Flexible and conductive nanofiber-structured single yarn sensor for smart wearable devices

Electrically conductive fibers or textiles are attractive for their potential applications in wearable devices. The creation of continuously aligned assembly (i.e., bundle or yarn) may enable the realization of supernormal electrical performance of individual nanofibers into macroscale devices. In this study, a conductive polymer based single yarn consisting of core–sheath polyaniline (PANI)/polyacrylonitrile (PAN) nanofibers was fabricated by combining a novel electrospinning method with in-situ solution polymerization process. The as-prepared PANI/PAN uniaxially aligned coaxial nanofiber yarn (UACNY) was utilized to construct an ammonia (NH3) sensor. We demonstrated that the nanofiber-structured construction in the PANI/PAN UACNY offered a high surface area for the free diffusion of NH3, and the highly-oriented nanofiber arrangement of the PANI/PAN UACNY facilitated the one-way charge carrier transfer for effectively unidirectional transmission of electrical signals, which both endowed the yarn sensor excellent sensitivity and fast response/recovery upon exposure to NH3 of 10–2000 ppm at room temperature. Furthermore, the yarn-based sensor presented excellent reproducibility and stability for NH3 detection. Importantly, the PANI/PAN UACNY sensor possessed robust mechanical strength with flexibility, which could be processed into defined electronic textiles using various textile-forming technologies, i.e., knitting, braiding, and embroidering techniques. The flexible and conductive PANI/PAN UACNY have the potential to be applied for the development of wearable smart textiles, due to their stable structure, handling convenience, excellent mechanical property, as well as high gas sensing performance.