Scientists created a model microscopic system to demonstrate the transmission of torque in the presence of thermal fluctuations, which is crucial for the creation of a nanoscale "clutch."
In vehicles, a clutch carries torque created by the engine to the chassis. This mechanism has been perfected for large vehicles, but creating the same effect on the nanoscale is more complicated, the University of Bristol reported. In these incredible small scales, different physics must be considered and thermal fluctuations play a much more important role in order to dissipate energy. In this new microscopic system, a ring of colloidal particles are localised in optical tweezers and translated onto a circular pathway, allowing for the transfer of a rotational motion to an assembly of identical colloids present in the interior region.
"This device looks a lot like a washing machine, but the dimensions are tiny. Through optical manipulation the particle ring can be squeezed at will, altering the coupling between the driven and loaded parts of the assembly and providing a clutch-like operation mode," said Paddy Royall of the University of Bristol.
Colloidal suspensions are considered to be "soft matter," and this softness opens the door for new "transmission phenomena" that has never before been observed in macroscopic machines.
"Exploiting the softness of nanomaterials gives us additional and unprecedented control mechanisms which may be employed when designing microscopic machines," Royall said.
Through these experiments and complex computer simulations, the researchers have pinpointed three different transmission regimes: a solid-like scenario that transmits torque in a similar fashion to a macroscopic gear; a liquid-like scenario in which most energy input is overtaken by friction; and an intermediate slipping scenario unique to soft materials that combines certain qualities of the two other scenarios.
"A basic understanding of the coupling process will give us insight into the construction of nanomachines, in which torque transfer is absolutely essential," concluded Professor Hartmut Loewen of the University of Düsseldorf.
The findings were published in a recent edition of the journal Nature Physics.
