Water uptake, distribution, and mobility in amorphous poly(D,L-lactide) by molecular dynamics simulation

Area of Science:

• Materials Science
• Computational Chemistry
• Polymer Science

Background:

• Amorphous poly(lactide) (PLA) is a widely used biodegradable polymer.
• Understanding PLA's physical properties and molecular interactions is crucial for its applications.
• Computational modeling offers a powerful tool to investigate polymer behavior at the molecular level.

Purpose of the Study:

• To develop an explicit all-atom computational model for amorphous poly(lactide) (PLA).
• To explore molecular interactions and predict physical properties of PLA glasses using molecular dynamics simulations.
• To investigate water sorption, local mobility, and diffusion dynamics in PLA.

Main Methods:

• Development of an all-atom computational model for amorphous PLA.
• Conducting molecular dynamics simulations of PLA glasses.
• Analysis of density, glass transition temperature, solubility parameter, water sorption, atomic fluctuations, and water diffusion.

Main Results:

• The computational model accurately predicted PLA density (1.23 g/cm(3)) and solubility parameter (20.6 MPa(1/2)).
• Simulated water sorption isotherm and water molecule localization near ester groups agreed with experimental data.
• Local mobility in PLA decreased with aging and near the glass transition temperature (Tg).
• Water diffusion exhibited non-Einsteinian behavior, correlating with PLA C=O group relaxation.

Conclusions:

• The developed computational model provides a reliable method for predicting PLA properties.
• Molecular dynamics simulations reveal key insights into water-PLA interactions and diffusion mechanisms.
• The findings contribute to a deeper understanding of amorphous polymer behavior and relaxation-diffusion coupling.