Nanocars comprising fullerene spherical wheels on hydrocarbon axles are shown to move on substrates by electrostatic forces from charges produced by quantum electrodynamics (QED)
Nanocars evolved from research that began over a decade ago. At the IBM Zurich Research Laboratory, synthetic molecules (S-molecules) on a metal substrate were moved in a controlled and repeatable manner by pushing them with the tip of a scanning tunneling microscope (STM). See http://domino.watson.ibm.com/comm/wwwr_thinkresearch.nsf … .
The S-molecules included an organic molecule called porphyrin comprising a ring of atoms about 1.5 nanometers in diameter with a metal atom at its center. Groups of hydrocarbons were added to the porphyrin to provide four leg supports. The function of the legs was thought to allow the S-molecule to grip the surface to stabilize random thermal motion. Friction between the legs and the substrate could not have been significant because upon nudging with the STM tip the S-molecules appeared as though they were on rollers.
Quantum Mechanics Explanation
The S-molecule motion may be explained by quantum mechanics (QM). The Einstein-Hopf relationship for the QM harmonic oscillator shows the thermal kT energy of an atom at ambient temperature resides in the far infrared (FIR) beyond 50 microns. Here, k is Boltzmann’s constant and T is absolute temperature. But the S-molecule by its size excludes all thermal radiation beyond a few nanometers, and therefore lacks the heat capacity to conserve the FIR heat absorbed from the contact of the legs with the substrate by an increase in temperature. Upon contact of the legs with the substrate, the S-molecule becomes a part of a macroscopic body that by QM is allowed to have kT energy. But in moving, the S-molecule breaks contact to be momentarily isolated from the substrate, and therefore has excess kT energy above the vanishing small amount allowed by QM.
Lacking heat capacity, the S-molecule cannot conserve the excess kT energy by an increase in temperature. Conservation therefore may only proceed by the QED induced frequency up-conversion of the excess kT energy in the FIR to the electromagnetic (EM) confinement frequency of the S-molecule, which at ultraviolet (UV) levels and beyond has the Planck energy to charge the S-molecule by the photoelectric effect.
The QED induced charge only produces momentary electrostatic interactions. Nevertheless, the S-molecule is held to the substrate by momentary electrostatic attraction instead of by gripping as initially thought. Lateral motion depends on the momentary electrostatic interaction with its neighbors. In a random arrangement of S-molecules, the electrostatic interactions are not symmetric and on that basis alone may initiate motion. Moreover, lateral motion over the substrate occurs by intermittent stick-slip, but small friction at contacts makes it appear as though the S-molecule is on rollers. Regardless, contact neutralizes the charge on the S-molecule and allows the kT energy to be reacquired from the substrate to allow subsequent breaking of contact to produce QED charge. During stick-slip motion, the intermittent QED induced charge occurs very rapidly and may be difficult to detect.
Today, nanocars moving on substrates are more complex than the S-molecules, but the QED charging is the same. Currently, many research groups are engaged in nanocar research typified by Rice University. See http://news.cnet.com/Here-come-the-nanocars/2100-11395_3 ….
In QED charging, nanocars like S-molecules are powered by converting EM energy into mechanical motion. The EM energy may take various forms of heating including light, thermal, Joule, and electron beams. Indeed, nanocars have been shown to move by simply heating the substrate, the form of heat being the same thermal kT energy driving the earlier S-molecules. In effect, nanocars act as FIR to higher frequency up-conversion devices that charge the nanocars by producing momentary electrostatic repulsive forces that produce the observed nanocar motions. Similar arguments allow QED charges to explain the motions of molecular motors under Joule and electron beam heating. See http://www.nanoqed.org at “Nanocars by Quantum Mechanics”, 2010.
Unfortunately, the QED charging by which thermal kT energy is converted into powering the nanocar is not included in a conventional MD solution that implicitly assumes atoms have kT energy at the nanoscale. Valid MD simulations in heat transfer need to specify vanishing kT energy in the MD computational algorithms, and if so included would give isothermal temperature solutions. The invalidity of MD in heat transfer at the nanoscale is widespread, e.g., in tribology, see http://www.scienceblog.com/cms/blog/8209-quantum-mechanics-questions-molecular-dynamics-submicron-structures-25639.html ; whereas, in nanocars, see http://pubs.acs.org/doi/full/10.1021/ct7002594
MD is not needed for heat transfer at the nanoscale because temperature solutions are, a priori known to be isothermal. However, QED induced charging in nanostructures can and should be included in MD simulations of dynamic response, at least within the restrictions of Newton’s equations.
1. Nanostructures including S-molecules, nanocars, CNT motors and the like act as frequency up-conversion devices that are charged from QED radiation by the photoelectric effect, thereby allowing pair-wise interactions by momentary electrostatic repulsion.
2. MD simulations of heat transfer in nanocars are precluded by QM. At ambient temperature, the thermal heat capacity resides in the FIR beyond 50 microns, and therefore nanocars by their size exclude the heat capacity necessary for heat transfer. MD simulations of heat transfer in nanostructures are simply meaningless.
3. Unlike heat transfer, MD simulations are valid if directed to deriving the dynamic response of nanostructures on substrates under momentary QED induced charges.