A hierarchical porous carbon-nanotube skeleton for sensing films with ultrahigh sensitivity, stretchability, and mechanical compliance

Wearable thin-film strain sensors attract increasing attention due to their minimal invasiveness onto the human skin and potential use in health monitoring; however, the simultaneous achievement of high sensitivity and stretchability with such sensors is challenging, and mechanical compliance is rarely considered. Using a thin and hierarchical porous carbon-nanotube (CNT) skeleton (30 mu m thickness) prepared by rapid and scalable microwave-assisted fabrication within 30 s, we developed strain sensors with highly enhanced performance. The as-prepared thin CNT skeleton consisting of macroporous, microporous, and hollow fiber architectures that are composed of numerous intertwined CNTs provides a sophisticated conductive network and intrinsic mechanical ductility to synergistically impart a strain sensor with high deformation (stretchability > 120%), high sensitivity in a wide strain range (gauge factor varying from similar to 42 at 5% strain to similar to 8470 at 120% strain), fast response (<30 ms), excellent durability (>5000 cycles under 40% strain) and outstanding mechanical compliance (a great resistance change (Delta R/R-0 > 500) at 12% strain under 0.05 N of minute tensile force). Consequently, the strain sensor with high spatial resolution can not only accurately detect a full-range of human motions, but also rapidly respond to a minimal force in the order of butterfly settling.