Three-dimensional microchannel design redefines strain-insensitive multifunctional liquid metal yarns
The emergence of smart textiles and wearable electronics demands conductive fibers that maintain stable electrical performance under dynamic mechanical deformation. Conventional conductive yarns, based on carbon nanomaterials, metallic coatings, or hybrids, suffer from a trade-off between conductivity and stretchability, often exhibiting resistance fluctuations or failure under strain. Liquid metals (LM) offer high conductivity and intrinsic deformability but suffer from interfacial instability, such as dewetting and leakage, without structural guidance. This work presents a hierarchical design strategy integrating capillary-guided infiltration and interfacial anchoring of LM within yarn microstructures. Electrospun poly(styrene-block-butadiene-block-styrene) (SBS) microfibers onto commercial spandex (PU) yarns create a porous base with three-dimensional microchannels. These channels are functionalized with silver nanoparticles (AgNPs) to enhance wettability and provide reactive sites for alloying with LM. Upon immersion, LM is drawn into the porous network via capillary action, forming stable intermetallic bonds (Ag9In4 and AgIn2) with the AgNP-modified fibers. Encapsulation with a second SBS layer yields the final SBS-LM/Ag-SBS (SLMAS) yarn. The resulting yarns exhibit exceptional electrical conductivity, with resistance as low as 0.082 Ω/cm at an LM loading of 6.88 mg/cm. They demonstrate strain-invariant performance, long-term durability, and functional convergence, supporting Joule heating and electrochromic display within a single fiber. Joule heating tests show a temperature rise from 86.4 to 122.7°C, following Ohm's and Joule's law. Integration of thermochromic microcapsules enables voltage-triggered color change, laying groundwork for electrothermally responsive textiles. Challenges remain in material costs, multi-step fabrication, and durability under environmental stressors. This work establishes a new paradigm for stretchable fiber electronics, reconciling conductivity with extreme mechanical compliance.