No abstract

This paper presents the results of a study of polyethylene terephthalate (PET) films irradiated with Ar and Kr ions at both normal orientation and an angle of 40° to the normal. Normal irradiation was performed using Ar8+ and Kr15+ ions with an energy of 1.75 MeV/au and fluences in the range (2–500) × 1010 cm−2 for Ar8+ ions and (1.6 − 6.5) × 1010 cm−2 for Kr15+ ions. Kr ions with an energy of 1.2 MeV/au and charges of 13+, 14+, and 15+ were used for angled irradiation. For each Kr ion charge value, three fluence values were used: 5 × 1010, 1 × 1011, and 2.5 × 1011 cm−2. It is well known that irradiation of PET films by swift heavy ions results in a red shift of the UV-vis transmission spectra absorption edge. The experimental transmission spectra exhibit well-defined interference fringes, which obscure the underlying transmission response. Using an existing technique to obtain interference-free transmission curves Tα(λ) for both pristine and irradiated PET film samples, we found that S, the total radiation-induced absorption of light by the PET film, is proportional to the logarithm of the fluence F. In addition to this dependence on the irradiating fluence, we also found that the charge of the irradiating ion has a significant influence on the position of the absorption edge in the UV-vis spectra. This provides experimentally independent evidence to confirm our previous results showing that ion charge has an effect on the post-irradiation state of PET films. We present a physical interpretation of the observed absorption edge red shift in irradiated PET films as being due to the growth of extended conjugated systems via the formation of intermolecular helical structures. Our investigations into the stability of irradiation-induced effects in PET films show that comparison of UV-vis transmission spectra before and after annealing can provide information about the structure of deep traps in PET.

This paper presents the results of a study of the ordering in polyethylene terephthalate (PET) film induced by Ar8+ ions with an irradiation fluence of 2 × 1012 ions/cm2, and of the temporal stability of the induced ordering in the irradiated sample, over a three month period. Immediately after irradiation, sharp new reflections not seen at lower fluences were observed in X-ray diffraction patterns, with angular positions of 2 θ = 9–10° and 19° and variable azimuthal intensities. X-ray reflections, previously observed at lower fluences, were also seen: at 2 θ = 26° and 23°, associated with PET crystallites, and at 2 θ = 5–12°, associated with induced ordering in the amorphous zone. Aging of the irradiated sample led to significant growth of the ordering region in the amorphous zone for angles up to 2 θ < 15°, as well as to dissipation and blurring of the new diffraction reflections at 2 θ = 9–10° and 2 θ = 19° and the formation of a new diffraction ring reflection in the range 2 θ = 11–16°. The azimuthal distribution of diffraction reflection intensities immediately after irradiation displays a clear oblique cross located predominantly along lines at angles of π/4 with respect to the direction of the texture of the PET film, indicating the formation of spiral structures based on the molecular strands of PET. Our experimental results lead us to conclude that the formation of coherent scattering areas in the amorphous region at 2 θ < 15° is due to intra-chain rotations of benzene-carboxyl subunits of repeat units of the PET chain molecules interacting with the residual electric field of a single latent track; whereas the formation of spiral structures is due to the inter-chain interaction of these preordered asymmetric subunits under the influence of the electric fields from overlapping latent tracks.

We report here experimental results investigating the influence of the initial swift heavy ion charge on the structure of polyethylene terephthalate (PET) film after irradiation, using a structurally sensitive X-ray diffraction method. Kr ions with an energy of 100 MeV and charges of 13+, 14+, and 15+ were each used at irradiation fluences of 5 × 1010, 7.5 × 1010, 1 × 1011, 2.5 × 1011 and 5 × 1011 ions/cm2. At constant energy and irradiation fluence, the post-irradiation structural changes in PET film show a clear dependence on the initial ion charge. As either the fluence or ion charge increase, the latent tracks begin to overlap, leading to cross-linking of PET chain molecules to form rotational isomers (rotamers). We use the fluence corresponding to the onset of overlapping to estimate the size of latent tracks for different ion charges. At the highest fluences, the latent tracks become entirely overlapped, and the interchain cross-linking extends throughout the whole film. Since this cross-linking is due to the dipole–dipole interaction of subunits of repeat units of PET chain molecules, it is reversible, in contrast to the well-known chemical cross-linking of polymer chain molecules under irradiation.

No abstract