Structure and dispersion of carbon nanotubes

Abstract

Small-angle light scattering and ultra small-angle X-ray scattering are used to assess the morphology of single-walled (SWNTs) and multi-walled carbon nanotubes (MWNTs). For MWNTs, a powerlaw scattered-intensity profile with a slope of -1.08 is consistent with the rod-like morphology. For SWNTs, however, scattering profiles characteristic of rod-like morphology are not observed on any length-scale from 1 nm to 50 µm. Rather, disordered objects are found that we identify as a network of carbon "ropes" enmeshed with polyelectrolyte dispersants. The effectiveness of polyelectrolyte dispersants is assessed using small-angle light scattering in conjunction with exposure to ultrasound. In the presence of an anionic polyelectrolyte, sonication can assist dispersion of both SWNTs and MWNTs. In the presence of a cationic agent, however, sonication can induce aggregation. SWNTs respond differently to ultrasound depending on whether residual synthesis catalyst is present. Four dispersants are studied, of which sodium polystyrene sulfonate is the most effective and polyallylamine hydrochloride is the least effective.

How Does Surface Modification Aid in the Dispersion of Carbon Nanofibers?

“…Such a slope, however, can also arise from more complex aggregated structures. 14,15 The crossover length scale (q -1 = 1 µm) between the two power-law regimes corresponds to the largest radius of the tube aggregates. Minimal change in R g and P is observed for q > 10 -4 Å -1 , indicating minimal change in morphology with time on length scales below ∼1 µm.…”

“…We recently used scattering to determine the morphology of carbon nanotube suspensions. 14,15 In this paper, we use this tool to quantify the state dispersion of as-received and acid-treated carbon nanofibers as a function of time. To understand the state of aggregation of the nanofibers, the size distribution from the light scattering data is determined using the maximum entropy (ME) method.…”

Comparative Measures of Single-Wall Carbon Nanotube Dispersion

“…Sources of imperfection in dispersing individual SWNTs are most likely bundles, defined here as the lengthwise "roping" of tubes, and aggregates, the fractal-type networking of tubes in a floc. Of all the measurement techniques currently used to evaluate SWNT dispersion in solutions and composites, small-angle scattering [2][3][4][5][6][7][8][9] is perhaps the simplest to interpret and understand. This technique directly probes twopoint correlations in composition and can thus distinguish true form scattering due to individual SWNTs from the structural scattering that arises from nanotube aggregates and bundles.…”

Morphology and Dispersion of Pristine and Modified Carbon Nanofibers in Water

“…D = 1 implies a linear objects and D > 1 indicates more branched or flexible structures. (Schaefer, Brown et al 2003;Schaefer, Zhao et al 2003) For our data, however, the scattering entities are polydisperse and the power-law regions extend over a very limited q range, so this approach is unworkable. An alternative is to use the relationship…”

“…Such a slope, however, can also arise from more complex aggregated structures. (Schaefer, Brown et al 2003;Schaefer, Zhao et al 2003) The crossover length scale (q -1 ≅ 1 μm) between the two power-law regimes corresponds to the largest radius of the tube aggregates. Minimal change in Rg and P is observed for q > 10 -4 Å -1 , indicating minimal change in morphology with time on length scales below ~1 μm.…”