Mechanical properties of carbon nanotube networks by molecular mechanics and impact molecular dynamics calculations

We report a theoretical investigation of the mechanical properties of idealized networks formed by single-walled carbon nanotubes showing crossbar and hexagonal architectures. The study was performed by using molecular mechanics calculations and impact dynamics simulations based on bond-order empirical potential. The studied networks were predicted to have elasticity modulus of $\sim 10–100\mathrm{GPa}$ and bulk modulus of $\sim 10\mathrm{GPa}$. The results show a transition from high to moderate flexibility during the deformation stages. This behavior was associated with the existence of two deformation mechanisms presented by the network related to the nanotube stretching and junction bending processes.

Figure 1

Crossbar (a) and hexagonal (b) unit cells of isolated SWCNT networks. The crossbar net is made by (6, 0) while the hexagonal one by (8, 0) SWCNTs.

Figure 2

(Color online) Representations of (a) a single layered and (b) multilayered ($AA$ stacking) crossbar carbon nanotube network. Different colors represent different layers.

Figure 3

Network models used in the impact molecular dynamics simulations. (a) A circular graphene sheet $(R=190\mathrm{\AA })$, (b) a hexagonal [$\mathrm{Hex}@(6,0)$, $a=47.5\mathrm{\AA }$], (c) a crossbar ($a=29.1\mathrm{\AA }$ and $b=29.9\mathrm{\AA }$), and (d) a disordered network. (e) Representation of a spherical particle which will collide with the center of the network.

Figure 4

(Color online) Temporal evolution of the kinetic energy $K$ of the incident particle for different values of $K_i$ (initial kinetic energy) for (a) $r_0=15\mathrm{\AA }$ and (b) $r_0=10\mathrm{\AA }$. The particle mass is the same for both cases and it equals 15% of the graphene sheet mass. In this figure, $K_0\equiv 211\mathrm{eV}$ and the target is a squared graphene sheet. The necessary time for the particle to interact with the target depends upon the particle mass and radius as seen in (b) on the early stages of the simulation.

Figure 5

(Color online) Necessary kinetic energy of the incident particle to cause the rupture of the graphene sheet. Results for two different particle masses are shown (10% and 15% of graphene sheet mass).

Figure 6

(Color online) Temporal evolution of the kinetic energy $K$ of the incident particle colliding with (a) a hexagonal network [$\mathrm{Hex}@(6,0)$, $a=47.5\mathrm{\AA }$], and (b) crossbar network ($a=29.1\mathrm{\AA }$ and $b=29.9\mathrm{\AA }$), and (c) a graphene sheet.

Figure 7

Snapshots of the impact of a $5\mathrm{keV}$ particle with a crossbar network [$\mathrm{Cb}@(6,0)$, $a=29.1\mathrm{\AA }$, $b=29.9\mathrm{\AA }$].

Figure 8

(Color online) Temperature profile for different times of the simulation of the collision of a $5\mathrm{keV}$ particle on the crossbar network (Fig. 7).

Figure 9

(Color online) Behaviors of the squared normal deformation ${\left(\Delta z\right)}^2$ as a function of the initial kinetic energy of the incident particle. The targets are the ones shown in Fig. 3. The colored lines are only to help visualization of the different regimes.