Siloxane Molecules: Nonlinear Elastic Behavior and Fracture Characteristics.

Area of Science:

• Soft matter physics
• Materials science
• Computational chemistry

Background:

• Fracture in soft materials presents multiscale challenges for computational modeling and predictive design.
• Accurate molecular-level representation is crucial for bridging length and time scales from molecular to continuum models.

Purpose of the Study:

• To derive the nonlinear elastic response and fracture characteristics of individual siloxane molecules.
• To establish a quantitative link between molecular behavior and macroscopic material properties.
• To develop a generalizable method for extending molecular dynamics simulations of fracture.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study individual siloxane molecules.
• A simple model of a nonuniform chain of Kuhn segments was developed to capture observed effects.
• Mean first passage time theory was utilized to extend the accessible rupture times in MD studies.

Main Results:

• Deviations from classical scalings were observed for effective stiffness and mean chain rupture times in short siloxane chains.
• A Kuhn segment model accurately reproduced the MD data for chain behavior.
• The dominant fracture mechanism exhibited a nonmonotonic dependence on the applied force scale.

Conclusions:

• Polydimethylsiloxane (PDMS) networks likely fail at cross-linking points.
• The derived molecular insights can be integrated into coarse-grained models.
• The presented methodology offers a general approach to overcome limitations in MD simulation timescales for fracture studies.