Ligand effects on semiconductor nanoparticles in two contexts: Self-assembly and environmental stability.

The research presented in this thesis examines the role of surface chemistry in the behavior of semiconductor nanoparticles in two different contexts. The first deals with effects that tuning the surface chemistry of CdSe and TiO2 nanospheres and nanorods has on their interactions with thin films of poly(styrene-b-methyl methacrylate). Through ligand exchange procedures, the surface chemistry of the studied nanoparticles can be altered in such a way as to effect preferential segregation of particles to either domain of the thin films. This technique is extended to separating a mixture of two chemically distinct nanoparticles through interactions between the surface ligands and polymer domains. Differences in dispersion of nanoparticles leads to a theoretical framework for manipulating nanoparticles in composites based on minimizing interfacial energy by mimicking interactions between localized homopolymer and block copolymer domains. The second context in which the role of nanoparticle surface chemistry is examined is that of environmental stability. CdSe nanoparticles encapsulated by a custom made copolymer of poly(ethylene glycol) and poly(maleic anhydride- alt-octadecene) are exposed to an in vitro biomimetic oxidative assay modeled on the extracellular chemistry of lignolytic brown rot fungi. The conditions of this assay are representative of those that might be found in temperate climate soils should nanoparticles be released into the environment. Analysis by a wide range of spectroscopic techniques suggests that copolymers do not provide absolute protection for the particles against oxidation by environmentally relevant conditions but may act as a trap for any released material from degraded particles and thereby protect the environment from potential sources of pollution.