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Relaxation dynamics in supercooled oligomer liquids: From shear-stress fluctuations to shear modulus and structural correlations

L. Klochko,J. Baschnagel,J. Wittmer,A. Semenov

Published 2019 in Journal of Chemical Physics

ABSTRACT

Static and dynamical properties of a model glass-forming oligomer liquid are analyzed using molecular dynamics simulations. The temperature and system size effects are assessed for the affine shear modulus μA, the quasistatic shear modulus μsf (obtained using the stress-fluctuation relation), and the shear relaxation modulus G(t). It is found that while both μA and μsf are nearly independent of the system size, their variances show significant system size dependence, in particular, below the glass transition temperature Tg. It is also shown that the standard deviation of the shear modulus, δμsf(T), exhibits a pronounced peak at T ≈ Tg whose position is nearly independent of the system volume V. Moreover, the whole function δμsf(T) is nearly the same for different system sizes above the glass transition. We propose a theory which quantitatively predicts δμsf(T) at T ≳ Tg and explains both its independence of V and its peak near Tg. It is also established that below Tg the variance of the affine modulus follows the standard power law, δμA2∝1/V, while δμsf shows anomalously a slow decrease with V as δμsf2∝1/Vα with α < 1. On this basis, it is argued that the studied glass-forming systems must show long-range structural correlations in the amorphous state.Static and dynamical properties of a model glass-forming oligomer liquid are analyzed using molecular dynamics simulations. The temperature and system size effects are assessed for the affine shear modulus μA, the quasistatic shear modulus μsf (obtained using the stress-fluctuation relation), and the shear relaxation modulus G(t). It is found that while both μA and μsf are nearly independent of the system size, their variances show significant system size dependence, in particular, below the glass transition temperature Tg. It is also shown that the standard deviation of the shear modulus, δμsf(T), exhibits a pronounced peak at T ≈ Tg whose position is nearly independent of the system volume V. Moreover, the whole function δμsf(T) is nearly the same for different system sizes above the glass transition. We propose a theory which quantitatively predicts δμsf(T) at T ≳ Tg and explains both its independence of V and its peak near Tg. It is also established that below Tg the variance of the affine modulus fol...

PUBLICATION RECORD

  • Publication year

    2019

  • Venue

    Journal of Chemical Physics

  • Publication date

    2019-08-05

  • Fields of study

    Materials Science, Physics

  • Identifiers
    DOI 10.1063/1.5110997
  • External record

    Open on Semantic Scholar

  • Source metadata

    Semantic Scholar

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