Molecular Dynamics Study of the Diffusion of Helium in High-Density Polyethylene Composites Reinforced with Monocrystalline and Bicrystalline Hexagonal Boron Nitride Nanosheets: Implications for Helium Storage

Diffusion of gaseous molecules through thermoplastic polymers is crucial for numerous applications including fuel liners, fuel containers, and gas bottle liners for space applications and packaging. Atomistic simulation techniques are emerging as viable techniques to study the diffusion of gases in different polymeric materials. In this article, the diffusion of nitrogen, oxygen, and helium as penetrant gases in amorphous polyethylene cells with low to high densities was investigated in the environment of molecular dynamics. Molecular dynamics-based simulations were performed with a hybrid-type force field. Adaptive intermolecular reactive empirical bond order (AIREBO) and Lennard-Jones were used to capture bonded and nonbonded interactions, respectively, whereas Beck was used for He gas. In this article, monocrystalline and bicrystalline h-BN nanosheets were used for reinforcing the barrier properties of polyethylene-based nanocomposites. The bicrystalline configuration of hexagonal boron nitride (h-BN) nanosheets helps in improving the alignment of the polymer chains at the interface that mitigates the diffusion characteristics of helium (He) gas. The results will help in developing liners for replacing titanium in bottles used for storing helium for space applications.