Abstract
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.
Highlights
Over the last three decades, the heavy ion irradiation of solid materials including polymers has been the subject of extensive research, studying both the fundamental interaction mechanisms and the opportunities for real-world applications
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 polyethylene terephthalate (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
Irradiation of polymers with swift ions leads to various irreversible effects, such as amorphization and destruction [4,5], surface modification [6,7,8], and chemical cross-linking of polymers [9,10,11]. The irreversibility of these effects is due to them being caused by highly energetic δ-electrons knocked out from the track core by the irradiating ions and cascades of secondary electrons formed in turn by these δ-electrons [9,10,11,12,13]
Summary
Over the last three decades, the heavy ion irradiation of solid materials including polymers has been the subject of extensive research, studying both the fundamental interaction mechanisms and the opportunities for real-world applications. The presence of a residual radial electric field in the latent track in PET is the cause of the induced ordering of benzene-carboxyl subunits of repeat units of polymer molecules seen in [20]. It is well-known that these subunits have the ability to rotate relative to the backbone of the molecule: the rotational properties of molecular subunits forms the basis of the field of stereochemistry, see e.g., [21]. After 3 months of observation, the changes in the structural characteristics provided clear evidence of the underlying mechanisms for their occurrence and temporal evolution
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