Core–Sheath Nanofiber-Encapsulated Phase Change Composite Films with Aligned Boron Nitride Nanosheet Networks for Multifunctional Thermal Management

Rising power-density demands in miniaturized electronics drive the need for advanced thermal management. However, phase change materials’ low thermal conductivity and leakage hinder application despite their high latent heat and isothermal phase-change properties. Herein, we developed a flexible phase change composite film using coaxial electrospinning and dip-coating techniques. The core–sheath structure encapsulated polyethylene glycol (PEG) in hexagonal boron nitride nanosheets (BNNS)/polyacrylonitrile matrix to form a well-aligned thermally conductive network while providing outstanding electrical insulation performance. Thanks to the highly aligned and overlapped BNNS, the prepared PEG@BPAN/BNNS-p composite film exhibited remarkable in-plane and out-of-plane thermal conductivities of 2.450 W/(m·K) and 0.210 W/(m·K), which were 168% and 425% higher than the original film, respectively. After 200 cycles, it still maintained a high phase change enthalpy of 113.05 J/g with a tiny enthalpy loss of only 0.6% and negligible leakage. Meanwhile, the composite film benefited from excellent mechanical properties, with tensile strength reaching 15.84 MPa and elongation reaching 16.17%. This study presents a composite film with high in-plane thermal conductivity, enabling efficient lateral heat dissipation for thermal management in high-power density devices.