Abstract
For the development of spacecraft with long-servicing life in low earth orbit (LEO), high-temperature resistant polymer films with long-term atomic oxygen (AO) resistant features are highly desired. The relatively poor AO resistance of standard polyimide (PI) films greatly limited their applications in LEO spacecraft. In this work, we successfully prepared a series of novel AO resistant PI composite films containing nanocaged polyhedral oligomeric silsesquioxane (POSS) components in both the PI matrix and the fillers. The POSS-containing PI matrix film was prepared from a POSS-substituted aromatic diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS) and a common aromatic diamine, 4,4′-oxydianline (ODA) and the aromatic dianhydride, pyromellitic dianhydride (PMDA) by a two-step thermal imidization procedure. The POSS-containing filler, trisilanolphenyl POSS (TSP-POSS) was added with the fixed proportion of 20 wt% in the final films. Incorporation of TSP-POSS additive apparently improved the thermal stability, but decreased the high-temperature dimensional stable nature of the PI composite films. The 5% weight loss temperature (T5%) of POSS-PI-20 with 20 wt% of DABA-POSS is 564 °C, and its coefficient of linear thermal expansion (CTE) is 81.0 × 10−6/K. The former is 16 °C lower and the latter was 20.0 × 10−6/K higher than those of the POSS-PI-10 film (T5% = 580 °C, CTE = 61.0 × 10−6/K), respectively. POSS components endowed the PI composite films excellent AO resistance and self-healing characteristics in AO environments. POSS-PI-30 exhibits the lowest AO erosion yield (Es) of 1.64 × 10−26 cm3/atom under AO exposure with a flux of 2.51 × 1021 atoms/cm2, which is more than two orders of magnitude lower than the referenced PI (PMDA-ODA) film. Inert silica or silicate passivation layers were detected on the surface of the PI composite films exposed to AO.
Highlights
Nanomaterials 2021, 11, 141 excellent radiation resistance, good mechanical properties, and so on [1]. They are usually subject to atomic oxygen (AO) erosion with an erosion yield at the level of 10−24 cm3 /atom in low earth orbit (LEO) space environments [4,5,6]. This means that the PI film designed and served as the protecting layers for LEO spacecraft themselves might be eroded by AO exposure first, thereby losing the protecting functions
In 2012, Minton and coworkers systemically reported the research and development of main-chain polyhedral oligomeric silsesquioxane (POSS)-substituted Kapton® PI film (MC-POSS-Kapton) and side-chain substituted one (SC-POSS-Kapton) [24]. Both POSS-containing PI films have been investigated as high-performance AO-resistant candidates in real LEO space environments and the results showed that it was a promising and practical pathway to enhance the AO-resistant properties of the standard Kapton® films by combining POSS units into the PI films via copolymerization
A serious of POSS-poly(amic acid) (PAA) composite varnishes were first prepared by the com of copolymerization and physical blending procedures according to the chemical
Summary
Nanomaterials 2021, 11, 141 excellent radiation resistance, good mechanical properties, and so on [1]. They are usually subject to AO erosion with an erosion yield at the level of 10−24 cm3 /atom in LEO space environments [4,5,6]. This means that the PI film designed and served as the protecting layers for LEO spacecraft themselves might be eroded by AO exposure first, thereby losing the protecting functions. Even if the PI films are protected by AO-resistant surface coatings or fillers, such as silica, titania, alumina, germanium, and so on, the highly active AO might destroy the PI film matrixes via an undercutting route [7,8]
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