In view of the recent advancements of electromechanical systems, the ubiquitous rotary device has experienced an evolution from micro to nanoscale; the art of miniaturization. This evolution from micro-electro-mechanical systems to nano-electromechanical systems is particularly important owing to its capability of making scientific revolutions in a number of fields such as nanorobotics, nanofluidics, and bio-nano-electromechanical systems. The micro-electromechanical systems have been developed based on conventional micromachining and photolithography technologies that necessitate an avalanche of fabrication steps and finally lead to low yield and short-life devices. Hence, it is challenging to implement these fabrication methods in the preparation of even smaller nano-electromechanical systems. Therefore, it is necessary to investigate new design methods in a bid to realize nano-scale devices, for instance, nanomotors. Numerous research works have been advanced for a class of nanomotors relying on rotary motion of nanoparticles or even nanostructures. Many researchers have focused on rotational nanomotors fabricated by different ways, such as optical, chemical, electrical and thermal means. Unfortunately, among the schemes reported, only a few have addressed nanomotors systems driven by electrical energy.
A team of researchers under the guidance of Dr. Md. Kawsar Alam at Bangladesh University of Engineering and Technology demonstrated that owing to electric field induced water dipole orientations, a nonpolar carbon nanotube in water could track a rotating field for suitable angular speed and magnitude. They designed a rotational nanomotor structure that utilizes this principle to drive nanoscale loads. Finally, they analyzed its capability to rotate molecular-scale blades and nanogear-based complex structures. Their research work is published in the peer-reviewed journal, Small.
The authors applied molecular dynamics simulations to show that carbon nanotubes suspended in water while subjected to a rotating electric field of appropriate magnitude as well as angular velocity could be rotated with the help of water dipole interactions. In view of this principle, the authors were able to come up with a rotational nanomotor structure, and analyzed its rotational characteristics. The fast responsiveness of electric field induced orientation of carbon nanotubes in water enabled the nanomotor to be operated at an ultrahigh speed of ~ 1011 r.p.m. Whenever a nanoparticle is immersed in water under the presence of an electric field, two effects come into play. First, the water dipoles tend to orient themselves with the surface of the CNT. Second, they also try to align towards the electric field just like every other dipolar fluid. As a result, the water molecules ‘push’ the CNT to orient its axis towards the direction of the electric field. Hence, in the presence of a rotating electric field, the nanomotor starts to rotate. To understand the role of water dipoles, the authors calculated the dipole moment of water molecules in the operation of their nanomotor. As opposed to previously reported electrical energy driven nanomotors, the proposed scheme also had a rotating shaft to connect a load, which was a unique feature.
In this regard, the first author of the manuscript, Mr. Rahman says, “Unlike many other previously reported nanomotors, our nanomotor is expected to require much simpler fabrication steps, and has a longer lifetime because of its unique design.”
In addition, the authors found that the force exerted by the motor was sufficient to rotate molecular-scale blades, such as pyrene molecules, attached to it. Moreover, the capacity of the proposed motor to rotate nanogear-based complex structures and its capability in rotating a load at an accurate angle was also investigated. Load rotation with a controlled angle exhibited the potential of implementing the nanomotor scheme as a nanorobotics arm. The results of their study will be of great interest for nano-electro-mechanical systems, microfluidics, bio-nano-electro-mechanical systems and nanofluidics architectures.
Md. Mushfqur Rahman, Mokter Mahmud Chowdhury, and Md. Kawsar Alam. Rotating-Electric-Field-Induced Carbon-Nanotube-Based Nanomotor in Water: A Molecular Dynamics Study. Small 2017, 13, 1603978Go To Small