Role of Dynamical Heterogeneities on the Mechanical Response of Confined Polymer

Abstract

Confinement induces various modifications in the dynamics of polymers as compared to bulk. We focus here on the role of dynamical heterogeneities on the mechanics of confined polymers. Using a simple model that allows computation of the mechanical response over 10 decades in frequency, we show that the local mechanical coupling controlling the macroscopic response in the bulk disappears in a confined geometry. The slowest domains significantly contribute to the mechanical response for increasing confinement. As a consequence, the apparent glass transition is broadened and shifted towards lower frequencies as confinement increases. We compare our numerical predictions with experiments performed on poly(ethylacrylate) chains in model filled elastomers. We suggest that the change of elastic coupling between domains induced by confinement should contribute significantly to the polymer mobility shift observed on filled systems.

Weak nonlinearities in viscoelastic mechanical properties of polymers near their glass transition: Local versus macroscopic laws for stress-induced acceleration of the mechanical response

“…Modelling the mechanical response of a polymer near its glass transition temperature Amorphous polymers near their glass transition temperature are heterogeneous at the nanometric scale. To model nonlinear effects at the macroscopic scale on such a heterogeneous system, we use the 3D version of the model developed by Masurel et al [30][31][32]. The space is tiled by mechanically coupled domains.…”

“…with the local deviatoric part of the stress and p its local pressure [30,31]. The coefficient α is set to 0.3 in agreement with experiments [34].…”

Segmental Rearrangements Relax Stresses in Nonequilibrated Polymer Films

“…When the time ( t ev ) required to evaporate the remaining solvent is smaller than the relaxation time of polymers, a condition reached at a concentration c c , chains will be frozen with nonequilibrium molecular conformations yielding films containing only partially interpenetrating chains (Figure b) . Since the lateral extent of the film is fixed by the substrate size, the film is compressed rapidly in the direction normal to the substrate (Figure c), creating in-plane residual stresses between molecules. , Such nonequilibrated polymer coils result in films (Figure d) with a heterogeneous structure causing residual stresses and potentially exhibiting a spatially varying degree of entanglements. − How do such heterogeneities affect the observed stress relaxation times? To shed light on this question and on the yet unknown microscopic reasons underlying the stress relaxation process, we performed a comprehensive study over a wide range of temperatures and also account for the differences induced by the preparation conditions.…”

Local versus Global Stretched Mechanical Response in a Supercooled Liquid near the Glass Transition

“…It is then a natural hypothesis to assume that the slow and fast regions associated with dynamical heterogeneity each have a simple exponential relaxation, and that the global stretching results from the different relaxation times associated with different regions, which may be broadly distributed. In fact, this natural assumption was recently formalized in a series of works by Masurel et al [10][11][12], who developed a mesoscale model to describe the viscoelastic spectrum in a polymer model near the glass transition temperature. In their model, every local region is described as a single Maxwell Voigt element, with a single relaxation time assigned randomly from a broad (log normal) distribution.…”