Siloxane molecules: Nonlinear elastic behavior and fracture characteristics

TL;DR

This study investigates the nonlinear elastic behavior and fracture mechanisms of siloxane molecules through molecular dynamics simulations, revealing deviations from classical models and providing a framework for multiscale material modeling.

Contribution

It introduces a simple non-uniform chain model that captures MD-observed effects and offers a general procedure to extend MD rupture time analysis to broader molecular systems.

Findings

Short chains deviate from classical stiffness and rupture time scalings.

Fracture mechanisms depend non-monotonically on applied force.

PDMS networks likely fail at crosslinking points.

Abstract

Fracture phenomena in soft materials span multiple length- and timescales. This poses a major challenge in computational modeling and predictive materials design. To pass quantitatively from molecular- to continuum scales, a precise representation of the material response at the molecular level is vital. Here, we derive the nonlinear elastic response and fracture characteristics of individual siloxane molecules using molecular dynamics (MD) studies. For short chains, we find deviations from classical scalings for both the effective stiffness and mean chain rupture times. A simple model of a non-uniform chain of Kuhn segments captures the observed effect and agrees well with MD data. We find that the dominating fracture mechanism depends on the applied force scale in a non-monotonic fashion. This analysis suggests that common polydimethylsiloxane (PDMS) networks fail at crosslinking points. Our results can be readily lumped into coarse-grained models. Although focusing on PDMS as a model system, our study presents a general procedure to pass beyond the window of accessible rupture times in MD studies employing mean first passage time theory, which can be exploited for arbitrary molecular systems.