Flexible, thermostable and flame-resistant epoxy-based thermally conductive layered films with aligned ionic liquid-wrapped boron nitride nanosheets via cyclic layer-by-layer blade-casting

Increasing power density and excess heat production in integrated electronic devices create the strong demand for polymeric thermal management materials with excellent thermal stability, flame retardancy and thermal conductivity. To this end, high-performance ionic liquid-wrapped boron nitride nanosheets (BNNS@IL) were firstly simultaneously exfoliated and flame-retardant functionalized via one-step ball milling process based on the strong mechanochemical action. Epoxy (EP)-based layered films with highly in-plane oriented BNNS@IL were then fabricated by a novel, effective and solvent-free cyclic layer-by-layer (CLbL) blade-casting method. Arising from the highly flat oriented structure and rich flame-retardant functional groups of BNNS@IL, as well as the high compatibility between filler and matrix, the as-fabricated EP/BNNS@IL films exhibited high anisotropic thermal conductivity (K∥ of 8.3 and K⊥ of 0.8 W m−1 K−1), outstanding thermal stability and flame retardancy with a dramatic decrease in PHRR (104.2 W/g) and THR (8.1 kJ/g) corresponding to reductions of 72.9% and 75.7% compared with neat EP, respectively. Additionally, the flat oriented structure and strong interfacial interaction also endow EP/BNNS@IL films with high flexibility and excellent mechanical properties. Therefore, the high-effective CLbL casting method and the obtained high-performance EP-based film exhibit a significant potential application in high power flexible electrical devices and thermal management products.