Abstract
We study the conformations of polymer chains in polymer-graphene oxide nanocomposites. We show that the chains have a reduced radius of gyration that is consistent with confinement at a solid interface in the melt, as is expected for well-dispersed, high aspect ratio nanoparticles that are much larger than the polymer coil size. We show that confinement of the polymer chains causes a corresponding reduction in interchain entanglements, and we calculate a contribution to the plateau modulus from the distorted polymer network via a simple scaling argument. Our results are a significant step forward in understanding how two-dimensional nanoparticles affect global material properties at low loadings.
Highlights
Graphene and related 2D materials have extraordinary physical properties that along with their high aspect ratio make them excellent candidate filler materials for polymer nanocomposites,[1] capable of producing significant gains in material properties at extremely low concentrations on the order of 1% by volume.[2,3] The conformation of polymer chains in the interfacial regions in the vicinity of nanoparticles is of great interest
In order to answer this problem, we investigate the effect of graphene oxide (GO), a highly functionalized form of graphene, upon the conformation of well-studied polymers poly(methyl methacrylate) (PMMA), where the GO is well-dispersed, and polystyrene (PS), where the GO dispersion is poor
Composites were formed of GO with poly(methyl methacrylate) and polystyrene, where each polymer matrix was formed from a blend of hydrogenous and deuterated polymer of closely matching molecular weight and polydispersity in order to highlight the individual chain conformations for small-angle neutron scattering (SANS) measurements
Summary
SANS was carried out on the Sans2d instrument at the ISIS Pulsed Neutron Source (STFC Rutherford Appleton Laboratory, Didcot, U.K.).[7,8] The fitting function applied within the SasView software comprises a model for the radius of gyration (Rg) scattering of a Gaussian polymer coil recast with a Schulz− Zimm polydispersity function,[9] an absolute power law describing the GO scattering, and a constant background term, with the overall expression. Such a nonmonotonic trend in the plateau modulus of the polymer has been observed by Liu et al.[29] for composites of ultra high molecular weight polyethylenes with reduced graphene oxide nanosheets (rGONs) where the minimum was interpreted to correspond with the rGON concentration value that gave the most efficient dispersion, before aggregation effects began to reduce the surface area to volume ratio ( reducing the available polymer−rGON interactions) and increase the storage modulus. The link between the structural picture of the polymer chain confined at the interface with the dynamical rheological response, via a simple scaling argument based on simple thin-film polymer physics applied to a bulk situation, significantly advances our understanding of the mechanisms by which entangled polymer melts may be strongly altered by the presence of small quantities of high aspect ratio nanoparticles. Experimental details: Composite preparation, SANS measurements, rheological measurements and additional interpretation, scaling analysis and correlation between GN0 ,SANS and GN0 (PDF)
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