# SKM 2021 – wissenschaftliches Programm

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# CPP: Fachverband Chemische Physik und Polymerphysik

## CPP 6: Poster Session II

### CPP 6.21: Poster

### Dienstag, 28. September 2021, 17:30–19:30, P

Systematic derivation of hydrodynamic equations for viscoelastic phase separation — •Burkhard Duenweg^{1}, Dominic Spiller^{1}, Maria Lukacova^{2}, Aaron Brunk^{2}, Herbert Egger^{3}, and Oliver Habrich^{3} — ^{1}MPI for Polymer Research Mainz — ^{2}Mathematics, JGU Mainz — ^{3}Mathematics, TU Darmstadt

We present a simple hydrodynamic two-fluid model aiming at the description of the phase separation of polymer solutions with viscoelastic effects. It is directly based upon the coarse-graining of a molecular model (such that all degrees of freedom have a clear molecular interpretation), and a free-energy functional. The dynamics is split into a conservative and a dissipative part, following the GENERIC formalism. In a first step, we derive an extended model where 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. The final simplified model is similar, though not identical, to models that have been discussed previously. 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. Notably, we find a rheological constitutive equation that differs from the standard Oldroyd-B model. This difference may be traced back to a different underlying statistical-mechanical ensemble that is used for averaging the stress.