Biogenic fibers exhibit a hierarchical structure with macromolecules organized in bundles that connect into ever larger structures. We are interested in anisotropic colloids with tunable interactions that can assemble into similar hierarchical structures . Here, we use ultrathin gold nanowires (AuNWs), stabilized by oleylamine ligands, with diameters below 2 nm and lengths of several micrometers that remind of linear polymers [2,3]. Such wires spontaneously form random but percolating bundles and networks when they agglomerate.
Polymers are commercially spun into hierarchical fibers by a process called wet spinning . A similar process yielded fibers from a AuNW spinning dope . The coagulation bath disrupted the colloidal stability of the wires and triggered the formation of bundles with diameters on the order of 100 nm. These bundles then formed a macroscopic hierarchical fiber, inorganic-organic hybrids with 80% organic content in volume. The concentration of the spinning dope and the injection speed controlled fiber thickness and structure, respectively. An in situ small angle X-ray scattering study of the flowing spinning dope confirmed shear alignment in the dope.
We propose a simple model to explain the impact of flow on the spun fibers’ structure . Comparison of fiber structures and tensile testing of the mechanical properties provided structure-property relations. The experimental findings on spinnability and structure-property relations of AuNW fibers are in striking analogy with polymer fibers: AuNW fiber spinning is only possible at flow rates that lead to sufficient elongation in the direction of the flow. Spherical gold nanoparticles could not be spun. This reminds of the minimal polymer molecular weight (that sets the absolute polymer length) required for polymer fiber spinning . We also observed an increase in yield stress but a decrease in the elongation at break for fibers with better alignment that is analogous to polymer fiber .
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