Sustainable high-yield h-BN nanosheet production by liquid exfoliation for thermal interface materials†

Abstract

Thermally conductive and electrically insulating hexagonal boron nitride (h-BN) is essential for thermal interface materials (TIMs) to effectively transfer heat from the source to sink in laptops and optoelectronic devices. Currently, thermal compounds rely on energy-intensive techniques and require nanofillers in very high loading percentages. Additionally, using mixtures of several fillers is an unreliable approach for heat management. In this work, we demonstrate the high-yield synthesis of atomically thin h-BN nanosheets in a natural surfactant/aqueous medium using liquid phase exfoliation (LPE). The exfoliated nanosheets are characterized by electron microscopy, absorbance spectroscopy, and XPS techniques. Extinction and gravimetry measurements confirm an overall yield of ∼89% after four cycles of exfoliation, successfully converting thick and bulk h-BN into h-BN nanosheets (h-BNNS) in water. Approximately 90% of the exfoliated nanosheets in ink form are recovered from the dispersion through low-speed centrifugation, indicating that the surfactant molecules are loosely bonded to the surface of the nanosheets. The quality of the exfoliated h-BNNS, including the lateral length (∼269 nm) and the number of layers (∼6), remains consistent during recycling. A 20 wt% h-BNNS in PVA thermal film reduces the surface temperature of a 10 W light-emitting diode (LED) bulb by ∼11 °C, while a 20 wt% h-BNNS in silicone oil (SO) thermal grease performs comparably to commercial thermal paste with 50 wt% particle loading for heat management. The thermal conductivity of the h-BNNS-based thermal film and thermal grease was measured using a modified transient plane source (MTPS) method and modelled using finite element analysis (FEA) to calculate thermal resistance. This study explores the utilization of a high-yield LPE process for h-BN nanosheets with natural stabilizers, enabling scalable exfoliation for heat management applications.