Mechanical transmission of rotational motion between molecular-scale gears

TL;DR

This paper uses molecular dynamics simulations to explore how molecular-scale gears transmit rotational motion, revealing different collective behaviors depending on driving torque and gear interactions.

Contribution

It introduces a theoretical framework for understanding molecular gear dynamics, including effective interaction potentials and collective motion regimes.

Findings

Rotational-angle dynamics of a single molecule resemble a Brownian rotor.

Effective interaction potential depends strongly on gear center distance.

Identifies three regimes of collective motion based on driving torque.

Abstract

Manipulating and coupling molecule gears is the first step towards 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 corresponds to the one 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.