Mechanistic Studies of Atomic Oxygen Reactions with Polymers and Combined Effects with Vacuum Ultraviolet Light

Abstract

This article focuses on mechanistic aspects of hyperthermal atomic oxygen reactions with polymers, which are the major contributor to material degradation in low Earth orbit. Due to the importance of well-controlled experiments in the understanding of the reaction mechanisms, ground-based experimental results obtained by a hyperthermal atomic oxygen beam generated by laser detonation facilities are mainly surveyed. Combined effects of atomic oxygen and vacuum ultraviolet (VUV) light on fluorinated polymers are also described. Such combined effects of hyperthermal atomic oxygen and VUV light are important not only from a fundamental point of view but also for engineering purposes (i.e., methodology for ground-based space environmental simulation). The VUV-sensitive polymers, poly(methyl methacrylate), and Teflonfluorinated ethylene-propylene do not show significant synergistic effects. Instead, the effect of combining atomic oxygen and VUV light produces erosion of the polymer that is the sum of the erosion caused by atomic oxygen and UV light acting individually. The experimental results suggest that material erosion in a complicated space environment may be quantitatively predicted if the erosion yields caused by the individual action of atomic oxygen and VUV light are known. sion energy, AO erodes many polymeric materials used in LEO. 1-3 The AO-induced erosion phenomena were recognized in early space shuttle missions. Many flight and ground-based experiments have been conducted to discover the reactivity of high-energy collisions of AO with various materials. 4-7 Since direct collisions with AO are restricted to the materials used on the exterior surface of spacecraft, AO reactions with the materials that are used in thermal control systems, solar panels, and other exposed facilities have been extensively studied. 8,9 The hydrocarbon polymer, polyimide, has been widely used in many space applications because of its superior physical and chemical properties, such as thermal stability, heat capacity, thermal conductivity, and heat resistance. It is well known that polyimide is eroded by hyperthermal AO bombardment in the LEO environment (see the Miller and Banks article in this issue). In fact, the erosion of Kapton H polyimide has been used as a standard to measure AO fluence, and such "Kapton equivalent fluence" is widely accepted for evaluating the erosion rate of other materials. 10 The erosion properties of polyimide need to be well understood, as the lack of knowledge of erosion behavior leads to uncertainty of the polyimide equivalent AO fluence.Another focus material in this article is fluorinated ethylene-propylene (FEP) copolymer. FEP also has been used as a thermal control material in many satellites. The erosion yield of FEP by AO is reported to be less than one tenth of that of polyimide in flight experiments; however, FEP erodes much faster in ground-based AO simulation experiments. 11 Due to the susceptibility of FEP to VUV degradation, it has been doubted that a strong synergistic effect of AO wi...

Intrinsically heat-sealable polyimide films with atomic oxygen resistance: Synthesis and characterization

“…Supposedly, there are several steps involved in the AO exposure process for a polymer, including erosion initiation by O-surface interaction, erosion propagation by chain scission, and material loss due to volatile removal. 62 Among the three steps, the first two ones are dominated by chemical interactions and the last one by physical interaction such as atom collisions. ARPI-0 and Kapton HN have the similar element compositions.…”

Erosion yield of epoxy–silica nanocomposites at the lower earth orbit environment of the International Space Station

“…Literature reports are not fully conclusive on the synergistic effect of UV and AO, although it appears that for several polymers, such as polymethylmethacrylate (PMMA), polyethylene (PE), polyimide, and Teflon FEP, no particular synergy is discernible. 14,35 UV radiation is absorbed only in the top 1-3 mm of the specimen surface; hence, the polymer specimens subjected to UV radiation underwent surface degradation that created a $ 2 mm thick carpet layer at the top surface. 19 The degraded polymer retarded further degradation of the underlying polymer due to UV radiation.…”

“…13 Although the concentration of AO in LEO is small, the flux of AO impinging a spacecraft's outer surface is significant (10 14 -10 15 atoms/cm 2 ) due to the high orbital velocity (7-8 km/s) of the spacecraft. 14 Thus, AO impacting polymeric materials over extended periods of time will cause surface erosion and mass loss.…”

Determination of Surface Temperature in ICP RF Plasma Treatments of Organic Materials

“…Comparing Figures 2 (a), and (c), it is possible to observe that the front position was more heated active species are able to diffuse during liquid phase, and promote reactions, increasing the heating of the sample at the moment. At the same time, Tagawa 27,28 found that when polymers are exposed to atomic oxygen and UV light, the angle of incidence can increase the rate of interaction considerably. However, since the increase on the incident angle due the melt puddle of SA is minimal on experimental conditions, the effect of the presence of a liquid phase on SA is considerably more important to the heating.…”