Sensors and Actuators B 140 (2009) 451–460 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Vapour sensing with conductive polymer nanocomposites (CPC): Polycarbonate-carbon nanotubes transducers with hierarchical structure processed by spray layer by layer Jianbo Lu, Bijandra Kumar, Mickaël Castro, Jean-Franc ¸ ois Feller ∗ Smart Plastics Group, Materials Engineering Lab. of Brittany (LIMAT B ), European University of Brittany (UEB), UBS-Lorient, France article info Article history: Received 6 December 2008 Received in revised form 27 March 2009 Accepted 7 May 2009 Available online 15 May 2009 Keywords: Conductive polymer nanocomposite Carbon nanotube Vapour sensing Chemo-electrical behaviour Atomic force microscopy Volatile organic compounds abstract The development of conductive polymer nanocomposite (CPC) sensors for volatile organic compounds (VOC) detection has been carried out using a spray layer by layer (LbL) process. This technique was successfully used to hierarchically structure polycarbonate-multiwall carbon nanotubes (PC- CNT) solutions into a double percolated architecture as attested by atomic force microscopy (AFM) and optical microscopy (OM). PC-CNT vapour sensing behaviour was investigated as a function of CNT content, films thickness, vapour flow and vapours solubility parameter. The response ranking A r (toluene) > A r (methanol) > A r (water) of PC-CNT was found to be coherent with  12 Flory–Huggins inter- action parameters provided that signals are normalised by analyte molecules number. Signals shape was interpreted to the light of Langmuir–Henry–Clustering (LHC) model and found to be proportional to vapour content. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Unique abilities towards solvent vapours sensing of electrically conductive polymer nanocomposites (CPC) have focused the atten- tion of many researchers during the past ten years [1–30]. The direct transduction of chemical information into an electrical sig- nal associated to existing low power microelectronics and sensing technology makes it an attractive material. CPC versatility comes from the wide variety of combinations of conductive fillers and insulating polymer matrices used for their development. Firstly CPC have been structured around a carbon nanoparticle (CNP) con- ducting network [1–9,12,14–19,21,24,25,29,30], assisted by double percolation of conducting fillers [20] or substituted by conducting polymer nanofibres [13]. More recently there has been some suc- cessful attempts to structure carbon nanotubes (CNT) architectures [10,11,17,22,23,26,27,31]. Actually, since their discovery in 1991 [32], many studies have concerned the dispersion of carbon nanotubes into polymer matrices to improve their mechanical [33–35,38] and electrical [36,37,39] properties. Actually, only a couple of groups have been working on CNT based CPC chemo-electrical properties [10,11,17,22,23,26–28]. The final objective of a vapour sensor being the quantification and ∗ Corresponding author. E-mail address: jean-francois.feller@univ-ubs.fr (J.-F. Feller). identification of target molecules, this will only be possible by simultaneously analysing the responses of a set of CPC assembled into an array [1–9]. Nevertheless, prior to combining all CPC trans- ducers responses it is necessary to select them pertinently after their chemo-electrical properties have been characterised and con- trolled individually. Consequently, a special attention must be paid to their formulation and processing to make sure of their integrity and reproducibility before their association. Concerning the formulation, it is generally admitted that crys- tallinity can be an influent parameter. Although a high sensitivity was reported using semi-crystalline matrices due to partial dissolu- tion of the amorphous phase in which CNP are concentrated [2,14], an amorphous matrix often leads to a more stable chemo-electrical behaviour [7,14,18,19]. Moreover, crystalline phases are known to be responsible for barrier effect modifying the diffusion kinetics through the polymer matrix [8]. Thus the simple amorphous mor- phology of poly(carbonate) appeared to be more suitable to reveal the vapour sensing mechanisms. The same kind of thinking deter- mined the choice of multiwall CNT that, although less conductive than single wall CNT, already proved to be easily dispersible in solu- tion and lead to CPC in suitable range of resistivity for sensing, i.e., 1 ˝ <  <1M [28]. Thus the only adjustable factor of the formula- tion is the filler content which changes vapour sensitivity according to percolation theory: CPC with filler content closer to the perco- lation threshold are expected to exhibit higher sensitivity due to a more easy disconnection of their conducting pathways upon vapour 0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2009.05.006