Variance Spectroscopy Studies of Single-Wall Carbon Nanotube Aggregation

Abstract

Early stages of single-wall carbon nanotube aggregation in aqueous surfactant suspension have been investigated through combined structure-resolved fluorescence and variance spectroscopies. Following the addition of NaCl to destabilize dispersed samples, variance data revealed strong decreases in the concentrations of emitting particles, while fluorescence spectra showed only modest changes. This indicates the formation of loose aggregates in which electronic contact between individual nanotubes is too limited to perturb their emission. Variance data showed that the initial formation rates of homoaggregates (clusters of the same (n,m) species) increase superlinearly with NaCl concentration. Co-variance analysis gave complementary structure-resolved data on emissive heteroaggregates. For both types of clusters, it is found that the initial aggregation rates correlate with species particle concentrations, but show no clear dependence on nanotube structure. Variance spectroscopy can sensitively detect and characterize small loose clusters of carbon nanotube that are not observable by other spectroscopic methods.