Microvoid formation and strain hardening in highly cross-linked polymer networks

Area of Science:

• Materials Science
• Polymer Physics
• Computational Materials Science

Background:

• Polymer glasses exhibit complex mechanical behaviors under stress.
• Understanding the microscopic origins of strain hardening is crucial for designing advanced materials.

Purpose of the Study:

• To investigate the microscopic mechanisms behind strain hardening in highly cross-linked polymer glasses.
• To identify the key structural factors contributing to strain hardening behavior.

Main Methods:

• Utilizing molecular dynamics simulations with a generic polymer model.
• Analyzing the formation and evolution of microvoids during tensile deformation.
• Comparing results from models with flexible cross-linkers versus fixed bond angles.

Main Results:

• Observed strain hardening in highly cross-linked polymer glasses under tensile load.
• Identified microvoid formation, without bond breaking, as the origin of strain hardening.
• Characterized a consistent void size distribution, similar to Lennard-Jones particle packings.
• Found no microvoid-based strain hardening in models with tetrahedral bond angle constraints.

Conclusions:

• Microvoid formation is the primary microscopic mechanism for strain hardening in these polymer glasses.
• Flexible cross-linkers are critical for enabling strain hardening.
• The findings provide insights into the mechanical response of cross-linked polymer networks.