On the penetration of aqueous solutions into pristine and radiation damaged polyimide

The penetration of aqueous solutions at different pH values into pristine a nd ion-irradiated commercial polyimide (PI, "Kapton") foils was examined, b y using Li ions as tracers to probe the corresponding penetrant depth distr ibutions. 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 solutio n penetration was observed up to some maximum penetrant uptake value. The p enetrant depth distributions point at nanocapillaric penetration mechanisms in this initial stage. At longer exposure times of the polymer, the penetr ant concentration diminishes transiently, suggesting that polymer swelling in the confined track zone leads to a reduction of the available free volum e. In the subsequent stage of penetrant uptake this process is reversed aga in which we explain by crazing and overall swelling. Whereas thereafter sat uration is reached for non-alkaline penetrants, alkaline solutions in irrad iated 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 resul ts in a pronounced increase of the uptake capability. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.