Thermophoresis of monatomic particles in open nanotubes

Using the method of molecular dynamics, it is shown that thermophoresis of particles (atoms) inside single-walled carbon nanotubes (CNTs) is highly efficient. Placing a particle inside the CNT involved in heat transfer causes it to move in the direction of the heat flow at a constant speed, the value of which weakly depends on the length of the nanotube. The heat flow along the CNT leads to the formation of a constant thermophoresis force for the particles inside. The direction of this force coincides with the direction of heat transfer. The monatomic nature of the particle allowed us to numerically calculate this force and to determine the contribution to this force of interaction with each thermal phonon of the nanotube. It is shown that the magnitude of the force is almost completely determined by the interaction of the particle with long-wave bending phonons of the nanotube, which have a long free run path. Therefore, the speed of the particle movement and the value of the thermophoresis force depend weakly on the length of the nanotube, but are determined by the temperature difference at its ends. Because of this, the mode of thermophoresis of particles inside nanotubes is ballistic, not diffusive.