Abstract
In this study, we investigated the synergistic effects of thermally conductive hybrid carbonaceous fillers of mesophase pitch-based carbon fibers (MPCFs) and reduced graphene oxides (rGOs) on the thermal conductivity of polymer matrix composites. Micro-sized MPCFs with different lengths (50 μm, 200 μm, and 6 mm) and nano-sized rGOs were used as the thermally conductive fillers used for the preparation of the heat-dissipation polymer composites. For all MPCF fillers with a different length, the thermal conductivity values of the MPCF/epoxy composites were proportional to the MPCF length and loading amount (0–50 wt%) of MPCFs. For an MPCF:rGO weight ratio of 49:1 (total loading amount of 50 wt%), the thermal conductivity values of MPCF-rGO/epoxy composites loaded with MPCFs of 50 μm, 200 μm, and 6 mm increased from 5.56 to 7.98 W/mK (approximately 44% increase), from 7.36 to 9.80 W/mK (approximately 33% increase), and from 11.53 to 12.58 W/mK (approximately 9% increase) compared to the MPCF/epoxy composites, respectively, indicating the synergistic effect on the thermal conductivity enhancement. The rGOs in the MPCF-rGO/epoxy composites acted as thermal bridges between neighboring MPCFs, resulting in the formation of effective heat transfer pathways. In contrast, the MPCF-rGO/epoxy composites with MPCF:rGO weight ratios of 48:2 and 47:3 decreased the synergistic effect more significantly compared to rGO content of 1 wt%, which is associated with the agglomeration of rGO nanoparticles. The synergistic effect was inversely proportional to the MPCF length. A theoretical approach, the modified Mori-Tanaka model, was used to estimate the thermal conductivity values of the MPCF-rGO/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 μm.
Highlights
In recent years, because of the fact that electronic devices have been downsized, integrated, and functionalized, the total amount of heat generated from devices, during their operation, has remarkably increased
Mori-Tanaka model, was used to estimate the thermal conductivity values of the mesophase pitch-based carbon fibers (MPCFs)-reduced graphene oxides (rGOs)/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 μm
In order to confirm the intrinsic properties of thermally conductive carbonaceous fillers used in this study, Field-emission scanning electron microscopy (FE-SEM) observation, Raman spectra, and electrical conductivity measurements of MPCFs with different lengths and rGOs were performed
Summary
Because of the fact that electronic devices have been downsized, integrated, and functionalized, the total amount of heat generated from devices, during their operation, has remarkably increased. It is important to design the optimal heat transfer pathways with single or hybrid fillers with high thermal conductivity in composite systems [10,11]. Efficient hybridization of micro- and nano-sized fillers can maximize the synergistic effects on the thermal conductivity enhancement of polymer composites, owing to the effective formation of heat transfer pathways [12,13]. We fabricated the epoxy-based composites loaded with the micro-sized MPCFs with three different lengths and hybrid fillers of the micro-sized MPCFs and nano-sized rGOs, and compared their morphologies and heat transfer properties. We investigated the synergistic effects of hybrid carbonaceous fillers of MPCFs and rGOs with different loading amounts on enhanced heat-dissipation capability of polymer composites. The theoretical thermal conductivity values were predicted to confirm the synergistic effect of hybrid carbonaceous fillers
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