Electrolyte penetration into high energy ion irradiated polymers

Several polymers such as polyimide (PI), polyethylene terephthalate (PET), polycarbonate (PC), and silicone rubber (PSiO) were irradiated with some hundred MeV to GeV heavy ions in various directions of α=0–70° to the sample normal. Subsequently, electrolytes (LiCl, LiOH) were allowed to penetrate into the irradiated foils at ambient temperature, and the emerging electrolyte depth distributions were measured in all samples. The different polymer foils showed a different angular dependence of the initial electrolyte uptake. Whereas in PI, the electrolyte uptake increased with increasing implantation angle, a strong decrease was observed with increasing angle for PSiO, and a minor decrease for the PET and PC foils. This is understood in terms of different penetration mechanisms. Whereas capillaric penetration into tracks predicts a proportionality of the electrolyte uptake with cos (α), diffusive penetration should scale with 1/cos(α). Therefore, we conclude that the electrolyte initially penetrates via diffusive mechanisms into PI, but via dominant nanocapillarity into the other examined polymers. This has immediate consequences for the track microstructures. Whereas tracks in PI have little or no additional open porosity as compared with the pristine matter, irradiated PSiO apparently has the most open structure. In tracks in PET, rapid onset of swelling appears to counteract efficiently the electrolyte uptake.