Electrospinning Machine | Limpet-Inspired Multifunctional Composite Fibers with Exceptional Mechanical Performance From Self-Assembled Aramid Nanofibers

The unique structure of teeth provides inspiration for the design of artificial materials, making combinations of properties once considered difficult to achieve together possible. Limpet teeth have garnered significant attention due to their combination of high strength, high modulus, and excellent toughness. In recent years, researchers have been dedicated to mimicking the structure of limpet teeth. However, constrained by issues such as insufficient interface control between anisotropic nanostructures, poor co-alignment orientation, and the poor mechanical performance of the polymer matrix, the performance of artificial materials remains far from the ideal state. Aramid nanofibers (ANFs), by virtue of their high mechanical strength and outstanding chemical stability, show great potential as fundamental building blocks for constructing high-performance biomimetic structures. However, their widespread application is hindered by the limitations of traditional top-down preparation methods: these methods are costly, inefficient, and offer limited control over molecular structure.

Recently, Professor Yang Ming's team from Jilin University published their latest research results, titled "Limpet-Inspired Multifunctional Composite Fibers with Exceptional Mechanical Performance From Self-Assembled Aramid Nanofibers" in the journal Advanced Science. By inducing the self-assembly of poly(p-phenylene terephthalamide) (PPTA) polyanions to form aramid nanofibers (ANFs) and simultaneously inducing the directional growth of β-FeOOH nanocrystalline whiskers during the wet-spinning process, the researchers successfully prepared composite fibers that mimic the structure of limpet teeth. This process produces paramagnetic fibers with co-aligned ANFs and nanocrystalline whiskers, while also demonstrating resistance to ultraviolet irradiation.

The exceptional mechanical properties of this composite fiber originate from the synergistic effect between efficient interfacial load transfer and the controllable adjustment of ANF crystallinity—both are driven by the robust interfacial interaction with the mineral phase. The resulting biomimetic structure combines the advantages of semi-crystalline self-assembled ANFs and orderly arranged inorganic reinforcements, endowing the composite fiber with excellent strength, stiffness, and toughness, making it one of the highest-performance structural fibers reported to date.

Figure 1: Self-assembly of PPTA polyanions forming ANFs.

A polyanion solution was obtained by dissolving PPTA powder in DMSO/KOH, and adding water induced its self-assembly to form ANFs. As the amount of water increased, the number of nanofibers increased and their diameter grew (Figure 1). WAXS analysis showed that after adding water, a transition from disordered polyanions to ordered ANFs occurred (Figure 1). Spectral analysis indicated (Figure 1) that as the amount of added water increased, intermolecular hydrogen bonding and aromatic stacking interactions strengthened.

Figure 2: Physicochemical properties of wet-spun aramid fibers and aramid composite fibers.

The aramid fiber prepared at a dope concentration of 5 mg/mL and a spinning speed of 10 mL/h exhibited optimal performance, achieving a tensile strength of 0.9 GPa, a modulus of 14.1 GPa, and a toughness of 178 MJ/m³. Post-stretching by 10% could further increase these to 1.3 GPa, 26.3 GPa, and 239 MJ/m³, respectively (Figure 2). Using an Fe³⁺ solution as the coagulation bath, ANFs and β-FeOOH nanocrystalline whiskers were synchronously assembled via wet-spinning to produce the ANF/β-FeOOH-6 h composite fiber. Its strength, modulus, and toughness were enhanced to 1.8 GPa, 42.7 GPa, and 336 MJ/m³, respectively, outperforming most high-performance fibers (Figure 2), and it demonstrated excellent anti-UV performance (Figure 2).

Figure 3: Structural characterization of the aramid composite fiber.

In the ANF/β-FeOOH-6 h composite fiber, β-FeOOH nanocrystalline whiskers with dimensions of approximately 9 nm × 31 nm are aligned along the ANF axis and uniformly distributed between the fibers. The structural compatibility between PPTA and β-FeOOH promoted the nucleation of β-FeOOH on the ANF surface (Figure 3). Hydrogen bonds and Fe-O-C bonds are present at the interface, enhancing the interaction, but this suppressed the crystallization of the amorphous regions of the ANFs, reducing their crystallinity to 38%. The modulus and hardness of the aramid composite fiber were significantly enhanced, reaching 8.56 GPa and 0.39 GPa, respectively, superior to those of the aramid fiber (Figure 3).

 Figure 4: Deformation mechanism.

During the tensile failure process, both the aramid fiber and the ANF/β-FeOOH-6 h composite fiber exhibited cavitation and fibrillation, accompanied by a blue shift in N-H vibration, indicating hydrogen bond breakage and the destruction of the ordered structure. As the strain increased, the birefringence first increased and then decreased, while stress whitening occurred simultaneously. The crystal size continuously decreased, while the crystallinity slightly recovered in the later stages due to a recrystallization mechanism (Figure 4). In its semi-crystalline structure, crystallites are connected by amorphous regions. After yielding, crystal slip, crystallite fragmentation, and extension of the amorphous regions occur, initiating cavitation and fibrillation, which effectively disperse stress and delay fracture. The β-FeOOH nanocrystalline whiskers enhance load transfer through the interface, while the moderately reduced ANF crystallinity preserves energy dissipation capacity while increasing strength. The organic-inorganic interfacial interaction provides an effective pathway for the synergistic optimization of the composite fiber's mechanical properties.

Paper link: https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202509321