Cross linking of thiolated carbon nanotubes: An ab initio study

We have studied the mechanism of covalent cross linking between carbon nanotubes functionalized with thiocarboxylic and dithiocarboxylic esters. The interconnected nanotube structures were modeled using density functional theory combined with the pseudopotential approximation. Our calculations revealed the important role of surface defects when forming chemical bonds that connect nanotubes to each other. The strength and stability of intertube bonds increased in the vicinity of defect sites. The computed binding energies and potential energy profiles of linked nanotubes were found to be sensitive to the choice of exchange-correlation functional used within the density functional formalism. The observed sensitivity could be explained by a nonuniform distribution of the electronic charge density near defect sites. This result suggests that gradient-corrected functionals are essential for accurate theoretical modeling of functionalized carbon nanotubes and nanotube-based composites.