E-CAM Case Study: The implementation of a hierarchical equilibration strategy for polymer melts, to help studying the rheological properties of new composite materials

Dr. Hideki Kobayashi, Max-Planck-Institut für Polymerforschung, Germany

Abstract

The ability to accurately determine and predict properties of newly developed polymer materials is highly important to researchers and industry, but at the same time represents a significant theoretical and computational challenge. We have developed a novel multiscale simulation method based on the hierarchical equilibration strategy, which significantly decreases the equilibrium properties calculation time while satisfying the thermodynamic consistency. A number of E-CAM modules was developed and implemented in he ESPResSo++ software package.

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Coarse-Graining module, a Component of the Hierarchical Equilibration Strategy for Polymer Melts

To study the properties of polymer melts by numerical simulations, equilibrated configurations must be prepared. However, the relaxation time for high molecular weight polymer melts is huge and increases, according to reptation theory, with the third power of the molecular weight. Hence, an effective method for decreasing the equilibration time is required. The hierarchical strategy pioneered in Ref. [1] is a particularly suitable way to do this. The present module provides a part of that method.

To decrease the relaxation time, microscopic monomers are coarse-grained (CG) by mapping each subchain with N_{b} monomers onto a soft blob. The CG system is then characterized by a much lower molecular weight and thus is equilibrated quickly. The present module provides a python script which performs this coarse-graining procedure. The implementation details can be seen in the module’s documentation on our software Library here. This module is part of a set of codes that together implement the Hierarchical Equilibration strategy of Ref. [1], in the ESPResSO++ [2] (for the complete list of modules, see here under ESPResSO++).

 

Practical application and exploitation of the code

The development of a multiscale method for polymer blends and block copolymers is fundamentally new and needs to be based on first-principles theory. This is therefore an intellectual challenge in its own right. Furthermore, this paves the way to analyze the physical properties of novel composite materials that attract the attention of industrial companies. Such materials may be promising ingredients of new products like e.g. efficient and environment-friendly car tires. The implementation of the Hierarchical Equilibration strategy in the ESPResSO++ package is a step towards achieving this goal. In particular,  the practical application of this strategy is the E-CAM pilot project in collaboration with Michelin aimed at studying the Rheological Properties of New Composite Materials.

E-CAM deliverables D4.2 and D4.3 contain more information on the suite of programs developed under this pilot project.

 

[1] Zhang, G., Moreira, L. A., Stuehn, T., Daoulas, K. C., and Kremer, K., Equilibration of High Molecular Weight Polymer Melts: A Hierarchical Strategy, ACS Macro Lett., 3, 198-203 (2014)

[2] ESPResSo++ is the “Extensible Software Package for Research in Soft Matter based upon C++”, a general-purpose simulation package for soft-matter research, mainly developed at the Max Planck Institute for Polymer Research Mainz. It is freely available under the GNU Public License. http://www.espresso-pp.de/

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