  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.
