Inorganic Nanotube Mesophases Enable Strong Self-Healing Fibers

Macroscopic assembly of nanomaterials in fibers can improve their mechanical characteristics and add new functions. One-dimensional nanomaterials are particularly suited to the uniaxial geometry of fibers. Researchers at Imperial College London and LPS have shown that the liquid-crystalline properties of imogolite nanotubes produce highly aligned fibers with a high degree of healing via evaporation-induced self-assembly.

Exploiting the exceptional properties of individual nanostructures in macroscopic assemblies is often challenging. Anisotropic nanoparticles provide the load transfer required for efficient mechanical reinforcement; however, they must be aligned, at high loading, without agglomeration, within a matrix. In this context, geo-inspired imogolite nanotubes (INTs) form ordered liquid crystal phases in aqueous media, facilitating spinning of highly aligned fibers, while their hydroxylated outer surface allows for strong interactions with water-processable polymer like polyvinyl alcohol (PVOH) (Figure a). Researchers from the Imperial College London and the LPS have been able to make the first imogolite nanotube-based fibers, introducing a new and potentially widely applicable nanocomposite system. Highly aligned fibers (Figure b), show very good tensile modulus and strength, up to 24 and 0.8 GPa respectively, significantly better than the pure polymer matrix. We quantitatively attribute it to both reinforcement and PVOH crystallisation effects induced by the presence of INTs. Moreover, most intriguingly, the fibers were found to be healable by an evaporation induced self-assembly (EISA) process (Figure c). Healed fibers recovered up to 44% and 19% of the original composite fibers tensile modulus and strength. This first example shows that it is possible to repair a strong fiber with recovery of almost half of the tensile modulus. The high aspect ratio and high hydrogen bonding capability play a crucial role in providing a scaffold for the repair of the aligned nanocomposite structure, and provides a strategy for future developments.

Figure: (a) Schematic representation of imogolite nanotubes in a polyvinyl alcohol (PVOH) matrix. (b) Typical X-ray scattering pattern of oriented INT/PVOH fiber. The experiments were carried out on the WAXS-Cu device (MORPHEUS platform, MATRIX team). (c) Photographs of the self-healing process by evaporation-induced self-assembly. (i) a failed INT/PVOH fiber, (ii) a heat droplet of water is pipetted onto the two fractured surfaces, (iii) the fiber is healed via an evaporation-induced self-assembly process.

Inorganic Nanotube mesophases enable strong self-healing fibers
Won Jun Lee, Erwan Paineau, David B. Anthony, Yulin Gao, Hannah S. Leese, Stéphan Rouzière, Pascale Launois & Milo S. P. Shaffer.
ACS Nano 2020, 14, 5570-5580

Erwan Paineau, Pascale Launois