Anomalous Temperature-Dependent Thermal Transport in Crystalline Polyethylene Driven by Strong Anharmonicity

Area of Science:

• Materials Science
• Condensed Matter Physics
• Polymer Science

Background:

• Thermal conductivity in crystalline materials typically decreases with increasing temperature due to phonon anharmonicity.
• Understanding thermal transport in polymers is crucial for designing materials with specific thermal management properties.

Purpose of the Study:

• To investigate the anomalous thermal transport behavior in crystalline polyethylene using first-principles calculations.
• To elucidate the underlying mechanisms responsible for contrasting thermal conductivity trends along and perpendicular to the polymer chain.

Main Methods:

• Solving the Wigner transport equation.
• Employing the stochastic self-consistent harmonic approximation.
• Conducting a comprehensive first-principles investigation.

Main Results:

• Thermal conductivity decreases along the chain direction but increases nearly linearly in out-of-chain directions.
• Anomalous behavior attributed to particle-like transport along the chain and wave-like transport perpendicular to it.
• Strong anharmonicity facilitates phonon tunneling in out-of-plane directions.

Conclusions:

• Findings provide fundamental insights into anisotropic thermal transport in crystalline polymers.
• Suggests that increased anharmonicity and disorder can enhance thermal conductivity in out-of-plane directions.
• Offers guidance for engineering thermal properties of polymers.