On the origin of the electrical response of vapor grown carbon nanofiber + epoxy composites

The origin of the electrical response of vapor grown carbon nanofiber (VGCNF) + epoxy composites is investigated by studying the electrical behavior of VGCNF with resin, VGCNF with hardener and cured composites, separately. It is demonstrated that the onset of the conductivity is associated to the emergence of a weak disorder regime. It is also shown that the weak disorder regime is related to a hopping depending on the physical properties of the polymer matrix.

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures.

The influence of matrix mediated hopping conductivity, filler concentration, aspect ratio and orientation on the electrical response of carbon nanotube/polymer nanocomposites

A model to simulate the conductivity of carbon nanotube/polymer nanocomposites is presented. The proposed model is based on hopping between the fillers. A parameter related to the influence of the matrix in the overall composite conductivity is defined. It is demonstrated that increasing the aspect ratio of the fillers will increase the conductivity. Finally, it is demonstrated that the alignment of the filler rods parallel to the measurement direction results in higher conductivity values, in agreement with results from recent experimental work.

Coating carbon nanotubes with a polystyrene-based polymer protects against pulmonary toxicity.

BACKGROUND: carbon nanotubes (CNT) can have adverse effects on health. Therefore, minimizing the risk associated with CNT exposure is of crucial importance. The aim of this work was to evaluate if coating multi-walled CNT (MWCNT) with polymers could modify their toxicity, thus representing a useful strategy to decrease adverse health effects of CNT. We used industrially-produced MWCNT uncoated (NT1) or coated (50/50 wt%) with acid-based (NT2) or polystyrene-based (NT3) polymer, and exposed murine macrophages (RAW 264.7 cell line) or Balb/c mice by intratracheal administration. Biological experiments were performed both in vitro and in vivo, examining time- and dose-dependent effects of CNT, in terms of cytotoxicity, expression of genes and proteins related to oxidative stress, inflammation and tissue remodeling, cell and lung tissue morphology (optical and transmission electron microscopy), and bronchoalveolar lavage fluid content analysis.RESULTS: extensive physico-chemical characterization of MWCNT was performed, and showed, although similar dimensions for the 3 MWCNT, a much smaller specific surface area for NT2 and NT3 as compared to NT1 (54.1, 34 and 227.54 m(2)/g respectively), along with different surface characteristics. MWCNT-induced cytotoxicity, oxidative stress, and inflammation were increased by acid-based and decreased by polystyrene-based polymer coating both in vitro in murine macrophages and in vivo in lung of mice monitored for 6 months.CONCLUSIONS: these results demonstrate that coating CNT with polymers, without affecting their intrinsic structure, may constitute a useful strategy for decreasing CNT toxicity, and may hold promise for improving occupational safety and that of general the user.

Thermal characterization of doped polyaniline and its composites with CoPc

Thermal diffusivity of the composites of camphor sulphonic acid (CSA) doped polyaniline (PANI) and its composites with cobalt phthalocyanine (CoPc) has been measured using open cell photoacoustic technique. Analysis of the data shows that the effective thermal diffusivity value can be tuned by varying the relative volume fraction of the constituents. It is seen that polaron assisted heat transfer mechanism is dominant in CSA doped PANI and these composites exhibit a thermal diffusivity value which is intermediate to that of CSA doped PANI and CoPc. The results obtained are correlated with the electrical conductivity and hardness measurements carried out on the samples

Thermal characterization of doped polyaniline and its composites with CoPc

Thermal diffusivity of the composites of camphor sulphonic acid (CSA) doped polyaniline (PANI) and its composites with cobalt phthalocyanine (CoPc) has been measured using open cell photoacoustic technique. Analysis of the data shows that the effective thermal diffusivity value can be tuned by varying the relative volume fraction of the constituents. It is seen that polaron assisted heat transfer mechanism is dominant in CSA doped PANI and these composites exhibit a thermal diffusivity value which is intermediate to that of CSA doped PANI and CoPc. The results obtained are correlated with the electrical conductivity and hardness measurements carried out on the samples.

Single-wall carbon nanotubes modified with organic dyes: Synthesis, characterization and potential cytotoxic effects

This work deals with the covalent functionalization of single-wall carbon nanotubes (SWNTs) with phenosafranine (PS) and Nile Blue (NB) dyes. These dyes can act as photosensitizers in energy and electron transfer reactions, with a potential to be applied in photodynamic therapy. Several changes in the characteristic Raman vibrational features of the dyes suggest that a covalent modification of the nanotubes with the organic dyes occurs. Specifically, the vibrational modes assigned to the NH(2) moieties of the dyes are seen to disappear in the SWNT-dye nanocomposites, corroborating the bond formation between amine groups in the dyes and carboxyl groups in the oxidized nanotubes. The X-ray absorption (XANES) data also show, that the intense band at 398.6 eV attributed to 1s -> 2p pi* transition of the nitrogen of the aromatic PS ring, is shifted due to the bonding with the carbonic structure of the SWNTs. The cytotoxicity data of dyes-modified SWNT composites in the presence and absence of light shows that the SWNT-NB (4 mu g/mL) composite presents a good photodynamic effect, namely a low toxicity in the dark, higher toxicity in the presence of light and also a reduced dye photobleaching by auto-oxidation. (C) 2010 Elsevier B.V. All rights reserved.

Nanostructured films from phthalocyanine and carbon nanotubes: Surface morphology and electrical characterization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Carbon nanotubes/polyamide 6.6 nanostructured composites crystallization kinetic study

Compared with the traditional composites, the incorporation of carbon nanotubes into polymeric matrices can generate materials with superior properties, especially thermal, electrical and tribological properties. The aim of this study was to study the polyamide 6.6/carbon nanotubes (PA 6.6/CNT) nanostructured composites crystallization kinetics. The solution mixing technique was used to obtain the nanostructured composites studied in this work. PA 6.6 films were produced with amounts of 0.1, 0.5, and 1.0 wt% (weight/weight) CNT. X-ray diffraction analyses were performed in order to determine the crystallographic properties of nanostructured composite. The nanostructured composites crystallization kinetic study was performed using the differential scanning calorimetry under isothermal and nonisothermal (dynamic) conditions. The results have shown addition of CNTs in the PA 6.6 reduces the Avrami exponent, affecting the crystallization process of the composite. © The Author(s) 2012.

Viscoelastic Behavior of Multiwalled Carbon Nanotubes into Phenolic Resin

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nonoxidative thermal degradation kinetic of polyamide 6,6 reinforced with carbon nanotubes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conductive Polymer Composites

In recent years, nanotechnologies have led to the production of materials with new and sometimes unexpected qualities through the manipulation of nanoscale components. This research aimed primarily to the study of the correlation between hierarchical structures of hybrid organic-inorganic materials such as conductive polymer composites (CPCs). Using a bottom-up methodology, we could synthesize a wide range of inorganic nanometric materials with a high degree of homogeneity and purity, such as thiol capped metal nanoparticles, stoichiometric geomimetic chrysotile nanotubes and metal dioxide nanoparticles. It was also possible to produce inorganic systems formed from the interaction between the synthesized materials. These synthesized materials and others like multiwalled carbon nanotubes and grapheme oxide were used to produce conductive polymer composites. Electrospinning causes polymer fibers to become elongated using an electric field. This technique was used to produce fibers with a nanometric diameter of a polymer blend based on two different intrinsically conducting polymers polymers (ICPs): polyaniline (PANI) and poly(3-hexylthiophene) (P3HT). Using different materials as second phase in the initial electrospun polymer fibers caused significant changes to the material hierarchical structure, leading to the creation of CPCs with modified electrical properties. Further study of the properties of these new materials resulted in a better understanding of the electrical conductivity mechanisms in these electrospun materials.

Multiscale-fiber-reinforced thermoplastic composites incorporating carbon nanotubes: A review

This article reviews recent literature on hierarchical thermoplastic-based composites that simultaneously incorporate carbon nanotubes (CNTs) and conventional microscale fibers, and discusses the structure?property relationships of the resulting hybrids. The mixing of multiple and multiscale constituents enables the preparation of materials with new or improved properties due to synergistic effects. By exploiting the outstanding mechanical, thermal and electrical properties of CNTs, a new generation of multifunctional high-performance composites suitable for a wide variety of applications can be developed.

Nanotube-polymer composites for ultrafast photonics

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Synthesis of copper carbon nanotube composite and its electrical conductivity measurement

The matrices in which Multi Walled Carbon Nanotubes (MWCNTs) are incorporated to produce composites with improved electrical properties can be polymer, metal or metal oxide. Most composites containing CNTs are polymer based because of its flexibility in fabrication. Very few investigations have been focused on CNT-metal composites due to fabrication difficulties, such as achievement of homogeneous distribution of MWCNTs and poor interfacial bonding between MWCNTs and the metal matrix. In an effort to overcome poor interfacial bonding for the Cu - MWCNT composite, silver (Ag) and nickel (Ni) resinates have been incorporated in the ball milling stage. Composites of MWCNT (16, 12, and 8 Vol %) - Cu+Ag+Ni were pelleted at 20,000 psi (669.4 Mpa) and sintered at 950 °C. The electrical conductivity results measured by four probe meter showed that the conductivity decreases with increase in the porosity. Moreover from these results it can also be stated that an addition of optimum value of (12 Vol %) MWCNT leads to high electrical conductivity (9.26E+07 s-m"), which is 50% greater than the conductivity of Cu. It is anticipated that the conductivity can be increased substantially with hot isostatic pressing of the pellet.