Ji Yeon Huh

Tailored Distribution of Single-Wall Carbon Nanotubes from Arc Plasma Synthesis Using Magnetic Fields

We report a method for tuning the distribution of single-wall carbon nanotubes (SWCNTs) produced by the anodic arc production method via the application of nonuniform magnetic fields to the gap region during synthesis. Raman, ultraviolet-visible-near-infrared absorbance and near-infrared fluorescence spectroscopies were used to characterize samples together with scanning electron microscopy. Application of the nonuniform magnetic field 0.2-2 kG results in a broadening of the diameter range of SWCNTs produced toward decreased diameters, with substantial fractions of produced SWCNTs being of small diameter, less than ∼1.3 nm, at the highest field. The ability to tune production of the arc production method may allow for improvement in achievable SWCNT properties.

Electronic durability of flexible transparent films from type-specific single-wall carbon nanotubes.

The coupling between mechanical flexibility and electronic performance is evaluated for thin films of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) deposited on compliant supports. Percolated networks of type-purified SWCNTs are assembled as thin conducting coatings on elastic polymer substrates, and the sheet resistance is measured as a function of compression and cyclic strain through impedance spectroscopy. The wrinkling topography, microstructure and transparency of the films are independently characterized using optical microscopy, electron microscopy, and optical absorption spectroscopy. Thin films made from metallic SWCNTs show better durability as flexible transparent conductive coatings, which we attribute to a combination of superior mechanical performance and higher interfacial conductivity.

Carbon Nanotubes: Measuring Dispersion and Length

Advanced technological uses of single-walled carbon nanotubes (SWCNTs) rely on the production of single length and chirality populations that are currently only available through liquid-phase post processing. The foundation of all of these processing steps is the attainment of individualized nanotube dispersions in solution. An understanding of the colloidal properties of the dispersed SWCNTs can then be used to design appropriate conditions for separations. In many instances nanotube size, particularly length, is especially active in determining the properties achievable in a given population, and, thus, there is a critical need for measurement technologies for both length distribution and effective separation techniques. In this Progress Report, the current state of the art for measuring dispersion and length populations, including separations, is documented, and examples are used to demonstrate the desirability of addressing these parameters.

Separation of Empty and Water-Filled Single-Wall Carbon Nanotubes

The separation of empty and water-filled laser ablation and electric arc synthesized nanotubes is reported. Centrifugation of these large-diameter nanotubes dispersed with sodium deoxycholate using specific conditions produces isolated bands of empty and water-filled nanotubes without significant diameter selection. This separation is shown to be consistent across multiple nanotube populations dispersed from different source soots. Detailed spectroscopic characterization of the resulting empty and filled fractions reveals that water filling leads to systematic changes to the optical and vibrational properties. Furthermore, sequential separation of the resolved fractions using cosurfactants and density gradient ultracentrifugation reveals that water filling strongly influences the optimal conditions for metallic and semiconducting separation.

Elasticity and rigidity percolation in flexible carbon nanotube films on PDMS substrates

The evolution of wrinkles and folds in compressed thin films of type-purified single-wall carbon nanotubes (SWCNTs) on polydimethylsiloxane (PDMS) substrates is used to study the mechanical response of pristine nanotube networks. While the low-strain moduli are consistent with the exceptional mechanical properties of individual nanotubes, the films are remarkably fragile, exhibiting small yield strains that decrease with increasing thickness. We find significant differences in the mechanical response of semiconducting as compared to metallic SWCNT networks, and we use simple scaling arguments to relate these differences to previously determined Hamaker constants associated with each electronic type. A comparison with conductivity measurements performed on identical films suggests more than a two-fold variation in the onset of rigidity vs. connectivity percolation, and we discuss the potential implications of this for both rigid-rod networks and the use of type-purified SWCNTs in flexible electronics.

SPR imaging study of DNA wrapped single wall carbon nanotube (ssDNA-SWCNT) adsorption on a model biological (collagen) substrate

The adsorption kinetics of single stranded-DNA dispersed single wall carbon nanotubes (ssDNA-SWCNTs) onto an immobilized collagen layer in a microfluidic channel was probed using surface plasmon resonance imaging (SPRi). The adsorption was measured for a range of both nanotube and solution parameters including the nanotube concentration, nanotube length, solution pH, and the type of medium (buffer and river water). The kinetic adsorption data suggests that the adsorption of the nanotubes to the collagen layer is irreversible in HEPES buffer, pH ≈ 7.4, at room temperature, with the nanotube adsorption displaying two different kinetic adsorption regimes for different concentration ranges. A stretched exponential function fit indicates that a transition of adsorption kinetics from single exponential (>40 μg/mL) to non-exponential kinetics (<40 μg/mL) occurs as the nanotube concentration decreases, suggesting that a diffusion-limited process was predominant at lower concentrations (<40 μg/mL). Adsorption measurements as a function of nanotube length also displayed differences in the apparent adsorption processes. Adsorption of shorter nanotubes (≈ 40 nm) was found to follow single exponential kinetics, while longer nanotubes (≈ 300 nm) adsorbed much more slowly, consistent with adsorption partially influenced by diffusion-limited processes. Finally, to evaluate the potential differences in adsorption for unintentionally released nanotubes in a riparian environment, nanotubes were stably dispersed in a sample of river water and exposed to the collagen layer. Compared to the adsorption under HEPES buffer the nanotubes in the river water were found to exhibit a reduced rate of adsorption. It is likely that passivation of the collagen layer by dissolved organic species could thus affect the fate of released nanotubes in a natural environment.