Flame-retardant and electromagnetic-interference-shielding silver nanowire/silicon dioxide/aramid nanofiber/sodium alginate lightweight porous composite for wearable sensors

With the rapid advancement of wearable electronics and smart devices, multifunctional wearable sensors have gained increasing attention. Therefore, a multifunctional silver nanowire/silicon dioxide/aramid nanofiber/sodium alginate (AgNWs/SiO 2 /ANF/SA) porous composite was fabricated via liquid‑nitrogen freeze-drying, combining lightweight structure, electromagnetic interference (EMI) shielding, flame retardancy, and sensing. The porous composite was crosslinked through dual interactions of calcium ions (Ca 2+ ) coordination and hydrogen bonding, forming a layered porous structure. The incorporation of AgNWs remarkably improved the electrical conductivity and EMI shielding capability of the porous composite. In particular, the AgNWs/SiO 2 /ANF/SA composite containing 40% AgNWs (40Ag-A) achieved a low density of 44.01 kg/m 3 together with outstanding EMI shielding effectiveness. Moreover, Ca 2+ crosslinking with ANF and SA, combined with the synergistic reinforcement of SiO 2 , enhanced the flame-retardant and smoke-suppression properties, lowering the heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and carbon monoxide production rate (COP) of 40Ag-A to 41.64 kW/m 2 , 2.98 MJ/m 2 , 0.12 m 2 , and 2.00 × 10 −3  g/s. The wearable strain sensor fabricated using the 40Ag-A demonstrated outstanding sensitivity (S = 7.40, 19.45, and 40.23) and fast response/recovery characteristics (36 ms), allowing real-time detection of human joint movements. Therefore, the porous composite achieved synergistic enhancement in lightweight structure, electromagnetic shielding, flame retardancy, and sensing performance, showing great potential for wearable electronics, safety protection, and Smart Internet of Things applications.