Thermophoresis of Single Atomic Particles in Open Nanotubes

Abstract

Using the molecular dynamics method, the high efficiency of thermophoresis of particles (atoms) inside single-walled carbon nanotubes (CNTs) is shown. The placement of a particle inside the CNT involved in the heat-transfer process leads to its movement in the direction of the heat flow with a constant velocity, the value of which weakly depends on the nanotube length. The heat flux along the CNT leads to the formation of a constant thermophoresis force that acts on the particles inside it, the direction of which coincides with the direction of heat transfer. The single-atom nature of the particle makes it possible to numerically calculate this force and to determine the contribution of the interaction with each thermal phonon of the nanotube to it. It is shown that the value of the force is almost completely determined by the interaction of the particle with long-wavelength flexural phonons of the nanotube, which have a large free path. Therefore, the particle velocity and the value of the thermophoresis force weakly depend on the length of the nanotube, but are determined by the temperature difference at its ends. Because of this, the nature of thermophoresis of particles inside nanotubes is ballistic rather than diffusive.