Enhancing Mechanical Properties of Multiwall Carbon Nanotubes via $s{p}^3$ Interwall Bridging

Molecular dynamics (MD) simulations under transverse shear, uniaxial compression, and pullout loading configurations are reported for multiwall carbon nanotubes (MWCNTs) with different fraction of interwall $s{p}^3$ bonds. The interwall shear coupling in MWCNTs is shown to have a strong influence on load transfer and compressive load carrying capacity. A new continuum shear-coupled-shell model is developed to predict MWCNT buckling, which agrees very well with all MD results. This work demonstrates that MWCNTs can be engineered through control of interwall $s{p}^3$ coupling to increase load transfer, buckling strength, and energy dissipation by nanotube pullout, all necessary features for good performance of nanocomposites.

Figure 1

Atomic structure of a CNT with interwall $s{p}^3$: (a) Initial geometry of a MWCNT with the surface undulations due to the presence of $s{p}^3$ bonds, (b) A close-up view of the atomic structure, showing $s{p}^3$ bonds bridging the walls and (c) An individual $s{p}^3$ interwall bond.

Figure 2

Buckling strain of SWCNTs and MWCNTs versus average tube diameter. Symbols are MD simulations and the solid line is the classical shell theory result; $n$ is the number of walls.

Figure 3

Buckling strain ${\epsilon }_b$ of MWCNTs, normalized as $\xi ({\epsilon }_b/{\epsilon }_c-1)$, versus the nondimensional interwall shear parameter $\eta$, predicted by MD simulation, and SCS and TIS models.

Figure 4

Buckling strain predicted by the SCS model versus the buckling strain obtained via MD simulations, for a range of MWCNT diameter, percentage of $s{p}^3$ bonds, and number of walls.

Figure 5

Pullout force versus pullout distance for double-wall CNTs with 0% and 0.5% $s{p}^3$ bonds ($L=5\mathrm{nm}$).