Flexible thermally conductive and electrically insulating silicone rubber composite films with BNNS@Al₂O₃ fillers

With the advent of 5G era, the electronic and electrical industries are in increasingly urgent demand for flexible materials with high thermal conductivity coefficients (λ). In this paper, alumina (Al₂O₃) was chemically grafted to the surface of boron nitride nanosheets (BNNS) to prepare hetero-structured thermally conductive fillers (BNNS@Al₂O₃), and two-component room temperature vulcanized silicone rubber (RTV-2SR) was used as the polymer matrix. Then BNNS@Al₂O₃/RTV-2SR flexible thermally conductive and electrically insulating composite films were prepared by shear-coating. Results of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) showed that the BNNS@Al₂O₃ hetero-structured thermally conductive fillers with “point-plane” structure were successfully prepared. The BNNS@Al₂O₃ hetero-structured thermally conductive fillers successfully achieved the synergy of Al₂O₃ and BNNS and had more significant improvement on λ than single Al₂O₃, single BNNS, and simply blending BNNS/Al₂O₃. When the amount of BNNS@Al₂O₃ was 30 wt% (BNNS/Al₂O₃, 1:1, wt:wt), the in-plane λ (λ_∥) and through-plane λ (λ_⊥) of the BNNS@Al₂O₃/RTV-2SR thermally conductive composite film reached 2.86 W/mK and 0.89 W/mK, 2.8 times λ_∥ (1.01 W/mK) and 4.2 times λ_⊥ (0.21 W/mK) pure RTV-2SR film, also higher than those of BNNS/RTV-2SR (with single BNNS, λ_∥ = 2.46 W/mK, λ_⊥ = 0.76 W/mK), Al₂O₃/RTV-2SR (with single Al₂O₃, λ_∥ = 1.62 W/mK, λ_⊥ = 0.49 W/mK), and (BNNS/Al₂O₃)/RTV-2SR (with simply blending BNNS/Al₂O₃, 1:1, wt:wt, λ_∥ = 2.04 W/mK, λ_⊥ = 0.62 W/mK) thermally conductive composite films with the same fillers amount. Meanwhile, the prepared BNNS@Al₂O₃/RTV-2SR thermally conductive composite film obtained excellent mechanical properties, electrical insulation properties, and thermal properties. Its tensile strength, elongation at break, hardness, dielectric constant (ε), dielectric loss (tanδ), volume resistivity (ρ_v), glass transition temperature (T_g), and heat resistance index temperature (T_HRI), respectively, reached 0.84 MPa, 175%, 27 HA, 3.89, 0.0088, 5.76 × 10¹¹ Ω·cm, − 40.1 °C and 185.3 °C. This work can provide a new idea for the preparation of hetero-structured thermally conductive fillers and flexible thermally conductive and electrically insulating composite films. Graphical abstract: Schematic diagrams for hetero-structured BNNS@Al₂O₃ fillers, BNNS@Al₂O₃/RTV-2SR thermally conductive composite films and corresponding thermal conduction mechanism.[Figure not available: see fulltext.]