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Asked by theo to Adam, Chris, Eleanor, Jessamyn, Sinead on 11 Nov 2013.
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Christian Wirtz answered on 11 Nov 2013:
Hi Theo,
things behave differently because of a few really neat effects.
One of the major ones is surface to volume ratio. If you take a single atom to be your material, you can most certainly say it it on the surface. Even if you make a cube of 8 atoms (2x2x2), they are still all at the surface. Only when you make a cube of 27 atoms (3x3x3) will you have one in the centre that’s only surrounded by atoms and the rest are at least partially at the surface. That’s still a surface-to-volume ratio of 26/27. As you make the structure bigger more and more atoms are in the centre, the so-called bulk of the material. By the time you get to our normal, big materials, almost all atoms are surrounded and only very few are on the surface. The properties of this materials (say your desk) are then determined by the atoms in the bulk, not the ones on the surface. On the nanoscale, the surface, where atoms are un-reacted and structurally possibly unstable, dominates the properties, making materials more reactive to environmental influences (and hence they are great sensors)!
Another example is electric conductivity. On very small length scales, say less than 1 nanometre, electrons, which carry most electric current, can “tunnel”, that is to say, they more or less teleport from one place to the next instantly. If you have a cable that is a metre long, you will never see this effect and cannot make use of it, but if you work on materials that are only 1 nanometre in size, you can use this for some really cool effects!
Hope that helps, there are many more things that change but I’d just be copying textbook chapters here!
Chris
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Eleanor Holmes answered on 11 Nov 2013:
Many reasons. Chris has already explained two of them very well.
Another reason has to do with scaling. The properties of an object are related to each other in many ways. Physicists explore these relationships and write them as equations. For example: Newton’s famous law that Force = Mass x Acceleration.
BUT! Most of these properties scale with size. So as you get down to the nano-scale any property that scales proportional to L (length) will get very small, while any property that scales as 1/L will get very big. This means that as you shrink things down some of their properties go a bit bananas. And you have to watch out for weird compatibility issues. Like two parts of an electrical circuit might not work together anymore if you were to suddenly shrink all the components down to nanocomponents.
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