Forced reptation revealed by chain pull-out simulations

Abstract

We report computation results obtained from extensive molecular dynamics simulations of tensile disentanglement of connector chains placed at the interface between two polymer bulks. Each polymer chain (either belonging to the bulks or being a connector) is treated as a sequence of beads interconnected by springs, using a coarse-grained representation based on the Kremer–Grest model, extended to account for stiffness along the chain backbone. Forced reptation of the connectors was observed during their disentanglement from the bulk chains. The extracted chains are clearly seen following an imaginary “tube” inside the bulks as they are pulled out. The entropic and energetic responses to the external deformation are investigated by monitoring the connector conformation tensor and the modifications of the internal parameters (bonds, bending, and torsion angles along the connectors). The work needed to separate the two bulks is computed from the tensile force induced during debonding in the connector chains. The value of the work reached at total separation is considered as the debonding energy G. The most important parameters controlling G are the length (n) of the chains placed at the interface and their areal density. Our in silico experiments are performed at relatively low areal density and are disregarded if chain scission occurs during disentanglement. As predicted by the reptation theory, for this pure pull-out regime, the power exponent from the scaling G∝na is a≈2, irrespective of chain stiffness. Small variations are found when the connectors form different number of stitches at the interface, or when their length is randomly distributed in between the two bulks. Our results show that the effects of the number of stitches and of the randomness of the block lengths have to be considered together, especially when comparing with experiments where they cannot be controlled rigorously. These results may be significant for industrial applications, such reinforcement of polymer-polymer adhesion by connector chains, when incorporated as constitutive laws at higher time/length scales in finite element calculations.

Relaxation of Rouse Modes for Unentangled Polymers Obtained by Molecular Simulations

“…Harnau et al 18) concluded that the deviation is due to the chain rigidity (CR) from the atomistic molecular simulations for polyethylenes, for which the molecular weight is larger than that used by Paul et al 13) . A similar discussion has been made for beadspring chains by Bulacu and van der Giessen 19) . Other possible mechanisms are the excluded volume interactions (EVI) and the hydrodynamic interactions (HI).…”

“…Indeed, the earlier results 17) have shown that for p < 4 the eigenfunction is fairly close to the sinusoidal function. It has also been noted that Bulacu and van der Giessen 19) have utilized the sinusoidal eigenfunction to discuss the effect of chain stiffness on the normal modes for bead-spring simulations even for larger values of p. Hirao et al 35) have obtained the exact eigenfunction numerically using the variational method 36) for single Kremer-Grest chain floating in vacuum to report that the obtained function is virtually identical to sinusoidal function for p ≤ 4. Hagita et al 37) have applied the variational method to obtain the relaxation time for normal modes for polymer melts simulated via dynamic Monte Carlo.…”

Characterization of local dynamics and mobilities in polymer melts —A simulation study

“…where n and m denote the monomer indices and α and β denote the three spatial directions. An important observable frequently discussed in the context of simulations of polymeric systems and the elucidation of the quality of the Rouse model is the mean square displacement (MSD) [3][4][5][6] . Naturally, the MSD of the monomers of a polymer chain shows subdiffusive motion on a time scale below the longest relaxation time τ R due to the chain connectivity.…”

Dynamic Arrest in Polymer Melts: Competition between Packing and Intramolecular Barriers

“…We implement intramolecular barriers by means of the bending, V B , and torsion potential, V T , proposed in Ref. [12] (see discussion there), which are defined for each…”