Investigation of interphase effects in silica-polystyrene nanocomposites based on a hybrid molecular-dynamics–finite-element simulation framework

Abstract

A recently developed hybrid method is employed to study the mechanical behavior of silica-polystyrene nanocomposites (NCs) under uniaxial elongation. The hybrid method couples a particle domain to a continuum domain. The region of physical interest, i.e., the interphase around a nanoparticle (NP), is treated at molecular resolution, while the surrounding elastic continuum is handled with a finite-element approach. In the present paper we analyze the polymer behavior in the neighborhood of one or two nanoparticle(s) at molecular resolution. The coarse-grained hybrid method allows us to simulate a large polymer matrix region surrounding the nanoparticles. We consider NCs with dilute concentration of NPs embedded in an atactic polystyrene matrix formed by 300 chains with 200 monomer beads. The overall orientation of polymer segments relative to the deformation direction is determined in the neighborhood of the nanoparticle to investigate the polymer response to this perturbation. Calculations of strainlike quantities give insight into the deformation behavior of a system with two NPs and show that the applied strain and the nanoparticle distance have significant influence on the deformation behavior. Finally, we investigate to what extent a continuum-based description may account for the specific effects occurring in the interphase between the polymer matrix and the NPs.

Extensive CGMD Simulations of Atactic PS Providing Pseudo Experimental Data to Calibrate Nonlinear Inelastic Continuum Mechanical Constitutive Laws

“…Figure 22 compares the force histories of the MD-simulation and an optimized FE-model containing a single Maxwell element. The resulting material parameters are reasonable and add up to an instantaneous stiffness of c0=E+c1=809.80.166667emMPa, which is close to the values we have determined elsewhere [10,28,42]. All error values er stated below to quantify the quality of the calibration are computed as the Euclidean norm of the difference between the MD goal and FE optimum vectors, divided by the number of data points in the goal, e.g., er=1377∥FxMD−FxFE∥2.…”

“…This kind of methods bases on the Arlequin approach introduced by Ben Dhia [6,7,8] and allows to model amorphous polymer systems concurrently. Inspired by this, Pfaller et al [9] proposed the Capriccio method and proved it [10,11] to be a well-suited approach for polymers.…”

Multiscale Molecular Simulations of Polymer-Matrix Nanocomposites

“…In any case, even the wide spectrum of molecular simulation methods developed till now cannot fully capture the macroscopic behavior of PNCs. Coupling molecular simulations to continuum calculations is the way to achieve this [ 329 – 331 ].…”

Investigation of the Mechanical Behavior of Polystyrene using Molecular Dynamics

“…The Capriccio method introduced in [1] couples a particle domain with a continuum and is used i.a. to investigate the effects of nano-sized silica additives embedded in atactic polystyrene (PS) [2]. The particles are modeled with Molecular Dynamics (MD) and so far, a simple hyperelastic constitutive law is used for the continuum description.…”