Local dynamics of polyethylene and its oligomers: A molecular dynamics interpretation of the incoherent dynamic structure factor

G. Arialdi, K. Karatasos, J. P. Ryckaert, V. Arrighi, F. Saggio, A. Triolo, A. Desmedt, J. Pieper, R. E. Lechner

Research output: Contribution to journalArticle

Abstract

We present a detailed study of the local dynamics of short polyethylene (PE) chains using molecular dynamics (MD) simulations and quasi-elastic neutron scattering (QENS) data. QENS measurements were carried out on two samples having different chain lengths: C44H90 and PE2K (Mw = 2150 g/mol). The incoherent dynamic structure factors obtained from experiments at T = 450 K and MD simulations carried out at the same temperature are compared in the range 0.5 = Q = 2.0 Å-1. Agreement between experimental data and simulations is quantitative. Attempts are made to characterize the momentum transfer and the chain length dependence of the I(Q,t) and S(Q,?) data on the basis of the Kohlrausch-Williams-Watts (KWW) function and two exponentials relaxation functions in time. As MD simulation data cover a broader frequency window and have a very low statistical noise, a more refined analysis of the intermediate scattering functions in terms of a continuous linear combination of exponentials weighted by a distribution of relaxation times has been performed. This analysis shows a systematic evolution of the shape of the distribution of relaxation times going from a two-process situation at low Q toward a single merged process at higher Q. This allows us to point out in a well-defined case the limitations of both the KWW and two exponentials descriptions which approximate the distribution of relaxation times either as one broad and asymmetric distribution or as a conjugation of two delta distributions.

Original languageEnglish
Pages (from-to)8864-8875
Number of pages12
JournalMacromolecules
Volume36
Issue number23
DOIs
Publication statusPublished - 18 Nov 2003

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oligomers
polyethylenes
molecular dynamics
relaxation time
elastic scattering
neutron scattering
simulation
scattering functions
data simulation
conjugation
momentum transfer
Q factors
temperature

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Arialdi, G. ; Karatasos, K. ; Ryckaert, J. P. ; Arrighi, V. ; Saggio, F. ; Triolo, A. ; Desmedt, A. ; Pieper, J. ; Lechner, R. E. / Local dynamics of polyethylene and its oligomers : A molecular dynamics interpretation of the incoherent dynamic structure factor. In: Macromolecules. 2003 ; Vol. 36, No. 23. pp. 8864-8875.
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Arialdi, G, Karatasos, K, Ryckaert, JP, Arrighi, V, Saggio, F, Triolo, A, Desmedt, A, Pieper, J & Lechner, RE 2003, 'Local dynamics of polyethylene and its oligomers: A molecular dynamics interpretation of the incoherent dynamic structure factor', Macromolecules, vol. 36, no. 23, pp. 8864-8875. https://doi.org/10.1021/ma0256789

Local dynamics of polyethylene and its oligomers : A molecular dynamics interpretation of the incoherent dynamic structure factor. / Arialdi, G.; Karatasos, K.; Ryckaert, J. P.; Arrighi, V.; Saggio, F.; Triolo, A.; Desmedt, A.; Pieper, J.; Lechner, R. E.

In: Macromolecules, Vol. 36, No. 23, 18.11.2003, p. 8864-8875.

Research output: Contribution to journalArticle

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T1 - Local dynamics of polyethylene and its oligomers

T2 - A molecular dynamics interpretation of the incoherent dynamic structure factor

AU - Arialdi, G.

AU - Karatasos, K.

AU - Ryckaert, J. P.

AU - Arrighi, V.

AU - Saggio, F.

AU - Triolo, A.

AU - Desmedt, A.

AU - Pieper, J.

AU - Lechner, R. E.

PY - 2003/11/18

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N2 - We present a detailed study of the local dynamics of short polyethylene (PE) chains using molecular dynamics (MD) simulations and quasi-elastic neutron scattering (QENS) data. QENS measurements were carried out on two samples having different chain lengths: C44H90 and PE2K (Mw = 2150 g/mol). The incoherent dynamic structure factors obtained from experiments at T = 450 K and MD simulations carried out at the same temperature are compared in the range 0.5 = Q = 2.0 Å-1. Agreement between experimental data and simulations is quantitative. Attempts are made to characterize the momentum transfer and the chain length dependence of the I(Q,t) and S(Q,?) data on the basis of the Kohlrausch-Williams-Watts (KWW) function and two exponentials relaxation functions in time. As MD simulation data cover a broader frequency window and have a very low statistical noise, a more refined analysis of the intermediate scattering functions in terms of a continuous linear combination of exponentials weighted by a distribution of relaxation times has been performed. This analysis shows a systematic evolution of the shape of the distribution of relaxation times going from a two-process situation at low Q toward a single merged process at higher Q. This allows us to point out in a well-defined case the limitations of both the KWW and two exponentials descriptions which approximate the distribution of relaxation times either as one broad and asymmetric distribution or as a conjugation of two delta distributions.

AB - We present a detailed study of the local dynamics of short polyethylene (PE) chains using molecular dynamics (MD) simulations and quasi-elastic neutron scattering (QENS) data. QENS measurements were carried out on two samples having different chain lengths: C44H90 and PE2K (Mw = 2150 g/mol). The incoherent dynamic structure factors obtained from experiments at T = 450 K and MD simulations carried out at the same temperature are compared in the range 0.5 = Q = 2.0 Å-1. Agreement between experimental data and simulations is quantitative. Attempts are made to characterize the momentum transfer and the chain length dependence of the I(Q,t) and S(Q,?) data on the basis of the Kohlrausch-Williams-Watts (KWW) function and two exponentials relaxation functions in time. As MD simulation data cover a broader frequency window and have a very low statistical noise, a more refined analysis of the intermediate scattering functions in terms of a continuous linear combination of exponentials weighted by a distribution of relaxation times has been performed. This analysis shows a systematic evolution of the shape of the distribution of relaxation times going from a two-process situation at low Q toward a single merged process at higher Q. This allows us to point out in a well-defined case the limitations of both the KWW and two exponentials descriptions which approximate the distribution of relaxation times either as one broad and asymmetric distribution or as a conjugation of two delta distributions.

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U2 - 10.1021/ma0256789

DO - 10.1021/ma0256789

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