We present an investigation into the dynamic relaxation mechanisms of a polybutadiene blend composed of a four-arm star (10 wt. %) and a linear polymer matrix in the presence of an applied shear flow. Our focus was the response of the star polymer, which cannot be unambiguously assessed via linear viscoelastic measurements since the signature of the star polymer can barely be detected due to the dominant contribution of the linear matrix. By utilizing small-angle neutron scattering (SANS) coupled with a Couette shear device and a deuterated matrix polymer, we investigated the dynamics of the minority star component of the blend. Our results confirm that the stars deform anisotropically with increasing shear rate. We have compared the SANS data with predictions from the well-established scattering adaptation of the state-of-the-art tube model for entangled linear polymer melts undergoing shear, i.e., Graham, Likhtman, Milner, and McLeish (GLaMM) approach, appropriately modified following earlier studies in order to apply to the star. This modified model, GLaMM-R, includes the physics necessary to understand stress relaxation in both the linear and nonlinear flow regimes, i.e., contour length fluctuations, constraint release, convective constraint release, and chain retraction. The full scattering signal is due to the minority star component and, although the contribution of the linear chains is hidden from the neutron scattering, they still influence the star polymer molecular dynamics, with the applied shear rate ranging from approximately 8 to 24 s−1, below the inverse relaxation time of the linear component. This study provides another confirmation that the combination of rheology and neutron scattering is an indispensable tool for investigating the nonlinear dynamics of complex polymeric systems.
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Research Article|
May 01 2020
Microstructural characterization of a star-linear polymer blend under shear flow by using rheo-SANS
L. T. Andriano;
L. T. Andriano
1Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106-5080
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N. Ruocco;
N. Ruocco
a)
1Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106-5080
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J. D. Peterson;
J. D. Peterson
1Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106-5080
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D. Olds;
D. Olds
2
National Synchrotron Light Source II, Brookhaven National Laboratory
, Upton, New York, 119733
National Security Education Center, Los Alamos National Laboratory, New Mexico Consortium
, Los Alamos, New Mexico 87545
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M. E. Helgeson;
M. E. Helgeson
1Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106-5080
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K. Ntetsikas
;
K. Ntetsikas
4Physical Science and Engineering Division,
King Abdullah University of Science and Technology
, Thuwal 23955, Saudi Arabia
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N. Hadjichristidis;
N. Hadjichristidis
4Physical Science and Engineering Division,
King Abdullah University of Science and Technology
, Thuwal 23955, Saudi Arabia
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S. Costanzo
;
S. Costanzo
5
Institute of Electronic Structure and Laser, FORTH, and Department of Materials Science and Technology, University of Crete
, 70013 Heraklion, Crete, Greece
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D. Vlassopoulos
;
D. Vlassopoulos
5
Institute of Electronic Structure and Laser, FORTH, and Department of Materials Science and Technology, University of Crete
, 70013 Heraklion, Crete, Greece
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R. P. Hjelm
;
R. P. Hjelm
3
National Security Education Center, Los Alamos National Laboratory, New Mexico Consortium
, Los Alamos, New Mexico 87545
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L. G. Leal
L. G. Leal
b)
1Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106-5080
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a)
Present address: ExxonMobil Chemical Company, Baytown Technology and Engineering Complex, Baytown, TX 77520.
b)
Author to whom correspondence should be addressed. Electronic mail: lgleal@ucsb.edu
J. Rheol. 64, 663–672 (2020)
Article history
Received:
July 23 2019
Accepted:
March 18 2020
Citation
L. T. Andriano, N. Ruocco, J. D. Peterson, D. Olds, M. E. Helgeson, K. Ntetsikas, N. Hadjichristidis, S. Costanzo, D. Vlassopoulos, R. P. Hjelm, L. G. Leal; Microstructural characterization of a star-linear polymer blend under shear flow by using rheo-SANS. J. Rheol. 1 May 2020; 64 (3): 663–672. https://doi.org/10.1122/1.5121317
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