A method to produce scalable, low-resistance, high-transparency, percolating networks of silver nanowires by spray coating is presented. By optimizing the spraying parameters, networks with a sheet resistance of R(s) ≈ 50 Ω □(-1) at a transparency of T = 90% can be produced. The critical processing parameter is shown to be the spraying pressure. Optimizing the pressure reduces the droplet size resulting in more uniform networks. High uniformity leads to a low percolation exponent, which is essential for low-resistance, high-transparency films.

The importance of molecular conformation to the nature and strength of noncovalent interactions existing between a series of increasingly nonplanar tetraphenylporphyrin (TPP) derivatives and carbon nanotubes was systematically investigated experimentally in solution using a range of linear and nonlinear optical techniques. Additional complementary molecular dynamics studies were found to support the experimental observations. Convincing evidence of binding between single walled nanotubes (SWNTs) and some of these porphyrins was discovered, and a nonplanar macrocycle conformation was found to increase the likelihood of noncovalent binding onto nanotubes. Nonlinear optical studies showed that the optical limiting behavior of the TPP derivatives deteriorated with increasing porphyrin nonplanarity, but that formation of nanotube composites dramatically improved the optical limiting properties of all molecules studied. It was also found that the significant photoluminescence quenching behavior reported in the literature for such porphyrin/SWNT composites is at least partly caused by photoluminescence and excitation self-absorption and is, therefore, an artifact of the system.

We have measured the dispersibility of graphene in 40 solvents, with 28 of them previously unreported. We have shown that good solvents for graphene are characterized by a Hildebrand solubility parameter of delta(T) approximately 23 MPa(1/2) and Hansen solubility parameters of delta(D) approximately 18 MPa(1/2), delta(P) approximately 9.3 MPa(1/2), and delta(H) approximately 7.7 MPa(1/2). The dispersibility is smaller for solvents with Hansen parameters further from these values. We have used transmission electron microscopy (TEM) analysis to show that the graphene is well exfoliated in all cases. Even in relatively poor solvents, >63% of observed flakes have <5 layers.

We have measured the dispersibility of single-walled carbon nanotubes in a range of solvents, observing values as high as 3.5 mg/mL. By plotting the nanotube dispersibility as a function of the Hansen solubility parameters of the solvents, we have confirmed that successful solvents occupy a well-defined range of Hansen parameter space. The level of dispersibility is more sensitive to the dispersive Hansen parameter than the polar or H-bonding Hansen parameter. We estimate the dispersion, polar, and hydrogen bonding Hansen parameter for the nanotubes to be = 17.8 MPa1/2, = 7.5 MPa1/2, and = 7.6 MPa1/2. We find that the nanotube dispersibility in good solvents decays smoothly with the distance in Hansen space from solvent to nanotube solubility parameters, Finally, we propose that neither Hildebrand nor Hansen solubility parameters are fundamental quantities when it comes to nanotube-solvent interactions. We show that the previously calculated dependence of nanotube Hildebrand parameter on nanotube diameter can be reproduced by deriving a simple expression based on the nanotube surface energy. We show that solubility parameters based on surface energy give equivalent results to Hansen solubility parameters. However, we note that, contrary to solubility theory, a number of nonsolvents for nanotubes have both Hansen and surface energy solubility parameters similar to those calculated for nanotubes. The nature of the distinction between solvents and nonsolvents remains to be fully understood.

Stable dispersions of single-walled carbon nanotubes have been produced using the surfactant sodium dodecylbenzene sulfonate (SDBS). Atomic force microscopy analysis. shows that, on dilution of these dispersions, the nanotubes exfoliate from bundles, resulting in a concentration-dependent bundle diameter distribution which saturates at D-rms approximate to 2 nm for concentrations, C-NT < 0.05 mg/mL. The total bundle number density increases with concentration, saturating at similar to 6 bundles per mu m(3) for C-NT > 0.05 mg/mL. As the concentration is reduced the number fraction of individual nanotubes grows, approaching 50% at low concentration. In addition, partial concentrations of individual SWNTs approaching 0.01 mg/mL can be realized. These values are far superior to those for solvent dispersions due to repulsion stabilization of the surfactant-coated nanotubes. These methods facilitate the preparation of high-quality nanotube dispersions without the need for ultracentrifugation, thus significantly increasing the yield of dispersed nanotubes.

Stable dispersions of single-walled carbon nanotubes in deionized water were prepared using six common surfactants: sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), lithium dodecyl sulfate (LDS), tetradecyl trimethyl ammonium bromide (TTAB), sodium cholate (SC), and Fairy liquid (FL). For all nanotube dispersions (C-NT = 1 mg/mL), the optimum concentration of surfactant was found to be close to C-Surf = 10 mg/mL by measuring the fraction of nanotubes remaining after centrifugation for a range of surfactant concentrations. The aggregation state of each nanotube-surfactant dispersion was characterized as a function of nanotube concentration by AFM analysis of large numbers of nanotubes/bundles deposited onto substrates. The dispersion quality could then be quantified by four parameters: the saturation value (at low concentration) of the root-mean-square bundle diameter, the maximum value of the total number of dispersed objects (individuals and bundles) per unit volume of dispersion, the saturation value (at low concentration) of the number fraction of individual nanotubes, and the maximum value of the number of individual nanotubes per unit volume of dispersion. According to these metrics, the dispersion quality of the six surfactant-nanotube dispersions varied as SDS > LDS > SDBS > TTAB > SC > Fairy liquid. It was found that each of these dispersion-quality metrics scaled very well with the measured zeta-potential of the surfactant-nanotube dispersion. This confirms that dispersion quality is controlled by the magnitude of electrostatic repulsive forces between coated nanotubes.