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International audience; The work aims to design a trilayer composite dedicated to electromagnetic shielding over a large frequency range, from 1 Hz to 20 GHz. Analytical and numerical models are used to determine the shielding effectiveness (SE) of this composite in the case of a planar shield. The shield is constituted of a support layer, a magnetic layer, and a conductive layer. Two possible designs are considered. To simplify the numerical calculation, a homogenization method and the Artificial Material Single Layer (AMSL) method are used. The proposed composite shows a good shielding capacity over the whole studied frequency range, with shielding effectiveness higher than 17 dB and 75 dB, respectively, in the near-field (1 Hz–1 MHz) and far-field (1 MHz–20 GHz). Both homogenization and AMSL methods show good suitability in near-field and allow one to greatly reduce the calculation time.

AlN skeleton structure-reinforced highly oriented graphite flake (AlN/GF) composites have become a promising candidate for thermal management materials owing to their high thermal conductivity and low thermal expansion. However, the applications of AlN/GF composites are still limited by their poor mechanical properties. Herein, a carbon nanotube-coated alumina (Al2O3@CNT) hybrid was used as a reinforcement to improve the mechanical performance of AlN/GF composites prepared via vacuum infiltration followed by spark plasma sintering. It was found that the relative density and orientation degree of the composites decreased slightly with an increase in the Al2O3@CNT content from 0 to 2 wt%. However, the fracture toughness and bending strength of the composites improved significantly after the introduction of the Al2O3@CNT hybrid reaching up to 1.66 MPa∙m1/2 and 95 MPa, respectively, which correspond to an improvement of approximately 50% and 20% over those of the AlN/GF composite. With the addition of the Al2O3@CNTs, the thermal expansion of the composites increased from 7.3 × 10-6/K to ∼15.5 × 10-6/K, while the thermal conductivity decreased from 442 to ∼253 W/m/K. The toughening and strengthening mechanisms as well as the thermal impact mechanism of the composites were also investigated.

La caractérisation à l’échelle de l’interface par microscopie électronique et des essais mécaniques in situ pour différents types de renfort carbonés dans une matrice polymère conduit à mieux comprendre la structure la matrice proche de l’interface, l’interphase, et permet de mesurer la performance de différents types de traitements de surface opérés sur le renfort.

International audience

Due to their outstanding intrinsic functional properties, carbon nanotubes (CNTs) and CNT-loaded composites have received intensive investigations in recent decades. The overall electrical conducting property of a composite is closely dependent on the dispersion, inherent electrical conductivity and interfacial interaction with the matrix of CNTs. However, owing to their high aspect ratio and intensive surface interaction, CNTs are hard to disperse homogeneously in polymer-based matrices. Amongst the ways of solving this issue, that of designing a reasonable CNT array hybrid construction could be a promising solution, without changing the inherent features of CNTs and the CNT–matrix interfacial chemical structure. In order to elevate both the intrinsic electrical conductivity of the hybrid and the construction efficiency of the conductive network in the matrix, a typical graphite nanoplatelet–carbon nanotube hybrid (GCH) was prepared. This chapter first outlines recent representative research developments in the microstructure, synthesis and applications of carbon nanomaterials and GCHs, and then summarises general strategies to optimise CNT dispersion in the matrix; moreover, concentrating on the crucial issues in dielectric and electrically conducting functional polymer-based composites. Possible regulation mechanisms of GCHs on the polymer crystalline structure, microcapacitor network development, conductive network construction and the overall electrical functional properties of the composites are analysed. Finally, a relatively comprehensive summary and several perspectives are provided to propose the critical challenges that need further research in this promising field.

International audience; Glass fiber (GF) reinforced polymer composites have attracted increasing attention due to their excellent performance. In this study, GF was coated by a thin layer of nickel, and then grafted carbon nanotubes (CNTs) array by a chemical vapor deposition method (CVD). The CNT contents can be varied by changing the CVD conditions. Three types of fillers, nickel coated GF (GF@Ni), GF with CVD grown CNTs (GF-CNTs) and nickel-coated GF with CVD grown CNTs (GF@Ni-CNTs), were used to prepare the epoxy composites. The electromagnetic interference shielding performances were investigated as a function of CNT contents. The GF@Ni-CNTs reinforced epoxy composites, which had the CNTs mass ratio of 9.2 wt% to the hybrids, showed the best EMI shielding performance among the composites. Their total EMI shielding effectiveness (SE) was higher than 35 dB in the range of 1–18 GHz, and above 50 dB in the X band. By incorporating the nickel layer on the GF surface, the same EMI performance can be achieved with lower CNTs content. For achieving a SE value of 35 dB in the X band, it needed GF@Ni-CNTs/epoxy with CNTs mass ratio of 3.8 wt% to the hybrids, instead of GF-CNTs/epoxy composites with CNTs mass ratio of 5.2 wt% to the hybrids.

A precise evaluation of the influence of the dispersion and interface on the mechanical properties is the foundation to fabricate high-performance composites. In this work, original CNTs and carbox...

The synthesis of core@double‐shells structured TiO2@C@SiO2 nanowires (NWs) with variable thickness of carbon inner shell and SiO2 outer shell was achieved by individually controlling the chemical vapour deposition time and amount of silicon precursor added in the sol–gel synthesis. The resultant TiO2@C@SiO2 NWs filled nanocomposites exhibited an excellent dielectric performance with simultaneously improved dielectric constant and suppressed dielectric loss, which could be further regulated by individually controlling the carbon inner shell and SiO2 outer shell thickness. More importantly, the influences of the conductive carbon inner shell and insulated SiO2 outer shell thickness on the dielectric performance of nanocomposites were clearly revealed. The increase of the conductive carbon inner shell thickness would lead to an increase in dielectric constant and loss of nanocomposites, while the insulated SiO2 outer shell exhibited a totally opposite law that the dielectric constant and loss of nanocomposites decrease with increasing SiO2 outer shell thickness. Numerical simulations were also carried out to theoretically verify the relationship between the dielectric loss and SiO2 outer shell thickness. This promising controllable multi‐shell structure could be extended to a variety of hybrids to develop high‐performance dielectric nanocomposites.

International audience; To expand the application of insulating glass fiber (GF) in the field of microwave absorption, one type of GF hybrids with carbon nanotubes (CNTs) and nickel (Ni) was successfully synthesized by chemical vapor deposition and electroless plating methods. By changing the reaction conditions, the morphology of GF hybrids including CNT's length, CNT's growth density, and Ni′s thickness could be adjusted. The as-produced hybrids were used as multifunctional reinforcement to fabricate epoxy composites. The dielectric properties of composites were particularly measured from 1 to 18 GHz. It was found that the variation of GF hybrids structure significantly changed the dielectric properties of the composites in the tested frequency range. Furthermore, the analytical simulation work based on the experimental results was conducted for optimizing the structural parameters of multilayered composites. The results showed that the best reflection loss of −60 dB with a −10 dB range of 5.6 GHz could be obtained in an absorber with a triple-layered structure composed by GF-CNTs/epoxy with different CNT contents and GF-CNTs@Ni/epoxy. Thus, the proposed hybrid method might be quite efficient for developing composites that can achieve high-performance electromagnetic absorbing

This paper studies the electromagnetic behavior of carbon nanotubes (CNTs) based nanocomposites. Such nanocomposites are meaningful for the material design, especially for shielding in EMC applications. A multiscale numerical homogenization method based on a finite element model and incorporating tunneling effect provides is implemented. CNTs are modeled by highly conductive line segments in order to avoid the mesh problems. Effective electrical conductivity is obtained both in statics and time harmonic cases. Numerical predictions are compared to experimental data.

In this work, we proposed a multiscale numerical model to estimate the electric conductivity and dielectric constants of the CNT/polymer nanocomposites, taking into account the tunneling effect between neighbouring CNTs separated at nanoscale and the frequency-dependent dielectric properties of each components. Finite element method was employed to solve the formulations, and the CNTs were modeled by highly conductive line segments in order to avoid the mesh problems. Experiments have been carried out in carbon nanotubes/epoxy nanocomposites in order to compare to the simulation results. The numerical estimations of the electric conductivity are in good agreement with the experimental measurement by network analyzers. Moreover, the calculated dielectric permittivity agrees with the experimental data for the nanocomposites whose CNT content is beyond percolation threshold. Below percolation threshold, the proposed model also works well in the prediction of dielectric constants when the frequency is over 1 0 3 Hz .

Polyvinylidene fluoride (PVDF), as an electroactive polymer, has been attracting increasingly attention for its broad potential applications ranging from film capacitors, actuators, to energy harvesters. The capability of a PVDF film to sustain a high working voltage is highly demanded to achieve these applications. Herein, we find that blending two PVDF polymers with low and high molecular weights can achieve higher dielectric strength (Eb = 479 MV/m) than either of the two original ones (PVDF-1 with Mw of ~180,000, Eb = 412 MV/m and PVDF-2 with Mw of ~441,000, Eb = 391 MV/m). The underlying synergetic effect is deduced from the analysis of the crystallization of PVDF by wide-angle X-ray diffraction and small-angle X-ray scattering from a synchrotron source. It involves crystallite polymorphism, the transition of crystalline phases, the variation of crystalline lattice spacing at different strain spaces, and the long periods and the distribution of crystallite sizes. Understanding these underlying influences is beneficial to process PVDF films with desirable and reliable dielectric properties.

Foam structures with epoxy as the matrix and both carbon nanotubes (CNTs) and their hybrids with graphene oxide (GO-CNTs) as absorbers were fabricated, and their microwave absorbing and electromagnetic properties were investigated in the frequency range of 1–18 GHz. The fillers and bubbles were uniformly distributed in the composites. The complex permittivity and electrical conductivity of the composites increased as the fillers’ content increasing. The best performance of the reflection loss (RL) can be obtained for a foam structure with 0.5 wt% GO-CNTs, which had a RL peak value of −20dB with a −10 dB range of 5.3 GHz (10.8–16.1 GHz). Multi-layered structures were also discussed in this work, a RL peak value of −40dB with a −10dB range of 7.1 GHz (9.9–17 GHz) had been obtained by combining two foam structures, which are 2 mm thick 0.5 wt% GO-CNTs/epoxy and 1 mm thick 2.0 wt% GO-CNTs/epoxy. Furthermore, the −10dB range can reach 11.5 GHz (6.5–18 GHz) when combining 2.6 mm thick 0.5 wt% GO-CNTs/epoxy and 1.3 mm thick 2.0 wt% GO-CNTs/epoxy.

The conductive path formed by carbon nanotubes (CNTs) in a polymer matrix is one of the most attractive topics for developing multifunctional nanocomposites. In this article, we studied the evolution of conductive paths and interactions in the interfacial regions in epoxy-based composites reinforced by an urchinlike hybrid of CNTs and alumina microparticles (μAl2O3). A homogeneous dispersion of CNTs in the epoxy matrix was achieved thanks to the core–shell structures of CNTs-μAl2O3 hybrids, resulting in the interpenetrated epoxy’s cross-linking network that strongly bonds with CNTs. Furthermore, thermal treatments at different temperatures around the glass-transition temperature (Tg) were conducted under vacuum on composites near the percolation threshold. It was found that the dielectric behavior and the Tg were shifted in spite of the constant CNT mass fraction used. This was mainly due to the fact that thermal treatment generated the adjustment of the cross-linking network of epoxy, and the distances b...

International audience; Film capacitors with high energy storage are becoming particularly important with the development of advanced electronic and electrical power systems. Polymer-based materials have stood out from other materials and have become the main dielectrics in film capacitors because of their flexibility, cost-effectiveness, and tailorable functional properties. A core issue for achieving films with high performance is to process a material with high dielectric permittivity and breakdown strength but low dielectric loss. Nanocomposites and all-polymer dielectrics are two promising avenues to address this issue. Thus, in this work, the advances of the past decade are highlighted to reflect the latest developments in polymer-based film dielectrics. The key factors of dielectric properties, including polarization mechanisms, dielectric breakdown strength, filler-matrix interface, and hierarchical structures are discussed in detail. A comprehensive understanding of the fabrication of polymer-based materials with special constituents, molecular segments, and microstructures will provide guidance to engineers on the fabrication of polymer-based materials with high performance.

International audience; Triboelectric-electret nanogenerator (TENG) has recently become a research hotspot in the field of energy harvesting due to its advantages in low-cost, compact structure, broad applicability, and high efficiency. In this work, we calculated the charge transfer process and the output voltage/current/power of a contact-separation mode TENG driven by continuous periodic reciprocating movements with acceleration/deceleration processes, using symbolic computations in MATLAB. The calculated amplitudes of output voltage/current peaks of the TENG vary during multiple working cycles over time in an exponential form and gradually convergence to steady ranges. For the first time, these variations, along with the asymmetry between the output positive and negative voltage/current peaks of the TENG, were attributed to the lag of the charge transfer cycle relative to the periodic movement cycle with both theoretical and experimental evidence. A detailed investigation was conducted on the influence of the initial condition and the load resistance on the variation of TENG output voltage peaks. The optimum load resistance (Ropt) was obtained by calculating the average output power of the TENG per movement cycle 2 (AvgP). Both Ropt and AvgP can be quite different in the steady output ranges from those in the first working cycle if the TENG starts working from the contact state. These results may be important for evaluating and optimizing the output of TENGs in a steady continuous working mode, and for designing TENGs in accordance with their working environment and circuit loads.

International audience

Polymer films composed of polypropylene (PP) and poly(vinylidene fluoride) (PVDF) have been fabricated by extrusion with filming system. Owing to the low content of crystallites and the lubricant of carbon black, the commercial product PVDF 370 can be compatible with PP by simply blending at the molten state and the obtained film has improved dielectric constant (e' = 4.5) and reduced dielectric loss (tan δ = 0.5%) at 1000 Hz. The modified dielectric properties result from the high dielectric constant of PVDF and low dielectric loss of PP. In addition, by introducing the third polymer, low-density polyethylene (LDPE), the dielectric constant of the ternary blends (PP/PVDF 370/LDPE) can further be increased.

International audience; In this study, laser-induced incandescence (LII) diagnostic technique was applied for iron-based nanoparticle (NP) sizing during the floating chemical vapor deposition (CVD) synthesis of carbon nanotubes (CNTs). Transmission electron microscopy (TEM) was used to characterize the nature and size of NPs. The LII signal was simulated by taking into account the carbon-encapsulated iron NP density, heat capacity, size distribution, etc. A detailed sensitivity and uncertainty of the key parameters on the evaluated particle size for this model has also been estimated. Using the developed approach, the evolution of NPs in the gas phase along the reactor axis was investigated at 650, 750 and 850 °C. It was found that the evaluated sizes from LII signals were in good agreement with the ones obtained by TEM measurements. The NP size is highly dependent on the temperature under the studied conditions but it does not show obvious difference along the reactor axis. This study reveals an important LII application prospect to understand the catalyst particle behaviors for better control over CNT growth during the floating CVD process.

International audience

International audience; Binary blends of polypropylene (PP) and poly(vinylidene fluoride) (PVDF) are often hard to process by extrusion because of the poor compatibility between the two semicrystalline polymers. Considering the fast crystallization during the stretching at room temperature, PVDF products with low molecular weight were selected in this study and consequently they presented improved compatibility with PP, which favored extruding and stretching the binary blending film (50−50 weight ratio) into micrometric thickness. The obtained binary blending film had a reasonable dielectric constant of over 3.6, a low dielectric loss of 0.54%, and a high breakdown strength of 439 MV/m. Furthermore, boron nitride nanosheets (BNNS) obtained by liquid exfoliation were introduced into PP/PVDF binary blends, and the composite film displayed further reduced dielectric loss of 0.41% and increased breakdown strength of 478 MV/m. In addition, the compositefilm with BNNS also had high Young’s modulus and tensile strength. The enhanced dielectric and mechanical properties made PP/PVDF (50−50)/BNNS 5% display potential values in the application of film capacitors for high-voltage direct current systems.

International audience; The synthesized core-shell hybrids, BaTiO 3 (shell) @ carbon nanotubes (core), (BT@CNT), can make the polyvinylidene fluoride (PVDF) matrix composite to exhibit high dielectric permittivity (ε') but low dielectric loss (tan δ) when approaching the percolation threshold. High ε' is attributed to BT coating which can strengthen the interfacial polarization in the composite. Low tan δ is attributed to the formation of the structure: CNT→BT→PVDF with the gradually decreasing dielectric properties from the centers of hybrid to the surrounding borders of PVDF. Additionally, AC conductivity of the composites can be deduced by the self-consistent effective medium (SCEM) approximation, which helps to understand the conductive behavior of CNT with a ceramic buffer layer in PVDF matrix more comprehensively.

International audience; 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.

Conventional structural materials and damping materials both don't combine excellent mechanical and damping properties at the same time, which makes them unable to meet the practical demand. Study on structural damping composites that possess higher mechanical and damping properties is becoming a hot research direction. Meanwhile dynamic mechanical analysis (DMA) could provide information on the mechanical and damping properties via storage modulus and loss factor, respectively, which makes it one of the most convenient and effective research methods on structural damping composites. In this paper, composites with polyamide non-woven fabrics (PNF) and functionalized PNF with crystalline thermoplastic polymer polyvinylidene fluoride (PVDF) and nanoscale carbon material vapor grown carbon fiber (VGCF) as interleaf materials are prepared firstly, then dynamic mechanical behaviors are measured and the microstructure is analyzed to study the effect of different interlayers on the mechanical and damping properties of the co-cured composites. The results indicate that PNF could improve the loss factors without significantly reducing the storage modulus, moreover, functionalized PNF with PVDF and VGCF are capable of further improving storage modulus and loss factors synchronously. Keywords: Structural damping composite, Polyamide nonwoven fabrics, PVDF, VGCF, DMA

A new kind of structural damping composites was prepared by interleaving polyamide nonwoven fabrics (PNF) between the carbon fiber reinforced epoxy composite laminates. The damping behaviors of the composites made were experimentally investigated using cantilever beam test and dynamic mechanical analysis. The damping ratios of the nonwoven fabrics interleaved composites were compared with the ones of non-interleaved composites. In addition, the interlaminar shear strength and flexible modulus of the composites were also investigated, as well as the composite compression after impact (CAI), Mode I and Mode II interlaminar fracture toughness (GIC and GIIC), in order to evaluate the influence of the polyamide nonwoven fabric layers on the composite mechanical properties. It has been observed that the interleaved polyamide nonwoven fabric layers greatly improved the composite damping loss factors, and the composites containing 7 layers of PNF showed the best damping behavior. Meanwhile, the addition of PNF showed a negligible influence on the composite flexible strength and modulus and interlaminar shear strength. Most importantly, the CAI, GIC and GIIC tests indicated that the composite interlaminar toughness and impact resistance were significantly improved by the interleaved PNF. Finally, the reinforcing mechanism of this kind of composites is discussed.

Carbon nanotubes (CNTs) serving as nano-fillers could endow polymer-based composites with excellent functionalities. However, a challenge always lies in the strong aggregation of loaded CNTs which hinders the sufficient improvement of composites’ properties. Here we describe polyvinylidene fluoride-based nanocomposites that contain graphite nanoplatelet–carbon nanotube hybrids (GCHs), the dielectric properties of which are improved more greatly than those of the general ternary composites loading an equivalent mixture of GNPs and CNTs. The permittivity and AC conductivity of a composite with 10 wt% GCHs are 3217 and 10−3 S m−1 at 1 kHz, respectively, which are correspondingly 105 times and 5 orders of magnitude larger than those of ternary composites with 10 wt% mixture (30.2 and 10−8 S m−1). Through the catalyst chemical vapor deposition process, the vertically-aligned CNT arrays were well synthesized on exfoliated GNP substrates, forming a totally-conductive GCHs architecture. The nanocomposites achieved by dispersing GCH particles into the matrix using a mechanical melt-mixing process show a strongly reduced percolation threshold (5.53 vol%) and a relatively high thermal stability compared to their ternary counterparts. Their improved dielectric properties can be attributed to the formed microcapacitor networks and the change of crystalline phase composition of the matrix, caused by well-designed CNT array constructions. These results indicate that the dielectric performance and percolation threshold of nanocomposites could be effectively ameliorated through the strategy of reasonably redesigning the CNT constructions.

A new type of structural damping composite was prepared by interleaving aramid nonwoven fabrics (ANF) modified with semi-crystalline polyvinylidene fluoride (PVDF) between carbon-fibre-reinforced bismaleimide (BMI) laminae. The co-cured composite exhibited an increase of 108% and 2.72% in loss factor and flexural modulus, respectively, compared with the original carbon-fibre-reinforced BMI composite. The damping behaviour of the co-cured composites was experimentally investigated using the single cantilever beam test and dynamic mechanical analysis. Furthermore, the composite interlaminar shear strength and flexural strength and modulus were also investigated. The results indicated that the composite interleaved with ANF/PVDF possessed higher flexural modulus and loss factor than the composites interleaved with ANF or PVDF films alone as a result of synergistic reinforcement of ANF and PVDF. Finally, the reinforcement mechanism of ANF/PVDF was investigated by analyzing the composite microstructure and the dynamical mechanical properties of ANF, PVDF, and ANF/PVDF interlayers.

International audience; Harvesting energy from the environment is a sustainable solution for powering decentralized sensor networks, Internet of Things systems, etc. In this work, a triboelectric nanogenerator (TENG) based on the fluorinated ethylene propylene (FEP) electret film is investigated to generate electricity from mechanical motions in the environment, and its working principle is explained with a variable capacitance model. For the first time, the validity of this model is verified with a capacitor discharge curve fitting method. Based on this model, the maximum output energy of the TENG per working cycle is calculated, which could be useful for comparing the property of TENGs working under different environmental conditions. An adhesive tape-peeling process is innovatively used to charge the FEP electret film, which is facile and effective for increasing the charge amount on the film without using any complex equipment. Through this method, the surface potential of a 4 cm × 4 cm FEP film is improved from-360V to 2-2850V, the output negative voltage peak of the same-sized TENG is improved from-83 V to-363 V, and for a wind-driven 8 cm × 8 cm sized TENG, its average output power to charge a 10 μF capacitor is improved from 2.5 μW to 19.8 μW. The ability of this TENG in generating electricity from low-frequency human motions to directly light up light emitting diodes (LEDs) is also demonstrated.

International audience; The core@double-shells structured TiO2@Carbon@SiO2 nanowires (TiO2@C@SiO2 NWs) with a uniform carbon inner shell and a SiO2 outer shell were successfully synthesized and subsequently incorporated into poly(vinylidene fluoride) (PVDF) matrix to prepare dielectric nanocomposites. Compared with the pristine TiO2 NWs/PVDF nanocomposites, the introduction of carbon interlayer as the inner shell between the TiO2 core and SiO2 outer shell offers the nanocomposites with two additional types of interfacial polarization, namely, (i) TiO2/carbon and (ii) carbon/SiO2 interfacial polarizations. These additional interfacial polarizations promote the dielectric constants, and simultaneously the SiO2 insulating barrier layer suppresses the losses of the nanocomposites. Moreover, the nanocomposite with 30 wt % filler loading (19.78 vol %) exhibits an excellent dielectric performance with a constant of 41 and a loss tangent of 0.05 at 103 Hz. The multi-shells strategy reported here could be extended to a variety ofinorganic hybrids to develop novel dielectric nanocomposites.

International audience; Graphical abstract The evolution of nanoparticles (NPs) in the gas phase during the floating chemical vapor deposition synthesis of carbon nanotubes (CNTs) was investigated. NPs were detected in the gas phase along the reactor axis, and their nature and size were characterized by high-resolution transmission electron microscopy equipped with energy-dispersive spectroscopy analysis. Their roles during the CNTs growth were also discussed by correlating the information about the morphology of the CNTs synthesized on the substrate along the reactor axis. It is found that iron NPs form and grow quickly in the front of the reactor at a temperature above 750 • C, whereas the NP growth finally terminate when they are encapsulated by the carbon layers during the downstream region of the reactor. Because of the carbon encapsulation, iron NPs could not directly contribute to the CNT growth on the substrate. These results demonstrate that homogeneous nucle-ation is not the prerequisite for the CNT growth on the substrate

Core–shell structure hybrids of carbon nanotubes (CNTs)/BaTiO3 (H-CNT-BT) and commercial multi-wall CNTs are respectively incorporated into poly(vinylidene fluoride) (PVDF) for preparing the composites near the percolation thresholds. A comprehensive investigation for CNT's dispersion and composite's conductivity is conducted between H-CNT-BT/PVDF and CNT/PVDF at different depths vertical to the injection's direction. Gradual increases of the conductivity in two composites are observed from the out-layer to the core part which infers an inhomogeneous CNT's dispersion in the interior of composites due to their migration under flow during the injection. However, the use of H-CNT-BT fillers with core–shell structure enables to reduce this inhomogeneous dispersion in the composite. Furthermore, the conductive network of CNTs in H-CNT-BT/PVDF is less sensitive to the thermal treatment than the one in CNT/PVDF composite, which infers the core–shell structure of hybrids can ameliorate the sensitivity of the conductive network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45693.

International audience; Sandwich-structured composites of polydimethylsiloxane/carbon nanotube (PDMS/CNT) bulk between two neat PDMS thin films with different thicknesses are prepared by the spin-coating method. Taking advantage of CNT's percolation behavior, the composite keeps relatively high dielectric constant (ε′ = 40) at a low frequency (at 100 Hz). Meanwhile, due to the existence of PDMS isolated out-layers which limits the conductivity of the composite, the composite maintains an extremely low dielectric loss (tan δ = 0.01) (at 100 Hz). Moreover, the same matrix of the out-layer and bulk can achieve excellent interfacial adhesion, and the thickness of the coating layer can be controlled by a multi-cycle way. Then, based on the experimental results, the calculation combining the percolation theory and core-shell model is used to analyze the thickness effect of the coating layer on ε′. The obtained relationship between the ε′ of the composite and the thickness of the coating layer can help to optimize the sandwich structure in order to obtain the adjustable ε′ and the extremely low tan δ.

International audience; A three-dimensional carbon nanotube-silica coated reduced graphene oxide hybrid (CNT-SiO2@RGO) was synthesized by floating-catalyst chemical vapor deposition (CVD), in which ferrocene was used as catalyst precursor and acetylene as carbon source. Graphene oxide (GO) was selected as the template and was pre-treated by tetraethyl orthosilicate (TEOS) to deposit a SiO2 layer on both sides of the platelet surface. The obtained hybrid has a uniform structure consisting of a platelet sandwiched by vertically aligned CNTs. The CNT length can be well controlled by the variation of growth time.

International audience; In-situ characterization of the fiber/matrix interfacial failure behavior at microscopic scale is important to optimize the fiber surface treatment and to design high performance composites. In this study, in-situ tensile tests in scanning electron microscope (SEM) were used to investigate the interfacial adhesion strength of epoxy composites reinforced by four kinds of carbon fibers (CF) raw CF, desized CF, carbon nanotube-grafted CF (CNT-CF) and oxidized CNT-CF. The crack initiation position and fracture failure mode were well recorded. The strains and the interfacial adhesion strength were obtained for these four kinds of composites. It was found that the interfacial strength decreased from 53 MPa to 48 MPa after removing the sizing on carbon fiber surface. However, by grafting CNTs on the CF surface, the interfacial strength reached 55 MPa and was further increased to 58 MPa after a simple thermal oxidation treatment. Moreover, energy dispersion X-ray analysis (EDX) was carried out using scanning transmission electron microscopy (STEM). The EDX mapping demonstrated that oxygen aggregated at the interfaces of raw CF/epoxy and oxidized CNT-CF/epoxy. Thus, a combination of CNT grafting with chemical functionalization should be necessary to achieve high performance carbon fiber reinforced polymer composites.

A new kind of structural damping composite was prepared by interleaving aramid non-woven fabrics (ANF) between the carbon fiber reinforced polymer laminates. The composite damping behaviors were experimentally investigated using single cantilever beam vibration test and dynamic mechanical analysis. Meanwhile, the influence of the ANF interlayers on the composite mechanical properties was investigated by measuring the interlaminar shear strength, flexural modulus, flexural strength, compression after impact ( CAI ), type I interlaminar fracture toughness ( G IC ) and type II interlaminar fracture toughness ( G IIC ). It was found that the interleaved ANF layers greatly improved the composite damping properties with an increase as high as 56.3% in the composite loss factor, with a negligible influence on their flexible strength and modulus and interlaminar shear strength. Most importantly, the CAI , G IC and G IIC tests indicated that the composite interlaminar fracture toughness was significantly enhanced by interleaving ANF. Finally, the ANF reinforcing mechanism inside composites was discussed.