Atomic Oxygen and UV Irradiation Effects on Fluorosilicone Rubber: Comparison of RF Plasma and In-Flight Exposure

Abstract

In this work the effect of a low Earth orbit (LEO) space environment on fluorosilicone rubber polymers was studied. The emphasis was made on the influence of atomic oxygen (AO) and UV irradiation on the polymer chemical, morphological, and mechanical properties. The fluorosilicone samples were exposed to the LEO space environment during the Passive Optical Sample Assembly (POSA-II) experiment on-board the MIR space station and in a ground simulation radio frequency (RF) oxygen plasma Asher system. LEO environment was found to have a pronounced destructive effect on the fluorosilicone rubber. Exposure of the samples in space for 18 months (AO fluence of 2.1 1 1020 O-atoms cm-2 ) resulted in surface cracking and changes in chemical composition, namely a decrease in the atomic concentration of fluorine and an increase in the amount of oxygen by formation of silicon oxide. These changes induce stresses in the modified region1 the affected material is characterized by increased hardness and elastic modulus. AO fluence is a dominant factor in the sample deterioration: the specimen facing the MIR space station received a lower AO fluence (8 1 1019 O-atoms cm-2 ) and, consequently, has less damage as compared to the specimen that faced the outer space. Ground simulation of LEO environment by exposure to RF oxygen plasma produces similar effects to those of the space environment. Its impact is even stronger due to higher levels of UV irradiation. It is deduced that fluorosilicone rubber is not suitable for long duration utilization when exposed to LEO due to its chemical and mechanical instability. The undesired effects may include both the destruction of the sealing and the contamination of neighboring parts within line-of-sight with its outgassing products.