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In this work, we have comprehensively studied the effect of auxiliaryintercalating agents on the thermal conductivity of expanded graphite (EG)polymer composites. We report an ultra-high enhancement of 4030% in thermalconductivity of polyetherimide/graphene nanocomposite (k = 9.5 Wm-1K-1)prepared through the use of EG with hydrogen peroxide (H2O2) as an auxiliaryintercalating agent at 10 wt% compositions (k of pure polyetherimide ~ 0.23Wm-1K-1). This ultra-high thermal conductivity value is found to be due to anEG-mediated interconnected graphene network throughout the composite,establishing a percolative environment that enables highly efficient thermaltransport in the composite. Comparative studies were also performed usingsodium chlorate (NaClO3) as an auxiliary intercalating agent. At 10 wt%composition, NaClO3 intercalated EG was found to lead to a smaller enhancementof 2190% in k of composite. Detailed characterization performed to elucidatethis advantage, revealed that hydrogen peroxide led to primarily edge oxidationof graphene sheets within EG, leaving the basal plane intact, thus preservingthe ultra-high in-plane thermal conductivity of ~ 2000 Wm-1K-1. Sodiumchlorate, on the other hand, led to a higher degree of oxidation, with a largenumber of oxygen groups on the basal plane of graphene, dramatically loweringits in-plane thermal conductivity. Thermal diffusivity of H2O2 prepared EGpaper was measured to be 9.5 mm2/s while that of NaClO3 case was measured to be6.7 mm2/s, thus directly confirming the beneficial impact of H2O2 on k ofgraphene itself. This study is the first to address the role of intercalatingagents on k of expanded graphite/polymer composites and has led to thediscovery of H2O2 as an effective intercalating agent for achieving ultra-highthermal conductivity values.

A comparative study of auxiliary intercalating agents on thermal conductivity of expanded graphite/polyetherimide composite