Highly enhanced thermal conductivity from boron nitride nanosheets and MXene phonon resonance in 3D PMMA spheres composites

Efficient thermal management materials are important for the proper operation of integrated circuits. In this work, the high-yield preparation of hydroxylated boron nitride nanosheets (BNNSs) was achieved by high-temperature ablation followed by ultrasonic exfoliation without the use of highly toxic solvents. The small-sized BNNSs have similar phonon vibration properties as the large-sized MXene, and they self-assemble by electrostatic adsorption on PMMA particles to form hybrid spheres. The appearance of thermal percolation threshold indicates the successful construction of thermal conductivity pathway. The exclusion effect is more pronounced for PMMA microspheres with a larger radius, and the best thermal conductivity of 4.13 W/m·K was achieved for the composite with 20 wt% nanosheet filling. The composite exhibited good thermal performance both in the finite element model and when used as an LED heat sink. Furthermore, the incorporation of fillers can also effectively improve the thermal stability and mechanical properties of the composite. Our study provides a facile and environmental exfoliation approach of h-BN and a new strategy for the preparation of high thermal conductivity electronic packaging materials.