Presence Of Single-walled Carbon Nanotubes Research Articles

A Novel Nanoparticle-Enhanced Photoacoustic Stimulus for Bone Tissue Engineering

In this study, we introduce a novel nanoparticle-enhanced biophysical stimulus based on the photoacoustic (PA) effect. We demonstrate that the PA effect differentiates bone marrow-derived marrow stromal cells (MSCs) grown on poly(lactic-co-glycolic acid) (PLGA) polymer films toward osteoblasts. We further show that the osteodifferentiation of the MSCs due to PA stimulation is significantly enhanced by the presence of single-walled carbon nanotubes (SWCNTs) in the polymer. MSCs, without the osteogenic culture supplements (0.01 M β-glycerophosphate, 50 mg/L ascorbic acid, 10(-8) M dexamethasone), were seeded onto plain glass slides, glass slides coated with PLGA, or glass slides coated with SWCNT-PLGA films and photoacoustically stimulated by a 527 nm Nd:YLF pulse laser, with a 200 ns pulse duration, and 10 Hz pulse frequency for 10 min a day for 15 consecutive days. The study had four control groups; three baseline controls similar to the three experimental groups but without PA stimulation, and one positive control where MSCs were grown on glass slides without PA stimulation but with osteogenic culture supplements. The osteogenic differentiation of all the groups was evaluated using quantitative assays (alkaline phosphatase, calcium, osteopontin) and qualitative staining (alizarin red). After 15 days, the PA stimulated groups showed up to a 350% increase in calcium content when compared with the non-PA stimulated positive control. Further, within the PA stimulated group, the PLGA-SWCNT group had 130% higher calcium values than the PLGA film without SWCNTs. These results were further corroborated by the analysis of osteopontin secretion, alkaline phosphatase expression, and qualitative alizarin red staining of extracellular matrix calcification. The results indicate that PA stimulation holds promise for bone tissue engineering and that the nanomaterials which enhance the PA effect should allow the development of biophysical rather than biochemical strategies to induce osteoinductive properties into tissue engineering scaffolds.

Poly(Butylene Terephthalate)/Single Wall Carbon Nanotubes Composite Nanofibers by Electrospinning

Poly(buthylene terephthalate)(PBT)/single wall carbon nanotubes (SWCNTs) composite nanofibers were prepared by electrospinning. The effect of carbon nanotubes on the morphology, crystallization, and mechanical properties of the electrospun composite nanofibers were investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of SWCNTs resulted in finer nanofibers for lower loading; however, a broader distribution, especially for the higher diameter ranges was found for nanofibers with higher amounts of carbon nanotubes. SWCNTs accelerated crystallization and acted as a nucleating agent; the degree of crystallinity increased with increasing content of SWCNTs, followed by a moderate decrease at higher content. Specific tensile strength and modulus of the PBT/SWCNTs composite nanofibers mats were higher than that of neat PBT nanofibers mat. However, the elongation at break of composite nanofibers mats was lower than that of the neat PBT nanofibers mat.

Incorporation of Single-Walled Carbon Nanotubes into Ferrocene-Modified Linear Polyethylenimine Redox Polymer Films

In this study, we describe the effects of incorporating single-walled carbon nanotubes (SWNTs) into redox polymer-enzyme hydrogels. The hydrogels were constructed by combining the enzyme glucose oxidase with a redox polymer (Fc-C(6)-LPEI) in which ferrocene was attached to linear poly(ethylenimine) by a six-carbon spacer. Incorporation of SWNTs into these films changed their morphology and resulted in a significant increase in the enzymatic response at saturating glucose concentrations (3 mA/cm(2)) as compared to films without SWNTs (0.6 mA/cm(2)). Likewise, the sensitivity at 5 mM glucose was significantly increased in the presence of SWNTs (74 μA/cm(2)·mM) as compared to control films (26 μA/cm(2)·mM). We demonstrate that the increase in the electrochemical and enzymatic response of these films depends on the amount of SWNTs incorporated and the method of SWNT incorporation. Furthermore, we report that the presence of SWNTs in thick films allows for more of the ferrocene redox centers to become accessible. The high current densities of the hydrogels should allow for the construction of miniature biosensors and enzymatic biofuel cells.

High-Performance Hydrogen Production and Oxidation Electrodes with Hydrogenase Supported on Metallic Single-Wall CarbonNanotube Networks

We studied the electrocatalytic activity of an [FeFe]-hydrogenase from Clostridium acetobutylicum (CaH2ase) immobilized on single-wall carbon nanotube (SWNT) networks. SWNT networks were prepared on carbon cloth by ultrasonic spraying of suspensions with predetermined ratios of metallic and semiconducting nanotubes. Current densities for both proton reduction and hydrogen oxidation electrocatalytic activities were at least 1 order of magnitude higher when hydrogenase was immobilized onto SWNT networks with high metallic tube (m-SWNT) content in comparison to hydrogenase supported on networks with low metallic tube content or when SWNTs were absent. We conclude that the increase in electrocatalytic activities in the presence of SWNTs was mainly due to the m-SWNT fraction and can be attributed to (i) substantial increases in the active electrode surface area, and (ii) improved electronic coupling between CaH2ase redox-active sites and the electrode surface.

Carbon nanotubes and silver nanoparticles for multifunctional conductive biopolymer composites

This article fabricates and characterizes the combination of single walled carbon nanotubes (SWCNTs) and silver nanoparticles (Ag) with a biodegradable polymer matrix. Different SWCNT amount were mixed with Ag nanoparticles and introduced in the poly(ε-caprolactone) (PCL) polymer matrix by solvent cast process. Nanostructure synergistic effects were evaluated in terms of morphological, electrical, dielectrical, mechanical and biological properties of binary PCL/Ag, PCL/SWCNTs and ternary PCL/Ag/SWCNTs composites. Results showed a good dispersion of nanostructures in the PCL and an increase of Young modulus with silver content in the binary systems. The PCL/Ag composites exhibited poor electrical properties, while in PCL/Ag/SWCNTs ternary films higher values of conductivity were measured compared to both binary composites. Results obtained in this research indicate that Ag particles facilitate the formation of conductive pathways in the presence of SWCNTs, they act as conductive bridges among nanotube bundles and facilitate the electron transfer. The addition of a small percentage of SWCNTs promoted significantly the electrical properties of PCL/Ag nanohybrid films. Biocompatibility of binary and ternary composites, evaluated by human mesenchymal stem cells-bone marrow derived (hBM-MSCs), suggests that the combination of Ag nanoparticles and SWCNTs with a biodegradable polymer opens new perspectives for biomedical applications.

Carbon nanotubes as photoprotectors of organic dyes: reversible photoreaction instead of permanent photo-oxidation

In this paper we report that single-walled carbon nanotubes (SWNTs) can protect surface adsorbed Rhodamine B (RhB) molecules from permanent photo-oxidation via a reversible reaction. Upon strong light irradiation at 514 nm, the SWNT-adsorbed RhB molecules were switched to a non-fluorescent form, which looked like ordinary bleaching behavior. However, after staying without light for several hours the non-fluorescent dye species turned back to the original fluorescent form. This on/off switching can be considered as a reversible photobleaching process of the dye molecules. Other irreversible photochemical pathways of RhB were strongly prohibited due to the presence of SWNTs, providing the dye molecules with a high resistance against permanent photodegradation. By determining the maximum number of reconvertable RhB molecules per unit length of the nanotubes, we have further proved that this effect only works for the first layer of adsorbed dye molecules on the SWNT surfaces.

Hybridization of Carbon Nanotubes with Si–π Polymers and Attachment of Resulting Hybrids to TiO2 Surface

Abstract The Sonogashira coupling of diethynyldisilanes with dibromopyrene in the presence of single-walled carbon nanotubes (SWNTs) produced soluble hybrid materials of poly(disilanylenediethynylpyrene)s and SWNTs. Ball milling of poly(disilanylenediethynylpyrene)s or poly(disilanylenequinquethienylene) with SWNTs also afforded the polymer–SWNT hybrids. Irradiation of TiO2 electrodes in chloroform solutions of the hybrids led to the attachment of the hybrids to the TiO2 surface via Si–O–Ti bonding. Applications of the hybrid-attached TiO2 electrodes to dye-sensitized solar cells were studied.

Role of single walled carbon nanotubes in improving the efficiency of poly-(3-hexylthiophene) based organic solar cells

Poly-(3-hexylthiophene) (P3HT)—single walled carbon nanotube (SWNT) solar cells were fabricated and compared with single layer P3HT devices. P3HT:SWNT devices were found to have higher efficiencies than P3HT only devices by at least a factor of two. Zero field mobility values of 1.20×10−7 cm2 V−1 s−1 and 5.97×10−7 cm2 V−1 s−1 were calculated from space charge regime for P3HT and P3HT:SWNT, respectively. The SWNTs were predominantly of metallic nature, as revealed by Raman spectroscopy. Morphology studies show that the SWNTs increase local ordering of P3HT nanocrystals which can improve hole transport. They also show that the cathode-organic surface roughness and volume increase in the presence of SWNTs which can have significant positive effect on charge generation and collection at this interface. Variation in short circuit current with incident light intensity shows higher superlinear slope with SWNTs which also indicates that SWNTs aid in charge extraction from the device.

Electrochemical sorption of hydrogen in single-wall carbon nanotubes encapsulated in palladium

The distribution of hydrogen in the palladium matrix and single-wall carbon nanotubes (SWCNs) in Pd-SWCN nanocomposite upon electrochemical hydrogenation is quantitatively studied in situ using voltammetry and chronoammetry. The high mobility of hydrogen in nanotubes is discovered and reflected in the low H-SWCN bond energy, which equals 0.073 ± 0.05 eV/H-atom and is close to the hydrogen activation energy (ɛH = 0.072–0.08 eV/H-atom) obtained using vacuum thermal desorption [7]. The presence of SWCN is shown to increase the hydrogen capacity of the Pd-SWCN composite compared to individual palladium by nearly 25%. The hydrogen storage capacity of nanotubes (CH) in Pd-SWCN composite increases with an increase in the Pd-to-SWCN volume ratio (V(Pd)/V(SWCN)). CH reaches the maximum limiting value of 12 wt % at V(Pd)/V(SWCN) > 12.

Oxidation Reactions Mediated by Single-Walled Carbon Nanotubes in Aqueous Solution

How single-walled carbon nanotubes (SWCNT) function in redox reactions may be related to their behaviors in the induction of oxidative stress. Herein, oxidation of several biologically relevant reducing agents in the presence of SWCNT was studied in aqueous solutions. The selected reductants included a common indicator for intracellular reactive oxygen species (ROS) (2,7-dichlorodihydrofluorescein), small antioxidants (vitamin C, Trolox, and cysteine), and a high-molecular-weight ROS scavenger (bovine serum albumin). The unmodified or carboxylated SWCNT acted as both the oxidants and the catalysts in reactions. Moreover, they accelerated the oxidation reactions mediated by horseradish peroxidase, a representative member of the enzyme family actively involved in balancing oxidative stress. These diverse roles in redox reactions may serve the chemistry basis for SWCNT to induce oxidative stress in biological systems as potential environmental pollutants.

A Study on the Chain−Particle Interaction and Aspect Ratio of Nanoparticles on Structure Development of a Linear Polymer

The stability of metastable flow-induced precursor (FIPs) in the polymer melts in presence of nanoparticles, viz. single-walled carbon nanotube (SWCNT) and zirconia nanoparticles, is studied at, 142 °C, close to the equilibrium melting point of unconstrained extended chain crystals of linear polyethylene (PE). The results conclusively demonstrate the influence of chain−particle interactions, between PE and the nanoparticles, on the stretch of the long chains. With the applied flow, SWCNTs together with PE chains are observed to align along the flow direction, giving rise a strong streak like pattern along the equator. At the initial stages, intensity of the observed streak in the presence of SWCNTs is stronger than that for the neat polyethylene. The streak intensity stabilizes with time, where the time required for the stabilization depends on the amount of the dispersed nanotubes in the polymer matrix. On the contrary, in the presence of zirconia nanoparticles, where the chain−particle interactions between PE and the nanoparticles are weak the initially observed streak tends to disappear with time, where the time required is strongly dependent on the concentration of the nanoparticles in the polymer matrix. Thus, compared to the neat polymer, the presence of zirconia nanoparticles destabilizes the shish formation. The chain orientation along the flow direction is determined using Herman’s orientation function and the length of the oriented chains (shish) by Ruland’s streak analysis. On cooling, with the crystallization of the polymer, scattering develops along the meridian, indicating the development of folded chain crystals, where the oriented chains present along the flow direction provide the epitaxy matching thus suppressing the nucleation barrier. The meridional intensity (arising with the formation of crystals, called kebabs) at room temperature, shows strong dependence on the stable streak intensity (chain orientation along the flow direction, called shish) along the equator prior to cooling.

Influence of shear in the crystallization of polyethylene in the presence of SWCNTs

It is well accepted that due to epitaxy matching, carbon nanotubes are good nucleating agent for linear polyethylene. We demonstrate that not only in the quiescent conditions but also at the relatively low shear rates the presence of single-walled carbon nanotube (SWCNT) accelerates the crystallization kinetics of polyethylene (PE). The influence of SWCNTs on the crystallization kinetics in the quiescent condition is followed with the help of rheological and differential scanning calorimetry studies. The influence of flow on the stretch of the polymer chain is probed using time-resolved small-angle X-ray scattering (SAXS) and is verified with the Deborah number. SAXS data indicates that the strong shearing conditions (shear rate > 50/s for 1 s) are requisite to form shish-kebab structure in the neat polymer. However, for the low shear (shear rate < 50/s for 1 s), the shish-kebab structure that arises due to chain orientation is enhanced in the presence of SWCNTs. The development of oriented structures in SWCNT/PE composites and their absence in the neat polymer under low shear rate indicates that the presence of SWCNTs plays a significant role in the chain orientation. Overall, the results manifest the influence of SWCNTs on chain relaxation of the polymer.

Label‐Free Colorimetric Detection of Single Nucleotide Polymorphism by Using Single‐Walled Carbon Nanotube Intrinsic Peroxidase‐Like Activity

Single-walled carbon nanotubes (SWNTs) have been considered to be leading candidates for nanodevice applications and novel drug delivery. Intriguingly, recent studies have shown that SWNTs have catalytic activity even in the absence of catalytic factors. Since hydrogen peroxide is an important oxidizing agent in biological systems, the catalytic reaction of SWNTs with H2O2 has received much attention. The SWNT catalytic mechanism is much debated, but it has been suggested that it is related to trace amounts of metal catalyst in SWNTs. H2O2 is a major reactive oxygen species in living organisms, and its overproduction is implicated in the development of numerous inflammatory diseases, such as atherosclerosis, chronic obstructive pulmonary disease, and hepatitis. Furthermore, as a product of many enzyme-catalyzed reactions, H2O2 can act as an indicator to monitor the quantity of biologically important molecules, such as glucose. Therefore, studying the catalytic reaction of SWNTs with H2O2 might offer a promising application for disease diagnosis and for the design of SWNT-based sensors. In this work, we report that SWNTs possess intrinsic peroxidase-like activity. That the catalytic activity does not depend on trace amounts of metal catalyst in the SWNTs is evidenced by energy-dispersive X-ray (EDX) analysis. In the presence of H2O2, SWNTs catalyze the reaction of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) thereby producing a color change (Scheme 1). Our results indicate that the catalytic efficiency of SWNTs is strongly dependent on pH, temperature, and H2O2 concentration, similar to horseradish peroxidase (HRP). More importantly, we compared the catalytic efficiency of SWNTs containing different amounts of cobalt residues. The results clearly show that the observed “catalytic” effect of SWNTs can be attributed to their intrinsic properties rather than metal residues. Peroxidase activity has a great potential for practical application and has been used in the bioremediation of waste water or as diagnostic kits. As peroxidase mimics, SWNTs were used here for label-free colorimetric detection of disease-associated single-nucleotide polymorphism (SNP) with a direct detection limit of 1 nm based on the color reaction of TMB. It is well known that SNP detection is very important, and different kinds of detection methods have been reported; however, to our knowledge, this is the first demonstration of applying intrinsic SWNT peroxidase-like activity and color change for this purpose. This work will provide new insights into the utilization of SWNT peroxidase-like activity. To increase SWNT solubility in aqueous solution, we treated SWNTs with a mixture of concentrated sulfuric and nitric acids, as described previously. Figure S1 in the Supporting Information shows the mixed solution of H2O2 and TMB in the presence or absence of SWNTs. In the absence of SWNTs, the color of the solution does not change in 12 h; however, in the presence of SWNTs, the color changes from black to blue immediately. This result suggests that SWNTs can catalyze the reaction of TMB in the presence of [a] Y. Song, X. Wang, C. Zhao, K. Qu, Dr. J. Ren, Prof. X. Qu Laboratory of Chemical Biology Division of Biological Inorganic Chemistry State Key Laboratory of Rare Earth Resource Utilization Graduate School of the Chinese Academy of Sciences Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun, Jilin 130022 (China) Fax: (+86)431-85262656 E-mail : xqu@ciac.jl.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.20090902643. Scheme 1. Schematic illustration of SWNTs catalyzing the reaction of peroxidase substrate TMB in the presence of H2O2 to give the blue product oxidized TMB (oxTMB).

Multifunctional poly(2,5‐benzimidazole)/carbon nanotube composite films

AbstractThe AB‐monomer, 3,4‐diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high‐molecular‐weight poly(2,5‐benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in situ polymerization of the AB‐monomer in the presence of single‐walled carbon nanotube (SWCNT) or multiwalled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid. The ABPBI/SWCNT and ABPBI/MWCNT composites displayed good solubility in methanesulfonic acid and thus, uniform films could be cast. The morphology of these composite films was studied by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved when compared with ABPBI, and their toughness (∼200 MPa) was close to the nature's toughest spider silk (∼215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10 × 10−5 and 2.53 × 10−1 S/cm, respectively, whereas that of ABPBI film was 4.81 × 10−6 S/cm. These values are ∼19 and 52,700 times enhanced by the presence of SWCNT and MWCNT, respectively. Finally, without acid impregnation, the ABPBI film was nonconducting while the SWCNT‐ and MWCNT‐based composites were proton conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1067–1078, 2010

Fabrication and characterization of single walled carbon nanotubes-iron phthalocyanine nano-composite: surface properties and electron transport dynamics of its self assembled monolayer film

Nano-composite of single walled carbon nanotubes (SWCNTs) and iron phthalocyanine, peripherally tetra-substituted with diethylaminoethanethiol (complex 2), was fabricated and characterized by infra red (IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM technique gave a convincing image of the nano-composite. Self-assembled monolayer (SAM) film of the composite (SWCNT-2-SAM) was formed on gold electrode. Its surface properties were investigated, relative to that of 2-SAM film, by cyclic voltammetry and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, using [Fe(CN)6]3− as redox probe, were used to investigate the dynamics of electron transport in the SWCNT-2-SAM film. Lower charge transfer resistance, RCT, of the SWCNT-2-SAM modified Au electrode, relative to that of the 2-SAM modified Au electrode, was an indication of enhanced electron transport in the presence of SWCNT. The SAM film of the nano-composite showed better electrocatalytic behaviour, relative to that of 2-SAM film, towards the oxidation of the insecticide, carbofuran. The electrode (SWCNT-2-SAM) showed good selectivity for carbofuran, in the presence of diazinon (a non-electroactive interferent) and at lower concentration of the electroactive interferents (chlorpyrifos and dichlorfos).

Abstract C142: Safety of single-walled carbon nanotubes for delivery of siRNA

Abstract siRNA is a leading potential new cancer therapy but currently lacks an adequate delivery mechanism. Ensysce has been exploring the use of single-walled carbon nanotubes (SWCNT) as delivery vehicles for siRNA delivery and has previously reported on the in vitro and in vivo efficacy of this platform. This study was conducted to determine what if any toxicities result from the use of SWCNT and identify toxicities that may be directly attributed to this delivery vehicle. For this application, it is not only necessary to determine the maximal load of SWCNT that can be tolerated, the dose limiting toxicities and the fate of the material in the body, but also to carefully prepare the SWCNT suspensions to ensure that contaminating metals, nanotube aggregates and other materials are not present when administered systemically. Ensysce Biosciences has been exploring the safe use of this material and here presents its latest findings from a toxicology study where the total dose of 50 and 100 g of fully suspended and individualized SWCNT were administered to groups of 3 mice. Mice were sacrificed at 12, 24, 48 hr and 1 week following i.v. administration. Blood chemistry and hematology were evaluated at each time point. Urine and feces were collected at 12, and 24 hr. Organs, including spleen, liver, kidney, heart, lung and brain were examined macroscopically and by near IR-fluorescence for the presence of SWCNT. The presence and persistence of SWCNT in the tissues was measured. Data to be presented will include details of the analytical characterization of the SWCNT preparations that were delivered, showing that the tubes were well dispersed and individualized. At both the 24 hr and 1 week timepoints, blood chemistry and hematology showed no evidence of toxicity, as values for all were within the normal ranges. Macroscopic examination of organs indicated that SWCNT were present in liver and spleen at 24 hr. Near IR-fluorescence spectroscopy demonstrated that the nanotube accumulation in the spleen decreased over a 1 week period. Data will be presented showing that a 100 g dose (equivalent to 30 mg in humans) was well tolerated and non-toxic. These studies have led to further work examining limits for use of SWCNT for siRNA delivery, including stability of the siRNA complexes in serum, siRNA loading efficiency and systemic efficacy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C142.

Natural Rubber-Carbon Nanotube Composites through Latex Compounding

Natural rubber (NR)-based nanocomposites have been prepared with single-walled carbon nanotubes (SWNTs) through a latex stage mixing method. SWNTs were dispersed in water through ultrasonication and stabilized by the subsequent addition of a surfactant. The stabilized aqueous dispersion of SWNTs was mixed with NR latex and the effect of nanofiller on the flow properties of NR latex was investigated. Casting the compounded latex followed by curing gave good quality composite films with significantly improved mechanical properties. For example, the tensile strength and modulus of the composite film containing 2.0 phr (parts per hundred parts of rubber) SWNTs were, respectively, 56% and 63% higher in relation to pure NR. Electrical percolation threshold concentration of SWNTs in the NR matrix was found to be 1.5 phr. Thermogravimetric analysis indicated that the thermal stability of NR remains unaffected by the presence of SWNTs at low concentrations.

Surface Enhanced Raman Scattering Studies on Poly(3,4-ethylene dioxythiophene)/Single-Walled Carbon Nanotubes Composites and Their Application to Rechargeable Lithium Batteries

In this paper, surface enhanced Raman scattering (SERS) studies on the chemical polymerization of 3,4-ethylene dioxythiophene (EDOT) in the presence of single-walled carbon nanotubes (SWNTs) are reported. Both a non-covalent and covalent functionalization of SWNTs with poly(3,4-ethylene dioxythiophene) (PEDOT) is invoked as a result of the following variations induced in the SERS spectra of PEDOT and SWNTs: (i) the appearance of a Raman line at 140 cm(-1) indicating the formation of a new covalent bond between PEDOT and SWNTs; (ii) an increase in the intensity of the Raman line at 705 cm(-1), associated with the deformation vibration mode of C-S-C bond, the result of a steric hindrance effect induced by the bonding of PEDOT on SWNTs; and (iii) the enhancement of the Raman band with maximum at 1540 cm(-1) (G- component) in SWNTs when the PEDOT weight in the PEDOT/SWNTs composite increases. Using the PEDOT/SWNTs composite as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity are reported for the PEDOT/SWNTs composite (ca. 218 mAh g(-1)) in comparison with PEDOT doped with FeCl4- ions (ca. 25 mAh g(-1)).

Single-walled carbon nanotubes dispersed in aqueous media via non-covalent functionalization: Effect of dispersant on the stability, cytotoxicity, and epigenetic toxicity of nanotube suspensions

As the range of applications for carbon nanotubes (CNTs) rapidly expands, understanding the effect of CNTs on prokaryotic and eukaryotic cell systems has become an important research priority, especially in light of recent reports of the facile dispersion of CNTs in a variety of aqueous systems including natural water. In this study, single-walled carbon nanotubes (SWCNTs) were dispersed in water using a range of natural (gum arabic, amylose, Suwannee River natural organic matter) and synthetic (polyvinyl pyrrolidone, Triton X-100) dispersing agents (dispersants) that attach to the CNT surface non-covalently via different physiosorption mechanisms. The charge and the average effective hydrodynamic diameter of suspended SWCNTs as well as the concentration of exfoliated SWCNTs in the dispersion were found to remain relatively stable over a period of 4 weeks. The cytotoxicity of suspended SWCNTs was assessed as a function of dispersant type and exposure time (up to 48 h) using general viability bioassay with Escherichia coli and using neutral red dye uptake (NDU) bioassay with WB-F344 rat liver epithelia cells. In the E. coli viability bioassays, three types of growth media with different organic loadings and salt contents were evaluated. When the dispersant itself was non-toxic, no losses of E. coli and WB-F344 viability were observed. The cell viability was affected only by SWCNTs dispersed using Triton X-100, which was cytotoxic in SWCNT-free (control) solution. The epigenetic toxicity of dispersed CNTs was evaluated using gap junction intercellular communication (GJIC) bioassay applied to WB-F344 rat liver epithelial cells. With all SWCNT suspensions except those where SWCNTs were dispersed using Triton X-100 (wherein GJIC could not be measured because the sample was cytotoxic), no inhibition of GJIC in the presence of SWCNTs was observed. These results suggest a strong dependence of the toxicity of SWCNT suspensions on the toxicity of the dispersant and point to the potential of non-covalent functionalization with non-toxic dispersants as a method for the preparation of stable aqueous suspensions of biocompatible CNTs.

Single walled carbon nanotube (SWNT)–polyimide nanocomposites as electrostrictive materials

The combination of properties offered by polymer nanocomposites provides opportunities for going beyond structural reinforcement where engineered electroactive responses and enhanced electrical and dielectric properties would result in multifunctionality. In our study, we show that adding single walled carbon nanotubes (SWNTs) to a non-actuating polyimide (PI) can create an electromechanical actuation response in the nanocomposite. The neat polyimide does not show any actuation response under an applied electric field, whereas the SWNT–PI composites above the percolation threshold exhibit an electrostrictive behavior that is highly dependent on SWNT content. Both bending and thickness–extension strains are obtained at very low electric field magnitudes; the study also evaluates the effect of applied electric field magnitude, frequency and SWNT content on the actuation strain and strain rate. Dielectric spectroscopy and thermally stimulated current measurements reveal an enhanced polarization in the presence of SWNTs. This enhancement is key to the actuation mechanism and is thought to arise from a combination of three sources: SWNTs acting as extended electrodes within the polymer, interfacial polarization and noncovalent interactions between the SWNTs and the polymer.