Dispersion Of Single-walled Carbon Nanotubes Research Articles

Highly efficient oxidation of single-walled carbon nanotubes in liquid crystalline phase and dispersion for applications in Li-ion batteries

Single-walled carbon nanotubes (SWCNTs), which have high electrical conductivity, are promising candidates for enhancing the energy storage capability of lithium-ion batteries (LIBs). However, their usage in energy storage devices is limited due to the large bundle size and difficulties in dispersion. Here, we implement the debundling and mild oxidation of SWCNTs in the liquid crystalline phase paste (2 wt% solid content) with strong acid and co-intercalant (NaNO3). The thermal treatment successfully introduced carboxylic acid groups without requiring other oxidizing agents. The pretreated SWCNTs were dispersed in organic solvents such as N-methyl pyrrolidone (NMP) without dispersant molecules and were utilized as conductive additives for LIBs. Raman spectroscopy analysis showed that the D/G ratio of the SWCNT film changed from 0.012 to 0.023, implying that the oxidation method proposed herein is less defective and efficient. The filtrated 15 μm film of the SWCNTs exhibited a high electrical conductivity of 2384 S/cm. SWCNT dispersion in NMP was utilized to fabricate LIB cathode electrodes. Compared to the carbon black-applied electrodes, the SWCNT-applied LiNi0.8Co0.1Mn0.1O2 (NCM811) electrodes exhibited enhanced dispersity of conductive additive/binder networks, leading to improved electrode integrity. The capacity retention after 100 cycles for cells with SWCNTs was approximately 23.3 % better than that of the cells without SWCNTs.

Superior photodynamic effect of single-walled carbon nanotubes in aprotic media: a kinetic study

It has been confirmed that single-walled carbon nanotubes (SWCNTs) could generate reactive oxygen species in aprotic media by utilizing photon energy. However, the impact of photon irradiation on SWCNTs and the kinetics of the generation process in aprotic media are still unclear, which significantly limits the yield performance. In this work, the kinetics for photodynamic effects has been investigated by performing characterizations on ultraviolet-treated SWCNTs using Raman spectroscopy, conductive atomic force microscope (in-situ), kelvin probe force microscope, and X-ray photoelectron spectroscopy. It is found that ultraviolet-treated SWCNTs are observed to have more defects, lower conductivity, and less surface charge after energy conversion. Starting from the fundamental intrinsic properties of SWCNTs, the kinetics and formation of these changes are thoroughly discussed. It turns out that the dispersion, chirality, and structural integrity of SWCNTs are important for achieving high-performance photodynamic effects, which are validated using several different SWCNTs as well as other carbon nanomaterials. A type of (6,5) s-SWCNTs exhibited the highest energy efficiency among a variety of other carbon nanomaterials. The yield rate is 2.15 mM/h, and the energy consumption is determined to be 2.79 W·h/mM. This work is expected to help dramatically boost the energy efficiency of the photodynamic effect in aprotic media, and pave the way for designing high-performance carbon nanomaterial-based photoinduced devices.

Single walled Carbon nanotube: Chitosan conjugate for sustained ophthalmic delivery of Ciprofloxacin from ointment; its evaluation and in vivo eye irritation study

ABSTRACT The current study aimed at the preparation and evaluation of single-walled carbon nanotube (SWCNTs) loaded Ciprofloxacin ophthalmic ointment. SWCNTs were functionalized and further Chitosan was loaded on the FSWCNT to achieve solubility of the SWCNT and further Ciprofloxacin was loaded on developed system. The developed system was mixed in ophthalmic ointment base and homogenized at high speed to ensure proper dispersion of drug-loaded SWCNT in the base. The prepared formulation was analyzed with hyphenated tools. The drug loading capacity of Ciprofloxacin on F SWCNT was found to be 86 ± 0.234%. In vitro drug release study exhibited 73.56% drug release at the end of 14 h which indicated the sustained release of drug from the SWCNT. The antimicrobial study, antimicrobial biofilm assay, and in vivo irritation tests were carried out as per OECD 405 guidelines. The results obtained were found to be satisfactory and within the limits of standard. Based on the results, it was concluded that the modified FSWCNT can be successfully used for drug loading and the formulation can be used for ophthalmic purpose. Moreover, the prepared system may be utilized in sustained release ophthalmic formulations and for treatment of chronic eye disease(s).

Manufacturing of Carbon Nanotube-Polystyrene Filament for 3D Printing: Nanoparticle Dispersion and Electromagnetic Properties

3D printing is a promising technology for creating polymer objects of a given architecture with specified functional properties. In fact, the choice of filaments for 3D printing is quite limited. Here, we report a process for producing polystyrene filaments with 0.0025–2 wt.% single-walled carbon nanotubes (SWCNTs) by extruding crushed polystyrene composites. The resulting filaments are characterized by a high uniformity of filler distribution and the absence of air pores. Comparison of microscopy data and electromagnetic properties of base composites and composite materials printed from filaments showed that extrusion and printing improve SWCNT dispersion. The proposed method can be used to create filaments for 3D printing of objects from various base polymers containing functional fillers up to the electrical percolation threshold and above.

Attachment of DNA-Wrapped Single-Walled Carbon Nanotubes (SWNTs) for a Micron-Sized Biosensor.

We fabricated a micron-sized biodevice based on the near-infrared photoluminescence (PL) response of single-walled carbon nanotubes (SWNTs). Various biosensors using the unique optical responses of SWNTs have been proposed by many research groups. Most of these employed either colloidal suspensions of dispersed SWNTs or SWNT films on flat surfaces, such as electrodes. In this study, we attached DNA-wrapped SWNTs (DNA-SWNTs) to frustule (micron-sized nanoporous biosilica) surfaces, which were purified from cultured isolated diatoms. After the injection of an oxidant and a reductant, the SWNTs on the frustules showed prominent PL responses. This suggests that the biodevice functions as a micron-sized redox sensor. Frustules can be easily suspended in aqueous solutions because of their porous structures and can easily be collected as pellets by low-speed centrifugation. Thus, the removal of unbound SWNTs and the recovery of the fabricated DNA-SWNT frustules for reuse were achieved by gentle centrifugation. Our proposal for micron-sized SWNT biodevices would be helpful for various biological applications.

Solvent-optimized monolithic SWCNT-based thermoelectric generator for efficient electricity harvesting from body heat and sunlight

A lightweight and flexible thermoelectric generator (TEG) based on monolithic designed single-walled carbon nanotubes (SWCNT) is successfully developed, which can effectively harvest electricity from hybrid sources of body heat and solar light with high energy output. By properly selecting SWCNT dispersion solvents, SWCNT films with an optimal p-type power factor of 526 μW m−1 K−2, and n-type power factor of 489 μW m−1 K−2 are achieved, among the highest reported power factors for solution-processed CNT-based films. Monolithic TEG based on the optimized SWCNT films leads to exceptionally high device performance both under constant heat and sunlight. The 8-leg TEG exhibits output power density over 110.2 μW cm−2 and 25.3 μW g−1 with a temperature gradient of 28 K, which is among the best energy-harvesting performance of CNT-based TEG. In addition, a large temperature gradient over 22.1 K is generated under AM1.5 1 sun illumination, owing to the SWCNT films act not only as TE modules but also solar-light absorber, and the TEG yields a record-high output power density of 66.0 μW cm−2 and 15.1 μW g−1 under 1 sun. Our TEG design based on SWCNT shows great potential in powering flexible micro-watt electronics by effectively harvesting electricity from both body heat and sunlight.

Sonication-Free Dispersion of Single-Walled Carbon Nanotubes for High-Sorption-Capacity Aerogel Fabrication.

Homogenously dispersing single-walled carbon nanotubes (SWNTs) in solvents has been one critical step towards exploiting their exceptional properties in high-performance components. However, the solubility of SWNTs is severely limited by the inert tube surfaces and strong tube-tube van der Waals attractions. Starting with carbon nanotubides, i.e., negatively charged SWNTs reduced by alkali metals, we herein propose a sonication-free approach to prepare an aqueous dispersion of SWNTs. The approach combines the spontaneous dissolution of nanotubides in polar aprotic solvents with polyvinylpyrrolidone wrapping and dialysis in deionized H2O, which results in well-dispersed, neutralized SWNTs. The gelation of concentrated SWNT dispersion leads to the formation of hydrogels, which is subsequently transformed into SWNT aerogels through lyophilization. The prepared SWNT aerogels exhibit high-mass-sorption capacities for organic solvent absorption, paving the way towards harvesting the extraordinary properties of SWNTs.

A Flexible Piezoelectric Device for Frequency Sensing from PVDF/SWCNT Composite Fibers.

Polymer piezoelectric devices have been widely studied as sensors, energy harvesters, and generators with flexible and simple processes. Flexible piezoelectric devices are sensitive to external stimuli and are attracting attention because of their potential and usefulness as acoustic sensors. In this regard, the frequency sensing of sound must be studied to use flexible piezoelectric devices as sensors. In this study, a flexible piezoelectric device composed of a polymer and an electrode was successfully fabricated. Polyvinylidene fluoride, the active layer of the piezoelectric device, was prepared by electrospinning, and electrodes were formed by dip-coating in a prepared single-walled carbon nanotube dispersion. The output voltage of the external sound was matched with the input frequency through a fast Fourier transform, and frequency matching was successfully performed, even with mechanical stimulation. In a high-frequency test, the piezoelectric effect and frequency domain peak started to decrease sharply at 300 Hz, and the limit of the piezoelectric effect and sensing was observed from 800 Hz. The results of this study suggest a method for developing flexible piezoelectric-fiber frequency sensors based on piezoelectric devices for acoustic sensor systems.

Continuous film casting of polycarbonate/single‐walled carbon nanotubes composites with ultrasound‐assisted twin‐screw extruder: Effect of screw configuration

AbstractPolymer films are widely used in various industries, and incorporation of nanofillers into polymer films can give much more versatility in their applications. Polymer/carbon nanotubes (CNTs) composite films with good electrical conductivity can easily find applications in anti‐static or electrostatic discharge (ESD) protection. In the present study, efforts were devoted to investigate novel ultrasound‐assisted twin‐screw extrusion technology on improving the dispersion and distribution of single‐walled carbon nanotubes (SWNTs) in polycarbonate (PC) composites films via extrusion process. As a key processing parameter, effect of screw configuration on the performance of the composite films were systematically studied. Electrical, rheological, morphological and mechanical properties were characterized to illustrate the processing‐structure–property relationship during continuous film casting of PC/SWNTs composites with ultrasound‐assisted twin‐screw extruder. Results indicated that the screw configuration containing more kneading blocks led to better SWNTs dispersion and distribution, while the effect of ultrasound was more prominent in screw design with less kneading blocks.

The Effects of Lengths of Flavin Surfactant N-10-Alkyl Side Chains on Promoting Dispersion of a High-Purity and Diameter-Selective Single-Walled Nanotube.

Flavin with defined helical self-assembly helps to understand chemical designs for obtaining high-purity semiconducting (s)-single-walled carbon nanotubes (SWNT) in a diameter (dt)-selective manner for high-end applications. In this study, flavins containing 8, 12, 16, and 20 n-alkyl chains were synthesized, and their single/tandem effects on dt-selective s-SWNT dispersibility were investigated at isomolarity. Flavins with n-dodecyl and longer chain lengths (FC12, FC16, and FC20) act as good surfactants for stable SWNT dispersions whereas n-octyl flavin (FC8) exhibits poor dispersibility owing to the lack of SWNT buoyancy. When used with small-dt SWNT, FC8 displays chirality-selective SWNT dispersion. This behavior, along with various flavin helical motifs, prompts the development of criteria for ‘side chain length (lS)’ required for stable and dt-selective SWNT dispersion, which also explains lS-dependent dt-enrichment behavior. Moreover, SWNT dispersions with flavins with dodecyl and longer lS exhibit increased metallic (m)-SWNT, background absorption-contributing carbonaceous impurities (CIs) and preferential selectivity of s-SWNT with slightly larger dt. The increased CIs that affect the SWNT quantum yield were attributed to a solubility parameter. Furthermore, the effects of flavin lS, sonication bath temperature, centrifugal speed, and surfactant concentration on SWNT purity and s-/m-SWNT ratio were investigated. A tandem FC8/FC12 provides fine-tuning of dt-selective SWNT dispersion, wherein the FC8 ratio governs the tendency towards smaller dt. Kinetic and thermodynamic assemblies of tandem flavins result in different sorting behaviors in which wide dt-tunability was demonstrated using kinetic assembly. This study highlights the importance of appropriate side chain length and other extrinsic parameters to obtain dt-selective or high-purity s-SWNT.

Liquid Crystalline Behaviors of Single-Walled Carbon Nanotubes in an Aqueous Sodium Cholate Dispersion.

Controlling the alignment of single-walled carbon nanotubes (SWCNTs) on the macroscopic scale is critical for practical applications because SWCNTs are extremely anisotropic materials. One efficient technique is to create an effective SWCNT dispersion, which shows a liquid crystal (LC) phase. A strong acid treatment can realize SWCNT liquid crystalline dispersions. However, strong acids pose a substantial safety risk, which renders the process unfit for mass production. Herein, an isolated SWCNT dispersion displaying an LC behavior is prepared using sodium cholate without an acid treatment, and its phase transition behaviors are systematically investigated across the isotropic to biphasic to nematic phases. As the SWCNT concentration increases, the dispersion undergoes an isotropic-to-nematic phase transition in which the spindle-shaped LC droplets, or the so-called tactoids, and the Schlieren textures can be observed in the intermediate biphasic state and the nematic phase, respectively. The arrangements of SWCNTs in the tactoids and the Schlieren structures are directly investigated by polarized optical microscopy. The clear LC behaviors of the CNT dispersion suggest that the CNT orientations can be controlled by the normal surfactant-assisted method, which is a crucial advantage for the liquid-phase processing of CNT fibers and films.

(Digital Presentation) Realistic Molecular Dynamics Modeling of ssDNA/SWCNT Hybrids

Despite the importance of single-wall carbon nanotubes (SWCNTs) coated with short oligos of single-stranded DNA (ssDNA), the structure-specific interactions in these hybrids remain poorly understood. It is known that the interactions can depend on the DNA base sequence and length, and on the nanotube diameter and roll-up angle. To study these phenomena, we are applying a combination of computational and experimental methods. A major goal for guiding and validating molecular dynamics simulations of the hybrid structures is finding the average length of nanotube covered by each ssDNA oligo. We have quantified this by carefully preparing dialyzed aqueous dispersions of SWCNTs in specific oligos and then measuring the absolute mass concentrations of both components using total organic carbon analysis. Corresponding absorption spectra were also measured to deduce ultraviolet SWCNT molar absorptivities (structurally averaged), which in combination with known ssDNA nucleobase absorptivities allow quicker determinations of mass ratios in the hybrids. Our results for a library of hybrids indicate that purine nucleobases on average cover a larger region on the nanotube surface than do pyrimidine nucleobases, as is consistent with the sizes of those aromatic structures. This average coverage is key to developing realistic atomistic molecular dynamics models for the conformations of ssDNA adsorbed on SWCNT sidewalls. Examples of such computed hybrid structures and their significance will be presented.

Polymethyl(1-Butyric acidyl)silane-Assisted Dispersion and Density Gradient Ultracentrifugation Separation of Single-Walled Carbon Nanotubes.

Individual single–walled carbon nanotubes (SWNTs) with distinct electronic types are crucial for the fabrication of SWNTs–based electronic and magnetic devices. Herein, the water–soluble polymethyl(1–butyric acidyl)silane (BA–PMS) was synthesized via the hydrosilylation reaction between 3–butenoic acid and polymethylsilane catalyzed by 2,2′–azodibutyronitrile. As a new dispersant, BA–PMS displayed a quite good dispersing capacity to arc–discharged SWNTs and moderate selectivity for metallic species. The application of sucrose–DGU, the density gradient ultracentrifugation with sucrose as the gradient medium, to the co–surfactants (BA–PMS and sodium dodecyl sulfonate) individually dispersed SWNTs yielded metallic SWNTs of 85.6% purity and semiconducting SWNTs of 99% purity, respectively. This work paves a path to the DGU separation of the SWNTs dispersed by polymer–based dispersants with hydrophobic alkyl chains.

Comprehensive Study of the Chemistry behind the Stability of Carboxylic SWCNT Dispersions in the Development of a Transparent Electrode.

Single-walled carbon nanotubes (SWCNTs) are well-known for their excellent electrical conductivity. One promising application for SWCNT-based thin films is as transparent electrodes for uncooled mid-IR detectors (MIR). In this paper, a combination of computational and experimental studies were performed to understand the chemistry behind the stability of carboxylic SWCNTs (SWCNTs-COOH) dispersions in different solvents. A computational study based on the density functional tight-binding (DFTB) method was applied to understand the interactions of COOH-functionalized carbon nanotubes with selected solvents. Attention was focused on understanding how the protonation of COOH groups influences the binding energies between SWCNTs and different solvents. Thin film electrodes were prepared by alternately depositing PEI and SWCNT-COOH on soda lime glass substrates. To prepare a stable SWCNT dispersion, different solvents were tested, such as deionized (DI) water, ethanol and acetone. The SWCNT-COOH dispersion stability was tested in different solvents. Samples were prepared to study the relationship between the number of depositions, transparency in the MIR range (2.5–5 µm) and conductivity, looking for the optimal thickness that would satisfy the application. The MIR transparency of the electrode was reduced by 20% for the thickest SWCNT layers, whereas sheet resistance values were reduced to 150–200 kΩ/sq.

Dispersion of Single-Walled Carbon Nanotubes in Ethanol–Cholic Acid Mixtures: Experiments and Molecular Dynamic Simulation

Dispersion of Single-Walled Carbon Nanotubes in Ethanol–Cholic Acid Mixtures: Experiments and Molecular Dynamic Simulation

Peptide-Encapsulated Single-Wall Carbon Nanotube-Based Near-Infrared Optical Nose for Bacteria Detection and Classification

Sense of smell has been used as a diagnostic tool for almost entire human history. While successful examples of the use of the human nose for diagnostics are rare in modern history, there are ample reports of use of animals to diagnose various medical conditions. Bacterial infections often result in strong odors. In recent years, electronic noses (e-nose) and optical noses (o-nose) are of high interest in diagnostics and classification of bacterial infections. Artificial olfactory sensors can perform noninvasively, immediately at the point of care, do not require extensive sample handling, and promise to be highly cost-effective. This manuscript demonstrates the development of a near-infrared optical sniffer comprised of peptide-encapsulated (6,5) single-wall carbon nanotubes (SWCNTs) for bacteria detection and classification. Sixteen different peptides that include tyrosine in different proportions and positions were synthesized. The ability of these peptides to disperse SWCNTs in water was tested, and the intensity of the resultant optical signal was evaluated. Overall, longer peptides provided better dispersion as compared to shorter peptides. Addition of the fluorenylmethyloxycarbonyl chloride (Fmoc) group to positively charged peptides tested in the current study significantly improved SWCNT dispersion and signal intensity. The sensors successfully distinguished between the odor of sterile growth medium, Escherichia coli, and Klebsiella pneumoniae. Moreover, we demonstrated the possibility of using the developed sensors for antibiotics susceptibility testing. The sensors provided results in real-time, enabled multiple-usage, and operated at room temperature.

Selective dispersion of semiconducting single-walled carbon nanotubes with aromatic polyimides

Individually dispersed single-walled carbon nanotubes (SWNTs) with the conductivity of metals or semiconductors only are crucial for their applications in electronics, optics and magnetism. In this work, five aromatic polyimides with varying backbones were initially applied to the study on the dispersion of arc-discharge SWNTs. Spectroscopic characterizations by vis-NIR absorption and Raman scattering confirm that the polyimide molecules possess various selective dispersing ability toward semiconducting SWNTs. The effective dispersion of SWNTs is a result of the spirally wound polyimides around SWNTs dictated by the π-π stacking interactions between the backbone of polyimides and the surface of SWNTs, and the selectivity in semiconducting SWNTs is attributable to the charge transfer from polyimide molecules to SWNTs. The various dispersing behaviors of the polyimides toward SWNTs could be accounted for by the difference in aromatic surface area and flexibility of their backbones.

Single-Walled Carbon Nanotube Membranes Accelerate Active Osteogenesis in Bone Defects: Potential of Guided Bone Regeneration Membranes.

Carbon nanotubes (CNTs) are potentially important biomaterials because of their chemical, physical, and biological properties. Our research indicates that CNTs exhibit high compatibility with bone tissue. The guided bone regeneration (GBR) technique is commonly applied to reconstruct alveolar bone and treat peri-implant bone defects. In GBR, bone defects are covered with a barrier membrane to prevent the entry of nonosteogenic cells such as epithelial cells and fibroblasts. The barrier membrane also maintains a space for new bone formation. However, the mechanical and biological properties of materials previously used in clinical practice sometimes delayed bone regeneration. In this study, we developed a CNT-based membrane for GBR exhibiting high strength to provide a space for bone formation and provide cellular shielding to induce osteogenesis. The CNT membrane was made via the dispersion of single-walled CNTs (SWCNTs) in hyaluronic acid solution followed by filtration. The CNT membrane assumed a nanostructure surface due to the bundled SWCNTs and exhibited high strength and hydrophilicity after oxidation. In addition, the membrane promoted the proliferation of osteoblasts but not nonosteogenic cells. CNT membranes were used to cover experimental bone defects made in rat calvaria. At 8 weeks after surgery, more extensive bone formation was observed in membrane-covered defects compared with bone defects not covered with membrane. Almost no diffusion of CNTs was observed around the membrane. These results indicate that the CNT membrane has adequate strength, stability, and surface characteristics for osteoblasts, and its shielding properties promote bone formation. Demonstration of the safety and osteogenic potential of the CNT membranes through further animal studies should facilitate their clinical application in GBR.

Quantum defects as versatile anchors for carbon nanotube functionalization.

Single-wall carbon nanotubes (SWCNTs) are used in diverse applications that require chemical tailoring of the SWCNT surface, including optical sensing, imaging, targeted drug delivery and single-photon generation. SWCNTs have been noncovalently modified with (bio)polymers to preserve their intrinsic near-infrared fluorescence. However, demanding applications (e.g., requiring stability in biological fluids) would benefit from a stable covalent linkage between the SWCNT and the functional unit (e.g., antibody, fluorophore, drug). Here we present how to use diazonium salt chemistry to introduce sp3 quantum defects in the SWCNT carbon lattice to serve as handles for conjugation while preserving near-infrared fluorescence. In this protocol, we describe the straightforward, stable (covalent), highly versatile and scalable functionalization of SWCNTs with biomolecules such as peptides and proteins to yield near-infrared fluorescent SWCNT bioconjugates. We provide a step-by-step procedure covering SWCNT dispersion, quantum defect incorporation, bioconjugation, in situ peptide synthesis on SWCNTs, and characterization, which can be completed in 5-7 d.

Carbon Nanotube Liquid Crystal Dispersion for Large-Area, Micropatterned Aligned Films

Aligned single-walled carbon nanotube (SWCNT) films are potential materials for devices with excellent electrical and optical properties. However, the fabrication of well-aligned SWCNT films is limited, along with practical issues such as the area size and mass production. In this study, we successfully developed a method to fabricate SWCNT films with high alignment by applying an SWCNT dispersion to a substrate using a general wet-coating technique. The prepared SWCNT film showed a high degree of orientation with a nematic order parameter of 0.86 and 0.56 based on Raman spectroscopy and near-infrared (NIR) absorption spectroscopy, respectively. An orientation film several tens of centimeters in length can be prepared on polyethylene terephthalate (PET) film by wet-coating and drying. Furthermore, using the photoresponsive property of the dispersant, micrometer-scale patterning is also possible. The proposed method paves the way for the development of SWCNT-aligned devices for electronic and optical applications, such as the NIR/infrared polarizer and the detector and the electrode.