Interfacial Capillary Spooling of Conductive Polyurethane–Silver Core–Sheath (PU@Ag) Microfibers for Highly Stretchable Interconnects

Conductive fibers are core materials in textile electronics for the sustainable operation of devices under mechanical stimuli. Conventional polymer–metal core–sheath fibers were employed as stretchable electrical interconnects. However, their electrical conductivity is severely degraded by the rupture of metal sheaths at low strains. Because the core–sheath fibers are not intrinsically stretchable, designing a stretchable architecture of interconnects based on the fibers is essential. Herein, we introduce nonvolatile droplet–conductive microfiber arrays as stretchable interconnects by employing interfacial capillary spooling, motivated by the reversible spooling of capture threads in a spider web. Polyurethane (PU)–Ag core–sheath (PU@Ag) fibers were prepared by wet-spinning and thermal evaporation. When the fiber was placed on a silicone droplet, a capillary force was generated at their interface. The highly soft PU@Ag fibers were fully spooled within the droplet and reversibly uncoiled when a tensile force was applied. Without mechanical failures of the Ag sheaths, an excellent conductivity of 3.9 × 10⁴ S cm^–1 was retained at a strain of 1200% for 1000 spooling–uncoiling cycles. A light-emitting diode connected to a multiarray of droplet–PU@Ag fibers exhibited stable operation during spooling–uncoiling cycles.