Clustering of Entanglement Points in Highly Strained Polymer Melts

Abstract

Polymer melts undergoing large deformation by elongation are studied by molecular dynamics simulations of bead–spring chains in melts. By applying a primitive path analysis to strongly deformed polymer melts, the role of topological constraints in highly entangled polymer melts is investigated and quantified. We show that the overall, large scale conformations of the primitive paths (PPs) of stretched chains follow affine deformation while the number and the distribution of entanglement points along the PPs do not. Right after deformation, PPs of chains retract in both directions parallel and perpendicular to the elongation. Upon further relaxation we observe a long-lived clustering of entanglement points. Together with the delayed relaxation time this leads to a metastable inhomogeneous distribution of topological constraints in the melts.

High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures

“…We hypothesize that the alternating behavior between structured nanofibers and amorphous connecting regions arises from the localization of entanglement points between neighboring nanofibers, similar to recent MD simulations that have shown nonaffine clustering of entanglements between homopolymer chains during elongation. 56 We posit that during strain, sections of the polymer chain between entanglement points are kinetically free to lengthen along the stretching axis, and chain sliding between neighboring chains aligns these lengthened sections into supramolecular nanofibers while simultaneously clustering the kinetically restricted entanglement junctions into the amorphous connecting regions between nanofibers. This hypothesis corresponds nicely with the observed nanofiber diameter, since the entanglement molecular weight ( M e ) of PPG is ∼2–3 kDa ( M c ≈ 2–3 M e ), 57 which corresponds to about 3–5 repeat units of PPG-MPU (0.65 kDa each) or a length of ∼6–10 nm.…”

Control of Polymer Properties by Entanglement: A Review

“…In recent years, many studies have proposed nonlinear molecular chain motion models, but the mechanism of molecular chain motion in polymer melts undergoing large deformation by elongation is still unknown. [ 50–52 ]…”

Investigation of Crystallization and Relaxation Effects in Coarse-Grained Polyethylene Systems after Uniaxial Stretching

“…Hsu and Kremer [12,13] investigate the relaxation behavior of a generic polymer model after large uniaxial stretching. Their main focus is on the analysis of the primitive path and the stress relaxation behavior.…”