Towards well-defined nanocrystal assemblies: Using size exclusion chromatography to understand soluble nanocrystal complexes

This thesis develops and applies size exclusion chromatography (SEC) for the accurate characterization and size separation of semiconductor and metallic nanoparticles. Size exclusion chromatography is employed for the first time to determine the size and size distribution of cadmium selenide nanocrystals. The method accurately determines nanocrystal size as well as the length of any surface capping ligands. The separation resolution is enhanced using recycling SEC and a shape separation of quantum dots and multipods is performed. SEC is further applied to measure the hydrodynamic diameter of gold and cadmium selenide nanocrystals passivated with polystyrene. Polystyrene occupies a brush conformation on the surface of these nanoparticles and the polymer length is found to scale linearly with molecular weight and as the cube root of polymer coverage. Using these measurements, a general formula is proposed to predict the hydrodynamic diameter of polymer coated nanoparticles. Gold and cadmium selenide nanocrystals discretely functionalized with different numbers of polystyrene molecules are also separated. Fluorescence and 1H-NMR measurements of collected fractions confirm the separation and the population of the species is studied as a function of polystyrene concentration. These discrete nanocrystal-polymer conjugates form ordered microphases upon drying that are dependent upon the tether number. Such data illustrates the potential of these species as building blocks for self-assembly.