Comparison of polyimide film surface properties exposed to real and simulated space environments: Relevance of atomic oxygen effects to wettability in space - Polyimides and Other High Temperature Polymers - page 432

hesive to be origin of the contamination. The other possible scenario is that the
contamination was due to vaporization of the thermal paint/tile of the orbiter body
flap [29].
The experimental results in this study suggest that the increase in wettability of
polyimide surfaces due to atomic oxygen bombardment generally occurs in an
LEO space environment. Such a hydrophilic surface easily allows for adsorption
of contamination. Fluorinated polymers such as PTFE are known to be resistant to
atomic oxygen attack as well as being extremely hydrophobic. The surface fluori-
nation of polyimide by plasma treatment [30] or using hyperthermal atom beam
technique [31] could be a solution which satisfies the requirements both for pro-
tecting from atomic oxygen attack as well as for preventing contamination
adsorption.
4. CONCLUSIONS
The polyimide surfaces exposed to an atomic oxygen beam with translational en-
ergy of 4.7 eV were characterized by AFM, XPS and contact angle analyses. The
AFM and XPS data showed that both the roughness and surface oxygen content at
the polyimide surface increased after atomic oxygen exposure. The contact angles
of water on the atomic oxygen-exposed polyimide film were found to decrease
linearly with increasing oxygen concentration at polyimide surfaces. It was also
made clear that the decrease in the contact angle was due to the increase in the
base parameter of the surface free energy. These experimental results showed that
adsorbed oxygen at the atomic oxygen-exposed polyimide surface formed surface
functional groups that behaved as electron donors. It was suggested that the in-
crease in wettability of polyimide surfaces due to atomic oxygen bombardment
occurred in LEO space environment. Such a hydrophilic polyimide surface allows
for easy adsorption of contamination and may accelerate the performance loss of
the thermal control system of spacecraft. Therefore, for the future application of
polyimide in space use, the development of atomic oxygen resistant polyimide
with a low energy surface for the prevention of contamination adsorption is re-
quired.
Acknowledgments
The authors would like to thank Y. Suzuki and K. Miyashita of Nara Women's
University, H. Kinoshita of Osaka University for their help with experiments.
S.Y. Chung, and T. K. Minton of Jet Propulsion Laboratory, California Institute
of Technology, and S. Kibe of National Aerospace Laboratory of Japan are all ac-
knowledged for providing flight samples. A part of this work was supported by
the Grant-in-Aid for Scientific Research from the Ministry of Education, Sports,
Culture, Science and Technology, Japan; and by the Space Utilization Promotion
Fund from the Japan Space Forum.