Extensional Rheology of Bimodal Blends Studied with Primitive
Chain Network Simulation
Keiko Takeda, Yuichi Masubuchi*, Sathish K. Sukumaran, Masataka Sugimoto, Kiyohito Koyama
Yamagata University, Jonan, Yonezawa, 992-8510 Japan*Institute for Chemical Research, Kyoto University, Gokasho, Uji, 611-0011 Japan
kei@yz.yamagata-u.ac.jp
1. Introduction
The extensional flow characteristics of a polymer material are relevant for many polymer
processing operations. For instance, strain hardening acts to stabilize the flow in fiber spinning.
Recently Minegishi et al. [ref.1] found that adding a small fraction of higher molecular weightcomponent to Polystyrene significantly enhanced strain hardening of the sample. We are interested
in obtaining a molecular understanding of these results and the extensional rheology of bimodal
blends in general, especially in terms of the deformation of the chain molecules themselves.
Therefore, we performed extensive simulations of several chain molecular weights blended at
different concentrations using the Primitive Chain Network (PCN) model of Masubuchi et al. [ref.2].
Further, we also investigate systems that can be directly compared with the experimental results
mentioned above.
2. Investigated Systems
We considered chains of about five entanglement segments on average (<Z>=5) blended withchain molecular weights, <Z>=10, 20, 40 and 80. For each of these blend systems, the criticalvolume fraction ( φ *) where the long chain begins to self entangle was calculated and at least three
concentrations were studied ( φ */2, φ *, 2 φ *). We also investigated blend systems appropriate fordirect comparison with experimental data of Minegishi et al. [ref.1]. We studied the start-up
extensional viscosity of the blends systems over a range of strain rates ε˙ that included
˙ < 1/ τR ) and ε˙ > 1/ τR where τd and τR are respectively( 1/ τ€d <ε€ time€and €0.4
the disentanglement
the Rouse time of the long chain.
0.16
0.08
3. Extensional viscosities of monodisperse samples
10 €
0.03
0.02
The τd €was determined fromthelinearrheology
ofthelong
0.014
€
€
0.007
chain. The Rouse time of the long chain was calculated using
3eta[ref.3]. Figure 1 shows the start-up transient extensional
10viscosities of polystyrene sample, <Z>=5 blended with 2.5%€<Z>=40. Figure 2 shows the start-up transient extensional
viscosities of polystyrene sample, <Z>=5. It is clear from these
10figures that this fraction of long chains is sufficient to induce
10101010t (s)extension hardening in this sample. The result is consistent withFig.1 Start-up extensionalthat obtained by Minegishi et al. [ref.1] and suggests that thePCN model can be used to study the extensional rheology of viscosities of Z5 blended with 2.5%
Z40 at different strain rates.
these systems. Further, we calculated the variation of the chain
0.40.16
10 2
end-to-end distance with extension ratio and investigated the0.08
0.03
relationship between the chain deformation and extensional
0.02
0.014
hardening. These and other results will be discussed in detail
0.007
13eta
during the presentation.
104. References:[1] A. Minegishi, A. Nishioka, T. Takahashi, Y. Masubuchi. J.
Takimoto, K. Koyama, Rheol. Acta, 40, 329 (2001)
10 010 010 110 210 3[2] Y. Masubuchi, J. Takimoto, K. Koyama, G. Ianniruberto, G.
t (s)Marrucci, and F. Greco, J. Chem. Phys., 115, 4387 (2001)
Fig.2 Start-up extensional[3] K. Furuichi, C. Nonomura, Y. Masubuchi, H. Watanabe, G.
viscosities of Z5 at different strain
Ianniruberto. F. Greco and G. Marrucci, Rheol. Acta, 47, 591 rates.
(2008)100

η+E(Pa s)€η+E(Pa s)

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