In this work, we demonstrate that edge oxidation of graphene can enable larger enhancement in thermal conductivity (k) of graphene nanoplatelet (GnP)/polyetherimide (PEI) composites relative to oxidation of the basal plane of graphene. Edge oxidation offers the advantage of leaving the basal plane of graphene intact, preserving its high in-plane thermal conductivity (k in > 2000 W m −1 K −1 ), while, simultaneously, the oxygen groups introduced on the graphene edge enhance interfacial thermal conductance through hydrogen bonding with oxygen groups of PEI, enhancing the overall polymer composite thermal conductivity. Edge oxidation is achieved in this work by oxidizing graphene in the presence of sodium chlorate and hydrogen peroxide, thereby introducing an excess of carboxyl groups on the edge of graphene. Basal plane oxidation of graphene, on the other hand, is achieved through the Hummers method, which distorts the sp 2 carbon−carbon network of graphene, dramatically lowering its intrinsic thermal conductivity, causing the BGO/PEI (BGO = basal-plane oxidized graphene or basal-plane-functionalized graphene oxide) composite's k value to be even lower than pristine GnP/PEI composite's k value. The resulting thermal conductivity of the EGO/PEI (EGO = edge-oxidized graphene or edge-functionalized graphene oxide) composite is found to be enhanced by 18%, whereas that of the BGO/PEI composite is diminished by 57%, with respect to the pristine GnP/PEI composite with 10 wt % GnP content. Two-dimensional Raman mapping of GnPs is used to confirm and distinguish the location of oxygen functional groups on graphene. The superior effect of edge bonding presented in this work can lead to fundamentally novel pathways for achieving high thermal conductivity polymer composites.
Metal coordinating comonomers influence the transition metal complex, polymer–metal ion binding, and subsequently material properties in magnetic responsive poly(ionic liquid)s.
Poly(ionic liquid) (PILs) are a rapidly growing subclass of polyelectrolyte which combines the diverse functionality of ionic liquids with the mechanical integrity, processability, and macromolecular design of polymeric systems. PIL properties are highly dependent on their counterion, which can be easily exchanged to tailor their material properties. Incorporation of metal halide counterions (FeCl4−, CoCl42−, etc.) into the PIL structure results in magnetically responsive metal-salt composites known as magnetic-PILs (MPILs). MPILs are predominately formed through electrostatic binding with anionic metal complexes typically resulting in paramagnetic properties at room temperature. The engineering properties and the ability to effectively apply these materials — is dependent on not only the chemical structure, but the nanostructure, co-materials, self-assembly, and stability in situ. In this study, a PIL copolymer, poly(acrylamide-co-diallyl dimethylammonium chloride), containing a quaternary ammonium PIL group and a comonomer capable of metal coordinating interactions, was combined with sodium dodecyl sulfate surfactant and cobalt (II) chloride salts to form magnetic polyelectrolyte-surfactant complexes. The self-assembly of these complexes was studied as a function of surfactant concentration through DLS, Zeta potential, and TEM characterizations. The magnetic properties were examined using AC susceptibility. The impact of the metal ion(s) and magnetic field on nanostructure alignment and film formation were also investigated through optical microscopy, GISAXS, and AFM imaging. Results were compared to well-defined ferrofluids as a comparative benchmark.
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