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

Highlights

• A new strategy was developed for nanofiber-structured single yarn sensor.

• Robust mechanical strength with flexibility is feasible for various textile-forming technologies.

• The special yarn structure promoted the improvement of ammonia sensing properties.

• The yarn senor showed great potential for fabricating wearable smart textiles.

Abstract

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.

Introduction

Electronic textiles have inspired tremendous interest recently due to their potential applications in wearable electronics and portable devices, such as healthcare detector [1], [2], portable power [3], [4], [5], work and military uniforms [6], [7], [8]. Compared with metals or metal oxides-based electronic components, conductive polymers are suited as the (semi)conductor with intrinsically mechanical toughness of plastics, and can be Assembled together with other appropriate polymers, which facilitate the manufacturing of flexible fiber-shaped platforms such as bundles, yarns, meshes or other textile constructs [2], [9], [10], [11].

Conductive polymers-based fibers or textiles gas sensors have generated increasing attention for their required mechanical toughness for easy processing, light weight, low cost, and especially their high sensing performance at room temperature [12], [13]. Traditionally, Conductive polymers are coated, polymerized or co-spun with other polymers to generate textile-used yarns, which can be employed as building blocks for generating fiber-shaped textiles architectures [14], [15], [16]. Alternatively, conductive polymers are directly synthesized on as-prepared textile constructs for electrically conductive smart textiles application [4], [17], [18]. However, the fibers utilized in the traditional textile industry usually possess much larger diameters (several microns or above) in comparison with innovative nanofibers. Hence, the microfiber-constructed textiles exhibit relatively low surface-area-to-volume ratio, leading to poor gas sensor performances [19], [20], [21], [22].

Many nanotechniques have been employed to manufacture sensing materials, taking advantage of their super-high surface-area-to-volume ratio of nanostructured materials [23], [24], [25], [26], [27]. Electrospinning has been recognized as an efficient and versatile technique to manufacture nano-sized fibers with diameters in the range of 50–1000 nm [28], [29], [30], [31]. Conductive polymers and their blends with other polymers have been electrospun into nanofibers for gas sensor application recently. However, these conductive polymer-based nanofibers were collected into uncontrolled and randomly packed nonwoven mats, resulting in relatively inferior mechanical properties [32], [33], [34], [35], [36], [37]. The obtained conductive polymers-based nanofiber mats are limited as an ideal manufacturing unit to further tailor into different fabric architectures for the application in smart textiles. To overcome the aforementioned concerns, the fabrication of conductive polymers-based nanofiber yarns by modified electrospinning technique would be of substantial interest to incorporate the excellent electrical-chemical characteristics of individual nanofibers with supernormal textile processibility. There have been no reports to date on conductive polymer-based nanofiber yarn gas sensors. Herein, we report a new processing method for effectively fabricating conductive polymers-based uniaxially aligned coaxial nanofiber yarns (UACNY). Polyacrylonitrile (PAN) core-layered nanofibers were electrospun from a novel electrospinning system and were employed as templates to generate uniform sheaths of polyaniline (PANI) by in-situ solution polymerization process. To pursue their potential gas sensing applications, the electrical responses of PANI/PAN UACNY towards ammonia (NH₃) gas were measured at room temperature. Moreover, PANI/PAN UACNY were explored to manufacture different textile architectures by employing various textile-forming techniques, demonstrating the versatility and feasibility of as-fabricated PANI/PAN UACNY for smart textile applications.