Epoxy/hybrid graphene-copper nanocomposite materials with enhanced thermal conductivity

Thermal conductivity of epoxy resins was highly improved (up to 1.95 W/mK) with the addition of 7, 10, and 15 wt% of a hybrid filler composed of 70-30 wt% ratio of graphene and copper nanoparticles, respectively. Hybrid filler was obtained by high energy mechanical milling in two manners; just the two nanoparticles "dry milling" and with the addition of ethylene-glycol "wet milling." The crystalline structure was severely destroyed with dry milling but not with wet milling. Wet milling was thereafter used to obtain the hybrid filler that was later used in producing the epoxy nanocomposites. Raman spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and electron microscopy were used to determine the interaction between both nanoparticles in the obtained hybrid graphene-copper filler. XPS findings suggest that certain amount of copper is bonded to the graphene surface nanoparticles. This bonding could be carried out by the charge-transfer interaction between graphene and copper or by physisorption of copper between the graphene nanosheets. The signals in 119.2 and 120.7 eV, observed in the deconvolution of Cu3s signal, correspond to copper carbon bonds CuC and Cu-C, respectively. This "wet" mechanical milling methodology represents a good option to prepare graphene/metal (hybrid) fillers.