DC and AC Conductivity of Carbon Nanotubes−Polyepoxy Composites

The dc and ac conductivities of carbon nanotubes−polyepoxy composites have been investigated from 20 to 110 °C in the frequency range 10-2−106 Hz as a function of the conductive weight fraction p ranging from 0.04 to 2.5 wt %. The frequency dependence of the measured conductivity obeys the universal dynamic response (UDR):  a dc plateau followed, above a critical frequency ωc, by the ωs power law with exponent s 0.6−1. The dc conductivity follows a percolation scaling law:  σdc (p − pc)t with pc = 0.3 wt % and t = 1.4−1.8, according to the temperature. σdc reached 10-4 S/cm for 2.5 wt % CNTs content and increases with increasing temperature. Considering a biased random walk in three dimensions approach, we may explain the scaling law of ωc with p and its proportionality to σdc. The universality of ac conduction in carbon nanotubes−polymer composites is examined by the construction of master curves

Spectroscopic detection of carbon nanotube interaction with amphiphilic molecules in epoxy resin composites

Incorporation of carbon nanotubes into epoxy resin composites has the effect of increasing electrical conductivity at low percolation levels. An amphiphilic molecule such as palmitic acid has been used to increase the surface contact area and improve the dispersion of the carbon nanotube bundles in the prepolymer. The chemical environment of the dispersed nanotubes has been probed using vibrational Raman spectroscopy. Spectroscopic Raman maps, on sample surfaces (60x60 µm2) with ratios of nanotubes to palmitic acid varying from 1:2 to 2:1 by weight, have been recorded to test the uniformity of the dispersion. Substantial spatial inhomogeneities have been observed in the G-band shift and an additional spectral band at 1450 cm-1. The 1450 cm-1 band has been attributed to the CH3 group of the amphiphilic molecules adsorbed onto the nanotube surface. The maps are correlated with the measured electrical conductivity values. The highest conductivity has been observed for the best dispersed nanotubes and nanotubes with the highest degree of interaction

Spectroscopic detection of carbon nanotube interaction with amphiphilic molecules in epoxy resin composites

Abstract Incorporation of carbon nanotubes into epoxy resin composites has the effect of increasing electrical conductivity at low percolation levels. An amphiphilic molecule such as palmitic acid has been used to increase the surface contact area and improve the dispersion of the carbon nanotube bundles in the prepolymer. The chemical environment of the dispersed nanotubes has been probed using vibrational Raman spectroscopy. Spectroscopic Raman maps, on sample surfaces (60x60 µm 2 ) with ratios of nanotubes to palmitic acid varying from 1:2 to 2:1 by weight, have been recorded to test the uniformity of the dispersion. Substantial spatial inhomogeneities have been observed in the G-band shift and an additional spectral band at 1450 cm -1 . The 1450 cm -1 band has been attributed to the CH 3 group of the amphiphilic molecules adsorbed onto the nanotube surface. The maps are correlated with the measured electrical conductivity values. The highest conductivity has been observed for the best dispersed nanotubes and nanotubes with the highest degree of interaction

Non Mycobacterial Virulence Genes in the Genome of the Emerging Pathogen Mycobacterium abscessus

Mycobacterium abscessus is an emerging rapidly growing mycobacterium (RGM) causing a pseudotuberculous lung disease to which patients with cystic fibrosis (CF) are particularly susceptible. We report here its complete genome sequence. The genome of M. abscessus (CIP 104536T) consists of a 5,067,172-bp circular chromosome including 4920 predicted coding sequences (CDS), an 81-kb full-length prophage and 5 IS elements, and a 23-kb mercury resistance plasmid almost identical to pMM23 from Mycobacterium marinum. The chromosome encodes many virulence proteins and virulence protein families absent or present in only small numbers in the model RGM species Mycobacterium smegmatis. Many of these proteins are encoded by genes belonging to a “mycobacterial” gene pool (e.g. PE and PPE proteins, MCE and YrbE proteins, lipoprotein LpqH precursors). However, many others (e.g. phospholipase C, MgtC, MsrA, ABC Fe(3+) transporter) appear to have been horizontally acquired from distantly related environmental bacteria with a high G+C content, mostly actinobacteria (e.g. Rhodococcus sp., Streptomyces sp.) and pseudomonads. We also identified several metabolic regions acquired from actinobacteria and pseudomonads (relating to phenazine biosynthesis, homogentisate catabolism, phenylacetic acid degradation, DNA degradation) not present in the M. smegmatis genome. Many of the “non mycobacterial” factors detected in M. abscessus are also present in two of the pathogens most frequently isolated from CF patients, Pseudomonas aeruginosa and Burkholderia cepacia. This study elucidates the genetic basis of the unique pathogenicity of M. abscessus among RGM, and raises the question of similar mechanisms of pathogenicity shared by unrelated organisms in CF patients

Elaboration et étude du comportement électrique et mécanique de composites nanotubes de carbone-polyépoxy

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Effect of post-annealing process on the Mechanical and Piezoelectric properties of Poly (L-lactic acid) electrospun nanofiber

International audienc

Characterization of piezoelectric bio-based polymers by means of SPM techniques

National audienc

Synthesis of lead-free (Bi0,5Na0,5)TiO3 thin film by RF magnetron sputtering: Impact of Na on the properties of film

International audienceThis work concerns the growth of (Bi0,5Na0,5)TiO3 on Si/SiO2/LNO by RF magnetron sputtering. We observed, for the first time on BNT thin films, reactions that destroy the film. This behavior is associated to sodium or sodium oxide segregation. After an extensive description of the sodium impact onto the film, a solution with adapted deposition conditions to suppress these effects is reported. Raising the sputter deposition temperature to 250 °C allows to have a pure perovskite BNT single phase. The ferroelectric, dielectric and piezoelectric properties of BNT films (thickness = 350 nm) were assessed. In particular, the macroscopic piezoelectric coefficient d33 attains a maximum value of 56 pm/V

Propriétés physiques de nanocomposites NTC-polyepoxy: influence du traitement de surface des NTC

Polymeric matrix nanocomposites provide great opportunities to overcome macroscopic properties of polymers. The shape factor of nanofillers is a key parameter, so carbon nanotubes (CNTs) have attracted much interest. To avoid aggregation, mechanical stirring has been used. In those conditions, the percolation threshold of conductivity is reached at 0.15 wt % for CNTs. To improve the shape factor, amphiphilic molecules have been successfully used: in this case, the percolation threshold is at 0.04 wt % for CNTs. After the percolation threshold, such nanocomposites allow the elimination of electric charges, while keeping the same mechanical properties than the polymeric matrix. RÉSUMÉ : Les nanocomposites à matrice polymère offrent de nouvelles opportunités pour améliorer les propriétés macroscopiques des polymères. Le facteur de forme des nanocharges est un paramètre clé, ce qui constitue le grand intérêt des nanotubes de carbone (NTC). Afin d’éviter les phénomènes d’agrégation un mélange mécanique a été utilisé. Dans ces conditions, le seuil de percolation électrique est de 0.15% en masse. Pour augmenter le facteur de forme, des molécules amphiphiles ont été utilisées : dans ce cas le seuil de percolation est de 0.04% en masse. Au dessus du seuil de percolation, ces nanocomposites permettent l’écoulement des charges électrostatiques tout en conservant les propriétés mécaniques de la matrice