Constructing a compacted network in polymer matrices is an important method to improve the thermal conductivity (TC) of polymer composites. In this paper, a compacted network was built using the Spatial Confining Forced Network Assembly (SCFNA) method. The homogeneous compound of polymer and fillers, prepared using a conical twin-screw mixer, was placed in a compression mold with confining space to carry out two-stage compression, free compression and spatial confining compression. Aluminum oxide (Al2O3) was studied as filler in a polydimethylsiloxane (PDMS) matrix to illustrate the applicability of the SCFNA method. The polymer composites with an Al2O3 filler ranging from 10 to 80 wt% were prepared. When the filler content was 80 wt%, the TC of the PDMS/Al2O3 composites prepared using the SCFNA method increased by 16.35 times in comparison to the TC of pure PDMS. Observing the SEM of PDMS/Al2O3 composites with various thicknesses, the gap between fillers decreased with a decrease in thickness. The composite with TC up to 2.566 W (mK)-1 obtained at 80 wt% filler was further employed as a heat spreader, causing a decrease of about 8.23 °C in the set-point compared with the temperature of the heat source.
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