Ultrafine aramid nanofibers prepared by high-efficiency wet ball-milling-assisted deprotonation for high-performance nanopaper

Aramid nanofibers (ANFs) with a nanoscale diameter, large aspect ratio, and exposed electronegative surface, as well as ultrahigh thermal/chemical inertness and extreme mechanical properties, provide promising applications in many emerging fields, but these are greatly limited by the low preparation efficiency and broad diameter distribution. Herein, we put forward a high-efficiency wet ball milling-assisted deprotonation (BMAD) strategy to rapidly prepare ANFs with an ultrafine diameter. The strong shear and collision forces from ball-milling induced stripping and splitting effects on the macroscopic fibers, which promoted the penetration and expanded the contact interfaces between reactants, thus accelerating the deprotonation reaction and refining the ANF diameter. As a result, ultrafine ANFs with a diameter of only 2.09 nm and high concentration (1 wt%) were successfully achieved within 30 min. This BMAD strategy represents a vastly advantageous approach compared to the existing reported ANF preparation approaches in terms of efficiency (20 g L^-1 h^-1) and fiber diameter. The ultrafine microstructure leads to the corresponding ANF nanopaper having more compact stacking and fewer defects, thus exhibiting extraordinary mechanical properties including tensile strength (271.7 MPa) and toughness (33.1 MJ m^-3). This work achieves significant progress toward high-efficiency production of ultrafine ANFs, bringing about appreciable prospects in preparing promising multifunctional ANF-based materials.