Adhesion of single functional groups to individual carbon nanotubes: Electronic effects probed by ab initio calculations

We investigated the interfacial interaction of simple functional groups ($-{\mathrm{NH}}_2$, $-\mathrm{CN}$, $-{\mathrm{CH}}_3$, $-{\mathrm{CHOCH}}_2$) with single wall carbon nanotubes, using ab initio calculations. We computed binding energies and attachment forces using the density functional theory (DFT) in the local density approximation, and we employed Quantum Monte Carlo calculations to test DFT accuracy in describing weak interactions for the controversial case of an oxygen molecule. We find that computed energies and forces are very sensitive to small variations of the electronic charge on the nanotube. In particular, the presence of a solvent (polar or nonpolar), and thus of a small charge transfer from or to the tube, may alter the relative strength of adhesion forces for different functional groups, as compared to the vacuum.

Figure 1

(Color) Ball and stick model of the equilibrium structure for the $-{\mathrm{NH}}_2$ functionalized tip interacting through the lone-pair (left panel) and a H atom (right panel). Gray spheres represent C atoms, dark blue (light blue) represent nitrogen (silicon) atoms, and white sphere hydrogen atoms. The isosurfaces represent the electron density difference between the interacting and noninteracting tip/NT system: blue (red) surfaces correspond to a charge density increase (decrease), respectively.

Figure 2

(Color) Ball and stick model of the equilibrium structure for the isopropanole (left), DMSO (center), and toluene (right) molecules. Gray spheres represent C atoms, yellow spheres sulphur, red spheres oxygen, and white spheres hydrogen atoms. The isosurfaces represent the electron density difference between the interacting and noninteracting tip/NT system: blue (red) surfaces correspond to a charge density increase (decrease), respectively.