Humidity-stable submicron magnesium oxide particles for high-performance thermally conductive composites

While spherical MgO microparticles provide high fluidity and dispersibility within polymer matrices, submicron MgO particles confer superior thermal conductivity to thermally conductive composites by increasing the number of particle contact points and optimizing the heat transport pathways. However, the effectiveness of submicron MgO particles as heat-dissipating agents is limited by conventional fabrication methods, which often fail to prevent moisture reactivity. In this study, we introduce a novel bottom-up approach for the synthesis of submicron MgO particles with superlative humidity resistance and thermal conductivity. Spray drying a polymeric precursor solution synthesized via the polymerization of citric acid and ethylene glycol followed by a two-step heat treatment involving oxidation and liquid-phase sintering affords MgO particles with dense morphologies and excellent humidity resistance (1.03% weight variation). These submicron-scale, humidity-stable MgO particles significantly enhance the thermal conductivity of a polydimethylsiloxane matrix, achieving 6.0 W m^-1 K^-1 at 80 vol% filler content, significantly higher than that of composites without submicron MgO at the same filler content (4.4 W m^-1 K^-1). The submicron MgO particles also provide additional electrical insulation; thus, this synthetic method is expected to facilitate the development of high-performance ceramic fillers for advanced heat management applications in next-generation electronic devices.