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

Abstract

High-energy heavy-ion irradiation of polycarbonate (PC) causes both chain scission and crosslinking. Ultraviolet spectroscopy was used to verify these chemical changes in 7 Li (fluence: 1×10 12 and 5×10 12 ions/cm 2 ) and 59 Ni (fluence: 1×10 12 ions/cm 2 ) 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 ( T α ) in the temperature range 300– 396 K for all the samples. T α was found to shift to lower temperature for the polycarbonate irradiated with 7 Li at a fluence of 1×10 12 ions/cm 2 , however for the PC irradiated at a higher fluence 5×10 12 ions/cm 2 ) the peak shifted to a higher temperature. This indicated that for 7 Li -irradiated sample in the first case chain scission occurred and in the second case end-linking had occurred . For the 59 Ni -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 ).