Surface Modification of Expanded Graphite with Copper Nanoparticles by Supercritical Method and its Thermal Properties

초록

Copper nanoparticle-expanded graphite (CuNPs/EG) composites were developed to improve through-plane heat transport in graphite-based thermal interface materials (TIMs). Copper nanoparticles (CuNPs) were synthesized by chemical reduction using polyethylene glycol and ascorbic acid to suppress aggregation and oxidation, and were then incorporated into expanded graphite (EG) by a supercritical carbon dioxide (scCO(2))-assisted intercalation process. X-ray diffraction (XRD) confirmed the formation of metallic CuNPs, and dynamic light scattering (DLS) showed a particle size distribution of approximately 150-650 nm with a main peak near 350 nm. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) indicated that ethanol used as a co-solvent produced a more homogeneous distribution of Cu species within the expanded interlayer voids and porous regions of EG than isopropyl alcohol. Cross-sectional SEM/EDS analysis further showed Cu-containing particles distributed inside the composite film. After 14 days of air exposure at 25 degrees C and 40% relative humidity, only weak oxygen signals were detected from CuNPs embedded within EG, indicating improved oxidation stability. Laser flash analysis showed that the CuNPs/EG composite prepared using ethanol exhibited a through-plane thermal conductivity of 8.402 W/m & centerdot;K, a 124.5% increase compared with pristine EG, while retaining an in-plane thermal conductivity of 90.854 W/m & centerdot;K. These results demonstrate that ethanol-assisted scCO(2) intercalation is an effective strategy for developing oxidation-stable CuNPs/EG composites with enhanced through-plane thermal transport.

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