Wong, Min Hao (2013-03). Colloidal Nanoparticles Tethered by Oligomers and Short Polymers in Organic and Polymeric Media. Doctoral Dissertation.
Thesis
Nanoparticles and related nanomaterials are increasingly being utilized in technological applications. Controlling the dispersion and organization of these advanced materials is crucial towards realizing their full potential. In this dissertation, we employ methods of tethering oligomers and short polymers to the surfaces of spherical nanoparticles and 2D crystals. ZnO quantum dots are spherical nanoparticles which are direct bandgap semiconductors (3.37 eV) with large exciton binding energies (60 meV) and show strong photoluminescence. We show that poly (methyl methacrylate) grafted onto ZnO quantum dots via radical polymerization yields polydisperse brushes that are particularly effective in forming stable, fine dispersions in melt-blended nanocomposites. Nanocomposites prepared via this method exhibit tunable properties in refractive index, glass transition temperature and energy bandgap as a result of their linear dependence on ZnO concentration. It is further shown that the glass transition behavior of these nanocomposites is analogous to that of polymer thin films. ?-ZrP nanoplatelets are 2D crystals which are being studied for use as a catalyst, drug delivery agent, proton conductor, nanofillers for nanocomposites, etc. Exfoliated ?-ZrP nanoplatelets of large aspect ratios tethered by polyoxyalkyleneamines form photonic structures in high polar, aprotic solvents. The polyoxyalkyleneamines form a brush layer on the nanoplatelets allowing the formation of lamellar phases with large d-spacings. Bragg reflection by the mesomorphic structures in the visible wavelengths gives rise to iridescence with brilliant colors that are tunable by adjusting the concentration of nanoplatelets. In epoxy, ?-ZrP nanoplatelets tethered by polyoxyalkyleneamines self-assemble into smectic phase when spray-coated onto polyimide substrates. These spray-coated thin films of smectic ?-ZrP/epoxy exhibit excellent gas barrier properties that perform consistently in low and high humidity conditions. The highly ordered nanoplatelets are aligned parallel to the substrate forcing gas molecules to traverse a tortuous path resulting in a reduction of permeability in the film. Observations of the occurrence of liquid crystalline phases in the bulk ?-ZrP/epoxy liquid shows that the self-assembly behavior of these smectic ?-ZrP are consistent with the predictions of Onsager's theory.
