Paper Number
SM26 

Session
Polymer Solutions & Melts

Title
Affine vs. non-affine deformation in fast flow of entangled polymers: New insight from small-angle neutron scattering

Presentation Date and Time
February 14, 2017 (Tuesday) 4:25

Track / Room
Track 5 / Snowy Egret

Authors (Click on name to view author profile)

1. Lam, Christopher N. (Oak Ridge National Laboratory)
2. Wang, Zhe (Oak Ridge National Laboratory)
3. Wang, Weiyu (Oak Ridge National Laboratory)
4. Liu, Jianning (University of Akron)
5. Hong, Kunlun (Oak Ridge National Laboratory)
6. Porcar, Lionel (Institut Laue-Langevin, Large Scale Structures)
7. Chen, Wei-Ren (Oak Ridge National Laboratory)
8. Wang, Yangyang (Oak Ridge National Laboratory)

Author and Affiliation Lines (in printed abstract book)
Christopher N. Lam¹, Zhe Wang¹, Weiyu Wang¹, Jianning Liu², Kunlun Hong¹, Lionel Porcar³, Wei-Ren Chen¹, and Yangyang Wang^1
1Oak Ridge National Laboratory, Oak Ridge, TN 37831; ²University of Akron, Akron, OH 44325; ³Large Scale Structures, Institut Laue-Langevin, Grenoble, France

Speaker / Presenter 
Wang, Yangyang

Text of Abstract
During the last several decades, the study of the dynamics of entangled polymers has been focusing on the application of the tube model. Despite the tremendous success of this theoretical approach, a key hypothesis of the tube model concerning nonlinear viscoelasticity has not been fully validated by experiments. In their seminal 1978 paper, Doi and Edwards proposed a unique elastic deformation mechanism to account for the nonlinear rheological behavior of entangled polymers. This mechanism asserts that the external deformation acts on the tube, instead of the polymer chain. A direct consequence of this assumption is that the evolution of chain conformation of an entangled polymer in flow is non-affine beyond the Rouse time, with entanglement strands being oriented but hardly stretched. This hypothesis, being a keystone of the tube model, stands in stark contrast to the elastic deformation mechanisms of other alternative theoretical approaches where the affine deformation mechanism is adopted. Here we will describe our recent effort to elucidate the molecular deformation mechanism of entangled polymers by using small-angle neutron scattering (SANS) experiments. A new approach, based on spherical harmonic expansion analysis, has been developed to decompose the 2D anisotropic scattering pattern. This development makes it possible to unambiguously examine the deformation mechanism predicted by statistical and molecular models of entangled polymers at the microscopic level. Our SANS measurements on uniaxially stretched polystyrene melts show that neither the tube model nor the affine model could provide a satisfactory description of the Q-dependent spherical harmonic expansion coefficients determined from experiments. Implications from these new experiments and analyses will be discussed in this talk.