Deformation-Induced Mobility in Polymer Glasses during Multistep Creep Experiments and Simulations

Abstract

Optical photobleaching experiments and molecular dynamics computer simulations were used to investigate changes in segmental mobility during tensile creep deformation of polymer glasses. Experiments were performed on lightly cross-linked PMMA, and the simulations utilized a coarse-grained model. For both single-step and multistep creep deformations, the experiments and simulations show remarkably similar trends, with changes of mobility during deformation exceeding a factor of 100. Both experiment and simulation show a strong correlation between strain rate and mobility in single-step creep. However, in multistep creep, the correlation between strain rate and mobility is broken in both experiment and simulation; this emphasizes that no simple mechanical variable is likely to exhibit a simple relationship with molecular mobility universally. Both simulations and experiments show many features that are inconsistent with the Eyring model.

Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening

“…N = 500 chains orient nearly affinely during strain: ǫ ef f ≃ǫt, while short chains orient much less. The solid lines are far more consistent with both experiments [3][4][5] and simulations [6,7], which show relaxation slows dramatically upon cessation of active deformation. Figure 3 shows simulation data for ǫ ef f (t) under the same procedure of compression followed by constantstrain relaxation.…”

Competition of time and spatial scales in polymer glassy dynamics: Rejuvenation and confinement effects

“…It was also shown that this different partitioning could be the main reason for the enhanced dynamics for the polymer rejuvenated samples. These results are supported by the recent MD simulations of Riggleman et al [14,15] who observed the acceleration of the segmental dynamics under deformation and corresponding changes in the potential energy landscape. Warren and Rottler showed recently [16] that both dynamics and mechanical shift factors change by the same relative amount with aging time and applied stress.…”

Evolution of collective motion in a model glass-forming liquid during physical aging

“…We measure our effective relaxation times during "time windows" as our systems undergo physical aging to equilibrium following approaches used in previous non-equilibrium simulations of the same polymer glass. [34][35][36] Briefly, we divide our simulation trajectory into overlapping windows of fixed widths in time δt win = 200 τ LJ . In each window, we calculate F s (q, t) at q = 7.14, which is approximately the location of the first peak in the static structure factor for this system at equilibrium.…”