Effect of chemical functionalization on the thermal conductivity of 2D hexagonal boron nitride

Abstract

Hexagonal boron nitride nanosheets (h-BNNSs) are excellent candidates as fillers of polymer-based thermal interface materials for electronic packaging. Chemical functionalization of h-BNNSs is necessary to improve the dispersity of the h-BNNSs and reduce the interfacial thermal resistance (ITR) in the composites. However, though studied extensively, the thermal conductivity (TC) of the chemically functionalized h-BNNS/polymer composites is still well below expectations. Among the possible reasons, the TCs of the functionalized h-BNNSs themselves need to be considered thoroughly, as it has been shown that TC of graphene could be dramatically reduced to less than 10 W m−1 K−1 by point defects. Here, we investigate the TCs of hexagonal boron nitride (h-BN) monolayers covalently adsorbed with -OH and -O(CH2)4CH3 groups based on equilibrium molecular dynamics simulations. The TC of the functionalized h-BN decreases monotonically with the increasing concentration of adsorbed groups and tends to saturate at high concentrations. We surprisingly find that the almost-saturated TCs of the functionalized h-BN monolayers are still over 100 W m−1 K−1, about 25% of the value of the pristine h-BN monolayer. The different functional groups have a similar effect on the TCs, which are mostly determined by the extent of distortion of the local 2D structure, and the functionalization introduces no additional anisotropy to the TC. Therefore, we conclude that the chemically functionalized h-BNs themselves are sufficiently thermally conductive as fillers of composites, and the chemical functionalization should be encouraged, with the focus on digging into how to reduce the ITR more effectively.