Controlled Vortex Formation and Facilitated Energy Transfer within Aggregates of Colloidal CdS Nanorods

Abstract

Vortex formation is observed in transmission electron microscopy (TEM) images of colloidal CdS narorod (NR) aggregates. Upon adding polar (poor) solvents into the NR dispersion, the NRs passivated with alkylphosphonic acids Start flocculating. When NR clustets are deposited on a TEM grid, the tips of the NRs are immobilized on the substrate, and capillary forces give rise to a net inward tilting as the solvent evaporates, eventually leading to the formation of vortices. Solvent polarity turns out to play a Critical role in controlling the structure of vortices. Fluorescence lifetime imaging microscopy (FLIM) of the ensembles reveals that the vortex structures have profound influence on the energy transfer rate within the NR assembly.