Quantum Dots/Polymer Hybrid Materials And Organometallic Polymers

With a title of "Quantum Dots/Polymer Hybrid Materials and Organometallic Polymers", the dissertation explores a new method for the preparation of fluorescent inorganic-nanoparticle (QDs) composite microgels. With a combination of laser light scattering (LLS), pulsed field gradient nuclear magnetic resonance (PFG NMR), transmission electronic microscopy (TEM) and fluorescence techniques, we characterize the physical chemistry aspects of QDs/polymer single hybrid nanoparticle systems and investigate the self-assembly of organometallic block copolymer in selective solvents.First, we demonstrate a new approach for the preparation of hybrid microgels containing inorganic nanoparticles, using TOPO-passivated Cadmium Selenide (CdSe) QDs and oleic acid capped Lead Sulfide (PbS) QDs as examples. In this method, nanoparticles prepared by traditional high temperature methods in organic solvents, and covered with a layer of organic ligands at their surface, are incorporated into the microgel in a water-miscible organic solvent such as tetrahydrofuran (THF). Functional groups introduced as part of the microgel structure exchange with ligands from the nanoparticle synthesis, and the nanoparticles become irreversibly incorporated into the polymer network. These hybrid structures can then be transferred back to water.Our experimental results demonstrate that the microgels, synthesized in water, retained their colloidal stability during the transfer from water to THF; and the QD-microgel hybrid particles retained their colloidal stability in THF and during transfer from THF to water. We were able to show that QD binding to the microgel took place by a ligand exchange process. This approach worked well for polymer microgels of two different compositions, one based upon Poly(N-isopropylacrylamide) (PNIPAM), and the other on a copolymer of acetoacetoxyethyl methacrylate (AAEM) with N-vinylcaprolactam. Small differences in behavior were noted and attributed to the different internal morphologies of these microgels. The QDs incorporated into the microgels remained photoluminescent, both in THF and in water. The hybrid microgels retained their temperature-sensitive properties in aqueous solution, but the presence of the QDs shifted the volume phase transition to lower temperatures.We believe that this new approach can be used to incorporate a broad range of nanoparticles into microgels and can also lead to the design of novel multifunctional materials.And then, PFG NMR measurements were used to characterize the interaction of TOPO-coated CdSe QDs in CDC1₃ with linear poly(2-N,N-dimethylaminoethyl methacrylate) (PDMA) (M_N=12,000,M_w/M_n=1.2,N_n=78).Polymer adsorption was accompanied by displacement of TOPO molecules from the QD surface. We have shown that ligand exchange with PDMA normally leads to a modest increase in the quantum yield of QD emission. Thus the DMA groups of the polymer in contact with the surface are effective at passivating the surface, presumably by binding to Cd ions. At low polymer binding level, PDMA enhanced the colloidal stability of the particles, but led to only a modest increase in the hydrodynamic volume of the particles. By comparing the amount of polymer added to the solution to the amount of TOPO released from the QD surface, we determined that at lower levels of added polymer,a chain segment of on average 19 DMA monomer units was associated with the displacement of each TOPO molecule from the QD surface. When additional polymer was added, the effective hydrodynamic diameter of the polymer increased substantially. Furthermore, an even smaller fraction of the PDMA repeat units became involved in binding to the surface as the amount of polymer adsorbed increased. At the highest level of binding, in which each nanoparticle on average had 6 polymer molecules attached, 28 DMA groups were bound for each TOPO displaced. This result indicates that, on average, only about 3% of the DMA groups interact directly with the surface, while the other 97% is present in the form of loops and tails. These experiments emphasize how useful PFG NMR experiments are for characterizing colloidal nanocrystals in solution and for the study of their interaction with polymers.Moreover,we have examined the sphere-to-cylinder transition for micelle solutions of poly(ferrocenyldimethylsilane)-b-poly(2-vinylpyridine) (PFS₂₃-b-P2VP₂₃₀) block copolymer in ethanol. The small spherical micelles formed initially (...