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Mechanical Transmission of Rotational Motion between Molecular-Scale Gears
H. H. Lin, A. Croy, R. Gutierrez, C. Joachim, and G. Cuniberti
Phys. Rev. Appl. 13 34024 (2020)
The manipulation and coupling of molecule gears is the first step toward realizing molecular-scale mechanical machines. Here, we theoretically investigate the behavior of such gears using molecular-dynamics simulations. Within a nearly rigid-body approximation, we reduce the dynamics of the gears to the rotational motion around the orientation vector. This allows us to study their behavior based on a few collective variables. Specifically, for a single hexa(4-tert-butylphenyl)benzene molecule, we show that the rotational-angle dynamics correspond to those of a Brownian rotor. For two such coupled gears, we extract the effective interaction potential and find that it is strongly dependent on the center-of-mass distance. Finally, we study the collective motion of a train of gears. We demonstrate the existence of three different regimes, depending on the magnitude of the driving torque of the first gear: Underdriving, driving, and overdriving, which correspond, respectively, to no collective rotation, collective rotation, and only single-gear rotation. This behavior can be understood in terms of a simplified interaction potential.
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