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Among a broad range of carbonaceous materials, such as exfoliated graphite, [1] graphene or diamond, carbon nanotubes (CNTs) are widely used as a thermal filler because of their exceptional intrinsic thermal conductivity (TC) and aspect ratios, which are larger than 1000. The TC of single-walled CNTs (SWNTs) has been reported [2] as high as 6000 W m À1 K À1, and that of multi-walled CNTs (MWNTs) was experimentally measured at 3075 W m À1 K À1 at room temperature, [3] which remains above the performances of diamond (TC ¼ 2200 W m À1 K À1 ). [4,5] Therefore the improvement of the TC of composites based on CNTs was extensively investigated over the past years. [6,7] A recent work revealed that a TC of 0.28 W m À1 K À1 or a 40% increase had been reached in composites with a 10% weight fraction (wt%) of CNTs dispersed in polyvinylacetate matrix by using the classical sonication method.[8] Another optimized configuration was proposed by Haddon and co-workers, who brought into play a hybrid filler based on the combination of SWNTs and graphite nanoplatelets.[9] An improved TC of 1.7 W m À1 K À1 -about a fivefold increase-was obtained for epoxy composites. The hybrid loading mass fraction was as high as 10%, including 7 wt% graphite nanoplatelets and 3 wt% SWNTs.Those wt% appear to be far larger than the one of percolation, which should be smaller than 0.1% in CNT-reinforced composites.[10] The percolation should yield a significant TC augmentation that has not yet been observed. A previous investigation on CNT-based nanofluids emphasized that the TC of the mixture remains thirty times lower than the expected theoretical value and much worse at low mass fractions.[11] This unsatisfying behavior was attributed to interfacial contact resistances, [12] which several teams tried to reduce, but with little success. We have also evaluated the TC of CNT pellets in vacuum from the number of thermal contacts between CNTs, and obtained stringent theoretical limitations that are confirmed by experiment.[13] It is very plausible that the TC improvement at percolation was never achieved in practice due to insufficient CNT dispersion leading to the predominance of thermal contact resistances.[11] In many cases indeed, no efficient percolating networks are visible. [8] In this communication, we demonstrate that epoxy composites with extremely low CNT wt% corresponding to the percolation can have the predicted TC values, which are as high as those previously obtained at a wt% one order of magnitude larger.This new field of properties can indeed be reached by a microarchitecture involving Al 2 O 3 microparticles and MWNTs. These multiscale fillers belong to a new generation of hybrid materials, where alumina microparticles provide efficient structures by dispersing the CNT network within the polymer matrix. To further improve the dispersion, we have also implemented mechanical dispersion of the Al 2 O 3 -CNTs hybrid fillers without any chemical pretreatment. The result is a drastic decrease in the number of thermal contacts between the C...

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Herein, polydimethylsiloxane (PDMS) composite films containing BaTiO3 particles with an average size of 70 and 500 nm are prepared and characterized, respectively. Then, triboelectric nanogenerators (TENG) based on the composite films are designed at different BaTiO3 sizes and mass ratios. In addition, multiwall carbon nanotubes (MWCNTs) are also used for uniform dispersion of BaTiO3 particles in composite films for the TENG device. With the synergistic effects of BaTiO3/MWCNT fillers, discrete conductive micronetworks surrounded by BaTiO3 particles form, and then, the effective filler–matrix interface effect in the three‐phase composite is enhanced, leading to superior triboelectric output performance, supported by much higher dielectric permittivity and COMSOL simulation. Moreover, the triboelectric output performance of TENG changes with different‐sized BaTiO3 particles. As to BT‐70‐MWCNT/PDMS composites, with the same mass ratio of BT, the peak output current is always higher than that of BT‐500‐MWCNT/PDMS. Furthermore, the optimum BT mass ratio of BT‐70‐MWCNT/PDMS composites is also higher than that of BT‐500. With BaTiO3 of size 70 nm, the maximum surface charge density is about 160 μC m−2 under an optimized mass ratio, whereas it is about 110 μC m−2 for BaTiO3 of size 500 nm.

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Floating catalyst chemical vapor deposition (FCCVD) is commonly considered as one of the most attractive process for the production of carbon nanotubes (CNTs). Understanding the phenomena occurring during the FCCVD synthesis of CNTs is critical to improve the process selectivity and scalability. The present work correlates information on gas chemistry and structural characteristics of the carbonaceous products, and show how both are strongly related to the hydrogen content in the reactor. Hydrogen plays different roles in the CNT growth process whose contributions depend on the synthesis conditions. Its presence induces an augmentation in carbon supply by promoting the decomposition of hydrocarbon vapors into more reactive byproducts, and by serving as an activation agent for the dissociation of physisorbed hydrocarbons on the surface of catalyst particles. However, high hydrogen content can induce catalytic hydrogenation of carbon and lead to surface modification of CNTs. Hydrogen also interferes with the decomposition of catalytic precursors, thus influencing the size and availability of catalyst nanoparticles. As a result, the mean and core diameters, crystallinity of the graphene walls, and length of CNTs are greatly influenced by the hydrogen flow, which offers the possibility to tune the CNT properties in a very simple, yet efficient way.

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