Multifunctional microcellular PVDF/Ni-chains composite foams with enhanced electromagnetic interference shielding and superior thermal insulation performance

Lightweight and multifunctional polyvinylidene fluoride/Nickel-chains (PVDF/Ni-chains) composite foams with good mechanical property, excellent thermal insulation and outstanding electromagnetic interference (EMI) shielding performance (SE) were prepared by a multi-step process including: (a) controllable synthesis of high-aspect-ratio Ni-chains, (b) Ni-chains introduced into PVDF matrix, (c) crystallinity tailoring of composite samples, (d) supercritical carbon dioxide foaming of the treated composites. Thermal treating and nanofiller existence effect are applied to tune the degree of crystallinity and crystal structures of semi-crystalline PVDF. Notably, with the optimized pre-treatment and foaming process, lightweight PVDF/Ni-chains composite foams with uniform closed-cell microcellular morphology were successfully developed. Thanks to the unique porous morphology, PVDF/10 wt% Ni-chains foams present decreased mass density (~1.0 g/cm3), high tensile strength (~42.0 MPa), enhanced electrical conductivity (~0.01 S/m) and superior thermal insulation performance (~0.075 W/(m·K)). Furthermore, conductive-magnetic PVDF/10 wt% Ni-chains foam exhibits a high EMI shielding effectiveness of 26.8 dB and an outstanding specific shielding effectiveness (SSE) of 127.62 dB cm2/g, with an absorption-dominated shielding feature in X-band region. The enhanced absorption is attributed to the multiple reflections, dielectric loss, polarization loss and magnetic loss originated from the unique porous structure and condensed Ni-chains networks. This study paves a low-cost and scalable method for the design of novel, lightweight, thermal insulation and efficient EMI shielding composite foams characterized by optimized microcellular structure and conductive-magnetic Ni-chains networks with promising prospect for applications in construction, aerospace and electronics filed.