Free volume evolution in 50 MeV Li3+ ion-irradiated polymers studied by positron annihilation lifetime spectroscopy

This article is aimed at studying the effect of ion irradiation on free volume of polyethersulphone (PES) and polyamide nylon-6 (PN-6) polymers by positron annihilation lifetime spectroscopy (PALS). Free volume properties of polymeric materials change with swift heavy ion irradiation. Free volume is found to have a strong correlation with the macroscopic properties of the polymer. PALS has recently emerged as a unique non-destructive and non-interfering nano-probe, capable of measuring the free volume hole size in polymers with high detection efficiency. PES and PN-6 polymer films of thickness of 250 mu m were irradiated with Li3+ ions of energy 50 MeV from the 15 UD Pelletron accelerator at the Inter University Accelerator Centre, New Delhi, India. PES films were irradiated to the fluences of 1011, 1012, 1013 and 1014 ions/cm2, whereas PN-6 films were irradiated to the fluences of 1011, 1012 and 1013 ions/cm2. The average free volume and fractional free volume obtained from the long-lived component, attributed to ortho-positronium lifetime, are found to vary with the variation of fluence in both the cases.