Significantly Enhanced Mechanical Strength by the Hollow Structure of Conductive Stretchable Silver Nanoflower‐Polyurethane Fibers

The conductive stretchable nanocomposite fibers, synthesized by the wet spinning technology, are typically composed of conductive nanofillers and polymer matrix to achieve both high electrical conductivity and stretchability. However, the inclusion of nanofillers blocks the solvent extraction passages, resulting in large voids (>3 μm²) and decreasing mechanical strength. Herein, hollow fibers synthesized using a coaxial spinneret with double concentric needles are presented. The dope mixture of silver nanoflower‐shaped particles (AgNFPs, 36 vol%), polyurethane (PU), and dimethylformamide is extruded through the outer nozzle, whereas the coagulant is supplied to the inner nozzle. This significantly shortens the maximum solvent diffusion length from 127.5 μm of solid fibers to 18.5 μm of hollow fibers. Resultantly, the large void becomes negligible in the hollow AgNFP‐PU fiber, and the mechanical strength increases by 100% (29 MPa) compared with that of the solid AgNFP‐PU fiber (14.5 MPa). The initial electrical conductivity (≈10 990 S cm⁻¹) and rupture strain (≈120%) of both hollow and solid fibers are similar. Furthermore, the change in resistance decreases by 50% at 50% strain when the inner space is filled with liquid metal. This demonstrates that versatile functionality can be implemented by filling the gap with functional materials.