Graphene and nanofi llers | materials research
nanocomposites, said Tony McNally of the University of Warwick, where the International Institute for Nano- composites Manufacturing will open in April 2014. These he said “are formed when a functional material having at least one dimension on the nanoscale is dispersed in a matrix”, translating their properties into the matrix material to create a composite with multi- functional properties. These materials may include CNTs or graphene, but also nano-cellulose, inorganic nanowires, layered silicates or double hydroxide, ceramics and others. Dr Cristina Valles of the School of Materials at the
University of Manchester, where the UK’s £61 million (US$100 million) National Graphene Institute is scheduled to open in early 2014, noted that graphene’s properties also make it a good reinforcing fi ller in bulk polymeric materials. It can offer signifi cant reinforce- ment of and improvements to the properties of the host matrix. “Graphene oxide (GO) is preferred over graphene for these applications,” she said. “It is obtainable in larger quantities, as well as being easier to exfoliate and to disperse in a polymer matrix – and functional groups are available to form a stronger interface with a polymer matrix.” GO is prepared via the Hummers method, which enables large quantities to be obtained relatively cheaply and easily, while achieving more complete exfoliation. A recent paper has shown that the GO is made up of sheets and oxidative debris (OD) bound to the surface. OD makes a big difference to the properties of GO; it lowers the Young’s modulus of the fl akes and improves the interface of the GO to the matrix by acting as a
compatibilising surfactant. OD can easily be removed through base washing with NaOH - the question is whether GO or base-washed GO (bwGO) is preferred in nanocomposites. Valles prepared composites of GO and bwGO with PMMA at loadings of 0.5-10% wt., by melt mixing in a twin-screw extruder, then analysed their matrix properties, dynamic-mechanical properties, stress- strain behaviour and effi ciency of reinforcement. Both GO and bwGO gave the polymer improved
thermal stability by forming a high-aspect ratio heat-resistant network in the matrix to act as a barrier. Shifts in the glass transition temperature suggested the existence of attractive interactions with the polymer. Both achieved good dispersion up to 1 wt. %, though
Graphene is described as “a single layer of sp2-hybridised carbon atoms arranged in a honeycomb structure”
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