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Shear Modulus and Shear-Stress Fluctuations in Polymer Glasses
I Kriuchevskyi1, J P Wittmer1, H Meyer1
1Institut Charles Sadron, Université de Strasbourg and CNRS, 23 rue du Loess, 67034 Strasbourg Cedex, France.
Physical Review Letters
|October 21, 2017
Summary
This study reveals that while the average shear modulus of polymer glasses decreases with temperature, its fluctuation peaks at the glass transition. Predicting the modulus for a single polymer configuration near this transition remains challenging.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Chemistry
Background:
- Polymer glasses exhibit complex mechanical properties influenced by temperature and time.
- Understanding shear modulus fluctuations is crucial for characterizing glass transition behavior.
Purpose of the Study:
- To investigate the temperature and time dependence of shear modulus (μ) and its fluctuations in a polymer glass model.
- To analyze the behavior of the standard deviation of shear modulus (δμ) around the glass transition.
Main Methods:
- Utilized molecular dynamics simulations with a standard coarse-grained polymer glass model.
- Employed the stress-fluctuation formalism to analyze shear modulus and its statistical properties.
- Examined the shear modulus as a function of temperature (T) and sampling time (Δt).
Main Results:
- The ensemble-averaged shear modulus (μ(T)) consistently decreases with increasing temperature for all sampling times.
- The standard deviation of shear modulus (δμ(T)) shows a nonmonotonic behavior, featuring a distinct peak at the glass transition temperature.
- Shear modulus (μ(Δt)) exhibits effective time-translational invariance, explainable via an integral of the shear-stress relaxation modulus G(t).
Conclusions:
- The glass transition is characterized by a singular peak in shear modulus fluctuations.
- Increasing sampling time sharpens the μ(T) crossover and enhances the singularity of the δμ(T) peak.
- Accurately predicting the shear modulus of an individual polymer configuration at the glass transition is inherently difficult.
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