Research on highly sensitive humidity sensor based on Tr-MWCNT/HEC composite films
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ng Huanga) School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei 230009, People’s Republic of China; and Institute of Intelligence Machines, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China
Yangyang Ma, Ping Liu, Caixia Liu, and Yugang Zhang School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei 230009, People’s Republic of China (Received 4 June 2014; accepted 20 October 2014)
This study demonstrates a highly sensitive humidity sensor based on treated multiwalled carbon nanotube (tr-MWCNT) and hydroxyethyl cellulose (HEC) composite films. Tr-MWCNTs are obtained by mixed acid treatment to enhance their hydrophilicity and improve their dispersion in distilled water. Compared to tr-MWCNT/silicone rubber (SR) composite film, the humidity sensitivity of tr-MWCNT/HEC film is much higher than tr-MWCNT/SR film with the same film thickness. The humidity sensing mechanisms of tr-MWCNT/HEC composites are explained by electron donation model and swelling mechanism. Speaking and blowing experiments were also carried out and the results show that tr-MWCNT/HEC composite film is sensitive to both speaking and blowing; furthermore, it can distinguish the small humidity level difference between speaking and blowing. Other sensing characteristics, including response and recovery time, stability, and temperature effect, are also investigated. The high humidity sensitivity of tr-MWCNT/HEC composite film indicates that it can be an excellent humidity sensitive material.
I. INTRODUCTION
Humidity sensors are widely applied in process control, environment monitoring, storage and electrical devices1–3; hence, the research to develop some new materials for humidity sensor devices attracts more and more attention. The construction of a good humidity sensor is rather complex, because high-performance humidity sensors must meet many requirements, including linear response, high sensitivity, short response and recovery time, chemical and physical stability, wide operating range of humidity, and low cost. Materials that have been studied with these qualities include polymers, ceramics, and composites, which have their own advantages and specific conditions of application.2,4,5 Carbon nanotubes (CNTs) are a kind of carbon allotrope, which were found in 1991 by Iijima.6 CNTs are one of the most attractive nanoscale fillers because of their high aspect ratio and combination of excellent thermal, electrical, and mechanical properties. Owing to these excellent properties, many CNTbased humidity sensors have been studied, including a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.328 J. Mater. Res., Vol. 29, No. 23, Dec 14, 2014
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capacitive-type,7–9 resistive-type, quartz crystal microbalance (QCM)-type sensors,10–12 etc. Capacitive-type sensors have the advantage of less power consumption, but the capacitance of a sensor relies on the frequency and is variable, which needs t
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