A superfast, responsive textile-based humidity sensor featuring single-walled carbon nanotube (SWCNT) nanocomposite fibers is described in a study available as a pre-proof in the journal Materials Today Nano.
Study: Ultrafast, Highly Sensitive, Flexible Textile-Based Humidity Sensors Made of Nanocomposite Filaments. Image Credit: m-agention/Shutterstock.com
Development of Wearable Humidity Sensors – Different Approaches and Current Limitations
Regional humidity monitoring and management are critical for improving human lifestyle, and local humidity may be tracked utilizing inbuilt wearable humidity detectors.
For that purpose, numerous kinds of wearable humidity detectors have already been produced by transplanting standard humidity detectors onto textile platforms.
Methods include applying a humidity absorbing film or a humidity detector to a textile medium or weaving conductive metallic wiring and cotton strands within textiles. The former serves as electrode material and the latter as a hygroscopic agent.
Regarding imprinted detectors, longevity is a concern, while poor comfort and fairly low responsiveness are limitations for sensors that employ conductive metallic strands as electrodes.
Integrating Carbon Nanomaterials in Humidity Sensors
Owing to their distinctive mechanical and electrical capabilities, carbon nanostructures like graphene, graphene oxide (GO), and carbon nanotubes (CNTs) are commonly employed as multipurpose nanoscale fillers in the fabrication of sophisticated nanocomposites.
Lately, film-type humidity detectors based on CNT, GO, or hybrid sheets have been investigated. Nonetheless, because of the difficulties in combining sensors with textile materials, there are constraints for film-type detectors employed as wearable sensing devices.
The much more viable option for creating textile-based detectors is using fiber-type sensors. Fiber spinning technologies such as wet-spinning, electrospinning, gel-spinning, and melt-spinning have been used extensively to organize carbon nanostructures into macroscopic composite fibers
Recap of Major Developments Thus Far
The team had already created durable, elastic textile-based humidity detectors utilizing wet-spun single-walled carbon nanotube (SWNT) / polyvinyl alcohol (PVA) fibers. Unfortunately, the detectors' reaction times were about 40 seconds, and the detectors had certain constraints for use in real-time humidity tracking.
Even though a significant proportion of the textile-based humidity detectors documented thus far show decent attributes in a couple or more criteria (like responsiveness or response time), they still fall short in overall effectiveness encompassing all criteria. This is particularly important for real-time textile micro-climate humidity measurement.
Textile-based humidity detectors with quicker response and recovering times, better sensitivity, and larger detection spans are unquestionably in high demand.
Experimental Methodology Followed by the Team
Wearable electronic fabrics that can detect external chemical or physical stimuli and interact with other digital equipment, like smartphones, are the most significant future research avenues.
The produced single-walled carbon nanotube (SWNT) / polyvinyl alcohol (PVA) / lithium chloride (LiCl) filament was sewn into a cotton shirt and connected with a lab-prepared printed circuit board (PCB) to illustrate the textile-based humidity detector's possible applicability in wearable technology.
A Bluetooth device was used to enable wireless connectivity with a mobile phone. In the test, a humidifier was used to produce vapors in the test space.
The output of the humidifier could be changed to the minimal, moderate, and maximal settings to control the humidity in the atmosphere. The humidity detector reacted quickly to changes in the humidity level in the surroundings. The high recoverability of the detector shown by cyclic testing indicated a viable use of this novel device for real-time humidity monitoring.
Highlights of the Study
The researchers described a superfast, extremely responsive textile-based humidity detector constructed of SWNT/PVA/LiCl fibers manufactured through a wet-spinning approach accompanied by a lithium chloride solvent exchange procedure.
When the relative humidity levels in the surroundings shifted from 100 to 40 percent, the humidity detector's electric resistance fluctuated nearly 6-fold in a quick response time. This response indicated the detector's excellent prospects for real-time textile micro-climate tracking with a quick response time across a wide humidity range.
Due to the deliquescence of lithium chloride, the single-walled carbon nanotube network added to the fiber's strength, and the generated ions influenced the electric conductance of SWCNT networks. An extremely responsive textile-based humidity detector was created using SWNT/PVA/LiCl fiber and an adequate lithium chloride concentration. It demonstrated a consistent electric resistance detection capability with humidity.
The produced SWNT/PVA/LiCl fiber might be utilized to create a textile-based detector for tracking human breathing and real-time measurement of local humidity changes with the capacity to distinguish relative humidity (RH). These sophisticated fibers may pave the way for developing innovative wearable humidity detectors capable of real-time humidity tracking.
He, Z., Zhou, G. et al. (2022). Ultrafast, Highly Sensitive, Flexible Textile-Based Humidity Sensors Made of Nanocomposite Filaments. Materials Today Nano. Available at: https://doi.org/10.1016/j.mtnano.2022.100214