Study of chain scission versus crosslinking in MeV ion-irradiated polycarbonate using dielectric constant measurements and UV spectroscopy

High-energy heavy-ion irradiation of polycarbonate (PC) causes both chain scission and crosslinking. Ultraviolet spectroscopy was used to verify these chemical changes in 7Li (fluence: 1x1012 and 5x1012 ions/cm2) and 59Ni (fluence: 1x1012 ions/cm2) irradiated PC films. The changes in chemical constitution, structure and composition of irradiated polycarbonate was also studied by dielectric constant measurements. The dielectric constant ε' and tan δ values were found to increase with increased fluences compared to pristine sample. The tan δ versus temperature (T) plots showed one relaxation peak (Tα) in the temperature range 300-396 K for all the samples. Tα was found to shift to lower temperature for the polycarbonate irradiated with 7Li at a fluence of 1x1012 ions/cm2, however for the PC irradiated at a higher fluence 5x1012 ions/cm2) the peak shifted to a higher temperature. This indicated that for 7Li-irradiated sample in the first case chain scission occurred and in the second case end-linking had occurred . For the 59Ni-irradiated samples the relaxation peak shifts to higher temperature indicating that end-linking has taken place. The activation energies for the relaxation process have also been determined using the tan δ versus temperature plots at various frequencies (1, 3, 5, 10 and 60 kHz)