Sebastian Pfaller (Friedrich-Alexander-Universität Erlangen, Germany). Multiscale Simulations of Polymers with the Capriccio Method.

Usually, the specific atomistic or molecular structure of matter is not taken into account in continuum mechanics. Hence, effects originating from very small time and length scales, like e.g. interphases in nanocomposites, are very difficult to be accessed by a continuum mechanical description. In contrast, particle-based considerations like Molecular Dynamics (MD) are specifically designed for describing the material behaviour at the level of atoms and molecules and are thus well suited for modelling materials at a very fine scale and eventually describing processes which cannot be captured by coarse scale methods.

A severe drawback of particle-based methods is the huge number of particles that has to be considered. Thus, such approaches are usually restricted to very small amounts of material and only suited for the simulation of very small periods of time. To overcome this, a variety of hybrid schemes has been proposed to benefit from advantages of particles-based and continuum modelling. However, most of them have been developed for crystalline materials and are thus rather not suited for the description of polymer materials which are typically amorphous.

Our novel Capriccio method has been specifically designed for polymers and embeds a particle-based region treated by molecular dynamics (MD) at finite temperature into a larger continuum solved by the finite element method (FEM). Both domains overlap in a so-called bridging domain, where an energy-based coupling together with a suitable kinematic constraint is established.

The suitability of the Capriccio method to study the complex behaviour of nano-scaled

filler particles embedded into a polymer is demonstrated by our recent publications [1, 2]. In this kind of materials, the interphases between filler particles and polymer matrix are of particular interest, but barely accessible by continuum approaches due to the lack of reliable constitutive descriptions. Beyond that, we are currently working on a multiscale description of fracture of polymers.

Acknowledgements

Our method has been developed in close collaboration with the Theoretical Physical Chemistry Group at TU Darmstadt within the EU project “Nanomodel” and the DFG Priority programme 1369 “Polymer-Solid Contacts: Interfaces and Interphases”. It is applied in the DFG Individual Research Grant “Identification of Interphase Properties in Nanocomposites” and in the DFG Research Training Group GRK 2423 “Fracture across Scales – FRASCAL”.

References

[1] S. Pfaller, M. Rahimi, G. Possart, P. Steinmann, F. Müller-Plathe, and M. C. Böhm, “An Arlequin-based method to couple molecular dynamics and finite element simulations of amorphous polymers

and nanocomposites,” Comput. Methods in Appl. Mech. Eng., 260, pp. 109–129, 2013.

[2] S. Pfaller, G. Possart, P. Steinmann, M. Rahimi, M. C. Böhm, and F. Müller-Plathe, “Investigation

of Interphase Effects in Silica-Polystyrene Nanocomposites Based on a Novel Hybrid MD-FE

Simulation Framework,” Phys. Rev. E, 93, p. 052505, 2016.