Delong He

Carbon Nanotube Microarchitectures for Enhanced Thermal Conduction at Ultralow Mass Fraction in Polymer Composites

[*] Dr. S. Volz, Y. Chalopin Laboratoire d’Energetique Moleculaire, Macroscopique et Combustion Ecole Centrale Paris, CNRS UPR288, PRES UniverSud Paris Grande Voie des Vignes, 92295 Châtenay-Malabry Cedex (France) E-mail: volz@iis.u-tokyo.ac.jp Dr. S. Volz Laboratory for Integrated Micro-Mechatronic Systems Institute of Industrial Science, University of Tokyo, CNRS UMI2820 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

One-pot synthesis of Ag/r-GO/TiO2 nanocomposites with high solar absorption and enhanced anti-recombination in photocatalytic applications

In this paper, we reported a simple one-pot solvothermal approach to fabricate Ag/reduced graphene oxide (r-GO)/TiO2 composite photocatalyst under atmospheric pressure. Based on the experimental data, we concluded that the introduction of Ag into classical graphene-TiO2 system (i) efficiently enlarges the absorption range, (ii) improves photogenerated electron separation and (iii) increases photocatalysis reaction sites. The optimized sample exhibits prominent photocatalysis ability as compared to pure TiO2 under simulated sunlight. We further proposed that besides the above three advantages of Ag, a different size of Ag nanoparticles is also responsible for the improved photocatalysis ability, where small size Ag nanoparticles (2-5 nm) could store a photoexcited electron that was generated from TiO2, while large-size Ag nanoparticles could utilize visible light due to their localized surface plasmon resonance (LSPR) absorption. Our present work gives new insights into the photocatalysis mechanism of noble metal/r-GO/TiO2 composites and provides a new pathway into the design of TiO2-based photocatalysts and promote their practical application in various environmental and energy issues.

Design of Electrically Conductive Structural Composites by Modulating Aligned CVD-Grown Carbon Nanotube Length on Glass Fibers

Function-integration in glass fiber (GF) reinforced polymer composites is highly desired for developing lightweight structures and devices with improved performance and structural health monitoring. In this study, homogeneously aligned carbon nanotube (CNT) shell was in situ grafted on GF by chemical vapor deposition (CVD). It was demonstrated that the CNT shell thickness and weight fraction can be modulated by controlling the CVD conditions. The obtained hierarchical CNTs-GF/epoxy composites show highly improved electrical conductivity and thermo-mechanical and flexural properties. The composite through-plane and in-plane electrical conductivities increase from a quasi-isolator value to ∼3.5 and 100 S/m, respectively, when the weight fraction of CNTs grafted on GF fabric varies from 0% to 7%, respectively. Meanwhile, the composite storage modulus and flexural modulus and strength improve as high as 12%, 21%, and 26%, respectively, with 100% retention of the glass transition temperature. The reinforcing mechanisms are investigated by analyzing the composite microstructure and the interfacial adhesion and wetting properties of CNTs-GF hybrids. Moreover, the specific damage-related resistance variation characteristics could be employed to in situ monitor the structural health state of the composites. The outstanding electrical and structural properties of the CNTs-GF composites were due to the specific interfacial and interphase structures created by homogeneously grafting aligned CNTs on each GF of the fabric.

Largely enhanced dielectric properties of carbon nanotubes/polyvinylidene fluoride binary nanocomposites by loading a few boron nitride nanosheets

The ternary nanocomposites of boron nitride nanosheets (BNNSs)/carbon nanotubes (CNTs)/polyvinylidene fluoride (PVDF) are fabricated via a combination of solution casting and extrusion-injection processes. The effects of BNNSs on the electrical conductivity, dielectric behavior, and microstructure changes of CNTs/PVDF binary nanocomposites are systematically investigated. A low percolation value (fc) for the CNTs/PVDF binary system is obtained due to the integration of solution and melting blending procedures. Two kinds of CNTs/PVDF binary systems with various CNTs contents (fCNTs) as the matrix are discussed. The results reveal that compared with CNTs/PVDF binary systems at the same fCNTs, the ternary BNNSs/CNTs/PVDF nanocomposites exhibit largely enhanced dielectric properties due to the improvement of the CNTs dispersion state and the conductive network. The dielectric constant of CNTs/PVDF binary nanocomposite with 6 vol. % CNTs (fCNTs   fc), it displays a 43.32% improvement from 1325 to 1899 after the addition of 3 vol. % BNNSs. The presence of BNNSs facilitates the formation of the denser conductive network. Meanwhile, the ternary BNNSs/CNTs/PVDF systems exhibit a low dielectric loss. The adjustable dielectric properties could be obtained by employing the ternary systems due to the microstructure changes of nanocomposites.

Enhanced dielectric performance of polyvinylidene fluoride composites with an all-carbon hybrid architecture: vertically aligned carbon nanotube arrays on graphite nanoplatelets

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.

Versatile Wafer-Scale Technique for the Formation of Ultrasmooth and Thickness-Controlled Graphene Oxide Films Based on Very Large Flakes

We present a new strategy to form thickness-adjusted and ultrasmooth films of very large and unwrinkled graphene oxide (GO) flakes through the transfer of both hemispherical and vertical water films stabilized by surfactants. With its versatility in terms of substrate type (including flexible organic substrates) and in terms of flake density (from isolated flakes to continuous and multilayer films), this wafer-scale assembly technique is adapted to a broad range of experiments involving GO and rGO (reduced graphene oxide). We illustrate its use through the evaluation of transparent rGO electrodes.

Interfacial studies of carbon fiber/epoxy composites using single fiber fragmentation test

Single fiber fragmentation tests were carried out to measure the properties of the fiber-matrix interface in several carbon fiber (CFs)/epoxy composite systems. Four kinds of CFs were studied: (1) primary CFs (used as received); (2) desized CFs (sizing removed through thermal treatment); (3) resized CFs (deposited with epoxy sizing by solution); (4) carbon nanotube (CNT)-grafted CFs (grown with CNTs using a chemical vapour deposition method). The interfacial shear strength decreased by around 30% for the desized CFs and the CNT-grafted CFs compared with the pristine CFs. The value of interfacial shear strength for the resized CFs was 20% larger than that of the desized CFs. There is a good agreement between the results of single fiber fragmentation tests and that of contact angle tests.

Carbon Coated Boron Nitride Nanosheets for Polymer Nanocomposites with Enhanced Dielectric Performance

Carbon coated boron nitride nanosheets (BNNSs@C) hybrids with different carbon contents were synthesized by a chemical vapor deposition (CVD) method. The content of carbon in as-obtained BNNSs@C hybrids could be precisely adjusted from 2.50% to 22.62% by controlling the carbon deposition time during the CVD procedure. Afterward, the BNNSs@C hybrids were subsequently incorporated into the polyvinylidene fluoride (PVDF) matrix to fabricate the BNNSs@C/PVDF nanocomposites through a combination of solution and melting blending methods. The dielectric properties of the as-obtained BNNSs@C/PVDF nanocomposites could be accurately tuned by adjusting the carbon content. The resultant nanocomposites could afford a high dielectric constant about 39 (103 Hz) at BNNSs@C hybrids loading of 30 vol %, which is 4.8 times larger than that of pristine BNNSs-filled ones at the same filler loading, and 3.5 times higher than that of pure PVDF matrix. The largely enhanced dielectric performance could be ascribed to the improved interfacial polarizations of BNNSs/carbon and carbon/PVDF interfaces. The approach reported here offers an effective and alternative method to fabricate high-performance dielectric nanocomposites, which could be potentially applied to the embedded capacitors with high dielectric performance.

Smart papers comprising carbon nanotubes and cellulose microfibers for multifunctional sensing applications

Composite nanocoating of cationic polyacrylamide and aqueous dispersion of hydroxyl-functionalized carbon nanotubes (CNTs) with pre-adsorbed alkali lignin on lignocellulose wood microfibers has been developed to produce lightweight, flexible, and electrically conductive paper sheets from a simple, low-cost, and well-established papermaking process. Electron microscopy and Fourier transform infrared spectroscopy revealed the formation of strong interfacial hydrogen bonding between the oxygen-containing functional groups on the CNT surfaces and the hydroxyl groups of the cellulose microfibers. As a result, the mechanical properties of the papers with CNT content as low as 2.5 wt% were greatly improved compared to the pristine materials, with up to 10, 55, and 422% increases in tensile strength, internal bonding strength, and wet strength retention, respectively. The multifunctional sensing behavior of the CNT–cellulose composite papers to tensile strain and liquid water was examined comprehensively. Results show that these papers have superior tensile strain sensitivity compared to conventional foil gauges. Moreover, the water-induced electrical resistance changes can be tailored by the paper composition and resistance variations of more than three orders of magnitude were achieved without any degradation of the sensing performance through cycling. These smart papers provide a low-cost and renewable alternative to petrochemical-based materials for portable electronics and sensing applications.

Influence of Thermal Treatments on the Evolution of Conductive Paths in Carbon Nanotube-Al2O3 Hybrid Reinforced Epoxy Composites

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 epoxys 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 between adjacent CNTs were reduced gradually. This study can provide insight into the evolution of conductive paths in the interfacial regions from a more straightforward perspective.