Large-scale preparation of high-performance boron nitride/aramid nanofiber dielectric composites

Dielectric polymers featuring high thermal conductivity, excellent mechanical, and stable dielectric properties over a broad temperature range have attracted extensive scientific attention. In this work, a large-scale, layered film was fabricated using blade-coating approach, which integrated aramid nanofibers (ANFs) and boron nitride nanosheets (BNNSs) through a typical sol-gel transformation procedure. The as-prepared film with 20 wt.% BNNS displays high thermal conductivity (14.03 W·m⁻¹·K⁻¹), 103-fold higher than pure ANF film, attributing to massive continuous thermal conduction pathway between BNNSs so as to facilitate fast phonon transmission. The film boasts excellent mechanical properties (stress 97.14 ± 5.17 MPa, strain 19.36 ± 0.35%), high degradation temperature (~ 542 °C), a moderate dielectric constant (~ 6.9 at 10⁴ Hz), together with low dielectric loss (~ 0.026 at 10⁴ Hz). Meanwhile, the film reveals high breakdown voltage (310 MV·m⁻¹) and volume resistivity (10¹³ Ω·cm). Notably, these dielectric properties remain largely unchanged over a wide temperature range (25 to 200 °C).