Abstract
In this dissertation, the investigations on the thermal properties and electromagnetic interference shielding efficiency (EMI SE) of nanoscale carbon materials/polymer composites have been studied. The fillers such single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphite nanosheets (GNS), graphene (GP), and the graphene decorated with Ag (Ag@GP) and Ni (Ni@GP) were synthesized successfully, and incorporated with various polymers including paraffin and polyaniline (PAni), respectively. Two paraffin composites filled separately with randomly distributed graphite nanosheets (R-GNS) and oriented graphite nanosheets (O-GNS) were fabricated, and their thermal properties and structural characteristics were investigated. The experimental results show that a conductive network at 1.0 wt% GNS loading was found. The thermal conductivities of the R-GNS/paraffin and the O-GNS/paraffin composites are 4.47±0.15 and 1.68±0.07 W/m K, respectively, when 5.0 wt% GNS were introduced. The Maxwell-Euken model and the modified rule of mixtures model were proposed to predict the thermal conductivities of the R-GNS/paraffin and the O-GNS/paraffin composites, respectively. The melting point and the solid-liquid phase transition temperature of the R-GNS/paraffin composites are approximately 53 and 60 0C, respectively, and neither of these values was significantly affected by the presence of GNS. Decreases in the latent heat of the R-GNs/paraffin composites with increased GNS loading were also found. This work demonstrates the fabrications and characterizations of PAni composites containing SWCNTs, GNS, or hybrid fillers SWCNTs/GNS. The characterization of microstructure, examination of fracture surface morphologies, and measurement of electric conductivity and EMI SE were performed. It was found that both the electric conductivity and the EMI SE increase with filler loading, and the nanocomposites filled with 1.0 wt% SWCNTs/GNS possessed the highest electric conductivity of 16.2 S/cm and total EMI SE of 27.0 dB. The experimental results also show that absorption is the primary mechanism of EMI SE for all of the loadings and fillers. To develop novel EMI shielding materials, PAni composites filled with GP, GP decorated with silver nanoparticles (Ag@GP), and GP decorated with nickel nanoparticles (Ni@GP) were prepared, and the microstructures, morphologies, electrical conductivities, and EMI SE of the composites with different filler loadings (0.5, 1.0, 3.0, and 5.0 wt%) were investigated. The PAni composite containing 5.0 wt% Ag@GP showed the best electrical conductivity of 20.32 S/cm and highest EMI SE of 29.33 dB. The uniform dispersion of fillers significantly enhanced the formation of conductive pathways in the PAni matrix, and the presence of metal nanoparticles on the GP surface and between the GP layers also increased the electrical conductivity. The results of this study show that absorption is the primary factor governing EMI shielding, which is attributed to the high permittivity of the composites. This study reveals that the Ag@GP/PAni composite is promising for applications as an EMI shielding material. Porous composites fabricated through a simple dip-coating method demonstrated excellent performance in EMI shielding. A commercial sponge was coated with silver nanoparticles before being dip-coated with GP, MWCNTs, or hybrid GP/MWCNTs to form Ag/carbon nanomaterial hybrid composites. Herein, we found an insignificant difference in EMI SE among the porous composites without the Ag nanoparticle coating, with values of approximately 14.4 dB. Interestingly, the hybrid composites with the Ag nanoparticle coating exhibited excellent EMI shielding (24.33 dB). The EMI SE measurements showed that reflection dominates the EMI SE for all the sponge composites studied in this work due to their porous structure.