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Open and Anisotropic Soft Regions in a Model Polymer Glass.
Carlo Andrea Massa1, Francesco Puosi2,3, Antonio Tripodo3
1Istituto per i Processi Chimico-Fisici-Consiglio Nazionale delle Ricerche (IPCF-CNR), Via G Moruzzi 1, 56124 Pisa, Italy.
Polymers
|April 30, 2021
Summary
Soft monomers in polymer glasses form tenuous, anisotropic clusters. These clusters, identified via molecular dynamics, are crucial for understanding glass anomalies and vibrational dynamics.
Area of Science:
- Polymer Physics
- Materials Science
- Computational Chemistry
Background:
- Polymer glasses exhibit thermodynamic anomalies attributed to low-frequency vibrational modes.
- Specific monomers, termed 'soft' monomers, significantly contribute to these modes.
Purpose of the Study:
- Investigate the structural and dynamic role of soft monomers in polymer glasses.
- Characterize the clustering behavior and properties of soft monomers.
Main Methods:
- Employed Molecular Dynamics (MD) simulations to model a polymer glass system.
- Implemented a stringent threshold to identify soft monomers, enabling analysis of smaller systems.
- Analyzed monomer clustering, fractal dimensions, and inertia tensors.
Main Results:
- Soft monomers exhibit a strong tendency to form quasi-local clusters (up to 15 monomers).
- Clusters are characterized by an open, tenuous structure (fractal dimension df<2) and significant shape anisotropy.
- A linear correlation was observed between the two largest eigenvalues of the soft cluster inertia tensor.
Conclusions:
- Soft monomers play a critical role in the collective dynamics and thermodynamic properties of polymer glasses.
- The observed clustering and anisotropy provide insights into the microscopic origins of glass behavior.
- Finite-size effects and polymer length dependence warrant further investigation.
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