Coincident Correlation between Vibrational Dynamics and Primary Relaxation of Polymers with Strong or Weak Johari-Goldstein Relaxation

The correlation between the vibrational dynamics, as sensed by the Debye-Waller factor, and the primary relaxation in the presence of secondary Johari-Goldstein (JG) relaxation, has been investigated through molecular dynamics simulations. Two melts of polymer chains with different bond length, resulting in rather different strength of the JG relaxation are studied. We focus on the bond-orientation correlation function, exhibiting higher JG sensitivity with respect to alternatives provided by torsional autocorrelation function and intermediate scattering function. We find that, even if changing the bond length alters both the strength and the relaxation time of the JG relaxation, it leaves unaffected the correlation between the vibrational dynamics and the primary relaxation. The finding is in harmony with previous studies reporting that numerical models not showing secondary relaxations exhibit striking agreement with experimental data of polymers also where the presence of JG relaxation is known.

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Vibrational dynamics of the filled skutterudite Yb1−xFe4Sb12: Debye-Waller factor, generalized density of states, and elastic structure factor

Physical Review B ◽

10.1103/physrevb.89.014302 ◽

2014 ◽

Vol 89 (1) ◽

Cited By ~ 9

Author(s):

Michael Marek Koza ◽

Andreas Leithe-Jasper ◽

Helge Rosner ◽

Walter Schnelle ◽

Hannu Mutka ◽

...

Keyword(s):

Density Of States ◽

Structure Factor ◽

Waller Factor ◽

Elastic Structure ◽

Vibrational Dynamics ◽

Filled Skutterudite ◽

Debye Waller Factor

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Finite-size effects in molecular dynamics simulations: Intermediate scattering function and velocity of sound. III. Theory and application to a model krypton fluid

Physical Review E ◽

10.1103/physreve.64.051201 ◽

2001 ◽

Vol 64 (5) ◽

Cited By ~ 3

Author(s):

J. J. Salacuse ◽

P. A. Egelstaff

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Size Effects ◽

Finite Size ◽

Velocity Of Sound ◽

Scattering Function ◽

Finite Size Effects ◽

Intermediate Scattering Function ◽

Dynamics Simulations

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Systematic coarse-graining of epoxy resins with machine learning-informed energy renormalization

npj Computational Materials ◽

10.1038/s41524-021-00634-1 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Andrea Giuntoli ◽

Nitin K. Hansoge ◽

Anton van Beek ◽

Zhaoxu Meng ◽

Wei Chen ◽

...

Keyword(s):

Machine Learning ◽

Epoxy Resins ◽

Large Scale ◽

Coarse Graining ◽

Waller Factor ◽

Diglycidyl Ether ◽

Debye Waller Factor ◽

Dynamics Simulations ◽

Renormalization Method ◽

Energy Renormalization

AbstractA persistent challenge in molecular modeling of thermoset polymers is capturing the effects of chemical composition and degree of crosslinking (DC) on dynamical and mechanical properties with high computational efficiency. We established a coarse-graining (CG) approach combining the energy renormalization method with Gaussian process surrogate models of molecular dynamics simulations. This allows a machine-learning informed functional calibration of DC-dependent CG force field parameters. Taking versatile epoxy resins consisting of Bisphenol A diglycidyl ether combined with curing agent of either 4,4-Diaminodicyclohexylmethane or polyoxypropylene diamines, we demonstrated excellent agreement between all-atom and CG predictions for density, Debye-Waller factor, Young’s modulus, and yield stress at any DC. We further introduced a surrogate model-enabled simplification of the functional forms of 14 non-bonded calibration parameters by quantifying the uncertainty of a candidate set of calibration functions. The framework established provides an efficient methodology for chemistry-specific, large-scale investigations of the dynamics and mechanics of epoxy resins.

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The effect of temperature on high-resolution TEM image contrast

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100139573 ◽

1995 ◽

Vol 53 ◽

pp. 640-641

Author(s):

T. Geipel ◽

W. Mader ◽

P. Pirouz

Keyword(s):

Form Factor ◽

Inelastic Scattering ◽

Accurate Method ◽

Waller Factor ◽

Effect Of Temperature ◽

Specimen Thickness ◽

Influence Of Temperature ◽

Debye Waller Factor ◽

Influence Of Temperature On ◽

Atomic Form Factor

Temperature affects both elastic and inelastic scattering of electrons in a crystal. The Debye-Waller factor, B, describes the influence of temperature on the elastic scattering of electrons, whereas the imaginary part of the (complex) atomic form factor, fc = fr + ifi, describes the influence of temperature on the inelastic scattering of electrons (i.e. absorption). In HRTEM simulations, two possible ways to include absorption are: (i) an approximate method in which absorption is described by a phenomenological constant, μ, i.e. fi; - μfr, with the real part of the atomic form factor, fr, obtained from Hartree-Fock calculations, (ii) a more accurate method in which the absorptive components, fi of the atomic form factor are explicitly calculated. In this contribution, the inclusion of both the Debye-Waller factor and absorption on HRTEM images of a (Oll)-oriented GaAs crystal are presented (using the EMS software.Fig. 1 shows the the amplitudes and phases of the dominant 111 beams as a function of the specimen thickness, t, for the cases when μ = 0 (i.e. no absorption, solid line) and μ = 0.1 (with absorption, dashed line).

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