Sensors and Actuators B 150 (2010) 308–313 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Multi-walled carbon nanotubes–cellulose paper for a chemical vapor sensor Sungryul Yun, Jaehwan Kim ∗ Center for EAPap Actuator, Dept. of Mechanical Engineering, Inha University, 253 Yonghyun-Dong, Nam-Ku, Incheon 402-751, South Korea article info Article history: Received 30 November 2009 Received in revised form 20 June 2010 Accepted 30 June 2010 Available online 8 July 2010 Keywords: Cellulose MWCNTs Covalent bonds Solvent vapor Chemical sensor Relative resistance response abstract This paper reports the multi-walled carbon nanotubes (MWCNTs)–cellulose paper as a chemical vapor sensor. Cellulose solution was prepared by dissolving cotton pulp in LiCl/N,N-dimethylacetamide solu- tion. MWCNTs were covalently grafted to cellulose by reacting imidazolides–MWCNTs with cellulose solution. Using this product, the MWCNTs/cellulose (M/C) paper was fabricated, followed by mechanical stretching to align MWCNTs with cellulose chains. Characteristics of the M/C paper were analyzed in terms of scanning electron microscope images, Young’s modulus and electrical resistance. The M/C paper was investigated as a chemical sensor that can detect vaporized analyte molecules, such as, methanol, ethanol, 1-butanol and 1-propanol. Their electrical responses on the sensor were evaluated by not only comparing their relative resistance response (A R ) depending on the concentration, but also checking signal reversibil- ity under cyclic exposure of each analyte. Due to sensitive and reversible expansion/contraction of the M/C paper in response to analytes, the M/C paper showed reversible and fast response with the follow- ing rank of A R : methanol < ethanol < 1-propanol < 1-butanol. Especially, the linear response to 1-propanol concentration proved that the M/C paper can be a qualified sensor for n-propanol. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Cellulose is one of the most naturally abundant biopoly- mers. Due to its biocompatible and biodegradable characteristics, application field of cellulose has been enlarged from textile to immobilization of proteins, antibodies and pharmaceuticals [1]. Recently, cellulose has been re-discovered as a smart material, which has advantages in terms of biocompatibility, easy modifica- tion, eco-friendly and low price [2,3]. This cellulose smart material, namely electroactive paper (EAPap), can be applied for strain sen- sors, chemical sensors many applications, of this material has been demonstrated by making actuators with the material. Carbon nanotube (CNT) has unique electronic, mechanical, and thermal properties [4]. Due to possible improvement of electrical characteristics of polymer via the homogeneous dis- tribution of CNTs, many researchers have investigated various reactions for covalently grafting of CNTs to polymer [5–8]. Recently, CNT–polymer composites have been widely utilized as functional materials for organic transistor devices [9], gas sensors [10,11], bio-sensors [12] and chemical vapor sensors [13–15]. Regarding sensor applications, a lot of functionalities have been given to CNT–polymer composites for quantitative, selective and sensitive detection of analytes molecules. CNTs in the composites act as conducting network as well as self-detection molecules using its electron donating and accepting ability [16] whereas, the functional ∗ Corresponding author. Tel.: +82 32 860 7326; fax: +82 32 832 7325. E-mail address: jaehwan@inha.ac.kr (J. Kim). polymers for the composites have been adopted by considering physical and chemical characteristics of specific analyte molecules. In our previous research, multi-walled carbon nanotubes (MWCNTs) have been introduced to cellulose to enlarge the cel- lulose functionalities via mechanical blending as well as covalent grafting [17,18]. MWCNTs have played an important role in improv- ing mechanical and electrical characteristics of cellulose. Especially, homogeneous distribution of MWCNTs in the cellulose matrix has predominantly contributed to improve its characteristics. The MWCNT/cellulose (M/C) paper has been used for actuators and transistor [18,19]. However, this M/C paper has not been tested for chemical sensor application. Since cellulose as a matrix polymer of M/C composite has good affinity to hydrophilic polar molecules and its sensitive volumetric change by polar molecules attack, the M/C composite can be a good candidate for chemical sensor. Fur- thermore, the alignment of MWCNTs may provide more stable conducting pathways and better sensitive electrical response in volumetric change of the cellulose due to absorption/desorption of polar molecules. Thus, this paper aims at investigating chemi- cal sensing ability of the aligned M/C paper detecting polar solvent analytes. Fig. 1 shows the schematic of the chemical vapor senor made with the M/C paper. 2. Experimental 2.1. Materials Cotton pulp (Buckeye) with degree of polymerization (DP), 4500 and LiCl (Junsei Chemical) were dried in an oven at 100 ◦ C to evap- 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.06.068