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J Phys Chem B. 2018 Feb 15;122(6):2023-2030. doi: 10.1021/acs.jpcb.7b12172. Epub 2018 Feb 1.

Optical Properties of Saturated and Unsaturated Carbonyl Defects in Polyethylene.

Author information

1
DEN-Service de Recherches de Métallurgie Physique, CEA, Université Paris-Saclay , F-91191 Gif sur Yvette, France.
2
Materials Research Laboratory, University of Nova Gorica , SI-5000 Nova Gorica, Slovenia.
3
CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, c/o SISSA Scuola Internazionale Superiore di Studi Avanzati , Via Bonomea 265, 34136 Trieste Italy.

Abstract

Polyethylene (PE), one of the simplest and most used aliphatic polymers, is generally provided with a number of additives, in particular antioxidants, because of its tendency to get oxidized. Carbonyl defects, a product of the oxidation of PE, are occurring in various forms, in particular saturated ones, known as ketones, where a C═O double bond substitutes a CH2 group, and various unsaturated ones, i.e., with further missing hydrogens. Many experimental investigations of the optical properties in the visible/UV range mainly attribute the photoluminescence of PE to one specific kind of unsaturated carbonyls, following analogies to the emission spectra of similar small molecules. However, the reason why saturated carbonyls should not be optically detected is not clear. We investigated the optical properties of PE with and without carbonyl defects using perturbative GW and the Bethe-Salpeter equation in order to take into account excitonic effects. We discuss the calculated excitonic states in comparison with experimental absorption/emission energies and the stability of both saturated and unsaturated carbonyl defects. We conclude that the unsaturated defects are indeed the best candidate for the luminescence of oxidized PE, and the reason is mainly due to oscillator strengths.

PMID:
29360369
DOI:
10.1021/acs.jpcb.7b12172

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