Thermal Conductivity of Platelet‐Filled Polymer Composites

Abstract

Platelet-shaped particles of similar size and shape were investigated as fillers for improving the thermal conductivity of polymer-ceramic composite materials. The conductivities of composites filled with hard, stiff ceramic particles exceeded 3.5 W⅐(m⅐K) ؊1 , or >20 times the conductivity of the polymer matrix, and were shown to be almost independent of the intrinsic filler conductivity range of 33-300 W⅐(m⅐K) ؊1 . In contrast, the thermal conductivity of composites filled with soft, platelet-shaped BN fillers reached over 13 W⅐(m⅐K) ؊1 . A mechanism is proposed whereby deformation of the soft filler particles provides improved particle-to-particle connectivity and allows greater packing density, resulting in the ability to achieve much higher conductivity than is possible for hard and stiff particles of similar initial morphology. Experimental results are discussed in light of various thermal conductivity prediction models in the literature.

Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers

“…[30,31] In the case of a BN powder and high-density polyethylene (HDPE), Zhou et al observed the improvement from 0.26 to 0.45, 0.76, and 1.02 W m À1 K À1 , respectively, when www.afm-journal.de [30] For the case of multiwalled CNTs, the results strongly correlated with the alignment of the CNTs; the numbers varied from 0.6 to 3.4 W m À1 K À1 for a 20 wt% CNT load, whereas the thermal conductivity for the misoriented CNTs was $0.7 W m À1 K À1 . [30] However, in some reports, remarkable improvements were recorded when a fraction of 70 wt% or more of surface-modified AlN powders were filled into an epoxy.…”

High thermal conductivity in soft elastomers with elongated liquid metal inclusions

“…To overcome this fundamental tradeoff with thermal transport in soft materials, attempts have been made to engineer composites with various fillers (10), including metals (11,12), ceramics (13), carbon fibers (14), and nanomaterials such as carbon nanotubes and graphene (4,15,16). Anisotropic thermal conductivity can arise in composite systems by using 1D fillers such as carbon fibers where thermal transport preferentially occurs along the major dimension of the filler (14).…”

Graphite-high density polyethylene laminated composites with high thermal conductivity made by filament winding

“…Figure 4 shows the ratio de- ), with respect to the filler particle's length scale. This clearly illustrates that the length scale associated with the filler particles is crucial, and that for small particles the interface resistance dominates, as has been widely acknowledged in the literature [4,18,22,23,45,55,56]. More importantly, Figure 4 shows that the usage of highly conductive fillers, i.e., with thermal conductivity on the order of 1000 W·m -1 ·K -1 would require even larger filler particles before the interface resistance ceases to dominate.…”

“…The net effect of the interface scales with the filler particle surface area, but the effect that the particle should have on the composite scales with its volume. Thus, for small particles the resistance associated with the surface area dominates, as compared to the resistance associated with its volume [13,22,45,46]. Here, a filler particle with a simple cubic geometry is used as an example to illustrate the point.…”