Molecular modeling and simulation of atactic polystyrene/amorphous silica nanocomposites

I Mathioudakis,C Tzoumanekas,G G Vogiatzis,D N Theodorou

doi:10.1088/1742-6596/738/1/012021

I Mathioudakis, C Tzoumanekas + Show 2 more

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https://doi.org/10.1088/1742-6596/738/1/012021

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Abstract

The local structure, segmental dynamics, topological analysis of entanglement networks and mechanical properties of atactic polystyrene - amorphous silica nanocomposites are studied via molecular simulations using two interconnected levels of representation: (a) A coarse - grained level. Equilibration at all length scales at this level is achieved via connectivity - altering Monte Carlo simulations. (b) An atomistic level. Initial configurations for atomistic Molecular Dynamics (MD) simulations are obtained by reverse mapping well- equilibrated coarse-grained configurations. By analyzing atomistic MD trajectories, the polymer density profile is found to exhibit layering in the vicinity of the nanoparticle surface. The dynamics of polystyrene (in neat and filled melt systems) is characterized in terms of bond orientation. Well-equilibrated coarse-grained long-chain configurations are reduced to entanglement networks via topological analysis with the CReTA algorithm. Atomistic simulation results for the mechanical properties are compared to the experimental measurements and other computational works.

Highlights

The complexity of intermolecular interactions and confinement in polymer-nanoparticle systems leads to spatial variations in structure and dynamics at both the meso- and nanoscale, which are of the order of 100 nm – 1 μm and 1 – 100 nm, respectively
The local structure, segmental dynamics, topological analysis of entanglement networks and mechanical properties of atactic polystyrene – amorphous silica nanocomposites are studied via molecular simulations using two interconnected levels of representation: (a) A coarse – grained level
Vogiatzis and Theodorou [18] observed that torsion angle distributions in their reverse – mapped structures are extremely close to those obtained from a 80mer structure that was directly equilibrated by Molecular Dynamics (MD) at the atomistic level, without intervention of any coarse – graining and reverse mapping

Summary

Introduction

The complexity of intermolecular interactions and confinement in polymer-nanoparticle systems leads to spatial variations in structure and dynamics at both the meso- and nanoscale, which are of the order of 100 nm – 1 μm and 1 – 100 nm, respectively. Nanomaterials fabricated by dispersing nanoparticles in polymer melts have the potential for unique optical, electrical, rheological, and permeability properties, as well as mechanical performance that far exceeds that of traditional composites [1, 2, 3, 4]. Measurements of the rheological properties of polymer matrix nanocomposites in the melt have revealed unexpected phenomena of great practical importance for the molding technology of polymers. Kumar and Krishnamoorti [5] has presented in a review article that despite intense research activity on polymeric matrix nanocomposites, the exact mechanisms by which nanoparticles affect the properties in often unexpected ways still remain largely unknown.

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