Carbon nanotubules (CNTs) have been proposed for use in a variety of applications such as membrane building blocks and fibers in carbon composite materials. This paper will review some work we have done using molecular dynamics simulations with the Brenner hydrocarbon potential  to shed light on some of the properties of nanotubules that are important for their use in these applications.
For example, to increase the strength of adhesion of nanotubules in a polymer matrix, researchers have recently attached dichlorocarbene covalently to the walls of single-wall carbon nanotubules . The goal of this work is to ultimately use standard methods to substitute polymer chains in place of the chlorine atoms. These functionalized tubules can then be used to create the next generation of ultra-strong composite materials. However, there is concern that since the covalent chemical tethers alter the sp2-hybridization of the tubule wall at the points of attachment, the mechanical properties that made CNTs desirable fibers in the first place could be destroyed. To determine the effects of covalent chemical attachments on the mechanical properties of single-wall CNTs, classical molecular dynamics simulations are used to determine the maximum compressive (buckling) force for various functionalized and non-functionalized CNTs.
Molecular dynamics simulations are also used to study dynamic and diffusive molecular flow through carbon nanotubules at room temperature. This work sheds light on some of the important processes that take place in ultrafiltration-membrane pores. Three types of fluid molecules, methane, ethane, ethylene, are considered. The simulations show that interactions between the molecules and the tubule walls slow the dynamic molecular flow. Additional simulations show that these interactions also affect the diffusion of molecules through nanotubules from areas of high to low density. The molecule-tubule interactions are affected by the tubule diameters and the density and type of fluid molecules. For methane in tubules with 8.0 Å diameters, the average moving distance is predicted to be proportional to the square root of the observed time (e.g., normal diffusion) with a calculated diffusion constant of 0.38 Å2/ps.
The authors gratefully acknowledge the support of NASA Ames Research Center (Grant Number NAG 2-1121).
Brenner, D.W. (1990) Phys Rev B, 42 No. 15, November 15, pages 9458-9471. Empirical potential for hydrocarbons for use in simulating the chemical vapor deposition of diamond films
Chen, Y., Haddon, R.C., Fang, S., Rao, A.M., Eklund, P.C., Lee, W.H., Dickey, E.C., Grulke, E.A., Pendergrass, J.C., Chavan, A., Haley, B.E., Smalley, R.E. (1998) J. Mat. Res. 13 No. 9, September (in press). Chemical attachment of organic functional groups to single-walled carbon nanotube material