We perform micro-rheological experiments with a colloidal bead driven through a viscoelastic worm-like micellar fluid and observe two distinctive shear thinning regimes, each of them displaying a Newtonian-like plateau. The shear thinning behavior at larger velocities is in qualitative agreement with macroscopic rheological experiments. The second process, observed at Weissenberg numbers as small as a few percent, appears to have no analog in macro-rheological findings. A simple model introduced earlier captured the observed behavior and implied that the two shear thinning processes correspond to two different length scales in the fluid. This model also reproduces oscillations, which have been observed in this system previously. While the system under macro-shear seems to be near equilibrium for shear rates in the regime of the intermediate Newtonian-like plateau, the one under micro-shear is thus still far from it. The analysis suggests the existence of a length scale of a few micrometres, the nature of which remains elusive.
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14 May 2021
Research Article|
May 12 2021
Two step micro-rheological behavior in a viscoelastic fluid
Rohit Jain
;
Rohit Jain
a)
1
Institute for Theoretical Physics, Georg-August Universität Göttingen
, 37073 Göttingen, Germany
a)Author to whom correspondence should be addressed: rohit.jain@theorie.physik.uni-goettingen.de
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Félix Ginot;
Félix Ginot
2
Fachbereich Physik, Universität Konstanz
, 78457 Konstanz, Germany
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Johannes Berner;
Johannes Berner
2
Fachbereich Physik, Universität Konstanz
, 78457 Konstanz, Germany
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Clemens Bechinger
;
Clemens Bechinger
2
Fachbereich Physik, Universität Konstanz
, 78457 Konstanz, Germany
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Matthias Krüger
Matthias Krüger
1
Institute for Theoretical Physics, Georg-August Universität Göttingen
, 37073 Göttingen, Germany
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a)Author to whom correspondence should be addressed: rohit.jain@theorie.physik.uni-goettingen.de
J. Chem. Phys. 154, 184904 (2021)
Article history
Received:
February 22 2021
Accepted:
April 27 2021
Citation
Rohit Jain, Félix Ginot, Johannes Berner, Clemens Bechinger, Matthias Krüger; Two step micro-rheological behavior in a viscoelastic fluid. J. Chem. Phys. 14 May 2021; 154 (18): 184904. https://doi.org/10.1063/5.0048320
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