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Discovery of repulsive Casimir forces might eliminate friction as a concern in nanotechnology

For years the existence of attractive quantum mechanical forces (Casimir forces) between some rigid surfaces separated by only fractions of a nanometer has been raised as potential source of damaging friction between surfaces in nanomachinery (See this post from three months ago). A newly discovered repulsive quantum mechanical force could be useful for nanotech applications by enabling a type of quantum levitation. From Harvard University, via AAAS EurekAlert “Researchers measure elusive repulsive force from quantum fluctuations“:

Researchers from Harvard University and the National Institutes of Health (NIH) have measured, for the first time, a repulsive quantum mechanical force that could be harnessed and tailored for a wide range of new nanotechnology applications.

The study, led by Federico Capasso, … builds on previous work related to what is called the Casimir force. While long considered only of theoretical interest, physicists discovered that this attractive force, caused by quantum fluctuations of the energy associated with Heisenberg’s uncertainty principle, becomes significant when the space between two metallic surfaces, such as two mirrors facing one another, measures less than about 100 nanometers.

“When two surfaces of the same material, such as gold, are separated by vacuum, air, or a fluid, the resulting force is always attractive,” explained Capasso.

Remarkably, but in keeping with quantum theory, when the scientists replaced one of the two metallic surfaces immersed in a fluid with one made of silica, the force between them switched from attractive to repulsive. As a result, for the first time, Capasso and his colleagues measured what they have deemed a repulsive Casimir.

To measure the repulsive force, the team immersed a gold coated microsphere attached to a mechanical cantilever in a liquid (bromobenzene) and measured its deflection as the distance from a nearby silica plate was varied.

“Repulsive Casimir forces are of great interest since they can be used in new ultra-sensitive force and torque sensors to levitate an object immersed in a fluid at nanometric distances above a surface. Further, these objects are free to rotate or translate relative to each other with minimal static friction because their surfaces never come into direct contact,” said Capasso.

By contrast, attractive Casimir forces can limit the ultimate miniaturization of small-scale devices known as Micro Electromechanical Systems (MEMS), a technology widely used to trigger the release of airbags in cars, as the attractive forces may push together moving parts and render them inoperable, an effect known as stiction.

Potential applications of the team’s finding include the development of nanoscale-bearings based on quantum levitation suitable for situations when ultra-low static friction among micro- or nano-fabricated mechanical parts is necessary. Specifically, the researchers envision new types of nanoscale compasses, accelerometers, and gyroscopes.

The research was published in Nature (abstract)
—Jim

2 Responses to “Discovery of repulsive Casimir forces might eliminate friction as a concern in nanotechnology”

  1. Says:

    I am Mark J. Fiore,Harvard 1982, Boston College Law School, 1987.I’m a substitute teacher here in San Francisco. I enjoy reading about cosmology, astrophysics, and nanotechnology.Current book:The Goldilocks Enigma, by Paul Davies.
    Nanotech comment is as follows.I have done a little research on the net, as an amateur, and have come across more and more stories on the subject of using the principles of quantum mechanics to aid in the production and use of nanotech devices.More and more, I am coming to the conclusin that almost all advances in nanotech over the next ten years must, of necessity, take into consideration quantum mechanics . In particular, the theory of “spooky action at a distance” more commonly referred to as nonlocal quantum effects, will be used in the area of quantum computing.Also,the sum of all paths, as exemplified by the electon field cloud, where the electron orbits in all possible three dimensional orbits around the nucleus, will also be critical in nanotech advances.Finally, if the many worlds theory is correct, and the LHC ,in 2010, finds evidence of the Higgs boson, and the LHC also measures gravity as it bleeds into the extradimensional space around us(according to string theory and brane theory), then quantum theory as it relates to string theory will become of the utmost concern to the nanotech world. If, as string theory, and the many worlds, or sum of all paths, theories, state, that, indeed, there are 10 to the 500th possible Universes, while, for comparison, there are only 10 to the 80th particles in the visible, baryonic Universe, then, by implication, quantum computing at a nanotech level could make use of almost infinite storage capacity at extremely small scale. Insted of fighting quantum effects as adversaries, as one goes lower and lower in scale, one could harnes these effects.I believe ,in 2010, the LHC will have profound implications for string theory, quantum computing, and nanotech in general.

  2. Says:

    Casimir effect forces drop off with distance as 1 over R squared – exactly the same as electric forces or gravity. In fact, Andrei Sakharov proposed a theory that gravity *IS* a Casimir effect force and hence is fundamentally electrical, which, if true, would render the “grand unification” of gravity with electromagnetism a rather trivial endeavor since they would already be the same thing.

    At any rate, there is no magic distance at which Casimir forces suddenly become significant, and certainly not 100 nm, With sufficiently large bodies, there could be measurable effects from light-years away.

    The Casimir force in a vacuum is ALWAYS attractive, so it may be questionable to even label the repulsive forces in bromobenzene as Casimir forces. The repulsion measured may well be real, but that doesn’t prove that the explanation of it is correct.

    Howard A. Landman

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