Molecular dynamics simulations suggest that the pumping rates of nanoscale molecular propellers vary depending on the properties of their blades
Molecular dynamics simulations show that it is possible to build nanoscopic propellers for pumping liquids, and to chemically tune them by altering the 'blades'. Boyang Wang and Petr Král1 from the University of Illinois in the USA, have proposed a propeller comprising blades — based on flat aromatic molecules (pyrene) — attached around a central carbon nanotube.
The effect of making the blades either hydrophobic or hydrophilic was investigated. It was found that the hydrophilic propeller rotated more slowly because of stronger interactions between the solvent molecules and its blades, particularly for water, which forms hydrogen bonds with them. Using hydrocarbon solvents of varying lengths, it was shown that the pumping rates speed up as the solvent molecules get longer because there are more atoms for the blades to grab onto. This effect disappears at very large lengths, however, because the pumping process is hampered by stronger interactions between the solvent molecules themselves. It was also discovered that the height at which the blades are mounted on the rotor is significant.
It is clear from these results that the rate of pumping depends greatly on the chemistry of the blade–liquid interface. These considerations, therefore, will be important in the design of such propellers for practical applications.
Wang, B. & Král, P. Chemically tunable nanoscale propellers of liquids. Phys. Rev. Lett. 98, 10.1103/PhysRevLett.98.266102 266102 (2007).
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Portman, R. Pump it up. Nature Nanotech (2007). https://doi.org/10.1038/nnano.2007.236