Paper Number
SM25 

Session
Polymer Solutions and Melts

Title
Chain conformation, entanglements, and the origin of stress overshoot during startup shear of entangled polymer melts

Presentation Date and Time
October 7, 2014 (Tuesday) 3:10

Track / Room
Track 3 / Commonwealth C

Authors (Click on name to view author profile)

1. Lu, Yuyuan (Changchun Institute of Applied Chemistry)
2. An, Lijia (Changchun Institute of Applied Chemistry)
3. Wang, Shi-Qing (University of Akron)
4. Wang, Zhen-Gang (California Institute of Technology)

Author and Affiliation Lines (in printed abstract book)
Yuyuan Lu¹, Lijia An¹, Shi-Qing Wang², and Zhen-Gang Wang^3
1Changchun Institute of Applied Chemistry, Changchun, China; ²University of Akron, Akron, OH; ³California Institute of Technology, Pasadena, CA

Speaker / Presenter 
Wang, Zhen-Gang

Text of Abstract
Using Brownian Dynamics simulation, we determine the chain orientation and stretching and their connection to stress overshoot in an entangled polymer melt undergoing startup shear at rates lower than the reciprocal of the Rouse time yet higher than the reciprocal reptation time. In this regime, the prevailing tube theory envisions little chain stretching, so that the coil size (as characterized by the radius of gyration) and shear stress are determined primarily by chain orientation. In contrast, our results reveal that there is significant chain stretching which persists well beyond the Rouse time and contributes substantially to both the initial stress growth and the evolution in the radius of gyration. In particular, stress overshoot is found to be primarily due to chain retraction after considerable stretching rather than chain orientation. The coil size shows a pronounced peak as a function of the strain. Furthermore, up to many Rouse times, the relaxation of the initial entanglements is slower than that under the quiescent condition. These results point to fundamental deficiencies in the molecular picture of the tube model for startup shear.