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Systematic derivation of hydrodynamic equations for viscoelastic phase separation

Spiller, Dominic ; Brunk, Aaron ; Habrich, Oliver ; Egger, Herbert ; Lukáčová-Medvid’ová, Mária ; Dünweg, Burkhard (2024)
Systematic derivation of hydrodynamic equations for viscoelastic phase separation.
In: Journal of Physics: Condensed Matter, 2021, 33 (36)
doi: 10.26083/tuprints-00020437
Article, Secondary publication, Publisher's Version

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Item Type: Article
Type of entry: Secondary publication
Title: Systematic derivation of hydrodynamic equations for viscoelastic phase separation
Language: English
Date: 25 March 2024
Place of Publication: Darmstadt
Year of primary publication: 2021
Place of primary publication: Bristol
Publisher: IOP Publishing
Journal or Publication Title: Journal of Physics: Condensed Matter
Volume of the journal: 33
Issue Number: 36
Collation: 22 Seiten
DOI: 10.26083/tuprints-00020437
Corresponding Links:
Origin: Secondary publication DeepGreen

We present a detailed derivation of a simple hydrodynamic two-fluid model, which aims at the description of the phase separation of non-entangled polymer solutions, where viscoelastic effects play a role. It is directly based upon the coarse-graining of a well-defined molecular model, such that all degrees of freedom have a clear and unambiguous molecular interpretation. The considerations are based upon a free-energy functional, and the dynamics is split into a conservative and a dissipative part, where the latter satisfies the Onsager relations and the second law of thermodynamics. The model is therefore fully consistent with both equilibrium and non-equilibrium thermodynamics. The derivation proceeds in two steps: firstly, we derive an extended model comprising two scalar and four vector fields, such that inertial dynamics of the macromolecules and of the relative motion of the two fluids is taken into account. In the second step, we eliminate these inertial contributions and, as a replacement, introduce phenomenological dissipative terms, which can be modeled easily by taking into account the principles of non-equilibrium thermodynamics. The final simplified model comprises the momentum conservation equation, which includes both interfacial and elastic stresses, a convection–diffusion equation where interfacial and elastic contributions occur as well, and a suitably convected relaxation equation for the end-to-end vector field. In contrast to the traditional two-scale description that is used to derive rheological equations of motion, we here treat the hydrodynamic and the macromolecular degrees of freedom on the same basis. Nevertheless, the resulting model is fairly similar, though not fully identical, to models that have been discussed previously. Notably, we find a rheological constitutive equation that differs from the standard Oldroyd-B model. Within the framework of kinetic theory, this difference may be traced back to a different underlying statistical-mechanical ensemble that is used for averaging the stress. To what extent the model is able to reproduce the full phenomenology of viscoelastic phase separation is presently an open question, which shall be investigated in the future.

Uncontrolled Keywords: viscoelastic phase separation, two-fluid model, GENERIC, Poisson brackets, coarse-graining, rheology
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-204379
Classification DDC: 500 Science and mathematics > 510 Mathematics
Divisions: 04 Department of Mathematics > Stochastik
Date Deposited: 25 Mar 2024 10:05
Last Modified: 25 Mar 2024 10:05
SWORD Depositor: Deep Green
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/20437
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