Yongseon Hwang

Effect of Al2O3 coverage on SiC particles for electrically insulated polymer composites with high thermal conductivity

Al2O3-covered SiC/epoxy composites were prepared using a simple sol–gel method. The results of FE-SEM, TGA, and XPS indicated that the surfaces of the SiC particles had a large, dense, and homogenous distribution of Al2O3. It was found that the introduction of Al2O3 on the SiC surface improved the interfacial adhesion between the epoxy matrix and SiC particles; this resulted in an increase in the thermal conductivity of the composites since the thermal boundary resistance at the filler–matrix interface was decreased. In addition, Al2O3-covered SiC composites showed decreased electrical conductivity owing to decreased electron tunneling compared with raw SiC composites. Thus, the Al2O3-covered SiC composites prepared in the present work could prove to be desirable polymer composites to be used as thermal interface materials that are employed in the electronics industry.

Enhancement of thermal and mechanical properties of flexible graphene oxide/carbon nanotube hybrid films though direct covalent bonding

The thermal conductivity and mechanical properties of graphene oxide/multiwalled carbon nanotube (GO/MWCNT) hybrid films with and without covalent bonding were examined. Chlorinated GO and amino-functionalized MWCNT were bonded covalently to fabricate chemically bonded GO/MWCNT hybrid films. Mixtures of surface-modified GO and MWCNT were filtered and then subjected to hot-pressing to fabricate stacked films. Examination of these chemically bonded hybrid films revealed higher thermal conductivity than in physically bonded hybrid films, because of the synergetic interaction of functional groups in GO and MWCNT in the films. However, the addition of excess MWCNT to the films led to an increased phonon scattering density and a decreased thermal conductivity. The hybrid films fabricated by the optimized process endured about 20000 bending cycles without rupturing or losing their thermal conductivity. The mechanical properties showed enhanced performance after increased MWCNT loading at elevated temperature due to the reinforcement effect of the MWCNT between GO layers.

Dependence of packing fraction and surface area of the particles in the composites made by the combination of aluminum oxide and nitride for improving the thermal conductivity

Aluminum oxide and aluminum nitride with different sizes were used alone or in combination to prepare thermally conductive polymer composites. Particle size can have an influence on the thermal conductivity of composites at the same volume loading, so the composites examined in this study were categorized into two systems. One included composites filled with large-sized aluminum nitride and small-sized aluminum oxide particles. The other included composites filled with large-sized aluminum oxide and small-sized aluminum nitride. The use of these hybrid fillers was found to be effective in increasing the thermal conductivity of the composite, which was probably due to the enhanced connectivity offered by the structuring filler. At total filler content above 53.5 vol.%, the maximum values of both thermal conductivities in the two systems were 3.402 W/mK and 2.842 W/mK, respectively, when the volume ratio of large particles to small particles was 7∶3. This result was represented when the composite was filled with the maximum packing density and the minimum surface area at the same volume content. As such, the proposed thermal model predicted thermal conductivity in good agreement with experimental values.