(131h) Designed Molecular Dynamics Investigation of the Thermal Conductivity and Mass Loss of Polyetherimide/Graphene Nanocomposites Exposed to Space Environments

Polyimide (PI)- and polyetherimide (PEI)-based nanocomposites generally possess good performance in the harsh space environment that may include electrical charge build-up, atomic oxygen bombardment, solar radiation, energetic particle bombardment, vacuum, and space plasma. These materials have previously been investigated as potential structural or sacrificial surface layer materials for spacecraft.¹ However, their thermal and chemical degradation performances are intricately related to lower-length-scale material phenomena involving the PEI and nanoreinforcement phases that warrant detailed investigation. In this project, we used an I-optimal (integrated variance) response surface design to investigate and model the effects of three factors, i.e., graphene (Gr) content (0-10 wt.%), temperature (0-200°C), and Gr type (monolayer vs. multilayer) on the thermal conductivity and mass loss of a PEI/Gr space material, which were determined using molecular dynamics (MD) simulation in the LAMMPS software package. The latter response was obtained by exposing the nanocomposites to energetic particles (hypervelocity atomic oxygen or stream of neutrons) during the MD simulations. Our computational approach utilizes non-reactive (pcff) force field for the thermal conductivity simulations and reactive (ReaxFF) force field for the particle bombardment simulations. All systems were built with finite Gr sheets (one vs. five layers with the dimensions of 10 Å*17 Å and with a sheet spacing of 3.4 Å) that are randomly dispersed in the PEI matrix (~167 chains with two repetitive units) and subsequently energy-minimized. To calculate the thermal conductivities of the different systems, a Müller-Plathe algorithm was followed similar to our previous work.² For this purpose, an isothermal-isobaric (NPT) simulation was first performed for 2 ns (a timestep of 1 fs) followed by an isothermal-isochoric (NVT) simulation for another 2 ns to thermally equilibrate the systems at the given temperatures, and finally there was a production run for 1 ns. We validated our force field predictions of the thermal conductivities of the neat PEI. Our predicted thermal conductivity of PEI at 0°C was about 0.167 W m^-1 K^-1, matching that of a commercially available Quantum PEI – Ultem® (about 0.167 W m^-1 K^-1). As for the bombardment of the PEI/Gr nanocomposites, we are currently following the method used in our previous work.³ Once all data are generated, we will perform a multi-response optimization to identify conditions that would maximize thermal conductivity and minimize mass loss of the nanocomposites. The simulations are still ongoing and preliminary results will be presented.

References:

(1) Gouzman, I.; Grossman, E.; Verker, R.; Atar, N.; Bolker, A.; Eliaz, N. Advances in Polyimide‐Based Materials for Space Applications. Adv. Mater. 2019, 31 (18), 1807738.

(2) Mansourian-Tabaei, M.; Asiaee, A.; Hutton-Prager, B.; Nouranian, S. Thermal Barrier Coatings for Cellulosic Substrates: A Statistically Designed Molecular Dynamics Study of the Coating Formulation Effects on Thermal Conductivity. Appl. Surf. Sci. 2022, 587, 152879.

(3) Rahmani, F.; Nouranian, S.; Li, X.; Al-Ostaz, A. Reactive Molecular Simulation of the Damage Mitigation Efficacy of POSS-, Graphene-, and Carbon Nanotube-Loaded Polyimide Coatings Exposed to Atomic Oxygen Bombardment. ACS Appl. Mater. Interfaces 2017, 9 (14), 12802–12811.