Surface and structural changes in polyimide by 100 MeV Ag7+ ion irradiation

Thin films of polyimide (PMDA-ODA, Kapton) were irradiated with 100 MeV Ag7+ ions at the fluences varying from 1011 to 5 × 1012 ions/cm2. Some bulk and surface properties of ion-irradiated polyimide were studied by FTIR, UV–Visible, XRD, SEM and contact angle measurements. The FTIR analysis reveals that the scissioning of various bonds in PMDA and ODA, namely C–H, O–H, N–H, C–N, C–O–C, O–C, C–C and CC occurred at the fluence of 5 × 1011 ions/cm2. Moreover, the over-all bond structure was found to be gradually damaged with increasing fluence. The decrease in optical absorbance at 1725–1780 cm− 1 indicates decarbonylation. UV–Visible spectra show a red shift from 505 to 538 nm and the subsequent decrease in optical band gap from 2.45 to 2.30 eV. This is mainly due to carbonization and conjugation. Further, the increased absorbance in UV–Visible regime and darkening of polyimide films clearly indicate the disruption of CTC complexes and subsequent carbonization. The XRD spectra of pristine and irradiated polyimide did not show sharp peaks, however, the intensity of the observed broad and diffused XRD peak was found to decrease at the fluence of 5 × 1012 ions/cm2. This confirms the amorphisation of polyimide. The contact angle was found to decrease from the pristine value of 82° to 43° at the maximum fluence of 5 × 1012 ions/cm2. This signifies formation of polar groups on the irradiated surface and roughening. This is also confirmed in SEM analysis.