Controlled conductive junction gap for chitosan–carbon nanotube quantum resistive vapour sensors

Abstract

The sensitivity of quantum resistive vapour sensors depends exponentially on the average gap between two conductive nanofillers at conductive junctions. The influence of this parameter on the chemo-resistive properties of chitosan (Chit)–carbon nanotubes (CNTs) has been investigated by modifying the processing conditions used to build hierarchically structured Conductive Polymer nanoComposite (CPC) transducers. Three vapour sensors assembled via spray layer by layer (sLbL) deposition: multiwall carbon nanotubes (CNTs), chitosan functionalized CNTs (Chit-f-CNTs) and chitosan embedded CNTs (Chit-CNTs) were deposited onto interdigitated electrodes and submitted to a typical set of volatile organic compounds (VOCs). Three model conducting architectures have been derived from these CPCs in which CNT/CNT junctions were respectively: in close contact (small gap), random contact (distribution of gap) and constant gap (controlled by the sheathing of CNT by crosslinked chitosan coating). The different CPC morphologies have been visualized by atomic force microscopy (AFM) and noncovalent bonding of chitosan on CNT was confirmed by UV spectra. Among the three CPC sensors exposed to water, methanol and toluene vapours, Chit-f-CNT was the most sensitive confirming the interest of controlling the gap between CNTs in the design of CPC transducers. Moreover a strong affinity of chitosan based sensors to water (and to a lesser extent to other polar vapours such as alcohols) was shown. It was taken benefit from this property to enhance the discrimination ability towards water vapour of a set of sensors assembled into an e-nose after the treatment of signals by principal component analysis (PCA).