Relationship of Extensional Viscosity and Liquid Crystalline Transition to Length Distribution in Carbon Nanotube Solutions

Effect of CNT Oxidation on the Processing and Properties of Superacid-Spun CNT Fibers

Spinning fibers from carbon nanotube (CNT)/superacid dispersions has emerged as a promising strategy for industrial-scale production of high-performance CNT fibers (CNTFs). The oxygen content and types of functional groups on CNT surfaces significantly influence dispersion, assembly processes, and fiber properties. In this study, Tuball-SWCNTs were purified and oxidized at varying levels. The dispersion behavior of CNTs with different oxidation levels in chlorosulfonic acid was systematically observed, and the mechanical properties of fibers spun from these dispersions were compared. By adjusting the dispersion concentration, highly oriented CNTFs were produced with a specific strength of 1.03 N/tex, a tensile strength of 1.59 GPa, and an electrical conductivity of 3.58 MS/m. Further investigations indicated that oxygen-containing functional groups decrease the coagulation rate, increasing the maximum draw ratio during spinning and improving CNT alignment in the fibers. Molecular dynamics simulations demonstrated that these functional groups (-OH, -COOH) enhance load transfer between CNTs through hydrogen bonding. This specific strength is the highest achieved using Tuball-SWCNTs for superacid-spun fibers, surpassing previous works due to the oxidation-controlled coagulation rate, enhanced fiber orientation, and improved load transfer via hydrogen bonding. This study provides insights for designing and optimizing high-performance CNTFs.

The Stability of UV-Defluorination-Driven Crosslinked Carbon Nanotubes: A Raman Study

Carbon nanotubes (CNTs) are often regarded as semi-rigid, all-carbon polymers. However, unlike conventional polymers that can form 3D networks such as hydrogels or elastomers through crosslinking in solution, CNTs have long been considered non-crosslinkable under mild conditions. This perception changed with our recent discovery of UV-defluorination-driven direct crosslinking of CNTs in solution. In this study, we further investigate the thermal stability of UV-defluorination-driven crosslinked CNTs, revealing that they are metastable and decompose more readily than either pristine or fluorinated CNTs under Raman laser irradiation. Using Raman spectroscopy under controlled laser power, we examined both single-walled and multi-walled fluorinated CNTs. The results demonstrate that UV-defluorinated CNTs exhibit reduced thermal stability compared to their pristine or untreated fluorinated counterparts. This instability is attributed to the strain on the intertube crosslinking bonds resulting from the curved carbon lattice of the linked CNTs. The metallic CNTs in the crosslinked CNT networks decompose and revert to their pristine state more readily than the semiconducting ones. The inherent instability of crosslinked CNTs leads to combustion at temperatures approximately 100 °C lower than those required for non-crosslinked fluorinated CNTs. This property positions crosslinked CNTs as promising candidates for applications where mechanically robust, lightweight materials are needed, along with feasible post-use removal options.

Controllable Preparation and Strengthening Strategies towards High-Strength Carbon Nanotube Fibers

Carbon nanotubes (CNTs) with superior mechanical properties are expected to play a role in the next generation of critical engineering mechanical materials. Crucial advances have been made in CNTs, as it has been reported that the tensile strength of defect-free CNTs and carbon nanotube bundles can approach the theoretical limit. However, the tensile strength of macro carbon nanotube fibers (CNTFs) is far lower than the theoretical level. Although some reviews have summarized the development of such fiber materials, few of them have focused on the controllable preparation and performance optimization of high-strength CNTFs at different scales. Therefore, in this review, we will analyze the characteristics and latest challenges of multiscale CNTFs in preparation and strength optimization. First, the structure and preparation of CNTs are introduced. Then, the preparation methods and tensile strength characteristics of CNTFs at different scales are discussed. Based on the analysis of tensile fracture, we summarize some typical strategies for optimizing tensile performance around defect and tube-tube interaction control. Finally, we introduce some emerging applications for CNTFs in mechanics. This review aims to provide insights and prospects for the controllable preparation of CNTFs with ultra-high tensile strength for emerging cutting-edge applications.

Liquid crystals of neat boron nitride nanotubes and their assembly into ordered macroscopic materials

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

Versatile acid solvents for pristine carbon nanotube assembly

Chlorosulfonic acid and oleum are ideal solvents for enabling the transformation of disordered carbon nanotubes (CNTs) into precise and highly functional morphologies. Currently, processing these solvents using extrusion techniques presents complications due to chemical compatibility, which constrain equipment and substrate material options. Here, we present a novel acid solvent system based on methanesulfonic or p-toluenesulfonic acids with low corrosivity, which form true solutions of CNTs at concentrations as high as 10 g/liter (≈0.7 volume %). The versatility of this solvent system is demonstrated by drop-in application to conventional manufacturing processes such as slot die coating, solution spinning continuous fibers, and 3D printing aerogels. Through continuous slot coating, we achieve state-of-the-art optoelectronic performance (83.6 %T and 14 ohm/sq) at industrially relevant production speeds. This work establishes practical and efficient means for scalable processing of CNT into advanced materials with properties suitable for a wide range of applications.

Washable, Sewable, All-Carbon Electrodes and Signal Wires for Electronic Clothing

Smart wearable electronic accessories (e.g., watches) have found wide adoption; conversely, progress in electronic textiles has been slow due to the difficulty of embedding rigid electronic materials into flexible fabrics. Electronic clothing requires fibers that are conductive, robust, biocompatible, and can be produced on a large scale. Here, we create sewable electrodes and signal transmission wires from neat carbon nanotube threads (CNTT). These threads are soft like standard sewing thread, but they have metal-level conductivity and low interfacial impedance with skin. Electrocardiograms (EKGs) obtained by CNTT electrodes were comparable (P > 0.05) to signals obtained with commercial electrodes. CNTT can also be used as transmission wires to carry signals to other parts of a garment. Finally, the textiles can be machine-washed and stretched repeatedly without signal degradation. These results demonstrate promise for textile sensors and electronic fabric with the feel of standard clothing that can be incorporated with traditional clothing manufacturing techniques.

A Meta-Analysis of Conductive and Strong Carbon Nanotube Materials

A study of 1304 data points collated over 266 papers statistically evaluates the relationships between carbon nanotube (CNT) material characteristics, including: electrical, mechanical, and thermal properties; ampacity; density; purity; microstructure alignment; molecular dimensions and graphitic perfection; and doping. Compared to conductive polymers and graphitic intercalation compounds, which have exceeded the electrical conductivity of copper, CNT materials are currently one-sixth of copper's conductivity, mechanically on-par with synthetic or carbon fibers, and exceed all the other materials in terms of a multifunctional metric. Doped, aligned few-wall CNTs (FWCNTs) are the most superior CNT category; from this, the acid-spun fiber subset are the most conductive, and the subset of fibers directly spun from floating catalyst chemical vapor deposition are strongest on a weight basis. The thermal conductivity of multiwall CNT material rivals that of FWCNT materials. Ampacity follows a diameter-dependent power-law from nanometer to millimeter scales. Undoped, aligned FWCNT material reaches the intrinsic conductivity of CNT bundles and single-crystal graphite, illustrating an intrinsic limit requiring doping for copper-level conductivities. Comparing an assembly of CNTs (forming mesoscopic bundles, then macroscopic material) to an assembly of graphene (forming single-crystal graphite crystallites, then carbon fiber), the ≈1 µm room-temperature, phonon-limited mean-free-path shared between graphene, metallic CNTs, and activated semiconducting CNTs is highlighted, deemphasizing all metallic helicities for CNT power transmission applications.

Macroscopic weavable fibers of carbon nanotubes with giant thermoelectric power factor

Low-dimensional materials have recently attracted much interest as thermoelectric materials because of their charge carrier confinement leading to thermoelectric performance enhancement. Carbon nanotubes are promising candidates because of their one-dimensionality in addition to their unique advantages such as flexibility and light weight. However, preserving the large power factor of individual carbon nanotubes in macroscopic assemblies has been challenging, primarily due to poor sample morphology and a lack of proper Fermi energy tuning. Here, we report an ultrahigh value of power factor (14 ± 5 mW m⁻¹ K⁻²) for macroscopic weavable fibers of aligned carbon nanotubes with ultrahigh electrical and thermal conductivity. The observed giant power factor originates from the ultrahigh electrical conductivity achieved through excellent sample morphology, combined with an enhanced Seebeck coefficient through Fermi energy tuning. We fabricate a textile thermoelectric generator based on these carbon nanotube fibers, which demonstrates high thermoelectric performance, weavability, and scalability. The giant power factor we observe make these fibers strong candidates for the emerging field of thermoelectric active cooling, which requires a large thermoelectric power factor and a large thermal conductivity at the same time.

Preserving the large power factor of carbon nanotubes is challenging, due to poor sample morphology and a lack of proper Fermi energy tuning. Here, the authors achieve a value of power factor of 14 ± 5 mW m⁻¹ K⁻² originating from the preserved conductivity and the ability to tune Fermi energy.

Enhanced ordering in length-polydisperse carbon nanotube solutions at high concentrations as revealed by small angle X-ray scattering

Carbon nanotubes (CNTs) are stiff, all-carbon macromolecules with diameters as small as one nanometer and few microns long. Solutions of CNTs in chlorosulfonic acid (CSA) follow the phase behavior of rigid rod polymers interacting via a repulsive potential and display a liquid crystalline phase at sufficiently high concentration. Here, we show that small-angle X-ray scattering and polarized light microscopy data can be combined to characterize quantitatively the morphology of liquid crystalline phases formed in CNT solutions at concentrations from 3 to 6.5% by volume. We find that upon increasing their concentration, CNTs self-assemble into a liquid crystalline phase with a pleated texture and with a large inter-particle spacing that could be indicative of a transition to higher-order liquid crystalline phases. We explain how thermal undulations of CNTs can enhance their electrostatic repulsion and increase their effective diameter by an order of magnitude. By calculating the critical concentration, where the mean amplitude of undulation of an unconstrained rod becomes comparable to the rod spacing, we find that thermal undulations start to affect steric forces at concentrations as low as the isotropic cloud point in CNT solutions.

Real-Time Visualization and Dynamics of Boron Nitride Nanotubes Undergoing Brownian Motion

We report the first real-time imaging of individualized boron nitride nanotubes (BNNTs) via stabilization with a rhodamine surfactant and fluorescence microscopy. We study the rotational and translational diffusion and find them to agree with predictions based on a confined, high-aspect-ratio rigid rod undergoing Brownian motion. We find that the behavior of BNNTs parallels that of individualized carbon nanotubes (CNTs), indicating that BNNTs could also be used as model rigid rods to study soft matter systems, while avoiding the experimental disadvantages of CNTs due to their strong light absorption. The use and further development of our technique and findings will accelerate the application of BNNTs from material engineering to biological studies.

Perovskite-Carbon Nanotube Light-Emitting Fibers

Active fibers with electro-optic functionalities are promising building blocks for the emerging and rapidly growing field of fiber and textile electronics. Yet, there remains significant challenges that require improved understanding of the principles of active fiber assembly to enable the development of fiber-shaped devices characterized by having a small diameter, being lightweight, and having high mechanical strength. To this end, the current frameworks are insufficient, and new designs and fabrication approaches are essential to accommodate this unconventional form factor. Here, we present a first demonstration of a pathway that effectively integrates the foundational components meeting such requirements, with the use of a flexible and robust conductive core carbon nanotube fiber and an organic-inorganic emissive composite layer as the two critical elements. We introduce an active fiber design that can be realized through an all solution-processed approach. We have implemented this technique to demonstrate a three-layered light-emitting fiber with a coaxially coated design.

The viscosity of dilute carbon nanotube (1D) and graphene oxide (2D) nanofluids

Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron-Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions.

Effect of Carbon Nanotube Diameter and Stiffness on Their Phase Behavior in Crowded Solutions

The unique carbon nanotube (CNT) properties are mainly determined by their geometry, e.g., their aspect ratio, diameter, and number of walls. So far, chlorosulfonic acid is the only practical true solvent for carbon nanotubes, forming thermodynamically stable molecular solutions. Above a critical concentration the system forms an ordered, nematic liquid-crystalline phase. That phase behavior is the basis for liquid-phase processing and the optimal translation of the carbon nanotube molecular properties to the macroscopic scale. The final material properties depend on the phase behavior of the "dope" from which it is prepared, which depends on the CNT parameters themselves. Earlier work determined that CNT aspect ratio controls the phase behavior, in accordance with classical rigid-rod theories. Here we use cryogenic transmission electron microscopy and Raman spectroscopy to understand the relation between the geometry of the CNTs, the chemical interaction with chlorosulfonic acid, and the phase behavior of crowded solutions. We show that the CNT diameter and number of walls also play an independent role in the phase transition and phase morphology of the system because of their effect on the CNT bending stiffness.

Self-Sorting of 10-µm-Long Single-Walled Carbon Nanotubes in Aqueous Solution

Single-walled carbon nanotubes (SWCNTs) are a class of 1D nanomaterials that exhibit extraordinary electrical and optical properties. However, many of their fundamental studies and practical applications are stymied by sample polydispersity. SWCNTs are synthesized in bulk with broad structural (chirality) and geometrical (length and diameter) distributions; problematically, all known post-synthetic sorting methods rely on ultrasonication, which cuts SWCNTs into short segments (typically <1 µm). It is demonstrated that ultralong (>10 µm) SWCNTs can be efficiently separated from shorter ones through a solution-phase "self-sorting". It is shown that thin-film transistors fabricated from long semiconducting SWCNTs exhibit a carrier mobility as high as ≈90 cm2 V-1 s-1 , which is ≈10 times higher than those which use shorter counterparts and well exceeds other known materials such as organic semiconducting polymers (<1 cm2 V-1 s-1 ), amorphous silicon (≈1 cm2 V-1 s-1 ), and nanocrystalline silicon (≈50 cm2 V-1 s-1 ). Mechanistic studies suggest that this self-sorting is driven by the length-dependent solution phase behavior of rigid rods. This length sorting technique shows a path to attain long-sought ultralong, electronically pure carbon nanotube materials through scalable solution processing.

Dynamic Strengthening of Carbon Nanotube Fibers under Extreme Mechanical Impulses

A monofilament fiber spun from individual carbon nanotubes is an arbitrarily long ensemble of weakly interacting, aligned, discrete nanoparticles. Despite the structural resemblance of carbon nanotube monofilament fibers to crystalline polymeric fibers, very little is known about their dynamic collective mechanics, which arise from van der Waals interactions among the individual carbon nanotubes. Using ultrafast stroboscopic microscopy, we study the collective dynamics of carbon nanotube fibers and compare them directly with nylon, Kevlar, and aluminum monofilament fibers under the same supersonic impact conditions. The in situ dynamics and kinetic parameters of the fibers show that the kinetic energy absorption characteristics of the carbon nanotube fibers surpass all other fibers. This study provides insight into the strain-rate-dependent strengthening mechanics of an ensemble of nanomaterials for the development of high-performance fibers used in body armor and other protective nanomaterials possessing exceptional stability in various harsh environments.

Bending behavior of CNT fibers and their scaling laws

Carbon nanotube (CNT) fibers are a promising material for wearable electronics and biomedical applications due to their combined flexibility and electrical conductivity. To engineer the bending properties for such applications requires understanding how the bending stiffness of CNT fibers scales with CNT length and fiber diameter. We measure bending stiffness with a cantilever setup interpreted within Euler Elastica theory. We find that the bending stiffness scales with a power law of 1.9 for the fiber diameter and 1.6 for the CNT length. The diameter scaling exponent for fiber diameter agrees with results from earlier experiments and theory for microscopic CNT bundles. We develop a simple model which predicts the experimentally observed scaling exponents within statistical significance.

Structure-Property Relations in Carbon Nanotube Fibers by Downscaling Solution Processing

At the microscopic scale, carbon nanotubes (CNTs) combine impressive tensile strength and electrical conductivity; however, their macroscopic counterparts have not met expectations. The reasons are variously attributed to inherent CNT sample properties (diameter and helicity polydispersity, high defect density, insufficient length) and manufacturing shortcomings (inadequate ordering and packing), which can lead to poor transmission of stress and current. To efficiently investigate the disparity between microscopic and macroscopic properties, a new method is introduced for processing microgram quantities of CNTs into highly oriented and well-packed fibers. CNTs are dissolved into chlorosulfonic acid and processed into aligned films; each film can be peeled and twisted into multiple discrete fibers. Fibers fabricated by this method and solution-spinning are directly compared to determine the impact of alignment, twist, packing density, and length. Surprisingly, these discrete fibers can be twice as strong as their solution-spun counterparts despite a lower degree of alignment. Strength appears to be more sensitive to internal twist and packing density, while fiber conductivity is essentially equivalent among the two sets of samples. Importantly, this rapid fiber manufacturing method uses three orders of magnitude less material than solution spinning, expanding the experimental parameter space and enabling the exploration of unique CNT sources.

Quantification of Carbon Nanotube Liquid Crystal Morphology via Neutron Scattering

Liquid phase assembly is among the most industrially attractive routes for scalable carbon nanotube (CNT) processing. Chlorosulfonic acid (CSA) is known to be an ideal solvent for CNTs, spontaneously dissolving them without compromising their properties. At typical processing concentrations, CNTs form liquid crystals in CSA; however, the morphology of these phases and their concentration dependence are only qualitatively understood. Here, we use small-angle neutron scattering (SANS), combined with polarized light microscopy and cryogenic transmission electron microscopy to study solution morphology over a range of concentrations and two different CNT lengths. Our results show that at the highest concentration studied the long CNTs form a highly ordered fully nematic phase, while short CNTs remain in a biphasic regime. Upon dilution, long CNTs undergo a 2D lattice expansion, whereas short CNTs seem to have an intermediate expansion between 2D and 3D probably due to the biphasic nature of the system. The average spacing between the CNTs scaled by the CNT diameter is the same in both systems, as expected for infinitely long aligned rods.

Purification and Dissolution of Carbon Nanotube Fibers Spun from the Floating Catalyst Method

In this study, we apply a simple but effective oxidative purification method to purify carbon nanotube (CNT) fibers synthesized via a floating catalyst technique. After the purification treatment, the resulting CNT fibers exhibited significant improvements in mechanical and electrical properties with an increase in strength, Young's modulus, and electrical conductivity by approximately 81, 230, and 100%, respectively. With the successful dissolution of the CNT fibers in superacid, an extensional viscosity method could be applied to measure the aspect ratio of the CNTs constituting the fibers, whereas high-purity CNT thin films could be produced with a low resistance of 720 Ω/sq at a transmittance of 85%. This work suggests that the oxidative purification approach and dissolution process are promising methods to improve the purity and performance of CNT macroscopic structures.

Influence of Carbon Nanotube Characteristics on Macroscopic Fiber Properties

We study how intrinsic parameters of carbon nanotube (CNT) samples affect the properties of macroscopic CNT fibers with optimized structure. We measure CNT diameter, number of walls, aspect ratio, graphitic character, and purity (residual catalyst and non-CNT carbon) in samples from 19 suppliers; we process the highest quality CNT samples into aligned, densely packed fibers, by using an established wet-spinning solution process. We find that fiber properties are mainly controlled by CNT aspect ratio and that sample purity is important for effective spinning. Properties appear largely unaffected by CNT diameter, number of walls, and graphitic character (determined by Raman G/D ratio) as long as the fibers comprise thin few-walled CNTs with high G/D ratio (above ∼20). We show that both strength and conductivity can be improved simultaneously by assembling high aspect ratio CNTs, producing continuous CNT fibers with an average tensile strength of 2.4 GPa and a room temperature electrical conductivity of 8.5 MS/m, ∼2 times higher than the highest reported literature value (∼15% of copper's value), obtained without postspinning doping. This understanding of the relationship of intrinsic CNT parameters to macroscopic fiber properties is key to guiding CNT synthesis and continued improvement of fiber properties, paving the way for CNT fiber introduction in large-scale aerospace, consumer electronics, and textile applications.

Line Tension of Twist-Free Carbon Nanotube Lyotropic Liquid Crystal Microdroplets on Solid Surfaces

Line tension, i.e., the force on a three-phase contact line, has been a subject of extensive research due to its impact on technological applications including nanolithography and nanofluidics. However, there is no consensus on the sign and magnitude of the line tension, mainly because it only affects the shape of small droplets, below the length scale dictated by the ratio of line tension to surface tension σ/τ. This ratio is related to the size of constitutive molecules in the system, which translates to a nanometer for conventional fluids. Here, we show that this ratio is orders of magnitude larger in lyotropic liquid crystal systems comprising micrometer-long colloidal particles. Such systems are known to form spindle-shaped elongated liquid crystal droplets in coexistence with the isotropic phase, with the droplets flattening when in contact with flat solid surfaces. We propose a method to characterize the line tension by fitting measured droplet shape to a macroscopic theoretical model that incorporates interfacial forces and elastic deformation of the nematic phase. By applying this method to hundreds of droplets of carbon nanotubes dissolved in chlorosulfonic acid, we find that σ/τ ∼ -0.84 ± 0.06 μm. This ratio is 2 orders of magnitude larger than what has been reported for conventional fluids, in agreement with theoretical scaling arguments.

Direct Imaging of Carbon Nanotube Liquid-Crystalline Phase Development in True Solutions

Using direct-imaging cryogenic transmission and scanning electron microscopy, we show different stages of liquid-crystalline phase development in progressively more concentrated solutions of carbon nanotubes in chlorosulfonic acid: a dilute phase of individually dissolved carbon nanotubes; semidilute and concentrated isotropic phases; coexisting concentrated isotropic and nematic phases in local equilibrium with each other; and a fully liquid-crystalline phase. Nanometric resolution of cryogenic electron microscopy reveals carbon nanotube self-assembly into liquid-crystalline domains of several nanometers in width at very early stages. We find significant differences in carbon nanotube liquid-crystalline domain morphology as a function of the carbon nanotube aspect ratio, diameter, and degree of purity.

Pinch-off dynamics and dripping-onto-substrate (DoS) rheometry of complex fluids

Liquid transfer and drop formation/deposition processes involve complex free-surface flows including the formation of columnar necks that undergo spontaneous capillary-driven instability, thinning and pinch-off. For simple (Newtonian and inelastic) fluids, a complex interplay of capillary, inertial and viscous stresses determines the nonlinear dynamics underlying finite-time singularity as well as self-similar capillary thinning and pinch-off dynamics. In rheologically complex fluids, extra elastic stresses as well as non-Newtonian shear and extensional viscosities dramatically alter the nonlinear dynamics. Stream-wise velocity gradients that arise within the thinning columnar neck create an extensional flow field, and many complex fluids exhibit a much larger resistance to elongational flows than Newtonian fluids with similar shear viscosity. Characterization of pinch-off dynamics and the response to both shear and extensional flows that influence drop formation/deposition in microfluidic and printing applications requires bespoke instrumentation not available, or easily replicated, in most laboratories. Here we show that dripping-onto-substrate (DoS) rheometry protocols that involve visualization and analysis of capillary-driven thinning and pinch-off dynamics of a columnar neck formed between a nozzle and a sessile drop can be used for measuring shear viscosity, power law index, extensional viscosity, relaxation time and the most relevant processing timescale for printing. We showcase the versatility of DoS rheometry by characterizing and contrasting the pinch-off dynamics of a wide spectrum of simple and complex fluids: water, printing inks, semi-dilute polymer solutions, yield stress fluids, food materials and cosmetics. We show that DoS rheometry enables characterization of low viscosity printing inks and polymer solutions that are beyond the measurable range of commercially-available capillary break-up extensional rheometer (CaBER). We show that for high viscosity fluids, DoS rheometry can be implemented relatively inexpensively using an off-the-shelf digital camera, and for many complex fluids, similar power law scaling exponent describes both neck thinning dynamics and the shear thinning response.

Impact of SWCNT processing on nanotube-silicon heterojunctions

Single-wall carbon nanotube (SWCNT) films are ideal components for thin, flexible, and durable electronic devices. Here, we use a variety of processing approaches to fabricate SWCNT-silicon heterojunctions from both unsorted and chirality-enriched SWCNTs. Through measured structure/processing/property relationships, we quantify the influence of SWCNT purity, alignment and residual doping on device performance and diode characteristics. Our results show that mixed-type unaligned SWCNTs processed in super-acid solvents can achieve state-of-the-art performance. The devices perform comparably to those fabricated from type or chiral-purified SWCNTs, despite what appear to be significant deviations from ideal diode behavior. Our results clarify a direct route for processing nanotube-silicon heterojunctions while providing additional insight into the underlying nature of these devices.