PROPERTIES OF CDSE NANOCRYSTAL DISPERSIONS IN THE DILUTE REGIME - STRUCTURE AND INTERPARTICLE INTERACTIONS

We report an investigation of the properties of CdSe nanocrystal dispe rsions using small-angle x-ray scattering. These nanocrystals are prep ared from organometallic precursors using high-temperature solution ch emistry. The study provides diner and accurate measures of the nanocry stal size and size distribution. The low polydispersity measured confi rms the high quality of the nanocrystals prepared using a high-tempera ture solution chemistry route, as anticipated from optical data. The s tudy also provides information on the interparticle interactions and t heir dependence on a few relevant parameters, such as nature of the ca pping molecules and solvent. Nanocrystal association, e.g., dimers, in dispersions characterized by weakly attractive interactions, and/or a ggregation in solutions with strong attractions, can be observed. The study also unveiled other features where interactions are reversed fro m repulsive stabilizing to attractive as the particle size is decrease d. This behavior, unexpected for colloidal dispersions, may be caused by a reduction of the cap density as the size is decreased. The genera l trend for the interparticle interactions in these dispersions can be under stood within the framework of a van der Waals core to core attr active potential, to which are superposed effects of cap affinity to t he core and to the surrounding solvent. Within these considerations, o ne can distinguish three types of dispersions: sterically stabilized d ispersions, dispersions thermodynamically stable but governed by weak attractions, and unstable dispersions where strong attractions induce macroscopic aggregation. [S0163-1829(98)04335-5].