Life at nanoscales
Nanoparticles might not behave how we expect them to
If you dive into a swimming pool, your momentum will keep you moving through the water for several metres. If you were nano-sized, however, the water would be like treacle – its viscosity would soon bring you to a gloopy halt.
Nanoscale objects show markedly different behaviour to large objects. For a nanoparticle in a swimming pool, inertia is negligible and viscosity dominates. The water molecules would also bombard the particle because of Brownian motion, throwing it around like an aeroplane in constant turbulence.
At nanoscales, the forces that hold surfaces together become very strong. For a ‘nanobot’, this could be a bad thing – it would tend to stick to the ﬁrst surface it met. For geckos, it’s extremely useful: nano-forces created by the extremely ﬁne hair on their feet allow them to walk on ceilings and even to hang upside down from ﬂat sheets of glass.
Another difference is that the ratio of surface area to volume increases (in a 30 nm particle, 5 per cent of the atoms are on its surface; in a 3 nm particle, half are). The atoms on the surface tend to be more available to react than those at the centre, so nanoparticle-based materials can be highly reactive (good for catalysis) or have unusual properties (nano-gold melts at much lower temperatures than the solid metal). At nanoscales, the behaviour of individual atoms and electrons becomes important, and interesting quantum effects come into play. These fundamentally alter the optical, electrical and magnetic behaviour of materials.Lead image:
Tambako The Jaguar/Flickr CC BY NC ND