ACS Appl. Mater. Inter. 2017, 9(5):4788-4797

High Sensitive Wearable Textile-based Humidity Sensor made of High-strength, Single-walled Carbon Nanotube (SWCNT)/Poly(Vinyl Alcohol) (PVA) Filaments

Gengheng Zhou1, Joon-Hyung Byun1, Youngseok Oh1, Byung-Mun Jung1, Hwa-Jin Cha1, Dong-Gi Seong1, Moon-Kwang Um1, Sangil Hyun2, and Tsu-Wei Chou3

1Composites Research Division, Korea Institute of Materials Science, 797 Changwondaero, Changwon, Gyeongnam, 51508, South Korea

2Analysis, Certification & Simulation Center, Korea Institute of Ceramic Engineering & Technology, Jinju 52851, South Korea

3Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA

 

Abstract

Textile-based humidity sensors can be an important component of smart wearable electronic-textiles and have potential applications in the management of wounds, bed-wetting, and skin pathologies or for microclimate control in clothing. Here, we report a wearable textile-based humidity sensor for the first time using high strength (~750 MPa) and ultra-tough (energy-to-break, 4300 J g-1) SWCNT/PVA filaments via a wet-spinning process. The conductive SWCNT networks in the filaments can be modulated by adjusting the intertube distance by swelling the PVA molecular chains via the absorption of water molecules. The diameter of a SWCNT/PVA filament under wet conditions can be as much as two times that under dry conditions. The electrical resistance of a fiber sensor stitched onto a hydrophobic textile increases significantly (by more than 220 times) after water sprayed. Textile-based humidity sensors using a 1:5 weight ratio of SWCNT/PVA filaments showed high sensitivity in high relative humidity. The electrical resistance increases by more than 24 times in a short response time of 40s. We also demonstrated that our sensor can be used to monitor human sweating and water leakage on a high hydrophobic textile (contact angle of 115.5°). These smart textiles will pave a new way for the design of novel wearable sensors for monitoring blood leakage, sweat and underwear wetting.

DOI:10.1021/acsami.6b12448

 

Supplement:

Wearable textile-based electronics is a highly influential and rapidly emerging research field relating to the development of new classes of materials with novel functionalities, such as stretchability, flexibility, and conductivity. This new technology, which is commonly referred to as electronic-textiles, aims to improve humans’ quality of life using built-in electronic elements [1]. Textile-based humidity sensors could be important smart wearable electronic-textiles and have potential applications in the management of wounds, bed-wetting, and skin pathologies or for microclimate control in clothing.

To date, several approaches to transfer conventional capacitive, impeditive and resistive humidity sensors onto textiles have been developed [2-3]. Although these approaches represent significant progress towards fabricating textile-based humidity sensors, major challenges remain to be overcome. For example, the durability of electrodes prepared by printing, deposition and coating remains an important issue to be addressed. Damage on the surface of the coated conductive layer may decrease the sensitivity of sensor. In addition, the sensitivity of sensors made of conductive yarn electrodes depends strongly on the wettability of the textile substrate into which the electrodes are woven, which may limit these sensors’ applications. To overcome the limitations of these sensors as discussed above, the state-of-the-art solution for textile-based humidity sensors is the development of strong smart filaments that can be used as humidity sensors. Our recent publication addresses this issue using ultra-strong SWCNT/PVA filaments as wearable textile-based sensors fabricated via a wet-spinning process.

Currently, the greatest challenge hindering the creation of a state-of-the-art textile-based humidity senor is the ability to fabricate a strong and tough filament with appropriate electrical conductivity and sensitivity to water molecules. One-dimensional SWCNTs are ideal materials to create an electrical conductive network with a small amount of SWCNTs [4]. In contrast, highly tough polymers are widely used in modern society. Poly(vinyl alcohol) (PVA) is an environmentally friendly polymer that swells via water absorption, which implies that the PVA molecular chain can be altered by water molecules. Our research takes advantage of SWCNTs’ electrical conductivity and strength to form conductive networks in a PVA matrix with excellent toughness and sensitivity to water molecules (Figure 1).

 

 

Figure 1 A textile-based humidity sensor made of SWNT/PVA filament stitched onto a hydrophobic substrate textile exhibits high sensitivity. SWNT conductive networks inside the sensor can be adjusted by PVA molecular chains via water molecules absorption, as reported in ACS Appl. Mater. Inter. 9(5):4788-4797 (2017).

 

The result of our experiments reveals that wearable textile-based humidity sensors can be achieved using ultra-strong SWCNT/PVA filaments fabricated via a wet-spinning process. The ultimate tensile strength of the SWCNT/PVA filament can be up to 750 MPa with an optimized weight ratio of SWCNT and PVA. The conductive SWCNT networks in the filaments can be modulated by adjusting the intertube distance by swelling the PVA molecular chains via the absorption of water molecules. The diameter of a SWCNT/PVA filament under wet conditions can be as much as two times that under dry conditions, and as a result, the electrical resistance increases significantly (by more than 220 times). We demonstrate that the textile sensor based on the SWCNT/PVA filament can be used to monitor water leakage on a high hydrophobic textile (contact angle of 115.5°). These smart textiles will pave a new way for the design of novel wearable sensors for monitoring blood leakage, sweat and underwear wetting.

 

References

[1] M. Stoppa, A. Chiolerio. Wearable Electronics and Smart Textiles: A Critical Review, Sensors 14 (2014) 11957-.

[2] J. Weremczuk, G. Tarapata, R. Jachowicz, Humidity Sensor Printed on Textile with Use of Ink-Jet Technology. Procedia Engineer 47 (2012) 1366-1369.

[3] T. Kinkeldei, G. Mattana, D. Leuenberger, C. Ataman, F. M. Lopez, A. V. Quintero, D. Briand, G. Nisato, N. F. de Rooij, G. Tröster, Feasibility of Printing Woven Humidity and Temperature Sensors for the Integration into Electronic Textiles. Adv. Sic. Technol. 80 (2013) 77-82.

[4] L. Hu, D. S. Hecht, G. Grüner, Percolation in Transparent and Conducting Carbon Nanotube Networks. Nano Lett. 4 (2004) 4, 2513-2517.