(13a) Chemical and Mechanical Stability of a Model Ionic Liquid Epoxy Material Exposed to Galactic Cosmic Ray in a Simulated Martian Environment

With NASA’s “Journey to Mars” mission progressing at a rapid rate, development of novel space materials that would withstand the extreme Martian environment has galvanized the materials research community. Ionic liquids (ILs) are currently being investigated as potential binders for Martian regolith in NASA’s in situ resource utilization efforts for the construction of Mars habitats. Ionic liquid epoxy (ILE) systems as potential IL derivatives also possess promising properties that may justify their use in space composite materials. To obtain a fundamental understanding of the chemical and mechanical stability of a model ILE system exposed to the extreme Martian environment, i.e., exposure to Galactic Cosmic Ray (GCR) and cold temperature extremes, we performed a series of molecular dynamics (MD) simulations, wherein a model amorphous ILE system composed of cationic imidazolium bis(epoxide) monomers with their bis(trifluoromethane)sulfonimide ([Tf2N]^-) anionic pairs were first energy-minimized and equilibrated at room temperature in a 3D-periodic system using the Reactive Force Field (ReaxFF). Since, to the best of our knowledge, the ReaxFF potential has not been used for an ILE system in the past, we parameterized the potential to obtain a stable ILE system and validated it by comparing the simulated ILE physical properties to those obtained experimentally. Next, the system was subjected to high-velocity inert He atoms, with their kinetic energy rate equivalent to the reported GCR energy rate of 30 μS/h on the surface of Mars, in a 2D-periodic system with a vacuum slab on top. The system temperature in the 2D-periodic system was first equilibrated at 210.15 K (-63°C), which is the average surface temperature on Mars near the Viking 1 Lander site. To account for statistical variations in the data, we used a total of three replicates in our simulations and used the average values for the calculated properties during post-processing. Finally, we determined the average mass loss, chemical species evolution, damage propagation depth, as well as initial/final stress-strain responses of the replicate material systems to evaluate the chemical and mechanical stability of the model ILE, respectively.