Induced clustering-enabled thermal transport enhancement in polymer composites for efficient thermal interface materials

Efficient removal of accumulated heat is essential to maintaining device efficiency and ensuring long lifetime span. Polymer composites composed of highly conductive ceramic fillers and flexible polymer matrix are popularly selected as thermal management materials owing to their moderate thermal transport properties, gap-filling capability and easy processing ability with low cost. High thermal conductivity of polymer composites is one of the primary requisites for thermal management materials of electronic devices. We report abnormal increase of thermal conduction of Al2O3-based silicone polymer composites by induced clustering of thermally conductive BN nanoplatelets. Initially, polymer composite containing various amount of spherical Al2O3 fillers have been prepared and measured thermal diffusivity along through-plane direction (dt) was 0.7 mm2/s at best. This value of DT is only 5% of known TDs for bulk polycrystalline Al2O3. The main cause of the low thermal transport properties is assumed to be discrete distribution of thermally conductive fillers. Then, small amount of nanocrystalline platelets with high thermal conductivity are incorporated to enhance the connectivity between fillers. As-received BN powders were surface-oxidized with high temperature treatment under ambient atmosphere and exfoliated to be nanoplatelets after further ball milling with water to ensure uniform dispersion in polymer matrix. Al2O3 containing composite showed dt of enhanced to 1.0 mm2/s after subsequent addition of surface modified BN nanoplatelets by 6 vol%. Further addition of BN nanoplatelets resulted in abrupt increase in DT up to 1.5 mm2/s which is almost twice as high as dt of a pristine Al2O3-containing polymer composite. The clustering of thermally conductive ceramic fillers enclosed with polymer matrix is shown to be induced by colloidal interaction between BN nanoplatelets in the gaps between macroscopic Al2O3 spheres. These can be attributed to be main cause of rapid improvement of thermal diffusivity in the composites. Here, the benefits of induced clustering for thermal management composite materials are illustrated.