149,891 research outputs found
Densification during hot-pressing of carbon nanotubeâmetalâmagnesium aluminate spinel nanocomposites
The densification by hot-pressing of ceramicâmatrix composites containing a dispersion of carbon nanotubes (CNT), mostly single-walled, is studied for the first time. Fifteen different CNTâCo/MoâMgAl2O4 composite powders containing between 1.2 and 16.7 vol.% CNT were prepared by catalytic chemical vapour deposition. The in situ growth of CNT within the oxide powder made it possible to obtain a highly homogeneous distribution of CNT. Low contents of CNT (up to 5 vol.%) are beneficial for the first shrinkage step (up to 1100 âŠC), dominated by the rearrangement process, while higher contents are detrimental. At higher temperatures (1100â1300 âŠC), CNT clearly inhibit the shrinkage, and this detrimental effect regularly increases with the CNT content. Several explanations are proposed, in relation with the particular mechanical properties of CNT and their highly connected web-like distribution within the material
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Effects of carbon nanotubes/graphene nanoplatelets hybrid systems on the structure and properties of polyetherimide-based foams
Foams based on polyetherimide (PEI) with carbon nanotubes (CNT) and PEI with graphene nanoplatelets (GnP) combined with CNT were prepared by water vapor induced phase separation. Prior to foaming, variable amounts of only CNT(0.1â2.0wt%) or a combination of GnP(0.0â2.0 wt %) and CNT (0.0â2.0 wt %) for a total amount of CNT-GnP of 2.0 wt %, were dispersed in a solvent using high power sonication, added to the PEI solution, and intensively mixed. While the addition of increasingly higher amounts of only CNT led to foams with more heterogeneous cellular structures, the incorporation of GnP resulted in foams with Âżner and more homogeneous cellular structures. GnP in combination with CNT effectively enhanced the thermal stability of foams by delaying thermal decomposition and mechanically-reinforced PEI. The addition of 1.0 wt % GnP in combination with 1.0 wt % CNT resulted in foams with extremely high electrical conductivity, which was related to the formation of an optimum conductive network by physical contact between GnP layers and CNT, enabling their use in electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications. The experimental electrical conductivity values of foams containing only CNT Âżtted well to a percolative conduction model, with a percolation threshold of 0.06 vol % (0.1 wt %) CNTPostprint (published version
Role of the particle size polydispersity in the electrical conductivity of carbon nanotube-epoxy composites
Carbon nanotubes (CTNs) with large aspect-ratios are extensively used to
establish electrical connectedness in polymer melts at very low CNT loadings.
However, the CNT size polydispersity and the quality of the dispersion are
still not fully understood factors that can substantially alter the desired
characteristics of CNT nanocomposites. Here we demonstrate that the electrical
conductivity of polydisperse CNT-epoxy composites with purposely-tailored
distributions of the nanotube length L is a quasiuniversal function of the
first moment of L. This finding challenges the current understanding that the
conductivity depends upon higher moments of the CNT length. We explain the
observed quasiuniversality by a combined effect between the particle size
polydispersity and clustering. This mechanism can be exploited to achieve
controlled tuning of the electrical transport in general CNT nanocomposites.Comment: 9 pages, 5 figure
Radius and chirality dependent conformation of polymer molecule at nanotube interface
Temperature dependent conformations of linear polymer molecules adsorbed at
carbon nanotube (CNT) interfaces are investigated through molecule dynamics
simulations. Model polyethylene (PE) molecules are shown to have selective
conformations on CNT surface, controlled by atomic structures of CNT lattice
and geometric coiling energy. PE molecules form entropy driven assembly
domains, and their preferred wrapping angles around large radius CNT (40, 40)
reflect the molecule configurations with energy minimums on a graphite plane.
While PE molecules prefer wrapping on small radius armchair CNT (5, 5)
predominantly at low temperatures, their configurations are shifted to larger
wrapping angle ones on a similar radius zigzag CNT (10, 0). A nematic
transformation around 280 K is identified through Landau-deGennes theory, with
molecule aligning along tube axis in extended conformationsComment: 19 pages, 7 figure2, submitted to journa
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