Exciton self-trapping in bulk polyethylene

Abstract

Abstract. We studied theoretically the behavior of an injected electron-hole pair in crystalline polyethylene. Time-dependent adiabatic evolution by ab-initio molecular dynamics simulations show that the pair will become self-trapped in the perfect crystal, with a trapping energy of about 0.38 eV, with formation of a pair of trans-gauche conformational defects, three C 2 H 4 units apart on the same chain. The electron is confined in the inter-chain pocket created by a local, 120 • rotation of the chain between the two defects, while the hole resides on the chain and is much less bound. Despite the large energy stored in the trapped excitation, there does not appear to be a direct non-radiative channel for electron-hole recombination. This suggests that intrinsic selftrapping of electron-hole pairs inside the ideal quasi-crystalline fraction of PE might not be directly relevant for electrical damage in high-voltage cables.

Surface excitation parameter for selected polymers

“…[32] for PA, PS, PE and PMMA. The energy band gap values are from Refs [33] (PA), [34] (PS), [35] (PE) and [36,37] as a model the expansion in Drude-Lindhard type oscillators [30] Im…”

“…[31] These parameters for PE, PS, PA and PMMA are essentially taken from Ref. [32] , while energy band gap values, E G , are from Refs [33] (PA), [34] (PS), [35] (PE) and [36,37] (PMMA). All parameters are listed in Table 1 and the ELF for PE, PS, PA and PMMA are displayed in Fig.…”

Aging of magnesium stearate under high doses gamma irradiation and oxidative conditions

“…This result has already been observed in different polymers under radiolysis or radio-oxidation [4,22,23]. It can be explained by the formation of new chemical groups formed under irradiation (such as double bounds [24], ester groups [10], or more generally oxidized groups [25,26]) which acts as energy sinks by energy and radicals transfers. This phenomenon has already been explained by Williams [9] as an electron deficiency localized on oxygen atom which will direct reaction to this oxygen atom to complete its valence shell of electrons.…”

Molecular modeling and electron transport in polyethylene

“…In contrast, very recent DFT calculations [54] have found a direct channel for the recombination of the exciton via the breaking of a C-H bond. The discrepancy with the results in [53] might be due to the exchange-correlation functional employed or the different methods chosen to improve the deficiencies of standard DFT. However, reference [54] presents a convincing scenario in which the recombination of an electron-hole pair under electrical stress could lead to degradation of PE.…”

“…In reference [53], an electron-hole pair, an exciton, was injected in a similar crystalline cell, being observed to be long-lived, displaying no apparent direct channel for nonradiactive recombination. In contrast, very recent DFT calculations [54] have found a direct channel for the recombination of the exciton via the breaking of a C-H bond.…”