Об анизотропии диффузии углеродных нанотрубок в жидкости

Abstract

This article discusses the methodology and results of molecular dynamics simulation of the diffusion of carbon nanotubes in water. The main goals of this work were to study diffusion longitudinal to an axis of the nanotube and transverse to this axis and determine the velocity autocorrelation functions and diffusion coefficients in these directions. The interaction of water molecules with each other was described by the Lennard-Jones potential, and that of carbon nanotube molecules by the AIREBO potential. The diameters of the nanotubes were 1.15 and 1.44 nanometers, their length varied from 5 to 15 nanometers. The number of water molecules in the simulation cell reached one hundred thousand. It is shown that the nanotube center of mass velocity autocorrelation function in the longitudinal direction decays much more slowly than in the transverse direction. The corresponding values of the diffusion coefficients differ by a factor of 2–4; this diffe¬rence increases with increasing ratio of the nanotube length to its diameter. The directionally averaged diffusion coefficients of flexible nanotubes decrease with increasing nanotube length. Its values exceed the corresponding values for their solid analogues. A nonmonotonic decay of the nanotubes center of mass velocity autocorrelation function was discovered. The characteristic time between the maxima of this function coincides with the period of bending vibrations of the nanotube.