Dispersion Of Single-walled Carbon Nanotubes Research Articles

Governing Factors for Carbon Nanotube Dispersion in Organic Solvents Estimated by Machine Learning

AbstractThe insolubility of single‐walled carbon nanotubes (SWCNTs) in most common organic solvents has been the cause of a bottleneck in their practical utilization. Aqueous SWCNT inks containing amphiphilic surfactants are widely used for processing including coatings and composite fabrication. Most practical processes are, however, designed to be compatible with organic solvents, generating a technological mismatch between production and utilization. This work reports on the surfactant‐assisted dispersion of SWCNTs in useful organic solvents, at up to quantitative yields. A feature extraction based on machine learning offers seemingly important, highly intuitive physicochemical factors that lead to efficient dispersion. These elucidated factors are associated not only with solvents–surfactant, but also solvent–SWCNT interactions. The organic SWCNT dispersion as well as its research methodology developed here may find widespread applications ranging from nanofluidics to functional materials design.

Synthesis of V2O5/Single-Walled Carbon Nanotubes Integrated into Nanostructured Composites as Cathode Materials in High Performance Lithium-Ion Batteries

Vanadium pentoxide (V2O5)-anchored single-walled carbon nanotube (SWCNT) composites have been developed through a simple sol–gel process, followed by hydrothermal treatment. The resulting material is suitable for use in flexible ultra-high capacity electrode applications for lithium-ion batteries. The unique combination of V2O5 with 0.2 wt.% of SWCNT offers a highly conductive three-dimensional network. This ultimately alleviates the low lithium-ion intercalation seen in V2O5 itself and facilitates vanadium redox reactions. The integration of SWCNTs into the layered structure of V2O5 leads to a high specific capacity of 390 mAhg−1 at 0.1 C between 1.8 to 3.8 V, which is close to the theoretical capacity of V2O5 (443 mAhg−1). In recent research, most of the V2O5 with carbonaceous materials shows higher specific capacity but limited cyclability and poor rate capability. In this work, good cyclability with only 0.3% per cycle degradation during 200 cycles and enhanced rate capability of 178 mAhg−1 at 10 C have been achieved. The excellent electrochemical kinetics during lithiation/delithiation is attributed to the chemical interaction of SWCNTs entrapped between layers of the V2O5 nanostructured network. Proper dispersion of SWCNTs into the V2O5 structure, and its resulting effects, have been validated by SEM, TEM, XPS, XRD, and electrical resistivity measurements. This innovative hybrid material offers a new direction for the large-scale production of high-performance cathode materials for advanced flexible and structural battery applications.

Dispersion of single-walled carbon nanotubes in water in presence of Direct Current field

Dispersion of single-walled carbon nanotubes in water in presence of Direct Current field

Quantification and removal of carbonaceous impurities in a surfactant-assisted carbon nanotube dispersion and its implication on electronic properties.

Carbonaceous impurities (CIs) affect the optoelectronic properties as well as the ability to use absorption spectroscopy to estimate the metallic content of a single-walled carbon nanotube (SWNT) dispersion. Therefore, a method for the accurate quantification and removal of CIs is required. We have devised methods to characterize and quantify CIs present in SWNT batches and to determine the effects of CIs on the optical and electrical properties of SWNT. Quantitative determination of CIs stems from the finding that chloroform selectively disperses CIs present in SWNT batches. CIs separated by dispersing the as-purchased SWNT batch in chloroform have the morphology of defective and agglomerated few-layered graphenes, whose sizes and locations depend on SWNT batches. Moreover, CIs exhibit a featureless UV-vis-mid-wavelength IR (MWIR) absorption curve and an extinction coefficient comparable to graphenes and show difference with carbon black, which is frequently used as the CI reference. The MWIR region that shows least absorptions caused by the transition of various SWNT types was utilized to assess the significant contribution made by CIs present in a surfactant-assisted SWNT dispersion, showing about 12–19 wt% of CIs in various SWNT dispersions. In addition, the extraction of CIs with chloroform results in a highly purified SWNT batch without any diameter distribution change originating from oxidative damage as compared to the commercially available purified SWNT batch. Finally, we found that increasing the weight of CIs present in a SWNT dispersion strongly lowers the thermal conductivity of a SWNT film when compared with the electrical conductivity. This study provides a way to understand the negative effects that CI has on the optoelectronic properties of SWNTs as well as the beneficial effects of excluding ubiquitous CIs in SWNTs batches.

Fabrication of Aluminum/Single-Walled Carbon Nanotube Oxidation Films through CNT-Added Surface Treatment

CNT-added surface treatment (CAST) is a newly developed technology that incorporates single-walled carbon nanotubes (SWCNTs) into a metal surface through alternate current electrolysis using a dispersion of SWCNTs in an alkaline aqueous solution. We apply this method to Al-plates and characterize their surface morphology and components through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. After CAST processing, protrusion structures of Al-oxide containing SWCNTs are formed on the surface of the Al-plate, and the surface morphology differs significantly from that of the surface of Al films treated through conventional anodic oxidation. The height and spacing of the protrusion structures formed on the surface of the CAST-treated Al-plates are 100 - 200 nm and 50 - 100 nm, respectively. In addition, we investigate the formation mechanism of the protrusion structure by applying a DC voltage between the working electrode (Al-plate) and a counter electrode immersed in a dispersion of SWCNTs in an alkaline aqueous solution. Comparing the Al-plate surface after treatment under both current directions, we propose a model for the formation process of protrusion structures containing SWCNTs based on catalyst surface etching.

Influence of ionic liquid on the dielectric relaxation behavior of SWCNT reinforced poly(vinyl alcohol) based nanocomposites

Polymer nanocomposites based on single-walled carbon nanotubes (SWCNT) and poly(vinyl alcohol) have been successfully prepared using a solvent casting approach. The dispersion pattern of SWCNT in the PVA matrix has been analyzed by a high-resolution transmission electron microscope (HRTEM). The mechanical and thermal stability of the films were assessed. The effect of SWCNT loading and imidazolium-based ionic liquid on the dielectric relaxation behavior of the PVA-based nanocomposites has been explored in the frequency range of 1 to 106 Hz at room temperature. The dielectric properties such as dielectric permittivity (εʹ), real and imaginary impedance (Zʹ and Zʹʹ), AC conductivity (σac) as well as Nyquist plot of the fabricated nanocomposites were explored in the presence and absence of ionic liquid (IL). The dielectric permittivity and AC conductivity increased with an increase in SWCNT loading and presence of IL due to the enhanced interfacial polarization of the SWCNT at the interface and proper dispersion of SWCNT throughout the polymer matrix. The decrease in impedance (Zʹ and Zʹʹ) with the increase in SWCNT loading is due to the enhanced proximity between the conductive channels. The reduction in semicircular area under the Nyquist plot in presence of IL and increasing SWCNT loading indicated the capacitive nature of fabricated nanocomposites and a decrease in bulk resistivity.

A facile method to enhance the flexibility and triboelectric output of PDMS using ionic liquid-coated single-wall carbon nanotubes

Energy harvesting devices based on triboelectric effect have gained much attention recently due to their significant potential in low-frequency applications, especially in wearable electronics. To enable these devices, flexible materials with relatively high electrical conductivity and large triboelectric output are needed. In this study, a PDMS composite is fabricated using embedded ionic liquid (IL) coated single-wall carbon nanotubes (SWCNTs). The ratio of IL to SWCNTs is tuned to achieve the desired material properties for wearable triboelectric nanogenerators. The SWCNT-IL-PDMS (IL: SWCNT= 20:1) composite exhibits a relatively high electrical conductivity (0.004 S/m) and an enhanced triboelectric output compared to unmodified PDMS. Specifically, the open-circuit voltage (Voc) and the short-circuit current (Isc) are increased by three folds. The relatively high electrical conductivity enables the composite to transfer charges without electrodes and reduces the internal impedance of triboelectric nanogenerators. The flexibility of the composite is also improved, as demonstrated by the decrease in both the tensile and compressive elastic moduli. In addition, the mechanism behind the change in electrical properties and triboelectric output is proposed and discussed in this paper. Specifically, the increase in the dielectric constant and electrical conductivity of the composites with IL is likely due to the better dispersion of SWCNT in the polymer matrix, and the change in the triboelectric output is a result of (1) the trade-off between dielectric constant and electrical conductivity, and (2) the shifting of triboelectric polarity with the addition of IL. This study not only provides a facile method to simultaneously increase the flexibility, electrical conductivity, and triboelectric output of polydimethylsiloxane (PDMS), but also generalizes the approach and paves the way to explore new flexible and electrically conductive materials for wearable triboelectric nanogenerators.

Noncovalent Functionalization of Single-Walled Carbon Nanotubes with a Photocleavable Polythiophene Derivative.

Single-walled carbon nanotubes (SWCNTs) have received extensive research attention owing to their extraordinary optical, electrical, and mechanical properties, which make them particularly attractive for application in optoelectronic devices. However, SWCNTs are insoluble in almost all solvents. Therefore, developing methods to solubilize SWCNTs is crucial for their use in solution-based processes. In this study, we developed a photocleavable polythiophene-derivative polymer dispersant for SWCNTs. The noncovalent surface functionalization of SWCNTs with a polymer allows their dispersal in tetrahydrofuran. The resultant solution-processed polymer/SWCNT composite film undergoes a hydrophobic-to-hydrophilic change in surface properties upon light irradiation (313 nm) because hydrophilic carboxyl groups are formed upon photocleavage of the hydrophobic solubilizing units in the polymer. Furthermore, the photocleaved composite film displays a 38-fold increase in electrical conductivity. This is due to the removal of the solubilizing unit, which is electrically insulating.

Dispersion of Single-Walled Carbon Nanotubes via Rapid Expansion of Supercritical Suspensions

Dispersion of Single-Walled Carbon Nanotubes via Rapid Expansion of Supercritical Suspensions

Strong and multi-responsive composite coiled yarn based on electrospun polyamide-6 nanofiber and carbon nanotube

Polymer based coiled yarns are a new kind of smart materials hold promising applications in various high-tech fields such as artificial muscle, soft robotic, prosthesis, and smart textile. In this paper, we report a facile method for preparation of composite coiled yarn consisted of polyamide-6 (PA6) and single-walled carbon nanotube (SWNT). The homogeneous dispersion of SWNT is first prepared and sprayed on both sides of PA6 nanofiber non-woven, the composite non-woven is then twisted into compact coiled yarn. The uniform coating of PA6 non-woven by SWNT is demonstrated and the incorporation of continuous SWNT network has significantly improved the mechanical properties of composite yarn in comparison with pure PA6 yarn. The good photothermal and electrothermal properties of the SWNT network also endow the composite yarn with near infrared light and electricity responsive ability in terms of contraction that are not possessed in pure PA6 coiled yarn. In addition, the controlled contractive behavior of composite yarn by different voltage is also demonstrated. It is expected that this work could provide an alternative method for strong and multi-responsive composite coiled yarns.

Nonlinear optical properties of single-walled carbon nanotubes/water dispersed media exposed to laser radiation with nano- and femtosecond pulse durations

The constant increase in the power of laser systems and the growth of potential fields for the application of lasers make the problem of protecting sensitive elements of electro-optical systems and visual organs from high-intensity radiation an urgent issue. Modern systems are capable of generating laser radiation in a wide range of wavelengths, durations, and pulse repetition rates. High-quality protection requires the use of a universal limiter capable of attenuating laser radiation, not causing colour distortion, and having a high transmission value when exposed to low-power radiation. For this, dispersed media based on carbon nanotubes with unique physicochemical properties can be used. Such media have constant valuesof their absorption coefficient and refractive index when exposed to low-intensity laser radiation and change their properties only when the threshold value is reached.The aim of this work was the study of the nonlinear optical properties of an aqueous dispersion of single-walled carbon nanotubes exposed to nano- and femtosecond radiation. For the characterization of the studied medium, Z-scan and fixed sample location experiments were used. The optical parameters were calculated using a threshold model based on the radiation transfer equation.As a result of the experiments, it was shown that the aqueous dispersion of single-walled carbon nanotubes is capable of limiting radiation with wavelengths from the visible and near-IR ranges: nano- (532, 1064 nm) and femtosecond (810 nm). A description of nonlinear optical effects was proposed for when a medium is exposed to radiation with a nanosecond duration due to reverse saturable absorption and two-photon absorption. When the sample exposed for a femtosecond duration the main limiting effect is spatial self-phase modulation. The calculated optical parameters can be used to describe the behaviour of dispersions of carbon nanotubes when exposed to radiation with different intensities. The demonstrated effects allow us to conclude that it is promising to use the investigated media as limiters of high-intensity laser radiationin optical systems to protect light-sensitive elements.

Development of Quality Control Methods for Dispersibility and Stability of Single-Wall Carbon Nanotubes in an Aqueous Medium.

The attractive properties of single-wall carbon nanotubes (SWCNT) such as mechanical strength and high electrical and thermal conductivity are often undercut by their agglomeration and re-agglomeration tendencies. As a result, the application of SWCNT as additives in advanced composite materials remain far from their potential, with proper dispersion being the major inhibitor. This work presents a dispersion quality control approach for water-based SWCNT dispersions (dispersed by a unique combination of physical and chemical methods), using complementary and easily scalable, characterization methods. UV-Vis spectroscopy, rheological measurements, and precipitant sheet resistance were used to understand the properties of the initial solution through processing and application. From an industrial perspective, these methods are fast and easy to measure while giving a repetitive and quick indication of dispersion quality and stability. The methods were correlated with microscopy and Raman spectroscopy to validate dispersion and SWCNT quality under various dispersing energies. The protocol was then applied to estimate the stability of SWCNT solutions, as well as the effectiveness of different surfactants in aiding dispersion. The simple, fast, and scalable combination of different characterizations provides good SWCNT dispersion and can be used as a quality control system for industrial production and usage.

Identification of Chiral-Specific Carbon Nanotube Binding Peptides Using a Modified Biopanning Method

Peptides can recognize and selectively bind to a wide variety of materials dependent on both their surface properties and the environment. Biopanning with phage or cell peptide display libraries can identify material-specific binding peptides. However, the limitations with sequence diversity of traditional bacteriophage (phage) display libraries and loss of unique phage clones during the amplification cycles results in a smaller pool of peptide sequences identified. False positive sequences tend to emerge during the biopanning process due to highly proliferating, yet nonspecific, phages. In order to overcome this limitation of traditional biopanning methodology, a modified method using high-throughput next generation sequencing (HTS) was tested to select for unique peptides specific to two types of single wall carbon nanotube (SWNTs) sources with varying diameter distribution and chirality. Here, the process, analysis, and characterization of peptide sequences identified using the modified method is further described and compared to a peptide identified in literature using the traditional method. Selected sequences from this study were incorporated in a SWNT dispersion experiment to probe their selectivity to the nanotube diameter. We show that NHTS can uncover unique binding sequences that might have otherwise been lost during the traditional biopanning method.

Dispersions of carbon nanotubes by helical flavin surfactants: Solvent induced stability and chirality enrichment, and solvatochromism

Although solvent governed stability, selection and optical behavior of single walled carbon nanotubes (SWNTs) brought about by using specialized surfactants have importance in relation to various optoelectronic and biological applications, their origins and solvatochromism have not been thoroughly explored owing to the lack of ideal surfactant dispersing SWNTs. We show that solvent driven SWNT selection and solvatochromism occurs in SWNTs wrapped by two flavin derivatives in solvents with dielectric constants (ε) ranging from 2.3 to 80.4. Flavin-SWNT nanocomposite dispersions exhibit near-armchair and chirality-specific enrichment in lower ε aromatic solvents, and those with broader chirality selectivity are formed in higher ε solvents. Those trends are also observed by controlling flavin concentration. Consideration of optical spectra provides relative quantum yields of flavin-SWNT in each solvent, showing toluene and p-xylene dispersions as best owing to highly individualized SWNT. The selectivities and relative stabilities of the flavin-SWNT nanoconjugates are associated with the solubility parameter (δ), which controls the respective morphology of the side chains and the relative Gibbs energies of the nanoconjugates relative to those of the free flavin and SWNTs. Differences between δ of side chains vs. the media results in extended and collapsed side chain conformations in respective lower and higher ε solvents, leading to diameters (dt) selection of SWNT owing to diameter modulation of the isoalloxazine assembly. In addition, with increasing ε optical transitions of flavin/SWNT exhibit lower bathochromic shifts owing to a passivating role played by the isoalloxazine that does not take place with other surfactants. The results suggest new guidelines for the design of good SWNT dispersions that take into consideration self-association of the surfactant, conformations of side chains and the nature of the solvent.

Visible near Infrared Spectroscopic Evidence of the Purification and Dispersion of Single-Walled Carbon Nanotubes

The application of dispersible single-walled carbon nanotubes in water is required in many fields, such as mechanics, thermology, electricity, etc. In this paper, single-walled carbon nanotube samples were dispersed in sodium deoxycholate aqueous solution with the assistance of ultrasonic crushing. The effects of centrifugal time, concentration and centrifugal velocity on dispersion were investigated. After centrifugal separation, the dispersible single-walled carbon nanotubes solution in water was obtained. The dispersion behavior of single-walled carbon nanotubes in sodium deoxycholate aqueous solution was further investigated by Uv-visible near infrared spectrum and electrochemical cyclic voltammetry curve. At the same time, characterization results of Uv-visible near infrared spectrum shew that the purity of single-walled carbon nanotubes was improved. The cyclic voltammetry curves of single-walled carbon nanotubes after purification and dispersion were tested by electrochemical method, and the electron transfer behavior of single-walled carbon nanotubes after purification and dispersion was investigated.

Flexible Chemiresistive Cyclohexanone Sensors Based on Single-Walled Carbon Nanotube-Polymer Composites.

We report a chemiresistive cyclohexanone sensor on a flexible substrate based on single-walled carbon nanotubes (SWCNTs) functionalized with thiourea (TU) derivatives. A wrapper polymer containing both 4-vinylpyridine (4VP) groups and azide groups (P(4VP-VBAz)) was employed to obtain a homogeneous SWCNT dispersion via noncovalent functionalization of SWCNTs. The P(4VP-VBAz)-SWCNT composite dispersion was then spray-coated onto an organosilanized flexible poly(ethylene terephthalate) (PET) film to achieve immobilizing quaternization between the pyridyl groups from the polymer and the functional PET substrate, thereby surface anchoring SWCNTs. Subsequent surface functionalization was performed to incorporate a TU selector into the composites, resulting in P(Q4VP-VBTU)-SWCNT, for the detection of cyclohexanone via hydrogen bonding interactions. An increase in conductance was observed as a result of the hydrogen-bonded complex with cyclohexanone resulting in a higher hole density and/or mobility in SWCNTs. As a result, a sensor device fabricated with P(Q4VP-VBTU)-SWCNT composites exhibited chemiresistive responses (ΔG/G0) of 7.9 ± 0.6% in N2 (RH 0.1%) and 4.7 ± 0.4% in air (RH 5%), respectively, upon exposure to 200 ppm cyclohexanone. Selective cyclohexanone detection was achieved with minor responses (ΔG/G0 < 1.4% at 500 ppm) toward interfering volatile organic compounds (VOC). analytes. We demonstrate a robust sensing platform using the polymer-SWCNT composites on a flexible PET substrate for potential application in wearable sensors.

Solution-phase p-type doping of highly enriched semiconducting single-walled carbon nanotubes for thermoelectric thin films

Single-walled carbon nanotubes (SWCNTs) are attractive materials for next-generation energy-harvesting technologies, including thermoelectric generators, due to their tunable opto-electronic properties and high charge carrier mobilities. Controlling the Fermi level within these unique 1D nanomaterials is often afforded by charge transfer interactions between SWCNTs and electron or hole accepting species. Conventional methods to dope SWCNT networks typically involve the diffusion of molecular redox dopant species into solid-state thin films, but solution-phase doping could potentially provide routes and/or benefits for charge carrier transport, scalability, and stability. Here, we develop a methodology for solution-phase doping of polymer-wrapped, highly enriched semiconducting SWCNTs using a p-type charge transfer dopant, F4TCNQ. This allows doped SWCNT inks to be cast into thin films without the need for additional post-deposition doping treatments. We demonstrate that the introduction of the dopant at varying stages of the SWCNT dispersion process impacts the ultimate thermoelectric performance and observe that the dopant alters the polymer selectivity for semiconducting vs metallic SWCNTs. In contrast to dense semiconducting polymer films, where solution-phase doping typically leads to disrupted morphologies and poorer TE performance than solid-state doping, thin films of solution-doped s-SWCNTs perform similarly to their solid-state doped counterparts. Interestingly, our results also suggest that solution-phase F4TCNQ doping leads to fully ionized and dimerized F4TCNQ anions in solid-state films that are not observed in films doped with F4TCNQ after deposition. Our results provide a framework for the application of solution-phase doping to a broad array of high-performance SWCNT-based thermoelectric materials and devices that may require high-throughput deposition techniques.

Study on the improvement of dispersibility and orientation control of fluorocarbon‐modified single‐walled carbon nanotubes in a fluorinated polymer matrix

AbstractA technique for improving the dispersibility of fluorocarbon‐modified, single‐walled carbon nanotubes (SWCNTs) in fluorinated polymers was investigated. Furthermore, we aimed to achieve uniaxial orientation of SWCNT aggregates via a simple high‐temperature drawing method to yield fluoropolymer‐based nanocomposites containing uniform dispersed SWCNTs. Highly water‐repellent SWCNTs were mixed with phase‐separable fluorinated polymers by the chemical modification of their surfaces with fluorocarbons. Introducing a fluorinated phosphonic acid surfactant with a high‐sublimation temperature as the third component to improve dispersibility in the polymer matrix resulted in an innovative improvement. The uniform dispersed SWCNTs in the matrix improved the crystallinity, crystallization temperature, and mechanical characteristics of the composites. The high‐temperature uniaxial orientation of the composite material reduced differences in the physical properties in the polymer due to differences in the initial dispersibility. This effect was expected since the drawing process promoted the deagglomeration of SWCNTs in the matrix. However, optimal physical properties were observed in SWCNT‐oriented composite samples with an excellent initial dispersion.

Unzipping Carbon Nanotube Bundles through NH-π Stacking for Enhanced Electrical and Thermal Transport.

Bundling of single-walled carbon nanotubes (SWCNTs) significantly undermines their superior thermal and electrical properties. Realizing stable, homogeneous, and surfactant-free dispersion of SWCNTs in solvents and composites has long been regarded as a key challenge. Here, we report amine-containing aromatic and cyclohexane molecules, which are common chain extenders (CEs) for epoxy curing in industry, can be used to effectively disperse CNTs. We achieve single-tube-level dispersion of SWCNTs in CE solvents, as demonstrated by the strong chirality-dependent absorption and photoluminescence emission. The SWCNT-CE dispersion remains stable under ambient conditions for months. The excellent dispersibility and stability are attributed to the formation of an n-type charge-transfer complex through the NH-π interaction between the amine group of CEs and the delocalized π bond of SWCNTs, which is confirmed by the negative Seebeck coefficient of the CE-functionalized SWCNT films, the red shift of the G band in the Raman spectra, and the NH-π peak in X-ray photoelectron spectroscopy. The high dispersibility of CEs significantly improves the electrical and thermal transport of macroscale CNT assemblies. The sheet resistance of the CE-dispersed SWCNT thin films reaches 161 Ω sq-1 at 80.8% optical transmittance after functional modification by HNO3. Moreover, the CEs cross-link CNTs and epoxy molecules, forming a pathway for phonon transport in CNT/epoxy nanocomposites. The thermal conductivity of the CE-CNT-epoxy composite is enhanced by 1850% compared with the original epoxy, which is the highest enhancement reported to date for CNT/epoxy nanocomposites. The CE-based NH-π interaction provides a new paradigm for the effective and stable dispersion of SWCNTs in a facile and scalable process.

(Invited) Glycopolymer-Wrapped Carbon Nanotubes for Profiling Carbohydrate-Protein Interactions

Stable dispersions of single-wall carbon nanotubes (SWCNTs) by biopolymers in an aqueous environment facilitate their potential biological and biomedical applications. Synthetic glycopolymers – polymers with carbohydrate pendant groups – have been used extensively to mimic the functions of naturally occurring glycoconjugates. In this work, we created water soluble glycopolymer-wrapped SWCNTs (Glyco-SWCNTs) via noncovalent complexation utilizing lactose-containing polymers with various carbohydrate densities and chain lengths. Subsequently, Glyco-SWCNT complexes are utilized as near-infrared fluorescent probes to detect multivalent interactions between carbohydrates and carbohydrate-binding proteins. These SWCNT-based fluorescent probes can be potentially utilized for profiling targeted carbohydrate-protein interactions in complicated biological samples and in vivo analysis.