Bijandra Kumar

Conductive bio-Polymer nano-Composites (CPC): Chitosan-carbon nanotube transducers assembled via spray layer-by-layer for volatile organic compound sensing

The chemo-electrical properties of chitosan-carbon nanotubes (Chit-CNT) Conductive bio-Polymer nano-Composites (CPC) transducers processed by spray layer-by-layer (LbL) technique have been investigated. Results show that unlike most synthetic polymer matrices, chitosan provides the transducer with high sensitivity towards not only polar vapours like water and methanol but also to a lesser extent toluene. Quantitative responses are obtained, well fitted with the Langmuir-Henry-Clustering (LHC) model allowing to link electrical signal to vapour content. Chit-CNT transducers selectivity was also correlated with an exponential law to the inverse of Flory-Huggins interaction parameter chi(12). These properties make Chit-CNT a good transducer to be implemented in an e-nose. Additionally, the observation by atomic force microscopy (AFM) of Chit-CNT morphology suggests a chemical nano-switching mechanism promoting tunnelling conduction and originating macroscopic vapour sensing.

Novel architecture of carbon nanotube decorated poly(methyl methacrylate) microbead vapour sensors assembled by spray layer by layer

For the first time vapour sensors were made by assembling multi-wall carbon nanotube (CNT) decorated poly(methyl methacrylate) microbeads (PMMAµB) by spray layer by layer (sLbL). This combination of materials and technique resulted in an original hierarchical architecture with a segregated network of CNT bridging PMMAµB. The chemo-resistive behaviour of these conductive polymer nanocomposite (CPC) sensors was studied in terms of sensitivity and selectivity towards standard volatile organic compounds (VOC), as well as quantitativity and reproducibility of responses Ar to methanol, water, toluene and chloroform. Results show that 3D sLbL assembly allows boosting CNT network sensitivity by a factor 2 and selectivity for methanol vapour by a factor of 5. Additionally CNT-PMMAµB sensors gave responses proportional to vapour molecules content that could easily be fitted by the Langmuir–Henry-clustering model. Such sensors are thus expected to be good candidates for implementation in electronic noses.

Polyaniline nanoparticle–carbon nanotube hybrid network vapour sensors with switchable chemo-electrical polarity

Chemo-resistive sensors were prepared from monodisperse poly(aniline) nanoparticles (PaniNP) synthesized via oxidative dispersion polymerization. Poly(styrene sulfonic acid) (PSSA) was used as the stabilizer and dopant agent. PaniNP transducers were assembled by spraying layer by layer a solution containing different concentrations of PaniNP and multi-wall carbon nanotubes (MWNT) onto interdigitated electrodes. This process led to stable sensors with reproducible responses upon chemical cycling. Chemo-electrical properties of these sensors have been investigated in sequential flows of pure nitrogen and nitrogen saturated with a set of volatile organic compounds (VOC). Interestingly the sensing mode of PaniNP transducers (the NVC or PVC effect) can be switched simply by increasing PaniNP content or by the addition of only 0.5% of MWNT to reach a resistance lower than 150 Omega. Due to their original conducting architecture well imaged by atomic force microscopy (AFM), i.e. a double percolated conductive network, PaniNP-MWNT hybrids present both higher sensitivity and selectivity than other formulations, demonstrating a positive synergy. Mechanisms are proposed to describe the original chemo-electrical behaviours of PaniNP-based sensors and explain the origin of their selectivity and sensing principle. These features make them attractive to be integrated in e-noses.

Fine control of carbon nanotubes–polyelectrolyte sensors sensitivity by electrostatic layer by layer assembly (eLbL) for the detection of volatile organic compounds (VOC)

Volatile organic compounds (VOC) sensors have recently extended their field of application to medical area as they are considered as biomarkers in anticipated diagnosis of diseases such as lung cancer by breath analysis. Conductive polymer nanocomposites (CPC) have already proved their interest to fabricate sensors for the design of electronic noses (e-noses) but, for the first time to our knowledge, the present study is showing that electrostatic layer by layer assembly (eLbL) is bringing an interesting input to tailor the sensitivity of carbon nanotubes (CNT)-polyelectrolyte sensors. By this technique transducers are progressively built in 3D alternating dipping into sodium deoxycholate (DOC)-stabilized SWNT and poly(diallyldimethyl-ammonium chloride) [PDDA] solutions, respectively anionic and cationic. The precise control of transducers thicknesses (between 5 and 40nm) resulting from this process allows a fine tuning of multilayer films resistance (between 50 and 2kΩ) and thus of their sensitivity to VOC. Interestingly the surfactant used to disperse CNT into water, DOC is also found to enhance CNT sensitivity to vapors so is it for the polyelectrolyte PDDA. Finally it is found that transducers with 16 bilayers of PDDA/DOC-CNT provide optimum chemo-resistive properties for the detection and discrimination of the eight vapors studied (chloroform, acetone, ethanol, water, toluene, dichloromethane, tetrahydrofuran and methanol).

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

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).

Thermo- and chemo-electrical behavior of carbon nanotube filled co-continuous conductive polymer nanocomposites (CPC) to develop amperometric sensors

The conductive polymer nanocomposite (CPC) of multiwall carbon nanotubes (MWNT) filled Polycaprolactone (PCL) was formulated by melt mixing method. PCL based conductive phase served as disperse phase, blended with polypropylene (PP) and polyamide 12 (PA12) respectively. The thermo- and chemo-electrical properties of mono- and bicomponent CPC have been investigated independently. Results show that PP/PCL-CNT CPC is a good temperature sensor whereas no significant response was observed while exposing it to toluene vapor. In contrast, PA12/PCL-CNT exhibits good vapor sensing capability and few sensitivity to temperature variations. It is assumed that PP phase prevents the diffusion of vapor molecules within PCL conductive phase whereas vapor sensing results indicate that PP external matrix provides the CPC with higher barrier effects than PA12.

Conducting Polymer nanoComposites (CPC): Nanocharacterisation of layer by layer sprayed PMMA-CNT vapour sensors by Atomic force Microscopy in current Sensing Mode (CS-AFM)

Organic vapour sensors based on poly (methylmethacrylate)-multi-wall carbon nanotubes (PMMA-CNT) conductive polymer nanocomposite (CPC) were developed via layer by layer technique by spray deposition. CPC Sensors were exposed to three different classes of solvents (chloroform, methanol and water) and their chemo-electrical properties were followed as a function of CNT content in dynamic mode. Detection time was found to be shorter than that necessary for full recovery of initial state. CNT real three dimensional networks have been visualized by Atomic force microscopy in a field assisted intermittent contact mode. More interestingly real conductive network system and electrical ability of CPC have been explored by current-sensing atomic force microscopy (CS-AFM). Realistic effect of voltage on electrical conductivity has been found linear.