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Download fileEdge-Functionalized Graphene as a Nanofiller: Molecular Dynamics Simulation Study
journal contribution
posted on 2015-12-22, 00:00 authored by Petra Bačová, Anastassia
N. Rissanou, Vagelis HarmandarisIn the present simulation work we
study graphene-based polymer
nanocomposites composed of hydrogenated and carboxylated graphene
sheets dispersed in polar and nonpolar short polymer matrices (i.e.,
matrices containing chains with low molecular weight). The aim of
our work is to examine spatial and dynamical heterogeneities of such
systems and to provide a compact picture about the effects of the
edge group functionalization of graphene sheets on the properties
of hybrid graphene-based materials. We perform atomistic molecular
dynamics simulations of edge-functionalized graphene sheets embedded
in poly(ethylene oxide) (polar matrix) and polyethylene (nonpolar
matrix). We choose a low loading of the graphene nanofiller (from
1.7% to 3.6%) in agreement with experimental data. We further implement
a detailed analysis of static and dynamic properties of polymer chains
on the level of both the entire hybrid material and the polymer/graphene
interface through a new approach that is able to distinguish between
the adsorbed and edge region around the nanofiller. At the local scale,
strong structural and dynamical heterogeneities are observed; i.e.,
the behavior of the polymer matrix appears to be highly affected by
the presence of the edge-functionalized graphene. Slow dynamics was
detected in the adsorbed layers in all nanocomposites. Additionaly,
interaction of grafted carboxylated groups with polar matrix led to
a further delay in the segmental as well as the chain relaxation close
to the graphene edges. This effect seems to slow down the chain dynamics
even more than the actual adsorption of the chain on the surface.
Overall average orientational dynamics of polymer chains in nanocomposites
as well as the collective dynamics quantified through the single chain
coherent structure factor reveal slight deviations from the bulk behavior
in the terminal region, presumably due to the small percentage of
the slow dynamic component at the given loading of the nanofiller.
Enhancement of the rheological properties is not observed within the
time window of our simulations. Our results emphasize the importance
of the surface/polymer interactions in the graphene-based nanocomposites
and suggest that by a proper choice of edge-grafted groups we can
achieve better material performance.