Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10−1 S·m−1 for a carbon nanotubes loading near 0.12 wt.%

High electrically conductive composites of Polyamide 11 filled with silver nanowires: Nanocomposites processing, mechanical and electrical analysis

Highly conductive composites of silver nanowires and semicrystalline polyamide 11 for different content were prepared. A newmethod was developed to introduce nanowires: a combination of solventway and an extrusion process. This technic provides pellets of composites directly suitable for sample molding. The silver nanowires poured in polyamide 11 were obtained by polyol process to reach large volume of nanowires. The dispersion of nanowires was evaluated by scanning electron microscopy and confirmed by a very lowpercolation threshold around 0.59 vol.%. The level of conductivity above the percolation threshold is about 102 S m−1. Differential scanning calorimetry and dynamic mechanical analyses have shown a stability of the composite physical structure and an optimization of the mechanical properties as a function of nanowires content until 3.6 vol.%. A simultaneous enhancement of the electrical conductivity of polyamide 11 was obtained

Mechanical improvement of P(VDF-TrFE)/nickel nanowires conductive nanocomposites: Influence of particles aspect ratio

Nickel nanowires with high aspect ratio (250) were elaborated and incorporated into poly(vinylidene difluoride-trifluoroethylene) up to 30 vol% via solvent mixing way. These nanocomposites are characterized by a conductive behavior with a high electrical conductivity value (102 S m−1) above a very low percolation threshold (0.75 vol% of metallic nanowires). The introduction of nanowires strongly depressed the matrix crystallinity. Static and dynamic mechanical analysis have been realized at low nanowire volume fraction (< 10 vol%). Below 5 vol% of nanowires, nanocomposites remain ductile. The dynamic mechanical properties are related to the volume fraction of nanowires. A strong increase of the viscoelastic contribution related to the increase of the percentage of amorphous phase is observed. The major effect is the increase of the rubbery modulus. The highest increase of 300% is obtained for only 5 vol% of nanowires; it represents an original mechanical result for low filled composites. The dependence versus nanowire content has been described by adapting the Halpin–Tsai model to high aspect ratio filler. Metallic nanowires create additional entanglements that are randomly distributed in the rubbery polymeric matrix. With their low percolation threshold, metallic nanowires based nanocomposites constitute a new class of multifunctional materials with a high conductivity associated with a ductile polymer matrix characterized by a high rubbery modulus

Structural and electrical properties of gold nanowires/P(VDF-TrFE) nanocomposites

High aspect ratio gold nanowires were uniformly dispersed into a poly(vinylidene difluoride–trifluoroethylene) [P(VDF-TrFE)] matrix. The nanowires were synthesized by electrodeposition using nanoporous anodic alumina oxide templates. The intrinsic optical conductivity of the gold nanowires was determined by valence electron energy loss spectroscopy. The effect of increasing volume fraction of Au nanowires on the morphology and crystallization of P(VDF-TrFE) matrix was investigated by differential scanning calorimetry. The crystallinity of P(VDF-TrFE) is strongly depressed by the randomly dispersed nanowires. Above 30 vol% the crystallization of P(VDF-TrFE) is suppressed. The bulk electrical conductivity of nanocomposite films, at room temperature, obeys a percolation behaviour at a low threshold of 2.2 vol% and this was confirmed using the surface resistivity value. An electrical conductivity of 100 S m−1 is achieved for a 3 vol% filler content

Low filled conductive P(VDF-TrFE) composites: Influence of silver particles aspect ratio on percolation threshold from spheres to nanowires

Polymer composites filled with silver nanowires enable the highest value of electrical conductivity known up to now in the case of conductive nanoparticle dispersion with a percolation threshold less than 1 vol%. Silver nanowires with high aspect ratio were elaborated by two types of synthesis: electrochemical deposition in a template and polyol synthesis. For the first time the influence of each kind of nanowires in composites was studied and compared to spherical nanoparticles as reference. The value of percolation threshold and conductivity level above the percolation threshold were measured and compared. These silver nanowires were introduced into poly(vinylidenedifluoride-trifluoroethylene) in comparison to spherical silver nanoparticles. The preparation method modified the effective aspect ratio of nanowires. The low percolation threshold and the microscopy observations confirmed the good dispersion of nanowires in composites. The lowest percolation threshold was determined in the case of the polyol synthesis nanowires (0.63 vol%) in comparison with electrochemical deposited nanowires (2.2 vol%). The level of conductivity above the percolation threshold obtained with each kind of particles is in the same range near 100 S.m− 1. The value of electrical conductivity obtained above the percolation threshold is unusual at this low content of conductive filler and is observed for the first time in a conductive polymer composite

Optical properties of metallic nanowires by valence electron energy loss spectroscopy

The determination of intrinsic conductivity of nanowires (NWs) is essential to understand the charge transport behaviour involved in hybrid nanocomposites. These high conductive metallic fillers are good candidate to improve electrical properties of composites in aeronautic industry. The main difficulty is often to achieve the combination of both high spatial resolution and information on the physical properties as electrical conductivity. One of the suitable methods to give the desired information is electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM) mode, especially in the low-loss region. This is demonstrated by studying the nickel and gold nanowire

Natural variation at XND1 impacts root hydraulics and trade-off for stress responses in Arabidopsis

Soil water uptake by roots is a key component of plant performance and adaptation to adverse environments. Here, we use a genome-wide association analysis to identify the XYLEM NAC DOMAIN 1 (XND1) transcription factor as a negative regulator of Arabidopsis root hydraulic conductivity (Lp). The distinct functionalities of a series of natural XND1 variants and a single nucleotide polymorphism that determines XND1 translation efficiency demonstrate the significance of XND1 natural variation at species-wide level. Phenotyping of xnd1 mutants and natural XND1 variants show that XND1 modulates Lp through action on xylem formation and potential indirect effects on aquaporin function and that it diminishes drought stress tolerance. XND1 also mediates the inhibition of xylem formation by the bacterial elicitor flagellin and counteracts plant infection by the root pathogen Ralstonia solanacearum. Thus, genetic variation at XND1, and xylem differentiation contribute to resolving the major trade-off between abiotic and biotic stress resistance in Arabidopsis

Les lésions médullaires traumatiques : épidémiologie et perspectives

AbstractObjectiveSpecify the epidemiological data on the acute spinal cord injuries and define a group of patients that could benefit from cellular transplantation therapy designed with the aim of repair and regeneration of damaged spinal cord tissues.Material and methodsFive years monocentric (Gui-de-Chauliac Hospital, Montpellier, France) retrospective analysis of patients suffering from spinal cord injury (SCI). Spinal cord injured-patients, defined as sensory-motor complete, underwent a clinical evaluation following American Spinal Injury Association (ASIA) and functional type 2 Spinal Cord Independence Measure (SCIM2) scorings as well as radiological evaluation through spinal cord magnetic resonance imaging (MRI).ResultsOne hundred and fifty-seven medical records were reviewed and we selected and re-examined 20 patients with complete thoracic spinal cord lesion. Clinical and radiological evaluations of these patients demonstrated, in 75 % of the cases, an absence of clinical progression after a mean of 49months. Radiological abnormalities were constantly present in the initial (at the admission to hospital) and control (re-evaluation) MRI and no reliable predictive criteria of prognosis had been found.Discussion/ConclusionWe compare our results to the literature and discuss advantages and limits of cellular transplantation strategies for these patients.RésuméObjectifsConnaître les données épidémiologiques de notre région sanitaire sur les traumatismes médullaires. Au sein de cette population, sélectionner les patients susceptibles de bénéficier de thérapie cellulaire dans la moelle épinière lésée dans l’objectif de régénérer le tissu nerveux. Évaluer à distance ces patients.Patients et méthodeAnalyse rétrospective de tous les patients pris en charge pour un traumatisme vertébro-médullaire. Réévaluation clinique et radiologique des patients présentant une atteinte médullaire thoracique sensitivomotrice complète. Réévaluation réalisée par le score de l’American Spinal Injury Association (ASIA), le score fonctionnel Type 2 Spinal Cord Independence Measure (SCIM2) et contrôle radiologique par une IRM médullaire.RésultatsCent cinquante-sept dossiers de patients ont été analysés et 28 patients présentaient une lésion médullaire complète. Une évaluation clinique et radiologique réalisée chez 20 patients sur 28 (71 %) a montré l’absence d’évolution clinique dans 75 % des cas dans un délai moyen de 49 mois. Les anomalies radiologiques étaient présentes dans 100 % des cas sur l’IRM initiale et de contrôle sans qu’aucun critère fiable prédictif de bon pronostic n’est retrouvé.Discussion/conclusionNous présentons ces résultats comparativement à ceux de la littérature et nous discutons chez ces malades les stratégies de transplantation cellulaire, leurs limites actuelles et les progrès nécessaires pour obtenir des résultats

High-performance thermoplastic composites poly(ether ketone ketone)/silver nanowires: Morphological, mechanical and electrical properties

High-performance conductive thermoplastic composites poly(ether ketone ketone) (PEKK)/silver nanowires were elaborated by melt blending. Silver nanowires (AgNWs) with high aspect ratio (ξ~220) were elaborated through the polyol process in presence of poly(vinyl pyrrolidone) (PVP) and ethylene glycol. Scanning electron microscopy observations of nanowires were performed after an adapted cleaning process. The dispersion of NWs in the polymeric matrixwas evaluated. A very lowpercolation threshold of 0.6 vol% was obtained. Electrical conductivity values obtained above the percolation threshold were among the highest measured for low-filled conductive polymer composites. The influence of AgNWs on the PEKK matrix has been investigated by differential scanning calorimetry and dynamic mechanical analyses. It is important to note that thermal and dynamic mechanical performances of the polymeric matrix were preserved in composites

Specific heat capacity and thermal conductivity of PEEK/Ag nanoparticles composites determined by Modulated-Temperature Differential Scanning Calorimetry

The thermal conductivity accurate measurement of polymer based composites is a challenge: it would allow us to understand the mechanisms of thermal transport in such materials. Silver nanoparticles were introduced in Polyetheretherketone matrix and their influence on thermal properties was studied. Thermal conductivity and specific heat capacity of composites were determined by Modulated-Temperature Differential Scanning Calorimetry and analysed as a function of particles volume content and temperature. The specific heat capacity of the composites decreases with increasing silver particles content below the electrical percolation threshold. Above the electrical percolation threshold the specific heat capacity decreases more slowly and converge toward the specific heat capacity of compressed silver nanoparticles. The evolution of the thermal conductivity with filler content exhibits a non-linear profile. Experimental data are coherent with the Maxwell model suggesting continuity of the polymer matrix and a contribution of the silver particles to the effective thermal conductivity greater than volume effect. The temperature dependence of the composites thermal conductivity is characteristic of amorphous phase, while a transition from vitreous-like to crystalline-like behaviour of the specific heat capacity is observed with the introduction of metallic particles