Dispersion Of Single-walled Carbon Nanotubes Research Articles

The role of the solvent and the size of the nanotube in the non-covalent dispersion of carbon nanotubes with short organic oligomers - a DFT study.

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents. Recently, we have carried out two computational investigations on the intermolecular interactions between conjugated organic oligomers and SWCNTs in order to gain insight into an important process of the non-covalent dispersion of carbon nanotubes with short oligomers. These studies highlighted the fact that two additional factors, namely, the effects of the solvent and the carbon nanotube's size on these interactions need further investigation. In this work, with the help of model compounds (which are molecular fragments of the short oligomers used in our previous investigations), we analyze the significance of these two factors. We employ three dispersion corrected density functional theory (D-DFT) approximations (B97D, wB97XD, and B3LYP-D3) to assess the effect of the DFT method, and two basis sets (6-31G(d) and 6-31++G(d,p)) to assess the importance of using a higher basis set in our computations. The main focus of this work is to assess the effect of solvation and nanotube's size on the structure, electronic properties, and binding energies of the respective pairs of model compounds and segments of carbon nanotubes. No significant differences are found between the results of (6,5) and (8,7) SWCNTs in either the geometrical parameters of interacting oligomers or the general tendency of wrapping of their long side chains (SCs) around the nanotubes. However, we find that the binding energies per atom between nanotubes and model compounds are larger for nanotubes with the smaller diameter. The results of electronic properties also show that all model compounds interact more strongly with the (6,5) SWCNT than with the (8,7) SWCNT. Polar solvents such as chloroform show lower binding energies relative to those obtained without a solvent or with non-polar solvents such as hexane. It appears that the presence of a solvent weakens the oligomer/nanotube interactions and, presumably, strengthens the oligomer/solvent and nanotube/solvent interactions to facilitate dispersion of SWCNTs.

Improvement of orientational order and display parameters of liquid crystalline material dispersed with single-wall carbon nanotubes

Composites were prepared by inserting Single-Walled Carbon Nanotubes (SWCNTs) in the Nematic Liquid Crystal (NLC) to fasten the reorientation dynamics of the system under the electric field. Dispersion of SWCNTs in NLC medium enhanced the orientational order and consequently the display parameters of composite systems improved. Various display parameters such as orientational order, dielectric anisotropy, threshold voltage and splay elastic constant were explored for pure and composite systems.

Individually isolated single wall carbon nanotubes with controlled surface charge density

Individually isolated single wall carbon nanotubes (SWNTs) with controlled surface charge density in water have been developed. First, the polymerizable cationic surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), is self-assembled on the hydrophobic surface of SWNTs in the presence of different amount of polymerizable co-monomer, sodium 4-styrenesulfonate (NaSS). Second, the self-assembled CTVB/NaSS monolayer is permanently fixed by in situ polymerization, making individually isolated SWNT dispersion in water. The surface charge density of functionalized SWNTs is controlled by the amount of NaSS relative to that of CTVB. The zeta potential of the functionalized SWNTs is systematically varied from positive to negative (+12.3 ∼ −47.8 mV) as the concentration of NaSS is increased from 0 to 60 mol % relative to the CTVB concentration. The charge variation is understood in terms of an overcharging effect in the charged colloidal system. The small angle neutron scattering (SANS) measurements show that electrostatic interaction between the functionalized SWNTs is strongly dependent on the NaSS concentration, which is consistent with the zeta potential measurements. The SANS measurements also show that the thickness of polymerized CTVB/NaSS monolayer adsorbed on SWNTs is almost constant at 1.89 nm regardless of the NaSS concentration, and the microstructure and surface charge are well maintained at high temperature (60 °C) as well as even after harsh condition such as freeze-drying.

Single-Walled Carbon Nanotube Dispersion in Tryptic Soy Broth.

There has been little research on the dispersion of carbon nanotubes in dispersions of standard microbiological media. We report that tryptic soy broth (TSB) containing casein digest disperses single-walled carbon nanotubes (SWNT) at concentrations similar to those achieved in lysozyme (LSZ), one of the best known biomolecular SWNT dispersants. Similar to LSZ, the proposed mechanism for SWNT dispersion in TSB is favorable π-π stacking interactions with l-tryptophan. This is supported by similar SWNT concentrations in both LSZ and TSB supernatants, and the absence of appreciable dispersion in TSB that does not contain a source of l-tryptophan. Since l-tryptophan alone is insufficient to enable dispersion, it was previously hypothesized that LSZ's macromolecular structure created steric hindrance that was critical for SWNT dispersion. These new results show that intermediately sized l-tryptophan containing species can also enable dispersion. In addition, since TSB is a commonly used growth medium for microbiological research, its dispersive ability presents new research avenues for studying the effect of SWNT on prokaryotic cells without the need to oxidize SWNT or add dispersants that may induce microbial stress.

Systematic comparison of single-walled carbon nanotube/poly(vinyl acetate) graft-to reactions

The covalent grafting of polymers to single-walled carbon nanotubes (SWCNTs) is widely used to improve solvent compatibility, as well as composite and functional performance. Here, three different graft-to strategies are directly compared, using azide, diazonium, and bromide terminated polymers, over four different molecular weights (oligomeric to 10 kDa) using specifically synthesized low polydispersity, end-group controlled poly(vinyl acetate) (PVAc) prepared by polymerisation using a bespoke protected-amine RAFT agent. Coupling of the bromo-polymer to reduced SWCNTs led to higher degrees of functionalisation (grafting ratios up to 68.9%) than the azide and diazonium grafting reactions, attributed to better initial dispersion of the pre-grafted SWCNTs. The use of higher molecular weight polymers led to a decrease in the total weight of polymer grafted, as the increase in per-polymer weight is more than offset by steric occlusion on the SWCNT surface. For these graft-to reactions, the dispersibility of grafted SWCNTs was found to depend most strongly on the polymer molecular weight, not total weight of grafted polymer or grafting chemistry, with an intermediate Mn∼5757 PVAc giving the best dispersibilities, at up to 118 mg L−1.

Determination of the Absolute Enantiomeric Excess of the Carbon Nanotube Ensemble by Symmetry Breaking Using the Optical Titration Method.

Symmetry breaking of single-walled carbon nanotubes (SWNTs) has profound effects on their optoelectronic properties that are essential for fundamental study and applications. Here, we show that isomeric SWNTs that exhibit identical photoluminescence (PL) undergo symmetry breaking by flavin mononucleotide (FMN) and exhibit dual PLs and different binding affinities (Ka). Increasing the FMN concentration leads to systematic PL shifts of SWNTs according to structural modality and handedness due to symmetry breaking. Density gradient ultracentrifugation using a FMN-SWNT dispersion displays PL shifts and different densities according to SWNT handedness. Using the optical titration method to determine the PL-based Ka of SWNTs against an achiral surfactant as a titrant, left- and right-handed SWNTs display two-step PL inflection corresponding to respective Ka values with FMN, which leads to the determination of the enantiomeric excess (ee) of the SWNT ensemble that was confirmed by circular dichroism measurement. Decreasing the FMN concentration for the SWNT dispersion leads to enantiomeric selection of SWNTs. The titration-based ee determination of the widely used sodium cholate-based SWNT dispersion was also demonstrated by using FMN as a cosurfactant.

A 104-week pulmonary toxicity assessment of long and short single-wall carbon nanotubes after a single intratracheal instillation in rats

We compared long-term pulmonary toxicities after a single intratracheal instillation of two types of dispersed single-wall carbon nanotubes (SWCNTs), namely, those with relatively long or short linear shapes with average lengths of 8.6 and 0.55 µm, respectively. Both types of SWCNTs were instilled intratracheally in male F344 rats at 0.2 or 1.0 mg/kg (long SWCNTs) or 1.0 mg/kg (short SWCNTs). Pulmonary responses were characterized at 26, 52 and 104 weeks after a single instillation. Inflammatory changes, test substance deposition, test substance engulfment by macrophages, and alveolar wall fibrosis were observed in the lungs of almost all test rats at 52 and 104 weeks after short nanotube instillation. The incidences of these changes were much lower in the long nanotube-treated groups. In almost all rats of the long nanotube-treated groups, fibrosis and epithelium loss in the terminal bronchiole with test substance deposition were observed. These bronchiolar changes were not observed after administering short nanotubes. Both bronchiolo-alveolar adenoma and carcinoma were found in the negative-control group, the high-dose long-nanotube group, and the short-nanotube group at 104 weeks post-instillation, although the incidences were not statistically different. The genotoxicity of the SWCNTs was also evaluated by performing in vivo comet assays with lung cells obtained 26 weeks post-instillation. No significant changes in the percent tail deoxyribonucleic acid were found in any group. These findings suggested that most long SWCNTs were deposited at the terminal bronchioles and that a considerable amount of short SWCNTs reached the alveolus, resulting in chronic inflammatory responses, but no genotoxicity in the lungs.

Organic dispersion of polyaniline and single-walled carbon nanotubes and polyblends with poly(methyl methacrylate)

Traditionally, in situ polymerization has been used to make polymer-carbon nanotube composites. Here, we report a simple method of mixing polyaniline with single-walled carbon nanotubes in a variety of organic solvents via ultrasonication. The maximum loading fraction of SWCNTs in the composites is determined by the conformation of the polyaniline chains. The type of solvent used has the greatest influence on the conformation of the polyaniline chains. Furthermore, the composites can be easily blended with poly(methyl methacrylate) (PMMA), to form polyblends. The electrical conductivities and transparencies of the polyblend films are reported.

An experimental study on the nonlinear free vibration response of epoxy and carbon fiber-reinforced composite containing single-walled carbon nanotubes

In this paper, the effects of additives of a single-walled carbon nanotube (SWCNT) on the nonlinear free vibration of neat resin and carbon fiber reinforced polymer composites (CFRPs) are investigated experimentally. To establish this purpose a sensitive noncontact setup is designed and prepared. In order to obtain a proper SWCNT dispersion pattern, a simple multistage method is presented to fabricate and test nanocomposite beams. First, the increase in the Young's modulus of the nanocomposites by adding carbon nanotube is investigated using the mechanical bending test and validated with available test results. Next, the nonlinear free vibration behavior of cantilever beams under small to large-deflection is investigated. The results of the vibration tests indicate that the nonlinear vibration behavior of all models is close to homogenous materials with increasing SWCNT. The results also show that transverse initial excitation (displacement) imposed an axial load on the slender beams, which thus leads to an increase in the nonlinear frequency of oscillation. In addition, the increase in frequency bears a relation to the initial displacement. Also, large initial displacements, especially on models without carbon fiber (reinforced epoxy), cause that the convergence of frequencies under different initial excitation did not occur. The results of this study show that adding SWCNT can lead to convergences of frequencies’ hybrid composites and reinforced epoxy during final cycles.

A printed SWCNT electrode modified with polycatechol and lysozyme for capacitive detection of α-lactalbumin

The authors describe an electrochemical sensor for the breast cancer marker α-lactalbumin (αLA). It is based on the use of printed single-walled carbon nanotube (SWCNT) electrodes that were modified with polycatechol. Impedance-derived electrochemical capacitance spectroscopy (ECS) is applied for detection at an applied potential of −0.14 V vs. Ag/AgCl reference electrode. The electrode was prepared in a two-step process. First, a dispersion of SWCNTs was drop-cast onto the surface of a poly(ethylene terephthalate) substrate to act as the working electrode. Next, catechol was electrochemically polymerized on the SWCNTs, prior to the immobilization of lysozyme. The strong interaction between lysozyme and αLA induced changes in the redox capacitance which are detected by ECS. The latter shows the device to be capable of detecting αLA in the 20 to 80 ng·mL−1 concentration range. The limit of detection is 9.7 ng·mL−1 at an S/N ratio of 3. The device was used to detect αLA in human blood serum with good recovery results.

Contribution of arabinogalactan protein to the stabilization of single-walled carbon nanotubes in aqueous solution of gum arabic

Nowadays, the application of gum arabic has been extended from food industry as a food gum to broad fields including pharmaceutical, personal care and nanomaterials as a versatile agent providing specific physicochemical properties and functional attributes. Despite of its excellent properties, the complex nature of multicomponent of gum arabic may act as an obstacle to understand profoundly its functionality and relevant mechanism in applications. In this study the effect of arabinogalactan protein (AGP), one of the main components in gum arabic, on the stabilization of single-walled carbon nanotubes (SWNTs) in aqueous gum arabic solution has been clarified. By using gel permeation chromatography coupled with multi-angle laser light scattering system (GPC-MALLS), fluorescence spectroscopy, circular dichroism, surface tension measurement and thermogravimetric analysis as well as atomic force microscope and transmission electron microscopy observation, it is found that the adsorption of AGP on the surface of SWNTs contributes to the stability of nanotubes in water by steric hindrance. The AGP physically modified SWNTs also shows improved biocompatibility. The use of AGP for stabilization of SWNTs dispersions may offer advantages of maintaining the initial properties of SWNTs, and providing biocompatibility and highly adhesive interfaces between individual carbon nanotubes and a biopolymeric matrix that are essential for tissue engineering and medical devices.

Anisotropic piezoresistivity characteristics of aligned carbon nanotube-polymer nanocomposites

Dielectrophoresis under the application of AC electric fields is one of the primary fabrication techniques for obtaining aligned carbon nanotube (CNT)-polymer nanocomposites, and is used here to generate long range alignment of CNTs at the structural level. The degree of alignment of CNTs within this long range architecture is observed via polarized Raman spectroscopy so that its influence on the electrical conductivity and piezoresistive response in both the alignment and transverse to alignment directions can be assessed. Nanocomposite samples consisting of randomly oriented, well dispersed single-wall carbon nanotubes (SWCNTs) and of long range electric field aligned SWCNTs in a photopolymerizable monomer blend (urethane dimethacrylate and 1,6-hexanediol dimethacrylate) are quantitatively and qualitatively evaluated. Piezoresistive sensitivities in form of gauge factors were measured for randomly oriented, well dispersed specimens with 0.03, 0.1 and 0.5 wt% SWCNTs and compared with gauge factors in both the axial and transverse to SWCNT alignment directions for electric field aligned 0.03 wt% specimens under both quasi-static monotonic and cyclic tensile loading. Gauge factors in the axial direction were observed to be on the order of 2, while gauge factors in the transverse direction demonstrated a 5 fold increase with values on the order of 10 for aligned specimens. Based on Raman analysis, it is believed the higher sensitivity of the transverse direction is related to architectural evolution of misaligned bridging structures which connect alignment structures under load due to Poisson’s contraction.

Realization of transparent conducting networks with high uniformity by spray deposition on flexible substrates

Optimization of the spreading and the evaporation behaviors of atomized coating solutions on a substrate is essential for achieving highly uniform network thin films of single-walled carbon nanotubes (SWCNTs) and silver nanowires (AgNWs) on plastic substrates by the spray coating method. We have demonstrated that efficient control of the surface energy of the substrate and the spray coating parameters improves the opto-electrical performance and the uniformity of the network thin film based on the characteristics of the coating solutions. In terms of network formation, the surfactant-assisted aqueous SWCNT dispersion was less sensitive to the surface tension of the substrate than the almost pure aqueous AgNW solution. In addition, the solution containing the AgNWs has to be highly atomized by increasing the gas flow rate to effectively scatter the nanowires on the surface, as the AgNW solution exhibits a high contact angle on hydrophobic substrates. Finally, UV/ozone irradiation of the substrates and deposition of atomically thin and transparent graphene oxide nanosheets on the network thin films enhanced the conductivity and the electrical uniformity of the spray-coated network films.

Improved Performance of Glucose Bioanodes Using Composites of (7,6) Single-Walled Carbon Nanotubes and a Ferrocene-LPEI Redox Polymer.

The effect of incorporating different types of carbon nanotubes into composite films of a redox polymer (FcMe2-C3-LPEI) and glucose oxidase (GOX) was investigated. The composite films were constructed by first forming a high-surface area network film of either single-walled carbon nanotubes (SWNTs) or multiwalled carbon nanotubes (MWNTs) on a glassy carbon electrode (GCE) by solution casting of a suspension of Triton-X-100 dispersed SWNTs. Next a glucose responsive redox hydrogel was formed on top of the nanotube-modified electrode by cross-linking FcMe2-C3-LPEI with glucose oxidase via ethylene glycol diglycidyl ether (EGDGE). Electrochemical and enzymatic measurements showed that composite films made with (7,6) SWNTs produced a higher response (3.3 mA/cm2) to glucose than films made with (6,5) SWNTs (1.8 mA/cm2) or MWNTs (1.2 mA/cm2) or films made without SWNTs (0.7 mA/cm2). We also show that the response of the composite films could be systematically varied by fabricating SWNT films with different weight ratios of (7,6) and (6,5) SWNTs. Optimization of the (7,6) SWNTs loading and the redox polymer-enzyme film produced a glucose response of 11.2 mA/cm2. Combining the optimized glucose films with a platinum oxygen breathing cathode into a biofuel cell produced a maximum power density output of 343 μW/cm2.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

Skewness Analysis in Variance Spectroscopy Measures Nanoparticle Individualization.

An important enabling step in nanoparticle studies is the sorting of heterogeneous mixtures to prepare structurally homogeneous samples. It is also necessary to detect and monitor aggregation of the individual nanoparticles. Although variance spectroscopy provides a simple optical method for finding low concentrations of heteroaggregates in samples such as single-walled carbon nanotube dispersions, it cannot detect the homoaggregates that are relevant for well-sorted samples. Here we demonstrate that variance spectral data can be further analyzed to find third moments of intensity distributions (skewness), which reveal the presence of emissive homoaggregates. Using experimental measurements on variously processed nanotube dispersions, we deduce a simple numerical standard for recognizing aggregation in the highly sorted samples that are increasingly available to nanoscience researchers.

Thiophene pyrenyl derivatives for the supramolecular processability of single-walled carbon nanotubes in thin film heterojunction

A major problem for the use of single-wall carbon nanotubes (SWCNTs) in electronic devices relates to their poor processability. Chemical modification inevitably introduces defects in the nanotube lattice, resulting in a loss of electronic properties. In this contest, we report on a supramolecular approach with the aim of increasing the dispersion of SWCNTs in solution and in organic semiconductor matrices by ensuring the optoelectronic properties. In particular, new pyrenyl derivatives of thiophene have been synthesized and used to improve the solubility of SWCNTs for electron transfer in thin film heterojunction with poly(3-hexylthiophene) (P3HT) as donor system. Photoinduced electron transfer to SWCNTs has been demonstrated and the effect of different alkyl spacers, between the pyrene unit and the thiophene moiety, has revealed to play a key role. Electron transfer has been maximized by the compound with a spacer coplanar with the pyrene moiety due to the reduced separation between P3HT and SWCNTs.

(Invited) Multifunctional Materials from Dispersions of Single-Walled Carbon Nanotubes and Biomolecules

Dispersions of single-walled carbon nanotubes (SWNT) and biological molecules can enable multifunctional materials that combine SWNTs’ intrinsic mechanical and/or electrical properties with the properties of the biomolecule. For example, functionalization of SWNT and organic phosphate hydrolase can be used for pesticide detection, and dispersions of SWNT and laccase can be used to make anodes for electrochemical fuel cells. Some of the most intriguing biological SWNT dispersants are double stranded DNA (dsDNA) and enzymes and protein digests containing tryptophan residues. For example, dilute dispersions of dsDNA/SWNT and lysozyme/SWNT have been used to produce conductive antimicrobial films using layer-by layer assembly. Higher concentration dsDNA/SWNT dispersions form either cholesteric or nematic liquid crystalline phases which can be processed into tightly packed aligned films with controlled optical properties. Higher concentration lysozyme/SWNT dispersions can be used to produce mechanically robust antimicrobial films and properties. Finally, dispersion of SWNT in tryptic soy broth (TSB) containing casein digest has recently been shown to enable direct investigation of SWNTs’ microbiological properties in standard biological growth media.

Variance Spectroscopy Monitors the Sonication-Induced Cutting and Debundling of Single-Walled Carbon Nanotubes

It is well known that ultrasonic processing is a crucial step for preparing suspensions of individualized single-walled carbon nanotubes (SWCNTs). Sonication disaggregates nanotube bundles but can also cut long nanotubes into shorter segments and introduce defect sites that degrade optical properties. To study these processes in detail, we have applied the newly developed method of variance spectroscopy.1 In this technique, we analyze fluorescence spectra from many different small regions of a dilute SWCNT sample to determine the variations in emission brought about by statistical changes in composition. By analyzing the first and second moments of the intensity distributions at each wavelength, we construct the mean and variance spectra. Simple analysis of these spectra then reveals the number of particles per unit volume of different (n,m) species present within the mixed sample and the average emission per particle for various (n,m) species. Deeper data analysis gives covariance plots, showing aggregation between different species, and third moment (skew) spectra, showing aggregation of individual species. Starting with a sample of relatively long SWCNTs that had been dispersed in surfactant solution by high shear mixing, we measured variance spectra as a function of sonication time and power. We found that the number density values for every (n,m) species increased with sonication time, reflecting initial further disaggregation and a slower cutting process. These rates of number density increase showed no apparent dependence on nanotube diameter or chiral angle. To confirm the changes in SWCNT length caused by cutting, we also measured full length distributions using the diffusion-based LAND method.2 Findings from these length distributions were compared to the change in number density values in order to disentangle the effects of debundling and cutting. We believe that this is the first study to separately observe these effects. Damage to SWCNTs during continued sonication was monitored through decreases in the values of emission per particle, as determined from variance spectra. We also introduce here the use of skew analysis to obtain a quantitative index of self-aggregation. The experimental results will be compared to findings from a numerical model constructed to represent the main processes occurring during sonication. Our study should allow the optimized preparation of SWCNT dispersions. 1. J. K. Streit, S. M. Bachilo, S. R. Sanchez, C.-W. Lin, and R. B. Weisman, J. Phys. Chem. Lett., 3976-3981 (2015). 2. J. K. Streit, S. M. Bachilo, A. V. Naumov, C. Khripin, M. Zheng, and R. B. Weisman, ACS Nano, 6 (9), 8424-8431 (2012).

Single-walled carbon nanotubes covalently functionalized with cysteine: A new alternative for the highly sensitive and selective Cd(II) quantification

This work is focused on the development of an electrochemical sensor for the quantification of Cd(II) based on the use of glassy carbon electrodes (GCE) modified with a dispersion of single-walled carbon nanotubes (SWCNTs) covalently functionalized with cysteine (Cys). Cd(II) is preconcentrated at the electrode surface by complex formation at open circuit potential, followed by the reduction at ∧0.900V and the final anodic voltammetric stripping in a 0.020M acetate buffer solution pH 5.00. The functionalization of SWCNTs was performed through the reaction between the carboxylic groups of oxidized SWCNT and amino groups of S-triphenylmethyl cysteine using a coupling chemistry agent based on benzotriazol for the activation of carboxylic residues.There was a linear relationship between Cd oxidation signal and Cd(II) concentration between 1.0 and 300.0α/4gL∧1 Cd(II), with a sensitivity of (49±2)í10∧3α/4Aα/4g∧1L and a detection limit of 0.3α/4gL∧1. The reproducibility was 1.7% using the same dispersion and 3.8% using 3 different dispersions. The sensor was challenged with groundwater samples enriched with Cd(II) showing excellent recovery percentages and excellent agreement with the values obtained by ICP-MS.