Aggregation kinetics of dendrimer-stabilized CdS nanoclusters

Precipitation of CdS in Starburst PAMAM dendrimer solutions offers a viable method of preparing CdS nanoclusters with long-term optical stability. Photoluminescence and UV-visible spectroscopy data show that the dendrimer stabilizes the precipitated CdS as nanoclusters with characteristic optoelectronic properties not seen in bulk CdS. However, photon correlation spectroscopy (PCS) indicates power-law growth of aggregates composed of dendrimer-stabilized nanoclusters. Temperature and reactant concentration are dominant variables controlling the aggregation kinetics. Power-law growth of the aggregate diameter and the intensity count rate suggest that the aggregation kinetics are diffusion-limited, at least at higher temperatures and reactant concentrations. The termination of the aggregation process and the stability of the final aggregates are confirmed by the absence of bulk CdS precipitate several months after synthesis. Photoluminescence and W-visible spectroscopy link the optical properties of the aggregates to those of the CdS nanoclusters formed immediately after the initiation of the synthesis process. This substantiates that the CdS nanoclusters remain as distinct entities within the dendrimer aggregates, presumably stabilized against further coalescence by the dendrimers.