Unraveling the effects of geometrical parameters on dynamic impact responses of graphene reinforced polymer nanocomposites using coarse-grained molecular dynamics simulations.

Nacre plays an important role in bionic design due to its light weight, high strength, and structure-function integration. The key to elucidate its reinforcing and toughening mechanisms is to truly characterize its multi-layer structure and properties. In this work, the dynamic impact responses of graphene reinforced polymer nanocomposites with a unique brick-and-mortar structure are investigated using coarse-grained molecular dynamics simulations, in which the interfacial coarse-grained force field between graphene and the polymer matrix is derived by the energy matching approach. The influences of various geometrical parameters on dynamic impact responses of the nanocomposites are studied, including the interlayer distance, lateral distance, and number of graphene layers. The results demonstrate that the impact resistance of the nacre-like structure can be significantly improved by tuning the geometrical parameters of graphene layers. It is also found that the chain scission and interchain disentanglement of polymer chains are the main failure mechanisms during the perforation failure process as compared to the stretching and breaking of bonds. In addition, the microstructure analysis is performed to deeply interpret the deformation and damage mechanisms of the nanocomposites during impact. This study could be helpful for the rational design and preparation of graphene reinforced nacre-like nanocomposites with high impact resistance.

Reactive Molecular Dynamics Study of the Mechanism and Effect of Various Protective Coatings on the Protection of Polyimide Antierosion from Atomic Oxygen.

Polyimide (PI), due to its exceptional performance, is commonly utilized in spacecraft. However, when such polymers are used in spacecraft navigating low Earth orbit, they are exposed to atomic oxygen (AO) that can cause the polymer to decompose. A protective coating method is a more effective way to safeguard the polymer from erosion caused by AO. This study employs the molecular dynamics simulation based on the reaction force field to investigate the protective effects of various coatings, including polydimethylsiloxane (PDMS), graphene (Gr), polytetrafluoroethylene (PTFE), and the (0 0 1), (0 1 1), and (1 1 1) surfaces of SiO2. The results indicate that the protective performance of the (0 1 1) surface is superior to that of the (0 0 1) and (1 1 1) surfaces. Moreover, protective coatings are classified into three categories based on different protective mechanisms: rebound, absorption, and sacrificial. The protective effectiveness of coatings depends on their anti-AO performance and ability to combine with the substrate. Gr displays exceptional anti-AO properties and can effectively shield the substrate from AO erosion. Silicone-based coatings have a superior ability to adhere to PI substrates, and PDMS is an excellent choice for protective coatings. This paper offers guidance for the protective coating method of PIs against AO erosion.