Paper Number
SM18 

Session
Polymer Solutions & Melts

Title
Nonlinear rheology and dynamics of dendritically branched macromolecules in shear and uniaxial extension

Presentation Date and Time
February 14, 2017 (Tuesday) 11:15

Track / Room
Track 5 / Snowy Egret

Authors (Click on name to view author profile)

1. Huang, Qian (Technical University of Denmark, Department of Chemical and Biochemical Engineering)
2. Costanzo, Salvatore (Foundation for Research and Technology Hellas, Institute of Electronic Structure & Laser)
3. Das, Chinmay (University of Leeds, School of Mathematics)
4. Vlassopoulos, Dimitris (Foundation for Research and Technology - FORTH, Institute of the Electronic Structure and Laser)

Author and Affiliation Lines (in printed abstract book)
Qian Huang¹, Salvatore Costanzo², Chinmay Das³, and Dimitris Vlassopoulos^2
1Department of Chemical and Biochemical Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark; ²Institute of Electronic Structure & Laser, Foundation for Research and Technology Hellas, Crete, Greece; ³School of Mathematics, University of Leeds, Leeds, United Kingdom

Speaker / Presenter 
Huang, Qian

Text of Abstract
The nonlinear rheological properties of model polymers with well-defined architectures provide profound implications in finessing molecular models. While rheology of polymer melts is highly sensitive to branching, the exact role of number, size and distribution of branches is not fully understood. In this work, we present nonlinear rheological measurements and model predictions of well-defined symmetric Cayley-tree poly(methyl methacrylates) with 3 and 4 generations in both shear and uniaxial extension. These dendritically branched macromolecules were synthesized anionically by Hirao and co-workers [1]. Each tree polymer consists of equal segments between generations. The number average molar mass of each segment is 11,000 g/mol (i.e., 2.4 entanglements) and the polydispersity index is 1.02. The linear viscoelastic properties and stress growth in uniaxial extension of the two polymers have been previously discussed by van Ruymbeke et al. [2]. Here we extend the work to nonlinear shear and stress relaxation following both shear and uniaxial extension by using state-of-the-art instrumentation, i.e., cone-partitioned plate (CPP) shear rheometry and filament stretching rheometry (FSR). The data shows that nonlinear shear is characterized by transient stress overshoots and the validity of the Cox-Merz rule. Nonlinear stress relaxation is much broader and slower in extension compared to shear. It is also slower at higher generation, and rate-independent for rates below the Rouse rate of the outer segment. It is suggested that coupling of stretch between generations is responsible for the observed effect in extension. The experimental results can be semi-quantitatively described by state-of-the-art modeling predictions using the Branch-on-Branch (BoB) algorithm [3][4].

[1] A. Hirao et al., Macromolecules 38, 8701–8711 (2005; [2] E. van Ruymbeke et al., J. Rheol. 54, 643 (2010); [3] C. Das et al., J. Rheol. 50, 207 (2006); [4] Q. Huang et al., J. Rheol. accepted (2016)