Amorphous epoxy is considered for investigating the role of graphene in enhancing elastic stiffness of polymers.Graphene is incorporated in the amorphous epoxy in order to develop graphene-epoxy systems. The mechanical properties of crosslinked graphene-epoxy (G-Ep) nanocomposites have been investigated using molecular mechanics (MM) and molecular dynamics (MD) simulations. The influences of graphene nanoplatelet weight concentrations, aspect ratios, and dispersion on elastic constants were studied. Both randomly oriented and stacked graphene-epoxy nanocomposites were considered. A polymer consistent force field (pcff) was used in the analysis. The G-Ep nanocomposites system underwent MD equilibration followed by uniform deformation. The stress-strain responses were evaluated in order to determine Young's modulus. MM simulation was also used to calculate the Young's modulus and shear modulus at 0 K. The results from MD and MM simulation showed reasonable improvement in Young's modulus and shear modulus for G-Ep system in comparison to neat epoxy resin. The graphene concentrations in the range of 1%-3% and graphene with high aspect ratio are seen to improve the Young's modulus by 82% approximately. The results from the simulations were compared with the results from micromechanics based analysis and nanoindentation tests. It was observed from both the atomistic scale simulation and nanoindentation tests that incorporation of graphene in neat epoxy at low weight concentration improves the elastic properties. Using similar MD scheme, it was also seen that the dispersed graphene-epoxy system possesses enhanced in-plane elastic modulus compared to the agglomerated graphene-epoxy system.
Received 15 March 2013Accepted 10 June 2013Published online 26 June 2013
The work was supported by NSF EPSCoR Research Grant No. 23669.
Article outline: I. INTRODUCTION II. THEORY A. Atomistic stress calculation B. Elastic modulus from molecular mechanics (MM) method C. Elastic modulus from stress-strain responses III. MODEL DEVELOPMENT A. Graphene's weight concentration model B. Graphene dispersion models IV. COMPUTATIONAL DETAILS A. Equilibration and deformation of fixed graphene (FGr) and varying graphene (VGr) models B. Equilibration and deformation of graphene dispersion models V. NANOINDENTATION TEST VI. RESULTS AND DISCUSSION A. Effects of graphene concentrations and aspect ratio on elastic constants B. Dispersion and agglomeration effects VII. CONCLUSION
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