Electrostatic self-assembly enabled flexible paper-based humidity sensor with high sensitivity and superior durability

Penghui Zhu; Yudi Kuang; Yuan Wei; Fang Li; Huajie Ou; Feng Jiang; Gang Chen

doi:10.1016/j.cej.2020.127105

Electrostatic self-assembly enabled flexible paper-based humidity sensor with high sensitivity and superior durability

Chem Eng J. 2021 Jan 15:404:127105. doi: 10.1016/j.cej.2020.127105. Epub 2020 Sep 24.

Authors

Penghui Zhu^{1

2

3}, Yudi Kuang^{4

5

6}, Yuan Wei^{1

2}, Fang Li^{1

2}, Huajie Ou^{1

2}, Feng Jiang³, Gang Chen^{1

2}

Affiliations

¹ State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510640, China.
² Guangdong Engineering Technology Research and Development Center of Specialty Paper and Paper-Based Functional Materials, South China University of Technology, Guangzhou 510640, China.
³ Sustainable Functional Biomaterials Lab, Department of Wood Science, University of British Columbia, Vancouver V6T 1Z4, Canada.
⁴ School of Biomedical Science and Engineering, South China University of Technology, Guangzhou 510006, China.
⁵ National Engineering Research Center for Tissue Restoration and Reconstruction (NERC-TRR), Guangzhou 510006, China.
⁶ Innovation Center for Tissue Restoration and Reconstruction, South China University of Technology, Guangzhou 510006, China.

Abstract

Humidity sensors have been widely used for humidity monitoring in industrial fields. However, the application of conventional sensors is limited due to the structural rigidity, high cost, and time-consuming integration process. Owing to the good hydrophilicity, biodegradability, and low cost of cellulose, the sensors built on cellulose bulk materials are considered a feasible method to overcome these drawbacks while providing reasonable performance. Herein, we design a flexible paper-based humidity sensor based on conductive 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose fibers/carbon nanotubes (TOCFs/CNTs) conformal fibers network. The CNTs are dispersed by cationic cetyl trimethyl ammonium bromide (CTAB), which introduces positive charges on the CNTs surface. The conductive fibers are achieved by an electrostatic self-assembly process that positively charged CNTs are adsorbed to the surface of negatively charged TOCFs. The vast number of hydrophilic hydroxyl groups on the surface of TOCFs provide more water molecules adsorption sites and facilitate the electron transfer from water molecules to CNTs, endowing the sensor with an excellent humidity responsive property. Besides, the swelling of the TOCFs greatly damages the conductive CNTs network and further promotes the humidity sensitive performance of the sensor. Benefiting from the unique structure, the obtained sensor exhibits a maximum response value of 87.0% (ΔI/I₀ , and the response limit is 100%), outstanding linearity (R² = 0.995) between 11 and 95% relative humidity (RH), superior bending (with a curvature of 2.1 cm^-1) and folding (up to 50 times) durability, and good long-time stability (more than 3 months). Finally, as a proof of concept, the sensor demonstrates an excellent responsive property to human breath, fingertip humidity, and the change of air humidity, indicating a great potential towards practical applications.

Keywords: Electrostatic self-assembly; High sensitivity; Humidity sensor; Respiration monitoring; Superior durability.