Bubble Nucleation on Carbon-Nanotube Studied by Molecular Dynamic Simulations

摘要

Bubble nucleation is usually takes place at sites as imperfections on the surface or foreign bodies. Grown carbon nanotubes (CNT) on surfaces can act as a nucleation site. Nucleation process due to the existence of CNT is interested and will be studied by molecular dynamics simulation in present study. Previous studies investigating the bubble nucleation process by molecular dynamic simulation include the works of bubble formation process in the homogenous Lennard-Jones liquid by adiabatic expanding the system [1], bubble nucleation in a homogenous Lennard-Jones liquid under heating with a constant negative pressure [2], and heterogeneous nucleation of a Lennard-Jones vapor bubble on a solid surface by gradually expanding the solid walls to the negative pressure [3]. Present study aims to simulate the vapor bubble nucleation in carbon nanotube – water system and identify the factors affecting the bubble nucleation and departure. All molecular dynamics simulations are carried out in the NVT ensemble with periodic boundary conditions on all system boundaries for the heterogeneous system of a carbon nanotube - water. The system temperature is kept at 300K by coupling to a Berendsen thermostat. The potential functions and parameters described the carbon-carbon interactions in carbon nanotube and the carbon-water interactions follow the study of Walther et al [4] and water molecules are described by the rigid SPC model. Simulations shows that the bubble embraces the CNT if the length of CNT is short (2.5nm in Fig. 1(a)) and the bubble moves to the top of the CNT as the length is doubled (Fig. 1(b)) Full paper will report the immigration of bubble as the length is increase further until bubble departs from the CNT. Other parameters such as the diameter, aspect ratio, single/multi-wall structures of CNT, and the based fluid system (CNT-argon system) on the bubble nucleation process, bubble departure and associated physics will be reported also.