Ion-confined ice template-driven advanced aramid nanofiber aerogels for efficient adiabatic applications in harsh environments.

Aramid nanofiber aerogels, derived from poly(p-phenylene terephthalamide) (PPTA) nanofibers with impressive thermal stability and durability, have emerged as high-performance thermal insulators in harsh environments. However, they are plagued by ice-crystal-induced structural destruction during the freeze-drying process, significantly compromising the volume fraction of thermal barrier voids and limiting the breakthrough in adiabaticity. Here, we present a new ion-confined ice-templating strategy to spatially weaken ice crystal growth, constructing nanofiber aerogels with distinctive separated and fine interconnected nanofiber network architectures (SN aerogels). The interfacial affinity between PPTA chains and ice crystals enhanced by innovative ion-bridging enables efficient confinement of ice crystal growth, producing lower nanofiber aggregation. This optimized nanofiber framework achieves more abundant voids, endowing SN aerogels with ultralow density (11.5 mg cm-3), ultrahigh porosity (99.75%), ultrahigh specific surface area (200 m2 g-1), and ultralow thermal conductivity (25.17 mW m-1 K-1). Moreover, SN aerogels display integrated properties of mechanical elasticity and extreme temperature durability (80% compressible strain from -196 to 400 °C), fire resistance, and recyclability, ensuring the strong adaptive capacity in harsh environments and the friendly closed-loop re-processibility. This study provides a versatile strategy for regulating ice-crystal growth in nanofiber aerogels and opens new opportunities for developing advanced ultralow-thermal-conductivity adiabatic materials.