Multiscale Simulation of Branched Nanofillers on Young's Modulus of Polymer Nanocomposites

Abstract

Nanoscale tailoring the filler morphology in experiment offers new opportunities to modulate the mechanical properties of polymer nanocomposites. Based on the conventical rod and experimentally available tetrapod filler, I compare the nanofiller dispersion and elastic moduli of these two kinds of nanocomposites via molecular dynamics simulation and a lattice spring model. The results show that the tetrapod has better dispersion than the rod, which is facilitate forming the percolation network and thus benefitting the mechanical reinforcement. The elastic modulus of tetrapod filled nanocomposites is much higher than those filled with rod, and the modulus disparity strongly depends on the aspect ratio of fillers and particle-polymer interaction, which agrees well with experimental results. From the stress distribution analysis on single particles, it is concluded that the mechanical disparity between bare rod and tetrapod filled composites is due to the effective stress transfer in the polymer/tetrapod composites.

Keywords: dispersion; lattice spring model; reinforcement; stress distribution.

Figure 1

The interconnectivity of the 3D lattice spring model in a typical layer which depicts the branched rod incorporated in a polymer matrix, nearest [100] and next nearest [110] neighbor spring interactions are considered. Three kinds of springs are represented by different colors (different spring constants). The schematic diagrams of rod and tetrapod with aspect ratio of 5 are shown in the right bottom corner.

Figure 2

Plot of interaction energy versus distance for various interaction parameters.

Figure 3

Plot of relative elastic modulus versus aspect ratio for tetrapod and nanorod nanocomposites. Blue lines represent results from the tetrapod filled composites, while red lines represent results from the rod filled composites.

Figure 4

Comparison of experimental results from ZnO/PDMS (Polydimethylsiloxane) composites with simulated data by a lattice spring model. Plot of relative elastic modulus versus nanoparticle concentration for tetrapod and nanorod nanocomposites. Fits are clamped to the (0, 1) point. The experimental data are replotted from Ref. [23] under open access license.

Figure 5

Comparison of bare particles with BPSL (Branched particles with surface ligands) on the relative elastic modulus of composites by lattice spring model. Plot of relative elastic modulus versus nanoparticle concentration. Blue lines represent results from BPSL filled composites, while black lines represent results from bare particles filled composites.

Figure 6

Normal stress profiles through the center of the particles with weak (a,c,e) and strong (b,d,f) NPI. Yellow double arrows indicate the stretching direction. Particles include tetrapods (a,b), vertically aligned rods (c,d) and horizontally aligned rods (e,f). The color bars indicate the value of stress for each bead.

Figure 7

Plot of relative elastic modulus versus nanoparticle concentration for various nanocomposites. (A) the aerographite filled epoxy with particle aggregation [49]; (B) pristine PCL filled with tetrapod ZnO [50]; (C) pristine PCL filled with spherical ZnO [50]; (D) SEBS filled with surfaced modified CdSe/CdS tetrapod nanoparticles [44] and simulation results; (E) SEBS filled with surfaced modified CdSe/CdS nanorod nanoparticles [44] and simulation results; (F) SEBS filled with aggregated CdSe/CdS tetrapod nanoparticles [44]; (G) PDMS filled with tetrapod ZnO [51]; (H) silicone elastomer filled with tetrapod ZnO [52]; (I) PLA/LNR nanocomposite filled with MWCNTs [53]; (J) SBR nanocomposite filled with MWCNTs [54]; (K) TPNR nanocomposite filled with MWCNTs [55].

Figure 8

The radial distribution function (RDF) of rod and tetrapod nanocomposites with different polymer-nanoparticle interactions: (a) inter-nanoparticle RDF; (b) RDF between nanoparticle and polymer matrix; the inset shows the partial enlarged view of the peak.

Figure 9

Plot of number density, ρ^*_n, of nearest neighbor polymer beads versus nanoparticle concentration, Φ_n, for tetrapod and rod nanocomposites.