Double walled carbon nanotube/polymer composites via in-situ nitroxide mediated polymerisation of amphiphilic block copolymers

Because of their unique physical, chemical, and structural properties, carbon nanotubes (CNT) are playing an increasingly important role in the development of new engineering materials [1]. Across many different applications, CNT/polymer composites have been extensively studied [2] S.B. Sinnot and R. Andrews, Carbon nanotubes: synthesis, properties, and applications, Crit Rev Solid State Mater Sci 26 (2001), pp. 145–249.[2]. The key problem for CNT/polymer composite elaboration is the dispersion, compatibilization, and stabilization of the CNT in the polymer matrix. To solve this problem, a structure with di-block copolymers, one with a good affinity to CNT (monomer M1), the other being the matrix (monomer M2), is proposed in this study, as shown on the two steps mechanism of Fig. 1

Analysis of electron transfer between electron irradiated metallic ball and insulators in vacuum: A specific alternative to the mirror method

International audienceIn order to improve the knowledge of dielectric properties of insulators, we have imagined an original method of characterization of the charge buildup. Electrons of an electron beam are implanted through a metallic ball directly in contact with the insulator in a scanning electron microscope. By calculating and modeling the capacitance and the electrostatic force between the ball and the insulator plane, it has been possible to determine the relationship between the injected charges in the metallic ball and its surface potential. The major role of the dielectric thickness has been evidenced when the insulator is placed on a grounded metallic plane. At high potential values, a dielectric breakdown of the medium surrounding the sphere occurs and electrical charges are transferred from the ball to the dielectric sample. This transfer has been evidenced and quantified in the case of sapphire and quartz. Analytical calculations and numerical simulations using the finite-element method have been performed for interpreting these experimental results

In Situ Nitroxide-Mediated Polymerized Poly(acrylic acid) as a Stabilizer/Compatibilizer Carbon Nanotube/Polymer Composites

Carbon nanotube (CNT) polymer composites were synthesized via in situ nitroxide-mediated diblock copolymerization. Poly(acrylic acid) (PAA) was chosen as a first block to obtain a precomposite CNT-PAA which is readily dispersible in various solvents including water. The immobilization of the stable poly(acrylic acid) alkoxyamine functionality on the nanotube surface occurs during the synthesis of the first block without CNT prior treatment. The living character of this block is established by spectroscopic methods and the nature of the CNT/PAA interaction is discussed. This living first block offers the opportunity to reinitiate the polymerization of a second block that can be chosen among a wide range of monomers. This versatility is illustrated with a second block containing methyl acrylate (MA) or styrene (S). Scanning and transmission electron microscopies confirm good CNT dispersion in the polymer network, while transmission electron microscopy also spots the anchorage locations of PAA on the CNT surface. Such nanotubes wrapped by diblock copolymers can be dispersed in various polymer matrices to create CNT—polymer composites. Conductivity measurements show that these composites obey a percolation-like power law with a low percolation threshold (less than 0.5 vol%) and a high maximum conductivity (up to 1.5 S/cm at room temperature)

Simulation du transport de charges dans l'alumine, Influence d'une couche en surface

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Injection and selfconsistent charge transport in bulk insulators

International audienceThe new flight-drift model (FDM) of selfconsistent electron transport and electrical charge storage in wide-gap insulators reflects a more realistic simulation of these processes in dielectric and insulating materials than the former mainly ballistic model. Thus, electron-hole creation, their ballistic flight, followed by field-drift transport, and finally trapping in localized states and/or recombination are taken into account. The experimentally accessable quantities of field assisted secondary electron emission σ as well as the resulting surface potential V0 due to internal current j(x,t), charge ρ(x,t), field F(x,t), and potential V(x,t) distributions are obtained. The calculations are performed for bulk Al2O3 ceramics with open and metal-coated and grounded surfaces

Electron beam excitation in thin layered samples

International audienceEnergy transfer distributions dE/dx and respective excitation depth functions Φ of electron beams in heterogeneous layered samples are described by a successive Effective Layer method. This method is based on electron transmission rates through the top multilayer system replaced by an “effective layer” of the following bottom material. Thus energy depositions in heterogeneous layered metal samples (Al, Ag and Au) and dielectric insulating samples SiO2–Al2O3 are given. For the latter ones special energy-range relations R(E0) have been deduced for the common energy regions (1–30) keV of scanning electron microscopy (SEM). Application are given by cathodoluminescence depth profiling and electron beam charging of non-conductive samples