Polyethylene Glycol Assisted Ball Milling Surface‐Modified Boron Nitride Nanosheets and Their Thermally Responsive High‐Performance Thermal Conductive Silicone Greases

ABSTRACT Efficient thermal management is critical for miniaturized electronic devices. While hexagonal boron nitride (h‐BN) is an ideal thermal interface material (TIM) filler, its application is hindered by exfoliation difficulties and phonon spectrum mismatch. Herein, we report a strategy for preparing functionalized boron nitride nanosheets (BNNSs) using polyethylene glycol 4000 (PEG4000)‐assisted ball milling and constructing high‐performance thermal silicone grease. PEG4000 undergoes a phase change during the ball milling process, which effectively reduces the normal impact forces while enhancing the interlayer shear forces, thereby achieving efficient exfoliation of h‐BN to obtain nanosheets with an average thickness of 8.6 nm and facilitating mechanochemical surface grafting onto BNNSs. The thermal conductive grease prepared by compounding dimethyl silicone oil and fluorosilicone oil matrices exhibits temperature‐responsive thermal conductivity: reaching 1.45 W·m −1 ·K −1 at 50°C, which is a 3.5% increase compared to that at 30°C. Mechanistic analysis reveals that the phase transition of PEG4000 and the dynamic hydrogen bond network formed with the matrix significantly reduce interfacial thermal resistance. Furthermore, at 5 wt% BNNSs loading, the grease achieves a 0.01% oil bleeding rate, demonstrating excellent long‐term stability. This study provides a facile and efficient approach for preparing thermal interface materials with high thermal conductivity and reliability.