Flexible thermally conductive and electrically insulating silicone rubber composite films with BNNS@Al 2 O 3 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 (Al 2 O 3 ) was chemically grafted to the surface of boron nitride nanosheets (BNNS) to prepare hetero-structured thermally conductive fillers (BNNS@Al 2 O 3 ), and two-component room temperature vulcanized silicone rubber (RTV-2SR) was used as the polymer matrix. Then BNNS@Al 2 O 3 /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@Al 2 O 3 hetero-structured thermally conductive fillers with “point-plane” structure were successfully prepared. The BNNS@Al 2 O 3 hetero-structured thermally conductive fillers successfully achieved the synergy of Al 2 O 3 and BNNS and had more significant improvement on λ than single Al 2 O 3 , single BNNS, and simply blending BNNS/Al 2 O 3 . When the amount of BNNS@Al 2 O 3 was 30 wt% (BNNS/Al 2 O 3 , 1:1, wt:wt), the in-plane λ ( λ ∥ ) and through-plane λ ( λ ⊥ ) of the BNNS@Al 2 O 3 /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), Al 2 O 3 /RTV-2SR (with single Al 2 O 3 , λ ∥ = 1.62 W/mK, λ ⊥ = 0.49 W/mK), and (BNNS/Al 2 O 3 )/RTV-2SR (with simply blending BNNS/Al 2 O 3 , 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@Al 2 O 3 /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 (tan δ ), 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 × 10 11 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@Al 2 O 3 fillers, BNNS@Al 2 O 3 /RTV-2SR thermally conductive composite films and corresponding thermal conduction mechanism.