Fingerprinting molecular relaxation in deformed polymers

Abstract

The flow and deformation of macromolecules is ubiquitous in nature and industry, and an understanding of this phenomenon at both macroscopic and microscopic length scales is of fundamental and practical importance. Here we present the formulation of a general mathematical framework, which could be used to extract, from scattering experiments, the molecular relaxation of deformed polymers. By combining and modestly extending several key conceptual ingredients in the literature, we show how the anisotropic single-chain structure factor can be decomposed by spherical harmonics and experimentally reconstructed from its cross sections on the scattering planes. The resulting wavenumber-dependent expansion coefficients constitute a characteristic fingerprint of the macromolecular deformation, permitting detailed examinations of polymer dynamics at the microscopic level. We apply this approach to survey a long-standing problem in polymer physics regarding the molecular relaxation in entangled polymers after a large step deformation. The classical tube theory of Doi and Edwards predicts a fast chain retraction process immediately after the deformation, followed by a slow orientation relaxation through the reptation mechanism. This chain retraction hypothesis, which is the keystone of the tube theory for macromolecular flow and deformation, was critically examined by analyzing the fine features of the two-dimensional anisotropic spectra from small-angle neutron scattering by entangled polystyrenes. It is shown that the unique scattering patterns associated with the chain retraction mechanism were not experimentally observed. This result calls for a fundamental revision of the current theoretical picture for nonlinear rheological behavior of entangled polymeric liquids.

17 pages, 7 figures

References in corpus (3)

• Fingerprinting Soft Materials: A Framework for Characterizing Nonlinear Viscoelasticity
• Diamondoid Molecules
• A Force-Level Theory of the Rheology of Entangled Rod and Chain Polymer Liquids. I. Tube Deformation, Microscopic Yielding and the Nonlinear Elastic Limit

Cited by in corpus (12)

• Structure-property relationships via recovery rheology in viscoelastic materials
• Dynamically Heterogeneous Relaxation of Entangled Polymer Chains
• Optical tweezers microrheology maps the dynamics of strain-induced local inhomogeneities in entangled polymers
• Clustering of entanglement points in highly strained polymer melts
• Relations between angular and Cartesian orientational expansions
• Chain retraction in highly entangled stretched polymer melts
• Scaling Behavior of Anisotropy Relaxation in Deformed Polymers
• Characterization of microscopic deformation through two-point spatial correlation function
• Localized elasticity governs the nonlinear rheology of colloidal supercooled liquids
• Dynamical structure of entangled polymers simulated under shear flow
• Understanding Flow Behaviors of Supercooled Liquids by Embodying Solid-Liquid Duality at Particle Level
• Identifying the Threshold Chain Length for Stress Overshoot in Ring-Linear Polymer Blends under Uniaxial Elongation: The Role of Multiple Threading