Dispersion Of Single-walled Carbon Nanotubes Research Articles

Effect of Single-walled Carbon Nanotube (SWCNT) Composition on Polyfluorene-Based SWCNT Dispersion Selectivity.

Applications of single-walled carbon nanotubes (SWCNTs) are hampered by the mixtures of metallic and semiconducting SWCNTs that are present in commercial samples. Separation of SWCNTs according to electronic type is therefore extremely important. Recently, the selective interaction between the conjugated polymer, poly(9,9-di-n-dodecyl-fluorenyl-2,7-diyl) and semiconducting SWCNTs has been reported. However, the mechanism responsible for this selectivity is poorly understood. To determine whether this polymer is only selective for semiconducting SWCNTs, we exposed it to mixtures of metallic and semiconducting SWCNTs in different ratios. We found that the polymer is indeed selective for semiconducting SWCNTs in toluene, but only when the starting ratio is below 67:33 metallic:semiconducting. When the starting ratio is increased to 67:33 or higher, the amount of metallic SWCNTs dispersed dramatically increases. If the solvent is changed to THF, the threshold ratio at which metallic SWCNTs begin to be dispersed is much lower. This indicates that the polymer exhibits a preference for interaction with semiconducting SWCNTs, but is not precluded from interaction with metallic SWCNTs if exposed to a high enough concentration.

A highly-sensitive VB2 electrochemical sensor based on one-step co-electrodeposited molecularly imprinted WS2-PEDOT film supported on graphene oxide-SWCNTs nanocomposite

A highly-sensitive electrochemical sensor based on single walled carbon nanotubes (SWCNTs) nanocomposite electro-catalyst supported molecularly imprinted poly(3,4-ethylenedioxythiophene) (PEDOT) film modified with two-dimensional layered tungsten sulfide (WS2) nanosheet for the detection of vitamin B2 (VB2) was successfully developed. Molecularly imprinted WS2-PEDOT film was prepared by the electrochemical co-polymerization of functional monomer 3,4-ethylenedioxythiophene in the presence of template molecule VB2 and WS2 nanosheet. SWCNTs nanocomposite modified electrode was obtained by drop-coating SWCNTs dispersion containing graphene oxide (GO) onto GCE surface. WS2 was used for improving the denseness and smoothness in the morphology and structure of PEDOT. GO was employed for enhancing the electro-catalytic capacity of SWCNTs and the interaction with template molecule via functional groups. The imprinted sensor was characterized, and its performance and parameters were investigated and optimized using linear sweep voltammetry. Under optimized conditions, the prepared imprinted sensor displayed a good linear response to VB2 in wide concentration ranges from 0.002 to 0.9 μM with a low detection limit of 0.7 nM, and successfully applied to electrochemically detect VB2 in drug samples with good reproducibility, repeatability and storage stability. The new design for the facile fabrication of mimic electrode will open up a new horizon in the development of highly-sensitive biomimic/imprinted sensors.

Efficient Production of Single‐Walled Carbon Nanotube Aqueous Dispersion Using Hexahydroxytriphenylene as a Dispersant and Stabilizer

AbstractDispersing single‐walled carbon nanotubes (SWNTs) is one of the key technologies for promoting the practical application of SWNTs in many fields. Herein, we report on an efficient dispersant, 2,3,6,7,10,11‐hexahydroxytriphenylene, for dispersing SWNTs through noncovalent functionalization. Typically, 68 wt% of the initial SWNTs (25 mg/L) were well dispersed in water at the low concentration of hexahydroxytriphenylene (25 mg/L). In order to compare the efficiency of various dispersants, we propose mole‐ and weight‐based dispersing efficiency index (m‐ and w‐DEI, respectively) based on the concentration of the dispersant employed (Cm‐DPS mmol/L or Cw‐DPS mg/L) and the concentration of the SWNTs dispersed (Cd‐CNT mg/L); m‐ and w‐DEI are defined as Cd‐CNT / Cm‐DPS and Cd‐CNT / Cw‐DPS, respectively. Although a biopolymer shows slightly better m‐DEI than hexahydroxytriphenylene, the w‐DEI of hexahydroxytriphenylene is better than that of all the dispersants we compared. For example, the m‐ and w‐DEI of hexahydroxytriphenylene are much better than those of sodium dodecylbenzenesulfonate (SDBS), one of the most widely used dispersant for SWNTs, by two and three orders of magnitude, respectively. The large difference of the DEI between 2,3,6,7,10,11‐hexahydroxytriphenylene and SDBS is found to be supported by the difference in their association constants (Ka) for the complexation with SWNTs, which were determined by the recently reported titration method.

Cysteine functionalized bio-nanomaterial for the affinity sensing of Pb(II) as an indicator of environmental damage

This work aims at the development of an electrochemical affinity biosensor for Pb(II) quantification using a platform that combines glassy carbon electrodes (GCE) and an aqueous dispersion of single-walled carbon nanotubes (SWCNT) covalently modified with cysteine residues (Cys). The biosensing protocol includes the accumulation of Pb(II) at the electrode surface through the affinity interaction promoted by Cys residues at open circuit potential, followed by the reduction of the accumulated Pb(II) at ‐0.900 V and the transduction step performed by linear sweep-adsorptive stripping voltammetry (LSAdSV) in a 0.020 M acetate buffer solution pH 5.00. There is a linear relationship between Pb(II) oxidation peak current and Pb(II) concentration. The dynamic linear range extends from 5.0 to 125.0 μg·L−1, exhibiting a sensitivity of 0.061 μAμg−1L and a detection limit of 0.69 μg·L−1. In addition, the selectivity of the biosensor was evaluated in the presence of high concentrations of possible interferents such as Cu(II), Cd(II), Ni(II), Hg(II), Rh(II), Ru(II), Zn(II), Ir(IV), Co(II) and As(III) demonstrating a high discrimination of Pb(II) in complex samples. The sensor was challenged with tap and rain water samples enriched with Pb(II), demonstrating outstanding properties in terms of recovery percentages showing an excellent agreement with ICP- MS.

Encapsulation of single-walled carbon nanotubes with asymmetric pyrenyl-gemini surfactants

Whereas the encapsulation technology of surfactants coating on the surface of single-walled carbon nanotubes (SWCNTs) attracts much attention, the mechanisms of asymmetric surfactants interacting with the SWCNTs and their molecular structures are rarely reported. Herein, we report a molecular dynamics (MD) simulation study on the investigation of surfactant adsorption and induced colloidal stability onto different SWCNTs. The surfactant-based encapsulation system, originating from the complementary π-π stacking, is validated through two-dimensional number density maps. We find that the asymmetric pyrenyl-gemini surfactants (APGSs) form double-layer assembled architecture films on nanotube surface. The inner layers of the films are packed with the pyrenyl groups of APGSs, which interact with SWCNTs via π-π stacking, while the outer layers composed of alkyl chains of APGSs coat at the nanotube surface through van der Waals interactions. In addition, we observe a configurational transformation of APGSs on the SWCNT surface from the folding configuration to unfolding patterns, when increasing the nanotube radius or the surface coverage of APGSs. Our study provides helpful insights into the encapsulation mechanism of APGSs on the SWCNT surface and the design of highly selective dispersants for SWCNTs.

A New Method for Quantifying SWCNT Dispersion Quality from Absorption Spectra

Individualization of single-walled carbon nanotubes (SWCNTs) in aqueous surfactant dispersions can vary greatly. We will present a new method for quantitatively assessing dispersion quality based on simple absorption spectra. In this method, the visible and short-wave infrared portions of a sample’s absorption spectrum are modeled as a superposition of two components. One component (labeled “S”) has sharp resonant features and is associated with the subpopulation of SWCNTs that are suspended as individuals or very small aggregates; the other (labeled “B”) has broad absorption features and is associated with stably dispersed materials such as carbonaceous impurities, imperfect nanotubes, and larger aggregates. Using absorption spectra from samples in various stages of purification by centrifugation or magnetic processing, we apply the method of multivariate curve resolution to extract the S and B component spectra and determine their relative contributions in samples of interest. The ratio of S to B content then provides a simple index of dispersion quality. We illustrate this new characterization method with measurements on both shear-dispersed and tip-sonicated SWCNT samples purified by three different processes: centrifugation, ultracentrifugation, and magnetic purification. We determine the dispersion efficiency of each sample preparation and find results that correlate well with those of established analytical techniques. In addition, we have further characterized the effects of these purification processes on the SWCNT length distribution (using the diffusion-based LAND method) and on SWCNT emissive properties (through variance spectroscopy). We believe that our new absorption-based method provides a practical tool for quickly assessing the dispersion quality of SWCNT samples.

(Invited) Variance Spectroscopy Studies of Single-Walled Carbon Nanotube Aggregation

Understanding aggregation in samples of dispersed, well-individualized single-walled carbon nanotubes (SWCNTs) is important for many basic studies and applications. We will describe a study that uses the recently developed technique of variance spectroscopy to monitor aggregation kinetics of SWCNTs in aqueous surfactant dispersions. Unlike other techniques used to investigate colloidal dispersions, variance spectroscopy resolves individual subpopulations in mixed samples based on their distinct fluorescence signatures. Following the addition of NaCl coagulant to unsorted SWCNT dispersions, we monitored changes in the independent particle concentrations of six semiconducting (n,m) species. These data were supplemented by time-resolved measurements of fluorescence intensity, which showed pseudo-first order kinetics that was independent of SWCNT structure and was attributed to quenching by energy transfer to metallic SWCNTs. The decreases in particle concentration directly revealed aggregation. They were found to fit reasonably well to a second-order rate law with some dependence on structure at higher salt concentrations. Finally, covariance analysis was applied to the variance data to monitor correlated spectral fluctuations arising from specific heteroaggregates. Those results showed equivalent associations between different semiconducting SWCNT species during salt-induced aggregation.

DNA Directed Self-Assembly of Single Walled Carbon Nanotubes into Three-Way Junction Nanostructures.

Utilization of a self-assembled two-dimensional DNA nanostructure to arrange single-walled carbon nanotubes (SWNTs) into predetermined structures at controllable angles is presented. A specially designed DNA three-way junction (3WJ) composed of three double-stranded DNA arms containing single-stranded overhang sequences was prepared by annealing of partially complementary ssDNA sequences and ultrasonicated with SWNTs, resulting in DNA-3WJ/SWNT hybrid nanostructures. Utilization of DNA-3WJ not only allowed the precise dispersion of SWNTs but also acted as a rigid template for the self-assembly of SWNTs into three-armed junctions at an angle of approximately 120° to each other as visualized by scanning electron microscopy and atomic force microscopy. Prepared DNA-3WJ/SWNT nanostructures were also demonstrated to have the appropriate binding sites for fluorophores, providing a simple method for the fluorescent labeling of SWNTs. When ssDNA sequences forming the DNA-3WJ are ultrasonicated with SWNTs, followed by annealing of resulting ssDNA wrapped SWNTs, instead of hybrid junctions composed of three SWNT molecules, a web-like structure composed of interconnected SWNT junctions was obtained. The design approaches demonstrated here provide simple methods for the arrangement of SWNTs into desired nanostructures utilizing pre-assembled DNA nanostructures as linkers in aqueous solution through noncovalent interactions which can greatly contribute to efforts along the controlled assembly of SWNTs.

Single-walled carbon nanotube (SWNT)-carboxymethylcellulose (CMC) dispersions in aqueous solution and electronic transport properties when dried as thin film conductors

ABSTRACTObtaining uniformly dispersed SWNT within an aqueous mixture for subsequent use as a dried coating in electronic biosensors is a challenge. The objective of this study is to relate SWNT dispersion conditions to resultant dried film properties. Aqueous solutions of SWNT dispersed with CMC (a dispersing agent with unique properties compatible with biomolecules) at different SWNT:CMC weight ratios and at different sonication conditions were studied. Solution particle size distribution data was obtained using dynamic light scattering. Differently formulated/processed SWNT/CMC solutions were used to form dry thin, conductive films. The resistance of each film was measured and its resistivity calculated. Response Surface Methodology (RSM) design of experiments (DOE) analysis was used as the tool to fit the data to establish a model and identify trends for the parameters studied. Profilometry was used to examine film surface uniformity. 3D optical microscopy was used to investigate film morphology and determine film thickness, and to relate these data back to solution dispersion conditions and dried film resistances. The lowest dried film resistivity (0.012 ohm-cm) was obtained at the highest levels of parameters studied in the DOE. Smaller solution particle size resulted in lower dried film surface roughness and better film uniformity.

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes (SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse (i.e. high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT- nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps

Highly Dispersible Buckled Nanospring Carbon Nanotubes for Polymer Nano Composites

We propose the unique structure of highly dispersible single-walled carbon nanotubes (SWCNTs) in various solvents and polymers using the ZnO nano particle template. Buckled nanospring-shaped carbon nanotubes (NS-CNTs) were synthesized by a chemical reaction of ZnO nanoparticles with acid-treated SWCNTs and then dissolving ZnO through chemical etching. The unique structure of distorted hexagonal NS-CNTs encircled around ZnO nanoparticles was formed by the bending of SWCNTs caused by the agglomeration of chemically adsorbed Zn(OH)2, which is further crystallized as the polycrystalline ZnO inner core. The highly dispersible NS-CNTs could be incorporated in the poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)] copolymer, one of widely studied ferro- and piezo-electric polymer, up to the value of 15 wt% as nanofillers. The relative dielectric constant (K) of polymer nanocomposite, at 1 kHz, was greatly enhanced from 12.7 to the value of 62.5 at 11 wt% of NS-CNTs, corresponding to a 492% increase compared to that of pristine P(VDF-TrFE) with only a small dielectric loss tangent (D) of 0.1.

Indexing the Quality of Single-Wall Carbon Nanotube Dispersions Using Absorption Spectra

We have found that absorption spectra of single-wall carbon nanotube (SWCNT) dispersions can be accurately represented as linear combinations of two underlying spectra. One, assigned to purified well-dispersed SWCNTs, is structured; the other, assigned to impurities and aggregates, is diffuse. To assess the quality of SWCNT dispersions, a small set of visible and short-wave IR spectra are first measured for a dispersed sample as it is purified by centrifugation. Those data are analyzed using a simple arithmetic process to estimate the pair of underlying component spectra. Then the spectra of other sample dispersions from the same SWCNT source are fit as linear combinations of the two component spectra, giving coefficients that provide a simple metric for sample quality (the S-index). We have validated this approach with measurements of fluorescence intensities, particle abundances, length distributions, and emissive aggregates in samples containing SWCNTs from three growth sources dispersed by high-shear mixing or tip sonication and then purified by moderate centrifugation, ultracentrifugation, or magnetic processing. Our absorption spectral analysis correlates closely with results from other characterization techniques. One unexpected outcome of our analyses is the estimate that no more than 7% by mass of raw SWCNT material used to prepare aqueous sodium deoxycholate suspensions becomes well-dispersed SWCNTs.

Semiconducting SWNTs sorted by polymer wrapping: How pure are they?

Short-channel field-effect transistors (FETs) prepared from semiconducting single-walled carbon nanotube (s-SWNT) dispersions sorted with poly(2,5-dimethylidynenitrilo-3,4-didodecylthienylene) are demonstrated. Electrical analysis of the FETs shows no evidence of metallic tubes out of a total number of 646 SWNTs tested, implying an estimated purity of our semiconducting SWNT solution higher than 99.85%. These findings confirm the effectiveness of the polymer-wrapping technique in selecting semiconducting SWNTs, as well as the potential of sorted nanotubes for the fabrication of short channel FETs comprising from 1 to up to 15 nanotubes without inter-nanotube junctions.

Towards balanced mechanical and electrical properties of thermoplastic vulcanizates composites via unique synergistic effects of single-walled carbon nanotubes and graphene

To achieve good dispersion of graphene and single-walled carbon nanotubes (SWNTs) in the nonpolar thermoplastic vulcanizate (TPV), polypropylene-graft-maleic anhydride (PP-g-MA) was compounded with graphene or SWNTs to obtain masterbatches, followed by their melt blending with TPV material. Morphological observations revealed the rather different distribution of graphene and SWNTs, which was directly related to the form of unique dual conductivity networks via the incorporation of SWNTs and graphene hybrid fillers, and also prevented the aggregation of fillers efficiently. The TPV ternary composites incorporated with hybrid fillers of graphene and SWNTs exhibited a low electrical percolation threshold of 0.37 wt % SWNTs, and higher electrical and thermal conductivity than the SWNTs incorporated binary systems at equal filler concentration. In contrast to the sharp decrease in tensile strength for TPV/SWNT composites, upon the addition of graphene into TPV/SWNT composite with a constant content of 0.5 wt% SWNTs, the increase in tensile modulus and tensile strength were 82% and 15% respectively at 2 wt % loading of graphene. Thermodynamic analysis was also applied to illustrate the different dispersion morphology of SWNTs and graphene in TPV. This study presents a new insight into the fabrication of high-performance TPV composites via the synergistic effects of hybrid fillers.

Improving the dispersion of SWNT in epoxy resin through a simple Multi-Stage method

This paper presents a new, univariate and improved Multi-Stage approach for dispersing of nanoparticles as well as nanotubes (CNTs) in polymeric resin. Unlike other old methods, the proposed improved technique is not dependent on various parameters and it is safer than old methods. This Multi-Stage approach includes functionalization of CNTs, mechanical dispersion and ultra-sonication (bath and probe). The quality of dispersion obtained by the proposed method, unlike the probe sonication method, is not affected by different variables such as frequency, cross-section and suspension's temperature. Because during the process, all these parameters are kept constant and linked to the time of process (Univariate system). In the planned tactic, the time of process is determined by a visual test in macro scale.In the next, in order to verify the presented method, Scanning electron microscopy (SEM) and viscosity tests were used. These tests were employed to examine and compare the quality of Single-wall carbon nanotubes (SWNT) distribution. This comparison was between the new presented approach and one of the known conventional methods (dispersion of functionalized nanotube via Ultra-sonic Probe). Also before these tests, FT-IR test was carryout for investigation of functionalized carbon nanotubes.The comparison between the results of the new proposed model and applied traditional method showed that the output quality achieved by the new method not only is not lower than the quality achieved by the traditional method but also sometimes is preferable. In addition, for validation, mechanical bending tests on samples made by the presented method showed that the proposed approach improves the mechanical properties of the nanocomposite. This increment was consistent with the results of previous researches that were based on the traditional method. Also, the proposed method was used for dispersing of another nanoparticle named Graphene Oxide, and the accuracy of the proposed method was re-confirmed. Finally, transmission electron microscopy (TEM) was used to show the full dispersion of SWNT based on the new proposed method.

Synthesis of Fluorophore Decorated Single-Walled Carbon Nanotubes for In-Vitro Cytocompatibility.

We report rhodamine based fluorophore derivative for the stable dispersion of single-walled carbon nanotubes (SWCNTs), which can afford better fluorescent label to carbon nanotubes (CNTs). The nanotubes-fluorophore conjugates are helpful in achieving stable dispersion in polar and non-polar solvents with intense fluorescence. The product was characterized through NMR, Mass spectrometry, Raman, XPS, SEM, AFM and Fluorescence measurements. The formation of SWCNT-g- Rhodamine was confirmed by the presence of D and G bands in Raman spectrum. The alkyl and aryl groups in the range of 14.8, 17.6, 38.1 and 96.3 ppm confirms the grafting of the nanocomposite through NMR. The morphological studies were carried out intensively for analyzing SWCNTs stable dispersion and the results from EDAX measurements shows the elements weight% of C: 35.09 and N: 30.1 concludes that SWCNTs are completely grafted onto rhodamine derivatives. The application of SWCNTs fluorophore conjugates were analyzed by cell viability studies using MTT assay and exhibits less toxic compare to other functionalized CNTs. The viability of percentage increases with decrease in the concentration of SWCNT-COCl with 91.7% of live cells even after 24 h at a concentration of 250 μg for SWCNT-g-Rhodamine. The fluorescent images obtained during viability analysis shows enhanced fluorescence for living cells in case of SWCNT-g-Rhodamine compared to SWCNT-COCl, which clearly shows the utility of decorating nanotubes with fluorophore. This research work further extends its application for molecular sensing and other biological process.

Determination of the length of single-walled carbon nanotubes by scanning electron microscopy

A methodology is presented to determine the length of well individualized single-walled carbon nanotubes (SWCNTs) by means of scanning electron microscopy (SEM). Accurate measurements on wide areas of the sample can be achieved in an easy, fast and trustworthy manner. We have tested several supports and solvents to optimize the dispersion of SWCNTs, as well as the SEM imaging conditions. The optimal methodology goes via dispersion of the sample in ortho-dichlorobenzene, deposition onto a continuous carbon film supported on a copper TEM grid, and SEM imaging at 2?kV in secondary electrons mode using a through-in-lens detector.•Individualization of SWCNTs is achieved by dispersion of SWCNTs in ortho-dichlorobenzene and deposition onto TEM grids•Individual SWCNTs are imaged by SEM•Length determination by SEM is as precise as AFM

Pyrene containing liquid crystalline asymmetric phthalocyanines and their composite materials with single-walled carbon nanotubes

In the present work we have studied the dispersion of single-walled carbon nanotubes in liquid crystalline asymmetrically substituted phthalocyanines (MPc, where M [Formula: see text] Cu, Co, and 2H) bearing one pyrene and six polyoxy groups as side chains. The influence of single-walled carbon nanotubes on the phase behavior of MPcs was investigated using X-ray diffraction, polarized optical microscopy and differential scanning calorimetry. It was demonstrated that the incorporation of small amounts of single-walled carbon nanotubes ([Formula: see text]1 wt.%) does not alter the MPc mesophases. The structural features and the sensor response of composite thin films of MPc with single-walled carbon nanotubes to ammonia vapor (10–50 ppm) was studied and compared with those of the films of pure MPc derivatives.

Synthesis of flexible nanotweezers with various metals and their application in carbon nanotube extraction

Flexible nanotweezers including Co(ii) dispersed single-walled carbon nanotubes in methanol.

Reversible dispersion and precipitation of single-walled carbon nanotubes using a pH-responsive rigid surfactant.

A pH-responsive rigid surfactant derived from rosin was used to disperse and precipitate single-walled carbon nanotubes (SWNTs) in aqueous solution. The precipitated SWNTs could be re-dispersed by changing the pH without sonication owing to the hydrophobic steric layers formed by the rigid group and π-π interactions from the azobenzene group.