Thermodynamically consistent coarse graining the non-equilibrium dynamics of unentangled polymer melts
P. Ilg , H.C. Öttinger , M. Kröger

Department of Materials, Polymer Physics, ETH Zurich, Switzerland

Abstract: We present a novel, thermodynamically guided strategy for the dynamic simulation of microscopic models for complex fluids that is able to efficiently bridge the time- and length scale gap between the microscopic level and macroscopic dynamics. The systematic coarse-graining method is exemplified for low-molecular polymeric systems subjected to homogeneous flow fields. We use established concepts of nonequilibrium thermodynamics and an alternating Monte-Carlo-molecular dynamics iteration scheme in order to obtain the model equations for the slow variables [1]. For chosen flow situations of interest, the established model predicts structural as well as material functions beyond the regime of linear response. The results are in quantitative agreement with those obtaind via standard nonequilibrium molecular dynamics simulations. As a by-product, we present the first steady state equibiaxial simulation results for polymer melts. The method is simple to implement and allows for the calculation of time-dependent behavior through quantities readily available from the nonequilibrium steady states. The proposed method is very efficient and particularly powerful for weak up to moderate external forcings, and therefore complements standard nonequilibrium methods which are better suited in the regime of strong external forcings.

[1] P. Ilg, H.C. Öttinger, M. Kröger, Phys. Rev. E, 2009, 79, 011802.