Shear-stress fluctuations and relaxation in polymer glasses

Area of Science:

• Materials Science
• Condensed Matter Physics
• Polymer Science

Background:

• Polymer glasses exhibit complex mechanical behavior near the glass transition.
• Understanding shear-stress fluctuations is crucial for characterizing material properties.

Purpose of the Study:

• To investigate shear-stress fluctuations in a polymer glass model using molecular dynamics simulations.
• To analyze the temperature and time dependence of the shear modulus and relaxation modulus.
• To examine the behavior of the shear modulus at the glass transition.

Main Methods:

• Molecular dynamics simulations of a coarse-grained polymer glass model.
• Analysis of quasistatic and dynamical shear-stress fluctuations.
• Calculation of ensemble-averaged shear modulus (μ_sf) and shear-stress relaxation modulus (G(t)).
• Examination of standard deviations across 100 independent configurations.

Main Results:

• The ensemble-averaged shear modulus (μ_sf) continuously decreases with increasing temperature (T).
• The standard deviation of the shear modulus (δμ_sf) shows a nonmonotonic behavior with a peak at the glass transition.
• The study confirms effective time-translational invariance, linking μ_sf dependence on sampling time (Δt) to G(t).

Conclusions:

• The behavior of the shear modulus at the glass transition is complex, making the question of continuity ill-posed.
• Shear-stress fluctuations provide critical insights into the mechanical properties of polymer glasses.
• The findings contribute to a deeper understanding of glassy dynamics and material response.