Phantom chain simulations for fracture of star polymer networks on the effect of arm molecular weight

TL;DR

This paper uses phantom chain simulations to study how the molecular weight of arms in star polymer networks affects their fracture behavior, revealing a power-law relationship between stretch at break and strand length.

Contribution

It introduces a simulation-based analysis of star polymer network fracture, highlighting the influence of arm molecular weight and network parameters on mechanical failure.

Findings

Stretch at break scales with strand length as N_s^0.67

Breakage fraction increases with arm molecular weight

Simulation results align with experimental observations

Abstract

This study investigated the fracture of star polymer networks made from prepolymers with various arm molecular weights in the range $2 \leq N_a \leq 0$, for node functionalities $3 \leq f \leq 8$ and conversion ratios $0.6\leq\phi_c\leq0.95$ by phantom chain simulations. The networks were created via end-linking reactions of star polymers dispersed in a simulation box with a fixed monomer density $\rho=8$. The resultant networks were alternatively subjected to energy minimization and uniaxial stretch until the break. The stretch at the break, $\lambda_b$, depended on the strand molecular weight $N_s=2N_a+1$ with a power-law manner described as $\lambda_b \sim N_s^0.67$, consistent with the experiment. However, the strand length before stretch is proportional to $N_s^0.5$, which does not explain the observed N_s-dependence of $\lambda_b$. The analysis based on the non-affine deformation theory does not interpret the phenomenon either. Instead, the increase of normalized prepolymer concentration concerning the overlapping concentration with increasing $N_s$ explains the result through a rise in the fraction of broken strands.