Crystalline Moduli of Polymers, Evaluated from Density Functional Theory Calculations under Periodic Boundary...

Area of Science:

• Computational Materials Science
• Polymer Physics
• Quantum Chemistry

Background:

• Accurate prediction of polymer crystal mechanical properties is crucial for material design.
• Existing methods may lack precision or require extensive experimental data.
• Quantum chemistry offers a powerful theoretical framework for molecular-level property calculations.

Purpose of the Study:

• To develop and validate a theoretical methodology for calculating polymer crystal mechanical properties.
• To apply this method to diverse polymer systems including poly(methylene oxide), polyethylene, and polyesters.
• To interpret calculated mechanical properties in relation to polymer chain conformation.

Main Methods:

• Utilized density functional theory (DFT) with dispersion force correction.
• Employed three-dimensional periodic boundary conditions for crystal structure optimization.
• Calculated mechanical properties such as crystalline moduli and compressibilities.

Main Results:

• Optimized crystal structures of PMO, PE, PET, PTT, and PBT were in excellent agreement with experimental diffraction data.
• Calculated crystalline moduli (E∥) for PMO, PE, PET, PTT, and PBT were 114, 333, 182, 7.1, and 20.8 GPa, respectively.
• Results were compared with experimental data from X-ray diffraction, Raman spectroscopy, and neutron inelastic scattering.

Conclusions:

• The developed quantum chemistry methodology accurately predicts polymer crystal mechanical properties.
• Calculated moduli correlate with polymer chain conformational characteristics.
• The study discusses the validity of the homogeneous stress hypothesis used in X-ray diffraction analysis.