Calculations of factors that affect thermal conductivity in epoxy composites with hybrid carbon nanotube and graphene nano platelet

Abstract

Carbon Nanotubes (CNTs) and Graphene Nano Platelets (GNPs) had been used to enhance the thermal conductivity of the epoxy composites and show a synergistic effect. Complex service conditions also put forward the requirements for the structural design of the composites to get better performance. Researches should be done to further understand the mechanism of enhancement in composites and find ways to assist the design and optimization of the structure. In this research, epoxy composites with CNTs, GNPs and hybrid CNTs-GNPs (5:2) were prepared, whose total content of fillers was kept constant at 0.4 vol%. Test of specific surface area shew the hybrid fillers had less aggregation and the composites with hybrid fillers had the highest thermal conductivity. Observing the microstructure of the composites, CNTs were absorbed on the surface of GNPs, forming a crossnetwork which could improve aggregation and provide channels for the heat. A series of finite element models were established using scripts to find the factors that affect the forming of network and heat flow. A parameter was created to reflect the distribution of the fillers: distance of non-network(DNN). Positions, orientations, ratios, shapes, and sizes are all factors. The effect of angles depends on the relative positions of the fillers. A proper bending degree of CNTs would have better enhancement. The vertical-structure network was created manually and heat flux on the network was shown: GNPs expanded the area of network for the acceptance and release of heat. CNTs provide efficient channels for the multidirectional heat flow. The combination of the geometry expanded the influence region of the network.

Investigations on the effect of hybrid carbon fillers on the thermal conductivity of glass epoxy composites

“…The presence of 2 wt% of MWCNT, appears to distort the preferential orientation of the GNP at 1 wt%, and hence in composite D, a decrease in thermal conductivity is observed in the in‐plane direction. From reported studies, [ 36 ] it is observed that the MWCNT get stuck to the surface of GNP. This does not seem to be true in all cases.…”

“…It is reported in literature, [ 28,36,37 ] that in addition to the aspect ratio of GNP, the orientation of the carbon fillers is strongly dependent on the ratio of the fillers used. Generally, it is observed that if the fillers establish contact with the fiber direction, highest thermal conductivity is observed, since the fillers preferentially orient along the direction of glass fibers for better phonon transfer.…”

Interface thermal resistance and thermal conductivity of polymer composites at different types, shapes, and sizes of fillers: A review

“…Furthermore, hybridization of 1D with 2D nanomaterial can also form an efficient 3D thermal conductive network that can supply fast phonon channel transport due to the extended contact area formed through the line contact. Figure 22 shows that the 3D network was formed when hybridizing GNPs and CNT reported by Wang e al 93 . The large surface of 2D fillers was observed gives enough adsorption space for 1D fillers like CNT to disperse in the polymer matrix that prevented the GNPs from agglomerate and built the bridges between them.The 2D filler is known to have a very high rigidity that can hinder it from bending, especially at high volume fraction 49 .…”

“…Figure 22 shows that the 3D network was formed when hybridizing GNPs and CNT reported by Wang e al. 93 The large surface of 2D fillers was observed gives enough adsorption space for 1D fillers like CNT to disperse in the polymer matrix that prevented the GNPs from agglomerate and built the bridges between them.The 2D filler is known to have a very high rigidity that can hinder it from bending, especially at high volume fraction. 49 Therefore, the AR of 2D fillers is maintained and can provide more contact area with 1D fillers, which reduces the TBR and ITR, thus exhibiting high TC.…”

“…Microstructure of (A) CNTs absorbed on the GNP surface. (B‐D) Bridges formed between CNTs and GNPs (Reprint with permission [93])…”