Stretchable, conductive and porous MXene-based multilevel structured fibers for sensitive strain sensing and gas sensing

Stretchable and conductive fibers are ideal for wearable intelligent electronics, especially wearable strain sensors. However, two main challenges strictly restrict the advancement of wearable strain sensors: the contradiction between sensitivity and sensing range and the trade-off between conductivity and mechanical properties. Herein, we design a multilevel structured fiber to address these two issues. The fiber contains a porous sensing core with MXene coated microspheres distributed in the elastic matrix (level I) and a microstructured MXene sheath with cracks (level II) embedded in wrinkle (level III) patterns. These multiple sensing levels could synergistically respond to different magnitudes of tensile strains, thus rendering high sensitivity (from 174 to 298 000) across a wide sensing range (0-150%). In addition, the macropores within the fiber core and the wrinkle patterns in the sheath offer the sensing fiber high stretchability (similar to 1000%) and a low modulus (7.6 MPa) similar to pure PU together with a high electrical conductivity. Along with strain sensing, this fiber is also suitable for some other applications, such as gas sensing, due to its combined high conductivity and large specific surface area. The structure design strategy presented in this study could guide future work in developing strain sensitive nanomaterials.