A new discovery shows how to reverse the attractive force of two objects in close contact. The Casimir force makes tiny moving parts in nanoscale and micromechanical devices stick together and grind to a halt. This is a long-standing problem that scientists working on such devices have struggled to overcome.
The Casimir force was first explained in 1948 by the Dutch physicist Hendrick Casimir. It is a consequence of quantum physics at solid surfaces. It gets very strong when two surfaces are close together and it normally attracts them to each other.
Recent work explains how to reverse the direction of the Casimir force, using specially designed chiral metamaterials, so surfaces repel each other. A metamaterial is an artificially structured material designed to manipulate the electromagnetic spectrum in ways materials in nature cannot. A chiral metamaterial has spiral structures and lacks mirror symmetry, which is a common feature among the materials currently used to make micromechanical devices. Mirror images of the structure cannot be superimposed atop each other in the same way a human hand cannot fit perfectly atop a reverse image of itself. Strong chirality is the key to reversing the attractive force and even potentially levitating nanoscale objects.
Researchers are working on the structural design and fabrication of these new metamaterials. If successful, micromechanical and nanomechanical devices unencumbered by friction will finally be possible.
- R. Zhao, J. Zhou, Th. Koschny, E. N. Economou, and C. M. Soukoulis. "Repulsive Casimir Force in Chiral Metamaterials" Phys. Rev. Lett. 103, 103602 (2009)