High thermal conductivity thermoplastic polyurethane/boron nitride/liquid metal composites: the role of the liquid bridge at the filler/filler interface

Abstract

Polymer composites with high thermal conductivity (TC) as electronic packaging materials play a critical role in dissipating heat in microelectronic devices. Among the several methods to improve their TC, connection of heat fillers in the heat pathway using the bridging technique is an effective strategy. In this article, we prepared thermoplastic polyurethane composites (TPU/BN/LM) with solid/liquid hybrid fillers of boron nitride (BN) and liquid metal (LM) via hand grinding and solution casting. The TPU/BN/LM composite with 40 vol% of a hybrid filler has a TC of 2.64 ± 0.10 W m⁻¹ K⁻¹, 2.02 times that of the TPU/BN composite (1.31 ± 0.07 W m⁻¹ K⁻¹). Moreover, this TPU/BN/LM composite has a tensile strength of 7.35 ± 0.85 MPa and elongation at break of 204 ± 7%, which is 2.07 times and 1.61 times those of the TPU/BN composite containing the same filler content, respectively. The enhancement of thermal conductivity and mechanical properties is originated from the connection of BN platelets by the liquid bridge of LM because LM wets BN platelets and LM fills up the gap of BN platelets. The thermally conductive bridge reduces the interfacial thermal resistance at filler/filler interface through strong interaction and surface-to-face (2D) contact. This liquid bridging technique is expected to provide an alternative strategy for preparing high thermal conductivity composites through enhancement of the filler/filler interface.