Friday Seminar - Nanomechanics and the Casimir force

We just had a rather cool seminar about the Casimir force and how it affects Nanoscale electrical and mechanic (NEMS) systems. The talk was given by Ramin Golestanian from Sheffield University.The Casimir force is usually described as the attractive force that arises between two metallic plates in a vacuum due to the quantization of the vacuum fluctuations between the two plates (virtual photons). The somewhat handwavey way I think of this is that the boundary conditions of the two plates only allow certain wavelengths or energies of photons between them, whereas outside the plates you are not constrained in this way. So you have more stuff 'pushing' on the outside that on the inside :)

Interestingly I was told that the Van der Waal's attraction between molecules (Lennard-Jones potential) is a solution of the same master equation as that which predicts the Casimir Force, just with different boundary/limiting conditions. Which I did not know - but is pretty obvious when you think about it. Maybe I just never had :)

The Casimir force is quite small, (of the order of pN), however, with modern micro and nano-engineering technologies, it is possible to make tiny gears, levers and other moving components on the scale that the force actually starts to become rather dominant in the system, moreso than electrostatic interactions, for example.

Here's a picture of a micro-mechanical device from Sandia labs

Not quite small enough yet to harness the Casimir force, but the technologies for producing these things are advancing all the time.

Anyway, the seminar focused on some theoretical and computational modelling work done on nanoscale rack and pinion mechanisms.

The Casimir effect can be a pain if it causes parts of your nano-system to unwantedly 'stick' together, however it can also be used to eliminate the need for contact between, say, the rack and pinion, and thus reducing wear. The teeth on the two parts are attracted to one another and can couple the motion from the rack to the pinion. With a Casimir-type coupling instead of a mechanical contact, the pinion can also be made to go at different velocity to the rack, or even backwards, under specific conditions, which is difficult to imagine in the case where the two elements are in physical contact. The system is highly non-linear and chaotic, demonstrating bistability and even amplification under some circumstances.It was all very interesting, I love these tiny NEMS and MEMS machines.