Properties and Improved Space Survivability of POSS (Polyhedral Oligomeric Silsesquioxane) Polyimides
- PDF / 1,654,965 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 193 Views
NN9.1.1
Properties and Improved Space Survivability of POSS (Polyhedral Oligomeric Silsesquioxane) Polyimides Sandra J. Tomczak*(1), Darrell Marchant(2), Steve Svejda(1), Timothy K. Minton(3), Amy L. Brunsvold (3), Irina Gouzman(4), Eitan Grossman(4), George C. Schatz(5), Diego Troya(5), LiPeng Sun(5), Rene I. Gonzalez (1) AFRL/PRSM, Materials Applications Branch, Air Force Research Laboratory, 10 E. Saturn Blvd, Bldg. 8451, Edwards AFB, CA 93524, USA,*[email protected] (2) ERC Incorporated, Materials Applications Branch, Air Force Research Laboratory, 10 East Saturn Blvd, Bldg 8451, Edwards AFB, CA 93524, USA (3) Department of Chemistry and Biochemistry, Montana State University, 108 Gaines Hall, Bozeman, MT 59717, USA [email protected] (4) Space Environment Section, Soreq NRC,Yavne 81800, Israel (5) Department of Chemistry, Northwestern University, Evanston, IL. 60208-3113 USA, [email protected] ABSTRACT Kapton polyimide (PI) is widely used on the exterior of spacecraft as a thermal insulator. Atomic oxygen (AO) in lower earth orbit (LEO) causes severe degradation in Kapton resulting in reduced spacecraft lifetimes. One solution is to coat the polymer surface with SiO2 since this coating is known to impart remarkable oxidation resistance. Imperfections in the SiO2 application process and micrometeoroid / debris impact in orbit damage the SiO2 coating, leading to erosion of Kapton. A self passivating, self healing silica layer protecting underlying Kapton upon exposure to AO may result from the nanodispersion of silicon and oxygen within the polymer matrix. Polyhedral oligomeric silsesquioxane (POSS) is composed of an inorganic cage structure with a 2:3 Si:O ratio surrounded by tailorable organic groups and is a possible delivery system for nanodispersed silica. A POSS dianiline was copolymerized with pyromellitic dianhydride and 4,4΄-oxydianiline resulting in POSS Kapton Polyimide. The glass transition temperature (Tg) of 5 to 25 weight % POSS Polyimide was determined to be slightly lower, 5 – 10 %, than that of unmodified polyimides (414 ºC). Furthermore the room temperature modulus of polyimide is unaffected by POSS, and the modulus at temperatures greater than the Tg of the polyimide is doubled by the incorporation of 20 wt % POSS. To simulate LEO conditions, POSS PI films underwent exposure to a hyperthermal O-atom beam. Surface analysis of exposed and unexposed films conducted with X-ray photoelectron spectroscopy, atomic force microscopy, and surface profilometry support the formation of a SiO2 self healing passivation layer upon AO exposure. This is exemplified by erosion rates of 10 and 20 weight % POSS PI samples which were 3.7 and 0.98 percent, respectively, of the erosion rate for Kapton H at a fluence of 8.5 x 1020 O atoms cm-2. This data corresponds to an erosion yield for 10 wt % POSS PI of 4.8 % of Kapton H. In a separate exposure, at a fluence of 7.33 x 1020 O atoms cm-2, 25 wt % POSS Polyimide showed the erosion yield of about 1.1 % of that of Kapton H. Also, recently at
Data Loading...
