Molecular dynamics simulation of carbon nanotubes diffusion in water

Abstract

ABSTRACT The present paper is devoted to the study of diffusion of carbon nanotubes in water by molecular dynamics method. Two nanotube models were used, namely, 1D rigid rod and 3D (6, 6) armchair. The nanotube diameter was 0.818 nm, and their length ranged from 5.25 to 32.2 nm. Both translational and rotational diffusion coefficients were calculated. Besides, longitudinal and transverse diffusion was studied, and the corresponding diffusion coefficients were determined. The first of them was much larger than the second, and the difference reached two times. The average diffusion coefficients are relatively well described by the analytical dependences for rigid cylinders. The diffusion coefficients were calculated using Green–Kubo formula and Einstein relation. Relaxation of autocorrelation functions of nanotube velocity and angular velocity was systematically discussed for all cases. It is shown that this relaxation has two stages and the first stage is an exponential. The corresponding relaxation times were estimated.