Preparation of Mechanically Strong Aramid Nanofiber Gel Film with Surprising Entanglements and Orientation Structure Through Aprotic Donor Solvent Exchange

Aramid nanofiber (ANF), a nanoscale building block with a prominently complex structure, can be prepared by splitting poly(p-phenylene terephthalamide) (PPTA) fibers into negatively charged ANFs in a deprotonating manner in a DMSO/KOH solvent system, followed by a subsequent re-protonation process using a proton-donor reagent. There are rare reports regarding the utilization of an aprotic donor reagent to convert deprotonated ANF dispersion into film or gel with a controllable structure and high mechanical properties. In this work, dichloromethane, as an anhydrous aprotic donor solvent, has been introduced into the deprotonated ANF dispersion to replace DMSO, containing PPTA molecules and hydroxyl ions, leading to the gelation of deprotonated ANF dispersions, forming a film (ANFDCM) possessing a surprisingly highly entangled and oriented structure, as proven by SEM results. Due to the attenuation of electrostatic repulsion in the dispersion, partially deprotonated ANFs intertwined and cross-linked through π-π conjugation among a large number of benzene rings in PPTA molecules. After treating ANFDCM with water for re-protonation, the as-prepared film (ANFDCM-W) exhibited high tensile strength (307.7 MPa) and toughness (74.7 MJ m-3).