The Cassimir effect between uncharged metallic surfaces originate from quantum-mechanical zero-point fluctuations of the electromagnetic field. For two parallel plates at a distance of about 10 nm from each other, there is an attractive Casimir force per unit area (Casmir pressure) of about 1atm. Will this cause two nanoparticles fuse together if they are brought close enough?
Dear Tapan,
very Interesting question ... I think that is very unlike the force attributed to the Casimir Effect between two nanoparticles be intense to cause their collapse (assuming that they are floating in the vacuum). Although the distance between two nanoparticles may be of the order of a few nanometers such distance is not uniform over the shared area between the particles once their shapes are often irregular ... Thus, the boundary conditions favorable to reducing of the number of photons attributed to vacuum-fluctuations between particles are not created like in the case of two parallel plates. I do not know how to perform such calculations and I suppose that they are extremely difficult for two objects of irregular shapes ... But, is interesting to think about this!
@Walter: The experimental verification of the Casimir force was undertaken by using a sphere and a plate because it is extremely difficult to have closely spaced exactly parallel plates. Calculation of the Casimir force can be done for a plate and sphere. In fact it has also been calculated for closely placed nanoparticles. I shall give you the references one I am in my office on Monday.
Here are the references of two recent works:
Garcia-Sanchez et al., Phys. Rev. Lett. 109, 027202 (2012)
Roman-Valasquez et al., arXiv:quant-ph/0211176v2
The Van der Waals and London forces which apply at this scale are the short-range manifestations of the Casimir Effect. They are indeed applicable to nanoparticles and can result in them agglomerating. Fortunately, theses forces are not always attractive and by choosing a fluid with proper properties, the force can be repulsive. Interestingly, Casimir's work with Polder on the London force was the inspiration for his work on the effect which now bears his name.
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