Molecular insight into the Mullins effect: irreversible disentanglement of polymer chains revealed by molecular dynamics simulations

Abstract

The debate regarding the possible molecular origins of the Mullins effect has been ongoing since its discovery. Molecular dynamics (MD) simulations were carried out to elucidate the underlying mechanism of the Mullins effect. For the first time, the key characteristics associated with the Mullins effect, including (a) the majority of stress softening occurring in the first stretch, (b) continuous softening with stress increase, (c) a permanent set, and (d) recovery with heat treatment, are captured by molecular modeling. It is discovered that the irreversible disentanglement of polymer chains is physically sufficient to interpret these key characteristics, providing molecular evidence for this long-controversial issue. Our results also reveal that filled polymers exhibit three distinct regimes, i.e., the polymer matrix, the interface, and the filler. When subjected to external strain, the polymer matrix suffers from excess deformation, indicating strong heterogeneity within the filled polymer, which offers molecular insight for the formulation of physics-based constitutive relations for filled polymers.

Novel Biobased Polyamide Thermoplastic Elastomer with Medium Hardness

“…The stress reduction and residual strain found during the cyclic tests of this elastomer are also observed in some other filled or unfilled elastomers, which show similar softening effect or Mullins effect. [29][30][31][32] The Mullins effect has several characteristics including stress softening and residual strain after the first loading-unloading cycle, and stabilization of the stressstrain curve after a few cycles [32,33] The Mullins effect of PA36,9 could be mainly attributed to chain disentanglement. [30] During the first loading, the entangled chain segments in the elastomer require a relatively high external stress for disentanglement due to the large motion barrier and upon unloading they could not all be recovered, which leads to stress softening and the residual strain.…”

Surface Treatment Effects on the Mechanical Properties of Silica Carbon Black Reinforced Natural Rubber/Butadiene Rubber Composites

“…It includes the cyclic stress softening and the ability to recover and return towards the virgin stress-strain path when the load rises over the previous maximum applied stress value. We suggest that there are several interactions involved in the stress softening resulting from the Mullins effect, which includes breakage or slippage of network chains connecting the filler particles [38,39,40], breakage of the filler aggregates [41], and macromolecular disentanglement [42]. To the best of our knowledge, no work has been conducted to investigate the Mullins effect of rubber composites filled by RHA.…”

A new elastomeric-sliding seismic isolation system

“…This mechanism reflects the Mullins effect [15]. One of the main factors causing this phenomenon is that in the initial loading, part of the energy is spent on the disentangling polymer chains, and in the next cycle, the chains move among themselves more freely [16]. In the ESI system, this effect is not evident under shear strains (Figs.…”