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.