Inherent fluctuation-mediated equivalent force drives directional motions of nanoscale asymmetric particles -- Surf-riding of asymmetric molecules in thermal fluctuations

TL;DR

This paper demonstrates that asymmetric nanoscale particles experience a fluctuation-driven unidirectional force, leading to directional motion, with implications for nanoscale transport and molecular processes.

Contribution

It introduces a theoretical model showing inherent fluctuation-mediated forces cause directional motion in asymmetric molecules, supported by molecular dynamics simulations.

Findings

Unidirectional transport occurs in asymmetric particles under constrained orientation.

Equivalent force exists in asymmetric molecules like water and ethanol at ambient conditions.

Molecular dynamics simulations confirm directional movement of water on surfaces at room temperature.

Abstract

Using a simple theoretical model of a nanoscale asymmetric particle/molecule with asymmetric structure or/and asymmetric charge distribution, here using a charge dipole as an example, we show that there is unidirectional transportation mediated by non-white fluctuations if the asymmetric orientation of the particle/molecule is constrained. This indicates the existence of an inherent equivalent force, which drives the particle/molecule itself along the orientation of the asymmetric particle in the environment of fluctuations. In practical systems, equivalent force also exist in the asymmetric molecules, such as water and ethanol, at the ambient condition since thermal fluctuations are not white anymore at nanoscale [Wan, R., J. Hu, and H. Fang, Sci. China Phys. Mech. Astron. 2012, 55, 751]. Molecular dynamic simulations show that there is unidirectional transportation of an ultrathin water layer on solid surface at room temperature when the orientations of water molecules have a preference. The finding will play an essential role in the understanding of the world from a molecular view and the developing of novel technology for various nanoscale and bulk applications, such as chemical separation, water treatment, sensing and drug delivery.