top of a million
small protruberances
• Hairs get into intimate contact with every microscopic feature of a surface
• As a result, a very large number of their constituent atoms get close enough
to experience significant attraction
One-sided velcro – ‘gecko tape’
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Plastic (polyimide) sheet with surface resembling gecko’s feet
Produced using electron beam lithography and dry etching in oxygen plasma
Surface has protrusions only two thousands of millimetre long
Attaching sheet to an object then allows object to be attached to any surface
Future developments:
• Synthetic material hydrophilic (water-loving),
while gecko’s protruberances are
hydrophobic (water-repellent)
• Surface tension effects between gecko’s
protruberances and film of water
covering most surfaces are important in
promoting full adhesion
• Development of practical tape product with
long service life will require switch to
hydrophobic polymer
Van der Waals Forces: Atoms or molecules that do not have a net electrical
charge or inherent magnetism do not attract one another very strongly. However,
even atoms with no overall electrical charge may, at any given moment, display a
small negative charge on one side and a corresponding small positive charge on
the other. This is due to the cloud of negatively charged electrons which surround
the positively charged nucleus temporarily becoming unevenly distributed. The
charge imbalance in one atom sets off a temporary charge imbalance in nearby
atoms, causing an attraction between them known as van der Waals force.
Although generally very weak, these forces can have significant magnitude over
very short distances. At a microscopic level, most surfaces are very uneven, and it
is only the higher protrusions that come into contact between two surfaces.
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