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Next CASA Minisymposium Wednesday January 11, 2017

 Modern Simulation Approaches in Soft Matter
 09.45 - 13:00 hrs
Location:  Ceres 0.31

Speaker 1:  Dr. Markus Huetter (TU/e)
Time:  10:00 - 10:45 hrs
 Minimalist two-scale model for the viscoelastic behavior of elastomers filled with hard nano-particles

Misha Semkiv (1,2), Didier Long (3), Markus Huetter (1, *)
(1) Eindhoven University of Technology, Polymer Technology, Department of Mechanical Engineering, P.O.
Box 513, 5600 MB Eindhoven, The Netherlands.
(2) Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
(3) Laboratory `Polymeres et Materiaux Avances', Unite Mixte de Recherche CNRS/Solvay, France.


A dynamic two-scale model is presented for describing the mechanical behavior of elastomers filled with hard nanoparticles, particularly the Payne effect and the Mullins effect. According to literature, both of these effects have their origin in the constraint-induced vitrification of the matrix material between neighboring filler particles, leading to so-called glassy bridges. Yielding of the latter amounts to the Payne effect, while physical aging of the glassy material gives rise to the Mullins effect. Many-particle models have been developed to describe the mechanical behavior of such composites [Merabia et al., Macromolecules 41, 8252-8266 (2008); Merabia et al., J. Polym. Sci. Pol. Phys. 48, 1495-1508 (2010); Papon et al., Macromolecules 45, 2891-2904 (2012)]. For computational efficiency and in view of macroscopically inhomogeneous deformations, we strive in this contribution to reduce the model complexity drastically, while keeping the essential physics in the model. Using nonequilibrium thermodynamics, we propose a dynamic two-scale model that couples continuum mechanics with the dynamics of a single representative particle-pair on the meso-scale. This reduced model is studied numerically in oscillatory deformation. The resulting stress-strain response (Payne effect) is compared to the many-particle model in the literature, and benefits as well as short-comings of the new approach are discussed. Finally, it is discussed how the physical aging of the glassy bridges (Mullins effect) can be incorporated, using the concept of kinetic/vibrational and conformational subsystems, akin to two-temperature models in the literature.

This research was funded by the European Union through the project COMPNANOCOMP under Grant Number 295355, and forms part of the research programme of the Dutch Polymer Institute (DPI), project EU-FP-001 COMPNANOCOMP.

Speaker 2:
 Prof. Dr. Martin Mueser (Universitaet des Saarlandes)
Time:  11:00 - 11:45 hrs
Modeling dielectric response functions and non-equilibrium redox reactions with charge transfer potentials

A central problem in the modeling of materials at the atomic scale is the simulation of non-equilibrium phenomena involving charge transfer. An important example is the fundamental difficulty to describe the processes occurring during the discharge or the recharging of a Galvanic cell. Most methods, including DFT and conventional charge-equilibration methods, fail because they (must) assume the chemical potential to be constant at the beginning of the simulation. Such minimizations automatically annihilate all voltage in a full (nanoscale) Galvanic model cell.
In my talk, I present the split-charge equilibration method, which allows one to describe non-equilibrium redox reactions in force-field based simulations. This in turn enables one to simulate from atomistic principles the generic processes that occur during the discharge and the recharge of a Galvanic cell. An interesting side aspect of the splitcharge method is that it can also be used to describe the dielectric response function of continuous media on coarse scales. This makes it a promising candidate for the multi-scale modeling of dielectric phenomena.

Speaker 3:
 Prof. Dr. Kurt Kremer (Max Planck Institute for Polymer Research, Mainz)
 12:00 - 12:45 hrs
 Co(non)solvency or the puzzle of polymer properties in mixed good or poor solvents

The relation between atomistic structure, architecture, molecular weight and material properties is of basic concern of modern soft matter science. Here computer simulations on different levels of resolution play an increasingly important role. To progress further adaptive schemes are being developed, which allow for a free exchange of particles (atoms, molecules) between the different levels of resolution. Typical examples include the solvation of polymers in mixed solvents, especially PNIPAM and PMMA in water alcohol mixtures. The first reveals an interesting coil-globule-coil transition. This conformational transition cannot be explained within the classical Flory-Huggins picture, which is the standard mean field theory for polymer solutions and mixtures. The results point towards a general design of 'smart stimuli responsive polymers'. The second displays a weak swelling in a mixture of two poor solvents.

This work has been performed in collaboration with D. Mukherji and C. Marques.

D. Mukherji and K. Kremer Macrom. 46, 9158 (2013)                                                                                               
D. Mukherji, C. M. Marques, K. Kremer, Nat. Comm. 5, 4882 (2014)                                                                   
D. Mukherji, C. M. Marques, T. Stuehn, K. Kremer, J. Chem. Phys.
142, 114903 (2015)
D. Mukherji, M. Wagner, M. D. Watson, S. Winzen, T. E. de Oliveira, C. M. Marques, K. Kremer, Soft Matter 12, 7995?8003 (2016)

Abstracts of previous minisymposia
Inquiries: Enna van Dijk casa@tue.nl
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