This is one of my favorite topics! - as they say "small is different" - This was known for quantum systems for about ~100 years but the laws of thermodynamics also defy macroscopic intuition when applied to nanoscale objects.
This article gives a great example.
For another example, the second law of thermodynamics which states the the entropy of an isolated system must increase is only true on average. It is possible for systems of very small size to display temporary fluctuations where the entropy of a system and it's heat bath both decrease.
This is like your car inhaling CO2 from the exhaust, running backwards, and combining the CO2 to give oxygen and gasoline which is pumped into the fuel tank.
This process has real implications for how the cell works. Biological organisms are full of microscopic motors that do all kinds of mechanical work - like transporting molecules against concentration gradients, viruses packing RNA into their protein capsids etc.. These motors are all very strange in that they only work forward on average.
Another phenomena which is very different at the nanoscale is melting and phase transitions. Everyone is familiar with the fact that sodium metal melts at a sharply defined temperature. But it turns out that this "melting" temperature is only sharp for macroscopic sized samples of sodium metal. For sodium clusters (sodium crystals with only a few hundred atoms) the melting temperature is blurred over a large range of temperatures.
Yeah I like Sethna a lot but he is a theorist - the experiment was done for Na clusters by a guy named Haberland. It was published in Science a few years ago.
[edit]
Sorry I mean nature:
M. Schmidt, R. Kusche, B. v. Issendorff und H. Haberland,
Irregular variations in the melting point of size-selected atomic clusters,
Nature, 393, 238-240 (1998).
"the most important mechanical tolerances in atomically precise fabrication are (with a caveat or two) proportional to the lattice constant (unit cell size) of the material in question"
This article gives a great example.
For another example, the second law of thermodynamics which states the the entropy of an isolated system must increase is only true on average. It is possible for systems of very small size to display temporary fluctuations where the entropy of a system and it's heat bath both decrease.
This is like your car inhaling CO2 from the exhaust, running backwards, and combining the CO2 to give oxygen and gasoline which is pumped into the fuel tank.
http://en.wikipedia.org/wiki/Fluctuation_theorem
This process has real implications for how the cell works. Biological organisms are full of microscopic motors that do all kinds of mechanical work - like transporting molecules against concentration gradients, viruses packing RNA into their protein capsids etc.. These motors are all very strange in that they only work forward on average.
Another phenomena which is very different at the nanoscale is melting and phase transitions. Everyone is familiar with the fact that sodium metal melts at a sharply defined temperature. But it turns out that this "melting" temperature is only sharp for macroscopic sized samples of sodium metal. For sodium clusters (sodium crystals with only a few hundred atoms) the melting temperature is blurred over a large range of temperatures.
See for instance..
http://www.lassp.cornell.edu/sethna/CrystalShapes/CopperClus...