Synthesis and Properties of Novel Inorganic/Polymer Nanocompositeart 1 Heterocoagulation of TiO2/Poly(AA-co-MMA) Nanoparticlesnd Blending with PETart 2 PEDOT Film with High Conductivity nd ZnO Nanorods/PEDOT Composite Thin Film
Date Issued
2008
Date
2008
Author(s)
Chen, Jui-Hung
Abstract
In this research, inorganic/polymer nanocomposites were synthesized and studied. The first part was heterocoagulation of TiO2/poly(AA-co-MMA) nanoparticles. Nano-sized TiO2 or SiO2/TiO2 particles were prepared by hydrolysis and condensation reactions in aqueous media, followed by mixing with poly(AA-co-MMA) latex to form different composite particles, then blending with poly(ethylene terephthalate), PET. The TGA results of composites indicated that negative charged latexes had greater interaction with TiO2/ or SiO2/TiO2 particles through strong electrostatic forces, while cationic latexes incorporated with TiO2/ or SiO2/TiO2 particles by pH induced coagulation, carbonyl group chelation and hydrogen bonding. The soapless latex polymer particles showed lower ability of adsorption to TiO2 particles due to the decrease of total surface area of these larger particles. If SiO2/TiO2 particles were used instead of TiO2 particles, unexpected high adsorption result was observed. Morphology results observed by SEM showed that PET blended with positive charged composites was more homogeneous than PET blended with negative charged composites. DSC results also indicated that the Tg of PET was increased, melting temperatures (Tm or Tm’) were increased, and the temperature range of crystallization was narrowed after blending with the composites. The presence of composites affected the mobility and packing of PET molecular chains therefore changing the thermal properties of PET. he second part was to synthesize highly conductive PEDOT film and ZnO nanorods/PEDOT composite thin film. PEDOT represented a class of conjugated polymers that could be potentially used as an electrode material for flexible organic electronics due to their superior conductivity and transparency. We demonstrated that the conductivity of a PEDOT containing copolymer film could be further enhanced by the oxidative chemical in situ copolymerization of a liquid film spin-coated from monomer mixture 3,4-ethylenedioxythiophene (EDOT) and 3-thienyl ethoxybutanesulfonate (TEBS), oxidant (iron(III) p-toluenesulfonate (Fe(OTs)3), weak base (imidazole, IM), and solvent (methanol). We investigated the effect of the processing parameters such as the molar ratios TEBS/EDOT, IM/EDOT, and Fe(OTs)3/EDOT on the surface morphology, optical property, and the conductivity of the resulting copolymer films. These parameters were optimized to achieve conductivities for the copolymer films as high as 170 S/cm, five times higher than the PEDOT film synthesized with method. This conductivity enhancement for the copolymer films was found to be resulted from the fact that the addition of TEBS monomer reduced the copolymerization rate, leading to the formation of much more uniform film surface without defects which increased the conductivity of the copolymer film. Kinetics study of copolymerization of EDOT/TEBS was conducted by calculation of the reactivity ratio, molecular weight ratio, and monomer distribution in the copolymer. The calculation of reactivity ratio revealed that EDOT was oxidized by oligomer more easily than TEBS. As TEBS/EDOT increased, the molecular weight also increased as a consequence of higher content of TEBS in the copolymer chain. Molecular weight was highest when IM/EDOT equaled 2. Higher content of Fe(OTs)3 resulted in lower molecular weight and shorter copolymer chain due to the increasing number of copolymer chains. nO nanorods/PEDOT film was fabricated by a three-step process: PEDOT polymerization, ZnO seeds annealing, and hydrothermal growth of ZnO nanorods. ZnO nanoparticles were synthesized from reaction of zinc acetate and sodium hydroxide in methanol medium and used as seed for ZnO growth. The presence of ZnO seed layer was important for ZnO rods to grow perpendicularly on substrates. For ZnO rods to grow on PEDOT films, hexamethylenetetramine, HMTA, was preferred as the source of base. By controlling the concentration and condition of hydrothermal growth, ZnO nanorods were able to grow perpendicularly on the PEDOT film. The pH buffering ability of ZnO nanorods/PEDOT film with four hydrothermal growth cycles was comparable to pure ZnO powders.
Subjects
TiO2
poly(AA-co-MMA)
emulsion polymerization
heterocoagulation
PEDOT
ZnO
conducting polymer
hydrothermal process
Type
thesis
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