Self-Stacked 3D Anisotropic BNNS Network Guided by Para-Aramid Nanofibers for Highly Thermal Conductive Dielectric Nanocomposites.

The enhancement of the heat-dissipation property of polymer-based composites is of great practical interest in modern electronics. Recently, the construction of a three-dimensional (3D) thermal pathway network structure for composites has become an attractive way. However, for most reported high thermal conductive composites, excellent properties are achieved at a high filler loading and the building of a 3D network structure usually requires complex steps, which greatly restrict the large-scale preparation and application of high thermal conductive polymer-based materials. Herein, utilizing the framework-forming characteristic of polymerization-induced para-aramid nanofibers (PANF) and the high thermal conductivity of hexagonal boron nitride nanosheets (BNNS), a 3D-laminated PANF-supported BNNS aerogel was successfully prepared via a simple vacuum-assisted self-stacking method, which could be used as a thermal conductive skeleton for epoxy resin (EP). The obtained PANF-BNNS/EP nanocomposite exhibits a high thermal conductivity of 3.66 W m-1 K-1 at only 13.2 vol % BNNS loading. The effectiveness of the heat conduction path was proved by finite element analysis. The PANF-BNNS/EP nanocomposite shows outstanding practical thermal management capability, excellent thermal stability, low dielectric constant, and dielectric loss, making it a reliable material for electronic packaging applications. This work also offers a potential and promotable strategy for the easy manufacture of 3D anisotropic high-efficiency thermal conductive network structures.

SnTe thermoelectric materials with low lattice thermal conductivity synthesized by a self-propagating method under a high-gravity field.

The conventional fabrication methods (for example, melting and powder metallurgy) of bulk thermoelectric materials are time- and energy-consuming, which restrict their large-scale application. In this work, ultra-fast self-propagating synthesis under a high-gravity field was used to prepare SnTe bulks, which shortened the synthesis time from several days to a few seconds. The grain growth was suppressed and some small pores were reserved in the matrix during the ultra-fast solidification process. The increased grain boundaries and pores (nanoscale to micron scale) enhanced phonon scattering, which greatly decreased the lattice thermal conductivity. The obtained minimum lattice thermal conductivity is 0.81 W m-1 K-1, and the maximum zT value is 0.5 (873 K), which is comparable to the best reported results of the undoped SnTe alloy. The ultra-fast non-equilibrium synthesis technique opens up new possibilities to prepare high-efficiency bulk thermoelectric materials with reduced time and energy consumption.