Density-Tunable Aramid\nNanofiber Foams for Flame Retardancy,\nJoule Heating, and Organic Solvent Absorption

Aramid nanofiber (ANF) based porous\nmaterials have been widely applied in thermal insulation, high-efficiency\nadsorption, and sensing technologies. However, significant volume\nshrinkage of ANF products during freeze-drying is inevitable due to\nthe organic solvent used in the fabrication. This shrinkage leads\nto increased density and a reduced performance. In this study, we\npropose a method for fabricating ANF foam that utilizes Ni foam as\nan antideformation sacrifice layer to suppress the shrinkage induced\nby dimethyl sulfoxide (DMSO). The Ni foam is immersed in an ANF-DMSO\ndispersion, followed by solvent exchange and freeze-drying, during\nwhich a thin ANF layer is coated onto the foam skeleton. Subsequently,\nthe ANF foam is obtained by etching the Ni skeleton and drying. The\nfabricated ANF foam exhibits an ultralow density of 7.98 mg/cm<sup>3</sup> and demonstrates exceptional structural stability. The foam\nexhibits outstanding mechanical properties and a remarkable load-bearing\ncapacity, withstanding a weight of over 1229 times its own weight\nwithout structural damage. Furthermore, the ANF foam showcases superior\nthermal insulation and flame-retardant properties. It retains the\nstructural characterization of abundant active sites on the surface\nand within its pores, enabling it to be functionalized with carbon\nnanotubes (CNT), designed to function as a self-heater and to absorb\nand degrade organic solvents.