Spiller, Dominic ; Brunk, Aaron ; Habrich, Oliver ; Egger, Herbert ; LukáčováMedvid’ová, Mária ; Dünweg, Burkhard (2021)
Systematic derivation of hydrodynamic equations for viscoelastic phase separation.
In: Journal of Physics: Condensed Matter, 33 (36)
doi: 10.1088/1361648X/ac0d17
Article, Bibliographie
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Abstract
We present a detailed derivation of a simple hydrodynamic twofluid model, which aims at the description of the phase separation of nonentangled polymer solutions, where viscoelastic effects play a role. It is directly based upon the coarsegraining of a welldefined molecular model, such that all degrees of freedom have a clear and unambiguous molecular interpretation. The considerations are based upon a freeenergy 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 nonequilibrium 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 nonequilibrium 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 endtoend vector field. In contrast to the traditional twoscale 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 OldroydB model. Within the framework of kinetic theory, this difference may be traced back to a different underlying statisticalmechanical 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.
Item Type:  Article 

Erschienen:  2021 
Creators:  Spiller, Dominic ; Brunk, Aaron ; Habrich, Oliver ; Egger, Herbert ; LukáčováMedvid’ová, Mária ; Dünweg, Burkhard 
Type of entry:  Bibliographie 
Title:  Systematic derivation of hydrodynamic equations for viscoelastic phase separation 
Language:  English 
Date:  2021 
Place of 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:  10.1088/1361648X/ac0d17 
Corresponding Links:  
Abstract:  We present a detailed derivation of a simple hydrodynamic twofluid model, which aims at the description of the phase separation of nonentangled polymer solutions, where viscoelastic effects play a role. It is directly based upon the coarsegraining of a welldefined molecular model, such that all degrees of freedom have a clear and unambiguous molecular interpretation. The considerations are based upon a freeenergy 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 nonequilibrium 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 nonequilibrium 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 endtoend vector field. In contrast to the traditional twoscale 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 OldroydB model. Within the framework of kinetic theory, this difference may be traced back to a different underlying statisticalmechanical 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, twofluid model, GENERIC, Poisson brackets, coarsegraining, rheology 
Classification DDC:  500 Science and mathematics > 510 Mathematics 
Divisions:  04 Department of Mathematics 04 Department of Mathematics > Stochastik 
Date Deposited:  28 Mar 2024 08:43 
Last Modified:  28 Mar 2024 08:43 
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Systematic derivation of hydrodynamic equations for viscoelastic phase separation. (deposited 25 Mar 2024 10:05)
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