Carbon Nanotube Wires Sheathed by Aramid Nanofibers

Coaxial fibers are the key elements in many optical, electrical, and biomedical applications. Recent success in materials synthesis has provided versatile choices for the core part, but the search of high-performance sheath materials remains much less productive. These surface coatings are however as important as the core for their role as protection layers and interaction medium with the externals, thereby critically affecting the real performance of coaxial fibers. Here it is shown that aramid nanofibers (ANFs) with exceptional environmental stability and mechanical properties can be advanced coating materials for both wet- and dry-spun carbon nanotube (CNT) wires. Co-wet-spinning ANFs with CNT aqueous dispersion can produce coaxial fibers with a compact sheath comprised of aligned ANFs, showing much enhanced mechanical properties by transferring stress to the sheath without sacrificing the conductivity. On the other hand, an immersion-precipitation process is used to prepare a porous sheath made from randomly distributed nanofibers on dry-spun CNT wires, which can be combined with ionic conductive gel electrolyte as a strong packaging layer for flexible solid-state supercapacitors. The excellent intrinsic characteristics as well as variable ways of structural organizations make ANF-based coatings an attractive tool for the design of multifunctional high-performance hybrid materials.