Silver (Ag) nanoparticle-decorated expanded graphite (EG) epoxy composite: evaluating thermal and electrical properties

Synthesized expanded graphite (EG) was decorated with Ag nanoparticles using solid-state decomposition by a simple 'mix and heat' technique. The epoxy composite was fabricated by a stir casting method with an ultrasonic procedure in order to enhance the thermal conductivity (TC). The morphology of filler (EG-Ag) studied under X-ray diffraction (XRD) technique and scanning electron microscopy (SEM) confirms the attachment of Ag nanoparticles on EG surfaces. The TC of the composite containing 10 wt% of EG-Ag hybrid filler (EG-Ag(10)-Ep(90)) measured using guarded heat flow meter technique was found to be 2.52 W/mK, which is almost 13-fold enhancement as compared to the neat epoxy. The thermo-gravimetric analysis (TGA) of EG-Ag(10)-Ep(90) confirmed thermal stability which enhanced from 289 to 327 degrees C at 5% weight loss, in N-2 atmosphere. The improvement in TC was ascribed to the synergistic effect of micro-nano (EG-Ag) hybrid filler, in which Ag nanoparticles acted as 'spacer' between EG threads by reducing interfacial Kapitza resistance as evidenced from fracture surface analysis. After attaining 3D percolation limit, the hybrid composite at 10% filler fraction (EG-Ag) entered the electrical conductivity of the semiconducting range which was enhanced by fourteen orders from neat epoxy.