Abstract
Abstract The penetration of aqueous solutions at different pH values into pristine and ion-irradiated commercial polyimide (PI, “Kapton”) foils was examined, by using Li ions as tracers to probe the corresponding penetrant depth distributions. These distributions were recorded for different polymer exposure times and temperatures. For comparison, examinations have also been made on the time dependence of the polyimide conductivity during water uptake. The results derived here for PI are compared with those of other polymers. For both pristine and low-fluence irradiated PI, an initially rapid solution penetration was observed up to some maximum penetrant uptake value. The penetrant depth distributions point at nanocapillaric penetration mechanisms in this initial stage. At longer exposure times of the polymer, the penetrant concentration diminishes transiently, suggesting that polymer swelling in the confined track zone leads to a reduction of the available free volume. In the subsequent stage of penetrant uptake this process is reversed again which we explain by crazing and overall swelling. Whereas thereafter saturation is reached for non-alkaline penetrants, alkaline solutions in irradiated PI show a pronounced continuous uptake, which is correlated with the ion track etching process. Whereas low-fluence ion irradiation of PI leads to a reduction in penetrant uptake compared with the pristine material, high-fluence irradiation results in a pronounced increase of the uptake capability.
Published Version
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