Variance Spectroscopy Studies of Single-Wall Carbon\nNanotube Aggregation

Abstract

Early\nstages of single-wall carbon nanotube aggregation in aqueous\nsurfactant suspension have been investigated through combined structure-resolved\nfluorescence and variance spectroscopies. Following the addition of\nNaCl to destabilize dispersed samples, variance data revealed strong\ndecreases in the concentrations of emitting particles, while fluorescence\nspectra showed only modest changes. This indicates the formation of\nloose aggregates in which electronic contact between individual nanotubes\nis too limited to perturb their emission. Variance data showed that\nthe initial formation rates of homoaggregates (clusters of the same\n(<i>n</i>,<i>m</i>) species) increase superlinearly\nwith NaCl concentration. Co-variance analysis gave complementary structure-resolved\ndata on emissive heteroaggregates. For both types of clusters, it\nis found that the initial aggregation rates correlate with species\nparticle concentrations, but show no clear dependence on nanotube\nstructure. Variance spectroscopy can sensitively detect and characterize\nsmall loose clusters of carbon nanotube that are not observable by\nother spectroscopic methods.