Abstract
The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. Double-walled aluminogermanate imogolite nanotubes are geo-inspired analogues of carbon nanotubes, synthesized at low temperature, with complementary properties. Here, continuous imogolite-based fibers are wet-spun within a poly(vinyl alcohol) matrix. The lyotropic liquid crystallinity of the system produces highly aligned fibers with tensile stiffness and strength up to 24.1 GPa (14.1 N tex–1) and 0.8 GPa (0.46 N tex–1), respectively. Significant enhancements over the pure polymer control are quantitatively attributed to both matrix refinement and direct nanoscale reinforcement, by fitting an analytical model. Most intriguingly, imogolite-based fibers show a high degree of healability via evaporation-induced self-assembly, recovering up to 44% and 19% of the original fiber tensile stiffness and strength, respectively. This recovery at high absolute strength highlights a general strategy for the development of high-performance healable fibers relevant to composite structures and other applications.
Highlights
The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance
Ge-imogolite nanotubes (INTs) with monodispersed external diameters of ca. 4.3 nm and lengths around 85 nm with some INTs showing lengths up to 500 nm[13,15] (Figure S1); a high aspect ratio is preferred for efficient reinforcement in composite fibers[34] and to encourage Liquid crystals (LCs) self-organization.[15]
To prepare solutions for spinning, DW Ge-INTs were added to a poly(vinyl alcohol) (PVOH)/dimethyl sulfoxide (DMSO) aqueous solution at ca. 1, 10, 20, and 30 wt %, corresponding to 0.4, 3.8, 8.1, and 13.2 vol %, respectively
Summary
The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. A liquid crystal columnar phase has been discovered in dilute aqueous suspensions of aluminosilicate and aluminogermanate imogolite nanotubes (INTs).[15] The existence of a lyotropic liquid crystal (LLC) phase at low concentration is attributed to strong Coulombic repulsion between high aspect ratio INTs. The INT structure can be described with a three-dimensional (HO)3Al2O3Si(Ge)OH elementary unit arranged in a rolled hexagonal lattice, with hydroxyl groups terminating both the exterior and interior wall.[16] INTs are inorganic analogues of carbon nanotubes,[17,18] with similar dimensions, but the advantage that they are synthesized at low temperatures (around 100 °C).[19] INTs can respond to external stimuli and to different environments and can be aligned, for example, via electric fields[15,20] or physical deformation.[21] The mechanical properties of INTs, though lower than those of SWCNTs, are still predicted to be significant,[22] with a modulus on the order of 300 GPa. INTs are highly soluble in water and have the potential to form strong interfaces with suitable matrices through their densely hydroxylated surface. As a convenient model system, because lyotropic mesophase formation has been previously observed in PVOH/INT mixtures,[33] and the materials were expected to be highly compatible through hydrogen bonding
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