Graphite nanoplatelet/silicone composites for thermal interface applications

Thermally conducting and effectively electrically insulating nanocomposites for thermal interface applications were developed by dispersing graphite nanoplatelets (GNP) into a silicone matrix by dual asymmetric centrifuge mixing. Thermal conductivity, electrical conductivity, compression and hardness properties of the resulting composites were measured. The effects of GNP particle size and wt.% of GNP on the thermal conductivity and curing behaviour of the composites were also investigated. The results showed that the thermal conductivity of the GNP/silicone composites (having GNP with an average particle size of 15 ¿m), measured by the hot disk technique, reached 1.4 W/m.K at a loading of 20 wt.% (compared to 0.65 W/m.K for the, otherwise identical, system with an average particle size of 5 ¿m). The former represents a 7-fold increase compared to the thermal conductivity at 20°C of silicone alone. SEM analysis revealed that the composites consist of homogeneous randomly dispersed GNP in silicone at loading levels greater or equal to 15 wt.%, whereas at lower loadings a concentration gradient effect (due to settling) can be inferred. Differential scanning calorimeter (DSC) analysis showed that GNP addition increased the curing temperature of silicone from 92°C to 116°C, probably by hindering the free movement (mobility) of the silicone chains. Compression and Shore hardness testing results, perhaps unexpectedly, showed that the presence of the GNP did not increase the stiffness and compressive strength of the silicone. The GNP/silicone composites have thermal conductivities that are comparable to commercially available thermal interface materials but they have increased compliance, which is an advantage in gap-filling applications, whilst offering potential cost savings by using cheaper filler at lower loadings.