Reactive emulsion mixing as a novel pathway toward water-borne reduced graphene oxide/polymer composites

A new, simple and versatile technique for synthesis of water-borne poly(methyl methacrylate/butyl acrylate)/reduced graphene oxide (rGO) composites is presented. The technique is based on an emulsion mixing process, during which a water dispersible polyurethane crosslinker containing free isocyanate functionalities on both chain ends is added. The crosslinker bonds covalently the polymer and the rGO, in one complex hybrid structure. The bonding was established through spontaneous NCO reaction with OH functionalities present on the rGO platelet's surface and through OH functionalities present on the polymer nanoparticle's surface (introduced by addition of functional monomer 2-hydroxyl ethyl methacrylate during polymer synthesis). As a result highly stable composites were obtained, in which the rGO platelets were strongly bonded within the polymer matrix. This good bonding resulted in highly improved mechanical properties of the composites; thus for a composite containing 1 wt% rGO, Young's modulus of elasticity increased about 14-fold, the storage modulus increased up to 100% and the modulus of elasticity increased about one order of magnitude with respect to the neat polymer. The composites exhibit electrical conductive properties, which open possibilities for their application as electrically conductive coatings in electromagnetic interference (EMI) shielding applications or as flexible electronics.