 We develop a systematic method for the derivation of closed-form and thermodynamically consistent constitutive equations of complex fluids from microscopic models. The method builds upon our recent work [Phys.~Rev.~E 79, 011802 (2009)] on thermodynamically-guided simulations within a consistent coarse-graining scheme. The method is illustrated for low-molecular polymer melts subjected to imposed, homogeneous flow fields. The differential constitutive equation we obtain for this model system is a simple, nonlinear equation of change for the conformation tensor, from which the stress tensor is readily obtained. The proposed constitutive model shows shear thinning (shear viscosity exhibiting fractional power laws in the range -0.40 to -0.86, the corresponding range for the first viscometric function is -1.20 to -1.43), stress overshoots, normal stress coefficients and elongational viscosities in agreement with reference results. The constitutive equation can be interpreted as a molecularly derived, modified Giesekus model with conformation- and rate-dependent coefficients.
for LaTeX users @article{PIlg2011-55,
author = {P. Ilg and M. Kr\"oger},
title = {Molecularly derived constitutive equation for low-molecular polymer melts from thermodynamically guided simulation},
journal = {J. Rheol.},
volume = {55},
pages = {69-93},
year = {2011}
}
\bibitem{PIlg2011-55} P. Ilg, M. Kr\"oger,
Molecularly derived constitutive equation for low-molecular polymer melts from thermodynamically guided simulation,
J. Rheol. {\bf 55} (2011) 69-93.PIlg2011-55
P. Ilg, M. Kr\"oger
Molecularly derived constitutive equation for low-molecular polymer melts from thermodynamically guided simulation
J. Rheol.,55,2011,69-93 |
mk@mat.ethz.ch
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