Collision-Assisted Erosion of Hydrocarbon Polymers in Atomic-Oxygen Environments

Molecular beam–surface scattering experiments have been used to study the mechanisms of material removal when a hydrocarbon polymer surface erodes in the highly oxidizing environment of low Earth orbit or in a simulated space environment on Earth. During steady-state oxidation, CO and CO 2 are produced. Formation of these volatile species is believed to account for a significant fraction of the mass loss of a polymer that is under atomic-oxygen attack. The rate of production of CO and CO 2 is dramatically enhanced when a continuously-oxidized polymer surface is bombarded with Ar atoms or N 2 molecules possessing translational energies greater than 8 eV. The yield of volatile products from the surface appears to increase exponentially with the collision energy of the inert atoms or molecules. Collisions of energetic inert species may accelerate the erosion of polymers in some exposure environments (e.g. in low Earth orbit, where N 2 may strike oxidized surfaces with collision energies greater than 8 eV, and in certain atomic-oxygen test facilities that subject oxidized surfaces to bombardment by O 2 molecules with average translational energies of approximately 10 eV).