Enhancing thermal conductivity of polydimethylsiloxane composites through spatially confined network of hybrid fillers

The thermal conductivity of polydimethylsiloxane (PDMS) composites containing short carbon fiber (SCF) and whisker carbon nanotube (wCNT) were studied by investigating the synergy of both fillers and the dimensions of the conducting filler network. The SCF was more effective in enhancing the thermal conductivity of PDMS than wCNT due to its larger aspect ratio and more homogeneous dispersion, which facilitated the formation of a continuous conducting network. The PDMS composites were further compressed to reduce the sample thickness from 2.0 mm to 0.2 mm by using a Spatial Confining Forced Network Assembly (SCFNA) process. Consequently, the thermal conductivity of the composites was further enhanced as the thickness decreased across the range of filler concentrations. The combination of wCNT and SCF increased the thermal conductivity of the PDMS composites to 2.087 W/(mK) when the sample thickness was 0.2 mm, which is ascribed to the bridging effect of wCNT with SCF network and the densified conducting network. In summary, the hybrid SCF/wCNT filler system facilitates the connections among fillers, and the SCFNA approach further densifies the conducting filler network. Both effects synergistically enhance the thermal conductivity of the composites without increasing the filler concentrations. The PDMS/SCF/wCNT composite was tested as a heat spreader, and it reduced the temperature by 12.23 degrees C as compared to the pure PDMS counterpart. The SCFNA method offers a facile route to produce higher thermally conductive yet light weighting polymer composites.