Ice-Template-Assisted Anisotropic Aerogel Monoliths: An Assembly Strategy of Aramid Nanofibers

The manipulation of aramid nanofibers (ANFs) into macroscopic monolithic aerogels with ordered microstructures is critical for enabling their extensive and large-scale practical implementations. This study introduces a top-down strategy utilizing ice templates to prepare aramid aerogel monomers. The process involves dissolving Kevlar fibers in dimethyl sulfoxide (DMSO) under alkaline conditions to produce aramid nanofibers (ANF). Subsequently, the self-assembly of ANF was effectively tailored by using ice templating (referred to as O-ANF) and the nondirectional freezing technique (designated as D-ANF), respectively. The O-ANF aerogel exhibits a distinctive long-range ordered sheet structure with a honeycomb surface pattern, attributed to the low melting point of DMSO (18.4 °C). Axial thermal conductivity of the O-ANF aerogel was 93.5% better compared to the D-ANF aerogel, while its tensile strength in this direction was approximately 5.2 times greater. Molecular dynamics (MD) simulations were utilized to elucidate the mechanisms underlying the enhanced mechanical and thermal properties. Moreover, the O-ANF demonstrated superhydrophilicity, whereas the D-ANF exhibited a contact angle of 67.52°. As an organic aerogel, ANF possesses typical characteristics of low density and high porosity. Additionally, ANF exhibits superior insulation performance from -196 to 200 °C and flame retardancy. Given its exceptional properties and straightforward preparation method, ANF aerogels hold significant potential for applications in aerospace and fire protection.