Electrical, dielectric and surface wetting properties of multi-walled carbon nanotubes/nylon-6 nanocomposites

This paper reports that the multi-walled carbon nanotubes(MWCNT)/nylon-6 (PA6) nanocomposites with different MWCNT loadingshave been prepared by a simple melt-compounding method. Theelectrical, dielectric, and surface wetting properties of theCNT/PA6 composites have been studied. The temperature dependence ofthe conductivity of the CNT/PA6 composite with 10.0 wt{\%} CNTloading ($\sigma _{\rm RT} \sim 10^{-4}$ S/cm) are measured, andafterwards a charge-energy-limited tunnelling model (ln $\sigma (T)\sim T^{-1/2})$ is found. With increasing CNT weight percentage from0.0 to 10.0 wt%, the dielectric constant of the CNT/PA6composites enhances and the dielectric loss tangent increases twoorders of magnitude. In addition, water contact angles of theCNT/PA6 composites increase and the composites with CNT loadinglarger than 2.0 wt%even become hydrophobic. The obtainedresults indicate that the electrical and surface properties of thecomposites have been significantly enhanced by the embedded carbonnanotubes.     

Synthesis, characterizations and applications of some nanomaterials (TiO2 and SiC nanostructured films, organized CNT structures, ZnO structures and CNT-blood platelet clusters)

TiO₂ nanostructured films have been synthesized by the hydrolysis of Ti[OCH(CH₃)₂]₄ as the precursor. These films have been utilized for the dissociation of phenol contaminant in water. Free-standing nanostructured film of silicon carbide (SiC) has been synthesized, employing a simple and new route of spray pyrolysis technique utilizing a slurry of Si in hexane. Another study is done on organized carbon nanotube (CNT) structures. These are made in the form of hollow cylinders (50 mm length, 4 mm diameter and 1.5 mm wall thickness). These CNT-based cylinders are made of conventional CNT and bamboo-shaped CNT. The filtrations of heavy hydrocarbons andE. coli bacteria from water have been carried out. In addition to this, ZnO nanostructures have also been studied. Another study concerns CNT-blood platelet clusters.     

Electronic behavior of visible light sensitive ZrO2/Cr2O3/carbon clusters composite materials

Nano-sized ZrO₂/Cr₂O₃/carbon clusters composite materials were successfully obtained by the microwave-irradiated calcinations of a Zr(acac)₄/Cr(acac)₃/epoxy resin complex. The compositions of the resulting composite materials were determined using ICP, elemental analysis and surface characterization by XRD, SEM and TEM. The UV–Vis spectra of the composites were also obtained. ESR spectral examinations of the composites indicate that an electron transfer takes place in the process Cr₂O₃ → carbon clusters → ZrO₂. The composite materials have been found to show visible light-responsive catalytic activities.     

Rapid microwave-assisted synthesis and electrochemical characterization of gold/carbon nanotube composites

Hybrid nanostructures composed of gold nanoparticles (NPs) and carbon nanotubes (CNTs) have been prepared by a microwave-assisted method in the mixed solvents of oleylamine and oleic. The morphology, structure and composition of as-obtained Au/CNT composites are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD). The composites show characteristic plasmon absorption of Au NPs in the Ultraviolet–visual spectrum. Fourier transform infrared spectrum shows the successful introduction of functional groups on the surface of CNTs, which are crucial factors to assist the nucleation in situ of Au NPs on the surface of CNTs. Electrochemical measurements show the enhancement electrochemical response for the gold electrode modified with Au/CNT composites.     

The interaction between unique hyperbranched polyaniline and carbon nanotubes,and its influence on the dielectric behavior of hyperbranched polyaniline/carbon nanotube/epoxy resin composites

Novel hybridized multi-walled carbon nanotubes (CNTs), consisting of a unique hyperbranched polyaniline (HSiPA) and CNTs, were prepared. The interaction between HSiPA and CNTs was investigated by many techniques, and results show that there are strong π–π and electrostatic interactions between HSiPA and CNTs, so HSiPA can stack firmly onto the surface of CNTs to form a coating. Based on this, a new kind of ternary composites made up of hybridized CNTs and epoxy (EP) resin was prepared, the influence of the ratio of HSiPA to CNTs on the structure and properties of the HSiPA/CNT/EP composites was intensively studied. The percolation threshold of HSiPA/CNT/EP composites is very low (1.26 wt%); besides, with a suitable ratio of HSiPA to CNTs, the HSiPA/CNT/EP composite has much higher dielectric constant and lower dielectric loss than the CNT/EP composite with the same loading of CNTs. When the ratio of HSiPA to CNTs is 0.5:1, the dielectric constant and loss at 100 Hz of the resultant HSiPA/CNT0.5/EP composite are 711 and 1.53, about 7.1 and 4.3 × 10^?3 times the corresponding value of CNT0.5/EP composite, respectively. In addition, compared with traditional CNT/EP composites, the HSiPA/CNT0.5/EP composites have different equivalent circuit models. These attractive results are attributed to unique structure of hybridized CNTs, and thus leading to greatly different structures between the CNT0.5/EP and HSiPA/CNT0.5/EP composites. This investigation reported herein suggests a new approach to prepare new CNTs and related composites with controllable dielectric properties.     

Synthesis and characterization of TiO2/MoO3/carbon clusters composite material

Nano-sized TiO₂/MoO₃/carbon clusters composite material has been successfully obtained by the calcinations of a TiO(acac)₂/MoO₂(acac)₂/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ultraviolet–visible (UV–Vis), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectra of the composite materials suggest that they have visible light-responsive catalytic ability with an electron transfer process of carbon clusters → MoO₃ → carbon clusters → TiO₂.     

Interphase phenomena in superconductive polymer-ceramic nanocomposites

Dynamic mechanical properties (elastic moduli, phase angle) for superconducting (SC) polymer–ceramic composites based on Y₁Ba₂Cu₃O_7?x SC oxide ceramic and superhighmolecular polyethylene have been investigated. The analysis of the obtained data shows a strong interaction of the polymeric binder with the surface of the ceramic grains. It is concluded that changes of packing and structure of the macromolecules occur at the ceramic–polymer interface. This is confirmed by melting enthalpy measurements of SC polymer–ceramic composites of different filler content. Scanning electron microscopy studies of the high temperature SC composites showed that the ceramic grains are evenly covered by the binder for both amorphous and crystalline polymers. EPR (electron paramagnetic resonance) spectra of polymer–ceramic composites have shown that the intensity of the EPR signals of Cu²⁺(1) depends on the nature and the content of binder. The Mn, Co, Zn, Ni containing superconducting composites have been obtained by frontal polymerization.     

Synthesis and characterization of LiMn1-x Fe x PO4/carbon nanotubes composites as cathodes for Li-ion batteries

Carbon nanotubes (CNT) coated with LiMn_1-x Fe _x PO₄ (0.2?≤?x?≤?0.8), as possible cathode materials, was synthesized by using a sol–gel process (Polyol method), after annealing under flowing nitrogen. X-ray diffraction (XRD) patterns of the composites confirmed the formation of the olivine structured LiMn_1-x Fe _x PO₄ phase and no secondary phases were detected. The morphological investigation revealed the formation of agglomerates with particles size ranging between 300 and 700 nm. XRD investigation of composites shows difference of the morphology by doping CNT and carbon black in the composites. Transmission electron microscopy shows the growth of nano-sized particles on CNT (20–70 nm) and the agglomeration of primary particles to form secondary particles. The X-ray photoelectron spectroscopy showed that the Fe and Mn ions are in divalent states in the LiMn_1-x Fe _x PO₄ composites. The cyclic voltamograms showed the oxidation peaks of iron and manganese ions at 3.53–3.63 and 4.05–4.33 V, respectively, while the reduction peaks were found at 3.21–3.42 V (iron reduction) and 3.85–3.93 V (manganese reduction) depending on the iron content in the composition. The LiMn_0.6Fe_0.4PO₄/CNT composite (x?=?0.4) (with 20 %?wt CNT) delivered a specific capacity of 120 mAhg^?1 (at a discharge rate of C/20 and RT).     

Optical properties of TiO2 anatase - Carbon nanotubes composites studied by cathodoluminescence spectroscopy

Luminescence spectra obtained by electron bombardment (cathodoluminescence, CL) on TiO₂ (anatase)/carbon nanotubes (CNT) composite, show only one visible band at 498 nm, while the spectra taken from pure anatase samples show two bands at 498 and 545 nm. We demonstrate that the visible luminescence bands are originated by TiO₂ surface defects due to oxygen vacancies, and that this luminescence signal is independent of TiO₂ mineral form (anatase or rutile). Moreover we obtain that the 545 nm band quenching in TiO₂/CNT composites is caused by empty oxygen vacancies (OV) related to oxygen given from oxygen-rich pristine powder of carbon nanotubes. Our conclusions are also supported by X-ray photoelectron spectroscopy (XPS), SEM analysis and energy dispersed X-ray measurements (EDX). Furthermore we can confirm that the NIR TiO₂ luminescence emission is linked only to the presence of Ti rutile form as described in several works in literature.     

Roughness and fibre reinforcement effect onto wettability of composite surfaces

Wettability of glass/epoxy and carbon/epoxy composites materials has been determined via sessile drop technique. Good-Van Oss approach has been used to evaluate surface free energy parameters of smooth and rough surfaces. Results obtained point out the influence of fibre reinforcement on surface free energy of composite materials. In addition, the interest of surface treatment to increase surface roughness has been discussed in terms of wettability. To sum up, results obtained clearly demonstrate the necessity of considering properties of a given composite surface not only as a polymer but a fibre/polymer couple. The drawn conclusions are of great interest as it may have numerous consequences in applications such as adhesion.     

Characterization and relative sonocatalytic efficiencies of a new MWCNT and CdS modified TiO2 catalysts and their application in the sonocatalytic degradation of rhodamine B

TiO₂ nanoparticles modified with MWCNTs and CdS were synthesized by the sol–gel method followed by solvothermal treatment at low temperature. The chemical composition and surface structure of the CdS/CNT–TiO₂ composites were investigated by X-ray diffraction, specific surface area measurements, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. Then a series of sonocatalytic degradation experiments were carried out under ultrasonic irradiation in the presence of CNT/TiO₂ and the CdS/CNT–TiO₂ composites. It was found that RhB was quickly and effectively degraded under different ultrasonic conditions. As expected, the nanosized CdS/CNT–TiO₂ photocatalyst showed enhanced activity compared with the non CdS treated CNT/TiO₂ material in the sonocatalytic degradation of RhB. The sonocatalyst CCTb with 34.68% contents of Ti heat treated at 500 °C for 1 h showed the highest sonocatalytic activity. The synergistic effect of the greater surface area and catalytic activities of the composite catalysts was examined in terms of their strong adsorption ability and interphase interaction by comparing the effects of different amounts of MWCNTs and CdS in the catalysts and their roles. The mechanism of sonocatalytic degradation over the CdS/CNT modified TiO₂ composites under different ultrasonic conditions was also discussed.     

Atomic structure and ionic conductivity of glassy materials based on silver sulfide

The effect of the composition of glassy ionic conductors AgGe_{1 + x} As_1–x S₃ and the composites based on these materials containing single-walled carbon nanotubes (CNT) AgGe_1+x As_1–x (S + CNT)₃, on the atomic structure and ionic conductivity is analyzed.     

Fabrication of Fe/Fe<Subscript>3</Subscript>C-functionalized carbon nanotubes and their electromagnetic and microwave absorbing properties

Fe/Fe₃C-functionalized carbon nanotubes (CNTs) have been prepared by the floating catalyst chemical vapor-deposition method. It is demonstrated that the Fe and Fe₃C nanostructures are both encapsulated in the CNTs or decorated on the surface of CNTs. The Fe/Fe₃C content in the composites can easily be adjusted by changing the ferrocene concentration in the preparation. The electromagnetic properties of the CNTs have been evaluated in the frequency range of 2–18 GHz, and the nanocomposites exhibit excellent microwave absorbing performance. The CNT composites with higher Fe/Fe₃C content show enhanced microwave reflection losses. The significant influence of the Fe/Fe₃C nanostructures on the microwave absorption is realized by tuning the characteristic impedance of the nanocomposites. With increasing thickness, the maximum reflection loss peak shifts to lower frequency. The microwave absorbing performance of the composites is mainly caused by dielectric loss, resulting from the continuous CNT networks with excellent electrical conductivity.     

The percolation staircase model and its manifestation in composite materials

We studied the tunneling percolation conductivity dependence on the site or bond occupation probability in the square lattice. The model predicts that in both, lattice and continuum systems in which there is a hierarchy of the local conductances, the dependence of the global conductivity on the site or volume occupation probability will yield a conductivity staircase. In particular we evaluate the implications of the staircase on the critical behavior of the conductivity. We then show experimental evidence for the predicted percolation-tunneling staircase in a Ag-Al₂O₃ granular metal system and in a carbon black-polymer composite. Following that, we propose that for carbon nanotube (CNT) polymer composites the data in the literature give ample support to a percolation-dispersion staircase behavior. The implication of the present findings on the percolation-hopping problem in composite materials is also discussed.     

Electrogenerated chemiluminescence of luminol at a carbon nanotube-perfluorosulfonate polymer (Nafion) modified gold electrode

A multi-wall carbon nanotube/Nafion modified gold electrode (CNT/Nafion/GE) was fabricated by casting the composite film on the electrode surface. Electrogenerated chemiluminescence (ECL) of luminol at the modified gold electrode was studied under conventional cyclic voltammetry in alkaline Na₂CO₃-NaHCO₃ buffer solution. Three ECL peaks were obtained. The most strong ECL peak (ECL-1) was enhanced about 20-fold at the CNT/Nafion modified gold electrode compared with that at the bare gold electrode. The emitter of all the ECL peaks was indentified as 3-aminophthalate. The intensities of ECL peaks were found to depend on the ratio of CNT/Nafion, the electrolytes, the pH, and the presence of O₂ and N₂. The mechanisms of all ECL peaks have been proposed. The results indicate that carbon nanotubes have a significantly catalytic effect on luminol ECL, which might further expand the analytical application of nanomaterial-modified electrode in the field of electrogenerated chemiluminescence.     

Purification of carbon nanotubes grown by thermal CVD

We show the results of a set of purifications on carbon nanotubes (CNT) by acid and basic treatments. CNTs were obtained by thermal decomposition of camphor at 850 °C in a CVD growth system, by means of a growth process catalyzed by iron clusters originating from the addition of ferrocene in the precursors mixture. The purification procedures involved HNO₃, H₂SO₄, HSO₃Cl and NaOH for different process temperatures.As-grown CNTs showed a consistent presence of metal catalyst (about 6 wt%), evidenced by TGA. The purification treatments led to a certain amount of opening of the CNT tips, with a consequent loss of metal catalyst encapsulated in tips. This is also confirmed by BET analysis, which showed an increase of the surface area density of CNT after the purification.FT-IR and XPS revealed the presence of carboxylic groups on the CNT surface chemically modified by the harsh environment of the purification process.Among the various treatments that have been tested, the 1:3 solution of nitric and sulphuric acid was the most effective in modifying the CNT surface and inducing the formation of functional groups.     

Enhanced β Crystalline Phase in Poly(vinylidene fluoride) via the Incorporation of Graphene Oxide Sheets assisted by Supercritical CO2 Treatment

Graphene oxide (GO) sheets were pre-modified with a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF), using a simple supercritical carbon dioxide (SC CO₂) method, and then the PVDF-decorated GO was added into a PVDF matrix by solution blending. Transmission electron microscopy (TEM) revealed that the decorating degree of PVDF on the surface of the GO increased significantly with increasing of SC CO₂ pressure and PVDF concentration. The mechanism of the polymer adsorption on the GO sheets through favorable interaction between the GO and PVDF chains was identified via Fourier transform infrared spectroscopy (FTIR). Further, the crystallization behavior of PVDF/GO composites was investigated by differential scanning calorimetry (DSC), FTIR and polarized optical microscopy (POM). Interestingly, the composite with PVDF-decorated GO as the filler showed higher β-phase content compared to the composite with pristine GO as the filler. The study showed that the supercritical fluid-induced epitaxial crystallization process has significant potential for fabricating functional GO-based nanocomposties containing piezoelectric or conducting materials.     

Heat capacity of the white pine biocarbon preform and the related biocarbon/copper composite

This paper reports on measurements in the 80–300-K temperature interval of the heat capacity at constant pressure C _p (T) of high-porosity amorphous white pine carbon preforms (biocarbon) prepared by pyrolysis (carbonization) at T _carb = 1000 and 2400°C in an argon flow. The dependences C _p (T) for biocarbon/copper composites based on the carbon preforms obtained have also been determined. It is shown that the mixture rule holds for the composites, i.e., that C _p (T) of the composite is a sum of the heat capacities of the constituent materials taken in the corresponding ratios. Phonon mean free paths for the white pine carbon preforms prepared at T _carb = 1000 and 2400°C have been calculated and used to estimate the size of the nanocrystallites contributing to formation of the carbon frameworks of these preforms.     

Synthesis and characterization of ZrO2/MnO2/carbon clusters nanocomposite materials

Nano-sized ZrO₂/MnO₂/carbon clusters composite materials has been successfully obtained by the calcination of a Zr(acac)₄/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). The ultraviolet–visible (UV–VIS), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectral examinations suggest the possibility of an electron transfer in the process of MnO₂ → carbon clusters → ZrO₂. The visible light-responsive oxidation–reduction ability of the calcined material was also investigated.     

Preparation and characterization by infrared emission spectroscopy and applications of new mineral-based composite materials of biomedical interest

New composite materials based on clay minerals had been prepared by reductive calcination. These materials exhibit very strong infrared (IR) emission at quite low temperatures. The structural properties and emission capabilities of the new materials have been studied by various theoretical and experimental methods. In addition, a brief overview of the medical and other practical applications of IR-emitting materials is presented. The basic principles of IR emission spectroscopy are discussed with special respect to low temperatures (close to human-body temperature). Furthermore, DFT calculations on a kaolinite structure of chemical composition of [Al₄Si₄ O₈(OH)₁₆]^4? have been performed. The calculated bond distances and IR spectrum are in good agreement with experimental observations. Structural and compositional characterization of the new composite materials have been performed by various structural analytical methods. An interesting effect on the IR phosphorescence of composite samples has been established. After 2 hours of IR light exposure at room temperature from the FT-IR spectrometer, the composite materials exhibited enhanced emission of IR radiation with relaxation time about 40 min. Finally, two practical applications of the composites have been investigated, namely polyamide-based fabrics and rubber preservatives.