Analyzing Surfactant Structures on Length and Chirality Resolved (6,5) Single-Wall Carbon Nanotubes by Analytical Ultracentrifugation

Abstract

The structure and density of the bound interfacial surfactant layer and associated hydration shell were investigated using analytical ultracentrifugation for length and chirality purified (6,5) single-wall carbon nanotubes (SWCNTs) in three different bile salt surfactant solutions. The differences in the chemical structures of the surfactants significantly affect the size and density of the bound surfactant layers. As probed by exchange of a common parent nanotube population into sodium deoxycholate, sodium cholate, or sodium taurodeoxycholate solutions, the anhydrous density of the nanotubes was least for the sodium taurodeoxycholate surfactant, and the absolute sedimentation velocities greatest for the sodium cholate and sodium taurodeoxycholate surfactants. These results suggest that the thickest interfacial layer is formed by the deoxycholate, and that the taurodeoxycholate packs more densely than either sodium cholate or deoxycholate. These structural differences correlate well to an observed 25% increase in fluorescence intensity relative to the cholate surfactant for deoxycholate and taurodeoxycholate dispersed SWCNTs displaying equivalent absorbance spectra. Separate sedimentation velocity experiments including the density modifying agent iodixanol were used to establish the buoyant density of the (6,5) SWCNT in each of the bile salt surfactants; from the difference in the buoyant and anhydrous densities, the largest hydrated diameter is observed for sodium deoxycholate. Understanding the effects of dispersant choice and the methodology for measurement of the interfacial density and hydrated diameter is critical for rationally advancing separation strategies and applications of nanotubes.

2D analysis of polydisperse core–shell nanoparticles using analytical ultracentrifugation

“…The c(s) algorithm is a subset of the PCSA algorithm (horizontal line parameterization) and is a popular 1D approach which has previously been used for the analysis of NPs using constant ${\overline{\nu }}_{p,\mathrm{italiceff}}$ and f/f 0 . 8, 14, 30, 31 For narrow PSDs, the c(s) analysis performs well if the correct ${\overline{\nu }}_{p,\mathrm{italiceff}}$ is provided. Detailed results are given in the SI, Figure S9.…”

Viscosity and Morphology Modification of Length Sorted Single-Walled Carbon Nanotubes in PIB Matrices

“…In this process, the difference in the buoyancy and frictional force between nanotubes of varying lengths is exploited in order to achieve separation in a transient regime. According to Fagan et al [21,24], nanotubes with larger length have a lower frictional coefficient and tend to travel with less opposition to the centrifugal acceleration. Thus, longer length nanotube accumulates near the top of the centrifuge tube, when suspended in a density gradient fluid and subjected to an accelerating field, while the shorter ones tend to sediment deeper.…”

Bile salts and derivatives: Rigid unconventional amphiphiles as dispersants, carriers and superstructure building blocks

“…The facial amphiphilic structure makes the BSs particularly suitable to exfoliate and disperse the latter nanostructures, avoiding aggregation and reboundling due to the strong π-π interactions among different nanotubes or graphene sheets. Some studies demonstrated that the packing density of natural BSs on specific types of single-walled CNTs (SWCNTs) [45] and their efficiency in exfoliating graphene [46] are dependent on the number of hydroxyl groups of the steroidal skeleton, highlighting their crucial role in the dispersion process. In particular, a comparative analysis of the interaction of NaC, NaDC and NaTC with (6,5) SWCNTs, showed that NaDC forms the thickest interfacial layer on the CNT surface, and NaTC the most densely packed [45].…”

“…Some studies demonstrated that the packing density of natural BSs on specific types of single-walled CNTs (SWCNTs) [45] and their efficiency in exfoliating graphene [46] are dependent on the number of hydroxyl groups of the steroidal skeleton, highlighting their crucial role in the dispersion process. In particular, a comparative analysis of the interaction of NaC, NaDC and NaTC with (6,5) SWCNTs, showed that NaDC forms the thickest interfacial layer on the CNT surface, and NaTC the most densely packed [45]. On the other hand, NaC and NaDC were used as dispersant of graphene nanosheets, and the absence of an OH group at the centre of the steroidal skeleton in NaDC was found to offer a flat and hydrophobic surface towards the graphene, which helps in the formation of uniform bilayer micelles on the carbon surface, thus making the exfoliation process more efficient [46].…”