Self-propelled directed transport of C60 fullerene on the surface of the cone-shaped carbon nanotubes.

Directed transportation of materials at molecular scale is important due to its crucial role in the development of nanoelectromechanical devices, particularly the directional movements along the carbon nanotubes (CNTs), due to the applications of CNTs as nano-manipulators, confined reactors, and drug or other materials delivery systems. In the present investigation, we evaluate the movements of C60 fullerenes on the surface of the cone-shaped CNTs. The fullerene molecules indicate directed motion toward the narrower end of CNTs, which is due to the potential energy gradient along the nanotube length. A continuum model is proposed to evaluate the mechanism of the directed motion and the results of the theoretical model are compared with numerical simulations. Directed movements have been examined at various opening angles of CNTs, considering the trajectories of motions, variation of potential energy, and diffusion coefficients. At smaller opening angles, the driving force on the C60 increases and the molecule experiences more directed transport along the nanotube. The motion of fullerene has also been simulated inside the cone-shaped CNTs, with similar opening angle, and different average radius. At lower average radius of the cone-like nanotubes, the motion of C60 is comparatively more rectilinear. Directional transport of fullerene has been observed in the opposite direction, when the molecule moves on the external surface of the cone-like CNTs, which is due to the stronger interaction of C60 with the parts of the external surface with larger radius. The effect of temperature has been evaluated by performing the simulations at the temperature range of 100 to 400 K. The direction of the velocity reveals that the thermal fluctuations at higher temperatures hinder the directed motion of molecule along the cone-shaped CNTs. The results of the present study propose a new method to obtain directed transport of molecules which can be helpful in different applications such as drug delivery systems.