Exploring the mechanisms of carbon-nanotube dispersion aggregation in a highly polar solvent

One of the main obstacles to the exploitation of single-wall carbon nanotubes (SWCNT) remarkable electronic and materials properties is their tendency to form ropes or bundles. This complicates drastically the processing and purification of carbon nanotubes. An understanding of the free energy landscape associated with transitions from isolated SWCNTs to bundles in solution would facilitate the control of the process, and is the motivation of this work. Extensive molecular dynamics studies of this problem for the highly polar solvent, N-methyl-2-pyrrolidone (NMP) indicate that i) pairs of SWCNTs in the form of bundles are far more stable than pairs of isolated tubes; and ii) free energy barriers lying between bundles and isolated tubes exist which are proportional to the surface tension of NMP, and are likely to be responsible for the long-lived transients reported in experiments