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Thin films (9 μm) of polyvinylidene fluoride (PVDF) are irradiated by swift heavy ions (180 MeV Ag14+) in the fluence range 1×1010–1×1012ions/cm2 with an electronic linear energy transfer LET∼11 keV/nm. In sharp contrast to the previous results, the most characteristic crystalline asymmetric and symmetric “CH2” doublets (located at 3025 and 2985 cm−1), have shown remarkable increase in their respective Fourier transform infrared (FTIR) absorbance intensities upon low fluence ion impact (1010 ions/cm2). This increase in absorbance is in consonance with the simultaneous decrease of the transmission intensities of other crystalline bending vibration bands located at 532 (CF2 bending), 614, 796, and 975 cm−1 (all due to CH2 bending) at the similar ion fluence. It appears most probable from the results that, being a polar polymer, the molecular dipoles in PVDF forming a hydrogen bond network get realigned upon irradiation into a highly ordered state of chain molecules in the crystalline regions and create volume elements as crystallites.

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Thin films (13 μm) of polyethelene terephthalate (PET) are irradiated by different swift metallic heavy ions (180 MeV Ag14+ and 200 MeV Au15+) with the projectile linear energy transfer (LET) (∼10–14 keV/nm), respectively. LET dependence on the molecular structural changes in PFT irradiated at different ion fluences has been studied by the Fourier transform infrared spectroscopy. The study has revealed that beyond a critical LET entirely different pathways of amorphization beginning with partial recrystallization at lower ion fluence impact occurs in PET, contrary to the earlier established results. At considerably higher LET (∼14 keV/nm), the most characteristic crystalline stretching and bending vibration bands such as at 850 cm−1 (CH2 rocking), 972 cm−1 (C=O stretching), 1341 and 1471 cm−1 (CH2 bending) in PET have shown a significant rise in the respective infrared absorbance intensities upon lower ion fluence (∼1011 ions/cm2) impact. The absence of previously reported unsaturations such as alkynes at both the LET beam used are also observed. Interestingly, the aromatic system also appears to be unstable and participating in the modification process, particularly at the higher LET (∼14 KeV/nm). Possible interpretations are discussed.