2018-04-11
10:15 at HCP F 43.4

Hierarchical multiscale simulations of polymeric nanostructured materials

Vagelis Harmandaris

Department of Applied Mathematics, University of Crete, Greece

We present a hierarchical simulation approach in order to study quantitatively multi-phase polymeric nanostructured systems, over a broad range of length and time scales. The proposed scheme consists of: (a) Ab-initio (density functional theory, DFT) calculations of small molecules adsorbed on solid surfaces. These calculations allow us to accurately describe the interaction energy between a small fragment of the polymer (e.g. a monomer) and the solid layer. Furthermore, they can be used in order to construct an accurate classical all-atom force field. (b) Atomistic molecular dynamics (MD) simulations of short polymer chains/solid interfacial systems and polymer nanocomposites. Various properties related to density, structure, and dynamics of the hybrid materials are predicted. We also develop a methodology to obtain systematically CG models from the atomistic description, for specific polymer/solid systems. (c) Mesoscopic coarse-grained (CG) simulations of specific polymer/solid (e.g. PS/Au) surfaces. First, the CG model was validated by studying small PS/Au systems, using all-atom and coarse-grained MD simulations. The CG model was then used to study the structural, conformational and dynamical properties of various films and longer polymer chains. --- Furthermore, we provide a detailed overview of different methods for obtaining optimal parametrized coarse-grained models, starting from detailed atomistic representation for high dimensional molecular systems. Methods such as inverse Boltzmann, force matching, relative entropy, provide parameterizations of coarse-grained models at equilibrium by minimizing a fitting functional over a parameter space. All the methods mentioned in principle are employed to approximate a many-body potential, the (n-body) potential of mean force, describing the equilibrium distribution of coarse-grained sites observed in simulations of atomically detailed models. Then, we further extend these studies using path-space methods (relative entropy rate) for coarse-graining and uncertainty quantification for non-equilibrium processes. Finally, I discuss main challenges and open questions in the field.