We report the electrical responses of water vapour and O2 adsorption onto macroscopic multi-walled carbon nanotube (MWCNT) ropes, and compare the results with mats of acid-treated MWCNTs on SiO2 substrates in order to investigate the importance of oxygen-containing defects on CNTs. In the outgassed state both carbon nanotube (CNT) materials exhibit rapid changes in electrical resistance when exposed to dry air, humid air or water vapour at standard temperature and pressure (STP). The measured electrical responses are highly reversible at STP when cycled between humid air, vacuum and dry air. We report a decrease in resistance for the CNT materials in dry air, attributed to O2 p-type doping of the CNTs, whereas there is an increase in resistance when exposed to a humid environment. This latter effect is attributed to the formation of hydrogen bonding from the polar water molecules with the oxygen-containing defects on the CNTs. Our observations indicate that the increase in electrical resistance upon water absorption affects a reduction of the electron-withdrawing power of the oxygen-containing defect groups, thus leading to a reduced hole carrier concentration in the p-type nanotubes.

We report an alternative method combining dielectrophoresis and impedance spectroscopy to provide rapid, accurate measurement of dielectrophoretic collection of single-walled carbon nanotubes ͑SWNTs͒ in real time. We analyzed a Triton X-100 suspension of mixed SWNTs to measure their precise dielectrophoretic collection behavior. Results indicate that our sample contains 21.5% of metallic and 78.5% of semiconducting carbon nanotubes before separation, and that the range of 1 -15 MHz is ideal to collect only the metallic ones. Optical absorption was used to confirm these proportions. We discuss the possible errors associated with using purely 2 Depending on their diameter and chirality, single-walled carbon nanotubes ͑SWNTs͒ can behave either as a metal or a semiconductor. Dielectrophoresis 3 ͑DEP͒, the movement of particles in nonuniform electric fields, has been used to separate mixtures of semiconducting and metallic SWNTs.4-6 Measurement of the frequency-dependent collection of DEP has thus far been based on Raman spectroscopy, which requires some complex interpretation of results. [7][8][9] In this letter, we report the application of combined dielectrophoresis and impedance measurements to provide real time rapid, accurate measurement of dielectrophoretic collection of SWNTs, and hence their dielectric properties and chiral proportions.SWNTs were made by laser ablation and suspended in a Triton X-100 solution. Measurements were performed on needle-shaped electrodes with a 10 m gap, energized with a sinusoidal 10 V pk-pk , at five or more frequencies per decade between 10 kHz and 20 MHz. A resistance was connected in series, and the voltage measured across the resistor and resistor/electrode combination using a digital oscilloscope. The oscilloscope output to a computer, which calculated the resistance of the interelectrode gap at 1 s intervals. The recording process began prior to the SWNTs suspension being placed on the electrodes, and continued for typically 5 min. The time constant of the change of resistance as a function of time was then obtained. Figure 1͑a͒ shows a representative selection of impedance versus time data which has been normalized to the electrode impedance. The solution conductivity was measured at 1.3 mS m −1 , causing a 30% decrease in resistance after application. Two types of behavior were observed in nanotube solutions. At high frequencies, an initial resistance drop at the application of the sample was followed by an exponential decrease to a stable value at approximately 200 s. The decrease in resistance ͑final with respect to initial values͒ was 53% for 1 MHz, 39% for 2 MHz, and 48% for 5 MHz. At lower frequencies, the reduction was more significant, e.g., 88% for 20 kHz, 79% for 50 kHz, and 67% for 100 kHz. At 20 MHz, the response indicated that the impedance change was due to the medium alone, that is, the result was identical to the control measurement and no collection occurred.If we hypothesize that the time taken for the impedance to change due to the collection of nanotub...

Hybrid nanomaterials consisting of multiwall carbon nanotubes (MWCNT) decorated with noble metal nanoparticles were produced by irradiating aqueous mixed solutions of the separate components with nanosecond lasers pulses at 248 nm. Specifically, the decoration with Au and Pd nanoparticles is discussed. No decoration of the MWCNT was observed by simple mixing with nanoparticle solutions. Hence, a photo-thermal mechanism is suggested, whereby the laser-heating of the nanoparticles induces melting, boiling and subdivision into smaller clusters and atoms, which then attach to the MWCNT.Send offprint requests to:

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This paper reports different routes combining photopolymerization of epoxy and acrylate monomers or photo sol-gel reaction yielding to organic or hybrid nanocomposites with enhanced thermomechanical properties. First homogeneous Interpenetrating Polymer Networks based on a dimethacrylate and an epoxide were straightforwardly synthesized by means of UV curing without any phase separation. Then, a dimethacrylate resin was mixed with a variable amount of a methacrylate trialkoxysilane precursor. Upon UV irradiation, a dual organic-inorganic polymerization occurred in one step leading to increased scratch resistance. The structural properties of the resulting coatings were investigated by Si solid state NMR spectroscopies. In addition, their thermomechanical behaviour was characterized by Dynamic Mechanical Analysis and scratch tests.