Thermal gradient induced actuation in double-walled carbon nanotubes.

Molecular dynamics simulations are applied to investigate the thermal gradient induced actuation in double-walled carbon nanotubes, where a temperature difference can actuate the relative motion of double-walled carbon nanotubes. The thermal driving force calculated through a stationary scheme is on the order of pico Newtons for a 1 K nm(-1) temperature gradient. The driving force is approximately proportional to the temperature gradient, but not sensitive to the system temperature. For the outer tube longer than 5 nm, the thermal driving force is nearly constant. For the outer tube shorter than 5 nm, however, the driving force decreases with decreasing tube length. The motion trace is found to depend on both the chirality pair and system temperature. A critical temperature can be defined by the potential barrier perpendicular to the minimum energy track of potential patterns. When the system temperature is higher than the critical temperature, the motion shows random behavior. When the system temperature is lower than the critical temperature, the motion, translational and/or rotational, is confined within the minimum energy track, which is indicative of the feasibility of directional control.