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 430

Figure 9. The Lifshitz-van der Waals component (●), the acid parameter (○), and the base parame-
ter (▼) of the surface free energy of polyimide films as a function of surface oxygen concentration.
significant because of their very small values. It is, therefore, concluded that the
increase in the wettability of polyimide by the atomic oxygen beam exposure is
mainly caused by the increase in the base parameter of the surface free energy due
to the formation of carbonyl and/or carboxyl groups.
3.3. Contact angles of water on polyimide surfaces exposed to real and simulated
atomic oxygen environments
As shown in the previous sections, XPS results on atomic oxygen-exposed sur-
faces coincide with the actual flight data. Carbon concentrations at the atomic
oxygen beam exposed polyimide surfaces after air exposure (Table 2) are close to
those of flight samples (STS-8 and STS-46 in Table 1). The XPS C1s spectra in-
dicated similar surface chemical states between flight and ground-based samples
(see Figures 4 and 6). A detailed comparison is reported elsewhere [23]. Addi-
tionally, contact angles of water on the polyimide surfaces exposed to atomic
oxygen by ground-based facility and by STS flight were compared in this study.
The results are shown in Figure 10. Figure 10 is the same plot as Figure 8, but the
data points for the flight samples are also added. As shown in Figure 10, both ad-
vancing and receding contact angles for the STS-8 and STS-46 samples lie on the