Reactive Molecular Dynamics Simulation on the Disintegration of Kapton, POSS Polyimide, Amorphous Silica, and Teflon during Atomic Oxygen Impact Using the Reaxff Reactive Force-Field Method

Atomic oxygen (AO) is the most abundant element in the low Earth orbit (LEO). It is the result of the dissociation of molecular oxygen by ultraviolet radiation from the sun. In the LEO, it collides with the materials used on spacecraft surfaces and causes degradation of these materials. The degradation of the materials on the surface of spacecrafts at LEO has been a significant problem for a long time. Kapton polyimide, polyhedral oligomeric silsesquioxane (POSS), silica, and Teflon are the materials extensively used in spacecraft industry, and like many other materials used in spacecraft industry, AO collision degradation is an important issue in their applications on spacecrafts. To investigate the surface chemistry of these materials in exposure to space AO, a computational chemical evaluation of the Kapton polyimide, POSS, amorphous silica, and Teflon was performed in separate simulations under similar conditions. For performing these simulations, the ReaxFF reactive force-field program was used, which provides the computational speed required to perform molecular dynamics (MD) simulations on system sizes sufficiently large to describe the full chemistry of the reactions. Using these simulations, the effects of AO impact on different materials and the role of impact energies, the content of material, and temperature of material on the behavior of the materials are studied. The ReaxFF results indicate that Kapton is less resistant than Teflon toward AO damage. These results are in good agreement with experiment. These simulations indicate that the amorphous silica shows the highest stability among these materials before the start of the highly exothermic silicon oxidation. We have verified that adding silicon to the bulk of the Kapton structure enhances the stability of the Kapton against AO impact. Our canonical MD simulations demonstrate that an increase in the heat transfer in materials during AO impact can provide a considerable decrease in the disintegration of the material. This effect is especially relevant in silica AO collision. Considerable experimental efforts have been undertaken to minimize such AO-based degradations. As our simulations demonstrate, ReaxFF can provide a cost-effective screening tool for future material optimization.