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

International audienceVolatile 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 40 nm) resulting from this process allows a fine tuning of multilayer films resistance (between 50 and 2 kΩ) 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)

Crosslinking of Epoxy-Modified Phenol Novolac (EPN) Powder Coatings: Particle Size and Adhesion

These studies were undertaken to examine holy particle size of epoxy phenol novolac (EPN) powder coatings may affect adhesion to metal substrates. Particle sizes of 21 and 83 mu m diameter were utilized. DSC analysis shows that the activation energies of crosslinking for the 21 mu m particle size is 41 kJ/mol and 58 kJ/mol for 83 mu m particle size which is attributed to the effect of particle size, and time-temperature-particle size (TTPS) parameters are used to describe powder-liquid-solid from transformation process. Although, the TTSP term represents a combination of intrinsic and extrinsic properties. We believe that this is the TTPS term that adequately describes the processes in which, in order for crosslinking reactions to occur, particles must initiate the flow. Quantitative attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopic analysis was used to follow crosslinking processes by monitoring the decrease of oxirane concentration, and showed that for thermal cure at 185 degrees C for 20 min, the oxirane concentration decreases at a similar rate for 21 mu m and 83 mu m particle sizes. The results of pull-off adhesion measurements from an Al substuate show that when the 21 mu m particle size is crosslinked for 10 min at 110, 140, and 170 degrees C, adhesion is consistently higher than for the same coating system at 83 mu m particle size. This difference is attributed to the finite time required for powder particles to reach a proper melt viscosity, followed by reactions of functional groups leading to crosslinking. Extended cure times to 120 min for the 83 mu m particle resulted in adhesion similar to the 21 mu m particle size

Flexible latex--polyaniline segregated network composite coating capable of measuring large strain on epoxy

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Chemo-sensitivity of latex-based films containing segregated networks of carbon nanotubes

International audienceIn contrast to conventional hydrophobic Conductive Polymer nanoComposites (CPCs) used to design vapor sensors, which are mostly soluble in organic solvents, monodispersed acrylate copolymer latexes present the double advantage of being more sensitive and selective towards polar vapors such as water. A hierarchically structured latex based CPC film was obtained by co-dispersion of an aqueous acrylic emulsion with multiwalled carbon nanotubes (CNTs), followed by spray layer by layer (sLbL) assembly. The analysis of CPC films morphology by AFM and TEM show that a segregated network of CNT as been achieved by partial coalescence of latex nanoparticles and homogeneously assembled in 3D. Transducer sensitivity was investigated as a function of CNT content, latex glass transition temperature (Tg), organic vapor nature and vapor concentration. The source of the high sensitivity and selectivity observed for these latex-based composites towards water vapor is assumed to mainly result from ionic interaction of SDS with water molecules offering interesting perspectives of development. The different diffusion regimes through the CPC transducer are visualized, modeled and interpreted with the Langmuir-Henry-Clustering (LHC) model, showing that only water is reaching a clustering mode at high vapor concentration. Finally it is believed that the unique hierarchical architecture of BA latex-CNT sensors is responsible for their quick, stable and reproducible responses to vapors