Effect of graphene and carbon-nitride nanofillers on the thermal transport properties of polymer nanocomposites: A combined molecular dynamics and finite element study

Low thermal conductivity of polymers, which is one of the considerable drawbacks of commonly used composite structures, has been the focus of many researchers aiming to achieve high-performance polymer-based nanocomposites through the inclusion of highly thermally conductive fillers inside the polymer matrices. Thus, in the present study, a multiscale scheme using nonequilibrium molecular dynamics and the finite element method is developed to explore the impact of different nanosized fillers (carbon-nitride and graphene) on the effective thermal conductivity of polyethylene-based nanocomposites. We show that the thermal conductivity of amorphous polyethylene at room temperature using the reactive bond order interatomic potential is nearly $0.36\pm 0.05\mathrm{W}/\mathrm{m}\mathrm{K}$. Also, the atomistic results predict that, compared to the ${\mathrm{C}}_3\mathrm{N}$ and graphene nanosheets, the ${\mathrm{C}}_2\mathrm{N}$ nanofilm presents a much stronger interfacial thermal conductance with polyethylene. Furthermore, the results indicate that the effective thermal conductivity values of ${\mathrm{C}}_2\mathrm{N}$-polyethylene, ${\mathrm{C}}_3\mathrm{N}$-polyethylene, and graphene-polyethylene nanocomposite, at constant volume fractions of 1%, are about 0.47, 0.56, and $0.74\mathrm{W}/\mathrm{m}\mathrm{K}$, respectively. In other words, the results of our models reveal that the thermal conductivity of fillers is the dominant factor that defines the effective thermal conductivity of nanocomposites.

Figure 1

Molecular dynamics setup for evaluating the thermal conductivity of amorphous polyethylene. The snapshot is captured from the polyethylene simulation box at the last time frame of the simulation. Carbon atoms are rendered in cyan and hydrogen atoms in pink.

Figure 2

(a) Finite element modeling of representative volume (RVE) of polyethylene nanocomposite representative volume element (RVE) with 1% concentration of 2D nanostructures (graphene, ${\mathrm{C}}_3\mathrm{N}$, and ${\mathrm{C}}_2\mathrm{N}$) nanofillers with an aspect ratio of 100. (b) 3D temperature profile for the finite element modeling of RVE of polyethylene nanocomposite.

Figure 3

(a) The steady-state temperature profiles of amorphous polyethylene specimen along $X$ direction due to the imposed temperature difference of $\mathrm{\Delta }T=40\mathrm{K}$ at $T=300\mathrm{K}$. (b) Accumulative added energy to the hot region and subtracted energy from the cold area during the simulation time.

Figure 4

Side and perspective view of the initial constructed atomistic models of 2D nanostructures (carbon-nitride or graphene) on amorphous polyethylene and the imposed heat pulse to the 2D nanostructures to calculate the interfacial thermal conductance.

Figure 5

Temperature and total energy evolutions for the evaluation of interfacial thermal resistance between (a) graphene and amorphous polyethylene, (b) the ${\mathrm{C}}_3\mathrm{N}$ and amorphous polyethylene, and (c) the ${\mathrm{C}}_2\mathrm{N}$ and amorphous polyethylene.

Figure 6

The interfacial thermal conductance between different 2D nanostructures (graphene, ${\mathrm{C}}_3\mathrm{N}$, and ${\mathrm{C}}_2\mathrm{N}$) and amorphous polyethylene substrate at $T=300\mathrm{K}$. The error bars are 3, 5, and $7\mathrm{MW}/{\mathrm{m}}^2\mathrm{K}$ for graphene, the ${\mathrm{C}}_3\mathrm{N}$, and the ${\mathrm{C}}_2\mathrm{N}$, respectively.

Figure 7

Phonon densities of states of 2D nanostructures (graphene, ${\mathrm{C}}_3\mathrm{N}$, and ${\mathrm{C}}_2\mathrm{N}$) and the polyethylene substrate.

Figure 8

The effective thermal conductivity of polyethylene nanocomposites consists of different types of additives at the distinct aspect ratio of fillers vs the thermal conductivity of fillers at a constant volume fraction of 1% (normalized by the thermal conductivity of amorphous polyethylene).

Figure 9

The impact of interfacial thermal conductance between different 2D nanostructures and polymer host on the effective thermal conductivity of polyethylene-based nanocomposites at the distinct aspect ratio of fillers (normalized by the thermal conductivity of amorphous polyethylene).

Figure 10

The effective thermal conductivity of polyethylene nanocomposites consists of different types of additives at the distinct volume fraction of fillers vs the thermal conductivity of fillers at a constant aspect ratio of 100. (Normalized by the thermal conductivity of amorphous polyethylene.)

Figure 11

Molecular dynamics setup for evaluating the interfacial thermal resistance between the 2D nanostructures and polyethylene.

Figure 12

(a) Accumulative added energy to the hot slab and subtracted energy from the cold slab as a function of the simulation time of the polyethylene box consisting of the graphene sheet. (b) The steady-state 1D temperature profiles of the polyethylene box consisting of the graphene sheet along $Y$ direction at $T=300\mathrm{K}$ and $\mathrm{\Delta }T=40\mathrm{K}$.

Figure 13

(a) Accumulative added energy to the hot slab and subtracted energy from the cold slab as a function of the simulation time of the polyethylene box consisting of the ${\mathrm{C}}_3\mathrm{N}$ sheet. (b) The steady-state 1D temperature profiles of the polyethylene box consisting of the ${\mathrm{C}}_3\mathrm{N}$ sheet along $Y$ direction at $T=300\mathrm{K}$ and $\mathrm{\Delta }T=40\mathrm{K}$.

Figure 14

(a) Accumulative added energy to the hot slab and subtracted energy from the cold slab as a function of the simulation time of the polyethylene box consisting of the ${\mathrm{C}}_2\mathrm{N}$ sheet. (b) The steady-state 1D temperature profiles of the polyethylene box consisting of the ${\mathrm{C}}_2\mathrm{N}$ sheet along $Y$ direction at $T=300\mathrm{K}$ and $\mathrm{\Delta }T=40\mathrm{K}$.