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Journal of Rheology / Volume 54 / Issue 3

J. Rheol. 54, 643 (2010); http://dx.doi.org/10.1122/1.3368724 (20 pages)

Viscoelasticity and extensional rheology of model Cayley-tree polymers of different generations

E. van Ruymbeke

Institute of Electronic Structure and Laser, FORTH, 71110 Heraklion, Crete, Greece and Unité de Physique et Chimie des Hauts Polymères, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium

E. B. Muliawan and S. G. Hatzikiriakos

Department of Chemical and Biological Engineering, University of British Columbia, 2216 Main Mall, Vancouver, BC, V6T 1Z4, Canada

T. Watanabe and A. Hirao

Department of Chemistry, Tokyo Institute of Technology, H-127, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8552, Japan

D. Vlassopoulos

Institute of Electronic Structure and Laser, FORTH, 71110 Heraklion, Crete, Greece and Department of Materials Science and Technology, University of Crete, Heraklion, Crete, Greece

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We investigated the rheology of a series of anionically synthesized, model symmetric Cayley tree poly(methylmethacrylates) having from 1 to 4 generations of identical molar mass. The hierarchical relaxation of the different generations was assessed from the linear data by accounting for both the plateau modulus and the characteristic relaxation times. Using a tube-model time-marching analysis based on the concept of hierarchy of motion, we described quantitatively the frequency spectra without adjustable parameters. We also performed uniaxial extensional measurements using the Sentmanat extensional rheometer fixture. The samples tested exhibited significant strain hardening compared to their linear analogs at lower and intermediate Hencky strain rates. This hardening was more pronounced with increasing number of generations, hence branch points. The extracted effective steady extensional viscosity was found to scale with the extensional rate with a power exponent of about −0.5, in agreement with earlier findings with linear polystyrenes. We also extended the time-marching-algorithm to predict the extensional behavior of these polymers using the conceptual framework developed recently for pom-pom and Cayley-tree polymers. Comparison between theoretical and experimental results was satisfactory when the maximum stretch which can be supported by the molecule was estimated by accounting for the recently proposed inter-chain pressure effects.

© 2010 The Society of Rheology

AKNOWLEDGMENTS

The authors appreciate helpful discussions with Tom McLeish, Manfred Wagner, Ole Hassager, Henrik Rasmussen, and Adrien Leygue. This work was partly supported by the EU (NoE Softcomp Contract No. NMP3-CT-2004-502235). E.v.R. thanks the F.N.R.S., Communauté Française de Belgique, for Financial support.

Article Outline

  1. INTRODUCTION
  2. MATERIALS AND METHODS
    1. Cayley-tree polymers
    2. Rheology
      1. Preparation of the samples
      2. Linear viscoelasticity
      3. Extensional rheology
  3. MODELING CONSIDERATIONS
    1. Linear regime
    2. Non-linear extensional rheology
      1. Pom-pom model
      2. ICP effects
  4. RESULTS AND DISCUSSION
    1. Experimental data
      1. Linear viscoelasticity
      2. Extensional rheology
    2. Prediction of the linear viscoelastic data: Comparison to experimental data
    3. Nonlinear transient extensional data
      1. Pom-pom model analysis
      2. ICP and branch point influence
    4. Tube diameter and stretch relaxation times
  5. CONCLUDING REMARKS

KEYWORDS and PACS

Keywords

polymers, rheology, viscoelasticity, work hardening, Extensional rheology, Cayley-tree polymers, Inter-chain pressure effect, Tube model

PACS

  • 81.40.Jj

    Elasticity and anelasticity, stress-strain relations

  • 81.40.Ef

    Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

  • 62.40.+i

    Anelasticity, internal friction, stress relaxation, and mechanical resonances

PUBLICATION DATA

ISSN

0148-6055 (print)  
1520-8516 (online)

Publisher

The Society of Rheology

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ARTICLE DATA

History
Received 22 Sep 09
Revised 04 Feb 10
Published online 11 May 10
Digital Object Identifier
http://dx.doi.org/10.1122/1.3368724

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