Glycine functionalized boron nitride nanosheets with improved dispersibility and enhanced interaction with matrix for thermal composites

Hexagonal boron nitride nanosheets (BNNS) have been widely investigated as promising fillers for thermal composites because of their high thermal conductivity and electrical insulation, which avoid the short circuit risk effectively when applied in electronics. However, the poor dispersibility and weak interaction with matrix have hindered the further improvement of BNNS based thermal composites. Here, we propose a simple and green amino acid-assisted ball milling exfoliation process for highly hydrophilic glycine (NH2-CH2-COOH)-functionalized BNNS (BNNS-Gly) to improve their dispersion and reduce the thermal interface resistance between fillers and matrix. Three different types of thermal management materials have been prepared by dispersing BNNS-Gly into water, epoxy resin, and cellulose respectively, and their thermal properties have been investigated. As a result, the BNNS-Gly water nanofluid exhibits a 110% increment in thermal conductivity at 1.6 vol% loading compared with pure water. For BNNS-Gly/Epoxy composite, an enhancement of 109% of thermal conductivity compared with pure BNNS/Epoxy is achieved. According to the calculation of the Maxwell-Garnett effective medium theory (EMT) model, the thermal interface resistance between BNNS-Gly and epoxy is reduced by 62%. Besides, the thermal conductivity of BNNS-Gly/cellulose nanofiber (CNF) film reaches up to 16.2 W/mK at 70 wt% loading, which is 1.8-fold of that for BNNS/CNF. In summary, BNNS-Gly fabricated by this work show great advantages in thermal properties compared with widely-used pure BNNS based composites for improved dispersibility and enhanced interaction with matrix.