Highly Durable Nanofiber-Reinforced Elastic Conductors for Skin-Tight Electronic Textiles.

ABSTRACT

Soft and stretchable electrodes are essential components for skin-tight wearable devices, which can provide comfortable, unobtrusive, and accurate physiological monitoring and physical sensing for applications such as healthcare, medical treatment, and human-machine interfaces. Metal-elastomer nanocomposites are a promising approach, enabling high conductivity and stretchability derived from metallic conduction and percolation networks of metal nano/micro fillers. However, their practical application is still limited by their inferior cyclic stability and long-term durability. Here, we report on a highly durable nanofiber-reinforced metal-elastomer composite consisting of (i) metal fillers, (ii) an elastomeric binder matrix, and (iii) electrospun polyvinylidene fluoride nanofibers for enhancing both cyclic stability and conductivity. Embedded polyvinylidene fluoride (PVDF) nanofibers enhance the toughness and suppress the crack growth by providing a fiber reinforcing effect. Furthermore, the conductivity of nanofiber-reinforced elastic conductor is four times greater than the pristine material because the silver-rich layer is self-assembled on the top surface by a filtering effect. As a result, a stretchable electrode made from nanofiber-reinforced elastic conductors and wrinkled structures has both excellent cyclic durability and high conductivity and is stretchable up to 800%. The cyclic degradation (ΔR/R0) remains at 0.56 after 5000 stretching cycles (50% strain), whereas initial conductivity and sheet resistance are 9903 S cm-1 and 0.047 Ω sq-1, respectively. By utilizing a highly conductive and durable elastic conductor as sensor electrodes and wirings, a skin-tight multimodal physiological sensing suit is demonstrated. Continuous long-term monitoring of electrocardiogram, electromyogram, and motions during weight-lifting exercises are successfully demonstrated without significant degradation of signal quality.