Graphene nanoplatelets (GNPs) can be produced by exfoliating graphite in solvents via high-power tip sonication. In order to understand the influence of tip sonication parameters on graphite exfoliation to form GNPs, three typical flaked graphite samples were exfoliated into GNPs via tip sonication at power of 60, 100, 200, or 300 W for 10, 30, 60, 90, 120, or 180 min. The concentration of GNP dispersions, the size and defect density of the produced GNPs, and the sedimentation behavior of GNP dispersions produced under various tip sonication parameters were determined. The results indicated that the concentration of the GNP dispersions was proportional to the square root of sonication energy input (the product of sonication power and time). The size and I_D/I_G values (determined by Raman spectrum) of GNPs produced under various tip sonication powers and times ranged from ~ 1 to ~ 3 μm and ~ 0.1 to ~ 0.3, respectively, which indicated that all the produced GNPs were of high quality. The sedimentation behavior of GNP dispersions showed that the dispersions were favorably stable, and the concentration of each GNP dispersion was ~ 70% of its initial concentration after sedimentation for 96 h. Moreover, the TEM images and electron diffraction patterns were used to confirm that the produced GNPs were few-layer. This study has important implications for selecting the suitable tip sonicating parameters in exfoliating graphite into GNPs.

Thermal management has become a critical challenge in electronics and portable devices. To address this issue, polymer composites with high thermal conductivity (TC) and low dielectric property are urgently needed. In this work, we fabricated perfluoroalkoxy (PFA) composite with high anisotropic TC and low dielectric constant by aligning boron nitride nanosheets (BNNs) via hot pressing. We characterized the thermal stability, microstructure, in-plane and through-plane TCs, heat dissipation capability, and dielectric property of the composites. The results indicate that the BNNs–PFA composites possessed good thermal stability. When the BNNs content was higher than 10 wt %, the BNNs were well layer aligned in the PFA matrix, and the composites showed obvious anisotropic TC. The in-plane TC and through-plane TCs of 30 wt % BNNs–PFA composite were 4.65 and 1.94 W m⁻¹ K⁻¹, respectively. By using the composite in thermal management of high-power LED, we found that alignment of BNNs in composite significantly improves the heat dissipation capability of composite. In addition, the composites exhibited a low dielectric property. This study shows that hot pressing is a facile and low-cost method to fabricate bulk composite with anisotropic TC, which has wide applications in electronic packaging.

With the rapid development of electronics and portable devices, polymer nanocomposites with high through-plane thermal conductivity (TC) are urgently needed. In this work, we fabricated graphene nanosheets−perfluoroalkoxy (GNs−PFA) composite sheets with high through-plane TCs via hot-pressing followed by mechanical machining. When the GNs content exceeded 10 wt%, GNs were vertically aligned in the PFA matrix, and the through-plane TCs of nanocomposites were 10–15 times higher than their in-plane TCs. In particular, the composite with 30 wt% GNs exhibited a through-plane TC of 25.57 W/(m·K), which was 9700% higher than that of pure PFA. The composite with 30 wt% GNs was attached to the surface of a high-power light-emitting diode (LED) to assess its heat-dissipation capability. The composite with vertically aligned GNs lowered the LED surface temperature by approximately 16 °C compared with pure PFA. Our facile, low-cost method allows for the large-scale production of GNs–PFA nanocomposites with high through-plane TCs, which can be used in various thermal-management applications.