Sacrificial Hydrogen-Bonded Interfacial Engineering for Boron Nitride-Based Polymer Composite Films with Enhanced Thermal Conductivity and Ultraductility

Although boron nitride nanosheets (BNNSs) are outstandingly thermally conductive and electrically insulating, it remains a challenge to design BNNS-based stretchable thermal conductors for waste heat cooling and the satisfactory deformation of advanced flexible electronic devices, owing to weak interfacial interactions. In most tough hydrogels, sacrificial structures bridge the interfacial gap between matrixes and fillers, enabling high-loading polymeric composites to exhibit ductile deformation behavior and, in turn, reduce interfacial phonon scattering between them. Inspired by this, we propose a soft-rigid interfacial design strategy to construct high-loading functionalized BNNS-based (BNNS–atPEG)/poly(vinyl alcohol) (PVA) composite films via evaporation-induced self-assembly (EISA) by introducing sacrificial bonds and incorporating a soft polymer reinforced agent, namely, hydroxypropyl cellulose (HPC). Benefiting from the densely hierarchical microstructure, dynamic hydrogen-bonding interaction, and successful wrapping of soft amino-terminated poly(ethylene glycol) (atPEG), the as-obtained PVA/HPC composite films containing high-loading BNNS–atPEG (>10 wt %) were endowed with rubberlike ductility (253.1–679.6%), ultralarg toughness (50.6–129.5 MJ/m 3 ), and enhanced in-plane thermal conductivity (6.21–20.87 W m –1 K –1 ). Additionally, the use of our P19H1/BNNS–atPEG composite film has been verified as a flexible heat sink, providing a cooling efficiency comparable to that of conventional alumina.