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Ultra-strong Dopamine-Conjugated Carboxymethylcellulose/Carbon Nanotube Fiber by Interfacial Strengthening

Ultra-strong fibers have been widely used in construction and aerospace materials, composites, as well as smart textiles. Carbon nanotube (CNT) fibers, with the Young’s modulus over 1 TPa, are advancing the next-generation, high-tech applications, given their intrinsic mechanical, electrical, and thermal properties. However, defects in CNT-based structures can limit the otherwise optimal strength, given the presence of weak interfaces between building blocks, leading to catastrophic fracture. To overcome this challenge, we propose super-strong fibers that use CNT wrapped with dopamine-modified carboxymethyl cellulose (DA-CMC). Such mussel-inspired system is presented for underwater adhesion, similar to that of interacting amino acid sequences of proteins and catechols. Wet stretching is applied during wet spinning of DA-CMC and CNT aqueous suspensions to induce unidirectional alignment of CNT, enabling mechanically strong microfibers, which are obtained without sacrificing electrical conductivity. For a better understanding of the mechanism of DA-CMC in producing defect-free, interfacial adhesion we conducted pull-off tests by atomic force microscopy. The otherwise weak interactions between CNTs are overcome by metal-catalyzed chemical crosslinking of DA-CMC and alignment, resulting in high tensile strength (~1 GPa) and superior electrical conductivity (~2.4×104 S m-1). This bioinspired system, with less defects and denser packing is clearly distinctive from previous constructs reported in the area, offering versatile applications for flexible and wearable devices as well as low-cost structural materials.