Carbon nanotubes have been proposed as good materials for the manufacture of tailored ultrafiltration membranes because of their nanometer-scale size and hollow, cylindrical structure. Therefore, the objective of this project is to characterize the flow (permeability and diffusion) and interaction (e.g., adsorption) of molecules with carbon nanotubes as a function of the molecule's size and the nanotube's helical structure, radius, and packing arrangement within the membrane. The approach is molecular dynamics simulations. The results of this work will be used to 1) understand fluid motion through nanometer-scale carbon pores and 2) ultimately tailor carbon nanotube ultrafiltration membranes to optimize separation processes. Molecules confined to nanometer-scale pores behave in a manner that is fundamentally different from the behavior of fluids in macroscopic porous systems, because motion is dominated by diffusion, and diffusion mechanisms are unique to nanometer-scale pore systems. This work is supported by grants from the National Aeronautics and Space Administration (Ames Research Center) and the National Science Foundation through the Network for Computational Nanotechnology at Purdue University.

      The electrical and mechanical properties of carbon nanotubes have extended the potential applications of nanoelectromechanical systems (NEMS) such as nano-switches, nano-sensors, nano-actuators, and nano-tweezers. Such devices are based on inducing external forces through the application of electric currents that flow through the nanotubes. In these cases, the force field is continuously varied over the entire material. When the nanotubes are exposed to irregular force fields, such as those induced by an irregular gas flow, the behavior will be different from the behavior of the nanotube under constant electrostatic fields. Irregularities in geometry or time can cause local heating, deformation, and damage. There is therefore incentive to investigate the mechanical responses of nanotubes to a variety of external stimuli.

      When nanotubes are exposed to an externally flowing fluid, the whole nanotube can be bent, translated, and bucked. Understanding the mechanical response of the nanotube subjected to a gas flow is important for NEMS devices related applications. In this work we examine the response of single and multi walled tubes to impacts with noble gas atoms using classical MD simulations.