YuanQiao Rao

Organic Solvent-Dispersed TiO2 Nanoparticle Characterization

Anatase titanium dioxide nanoparticles are derivatized with the polymerizable reagent (3-methacryloxypropyl)trimethoxysilane to provide dispersions in organic solvent. The titania core particles are characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The organic component structures and thickness are elucidated using nuclear magnetic resonance (NMR), quasielastic light scattering (QELS), and size-exclusion chromatography (SEC). Thin, high-refractive-index coatings prepared from the organic dispersions are characterized by atomic force microscopy (AFM). The combination of microscopies, spectroscopy, light scattering, and separation techniques provides unique information on the structure, thickness, morphology, and size distributions of the surface-treated nanoparticles that is difficult to obtain by any single technique. The findings indicate titania platelets with a modal diameter of 9.8 nm and a thickness of approximately 1.5 nm. The particles are coated with a 1.5-1.9 nm thick organic ligand layer, and a substantial population of 2 nm siloxane oligomers is detected. The analytical methodology presented may also be useful for characterizing other anisotropic organic-inorganic nanoparticles and their dispersions.

P-108: Birefringence Dispersion of Polymer Films As Applied to Optical Compensation in LCD

Minimizing color shift effects in a liquid crystal display (LCD) requires close attention to the optical dispersion of compensation layers used to increase the contrast ratio and viewing angle of the display. This paper describes our attempt to systematize and characterize the birefringence dispersion of solvent-cast polymer films and relate it to the “native” out-of-plane birefringence (Δnth) of the polymer and its structure. Results for a wide range of polymers show general correlation between the dispersion parameter DPΔn [≡Δn(450)/Δn(590)] and Δnth. for all positively birefringent polymers, DPΔn is always > 1, suggesting “normal” dispersion at any level of Δnth, while for negatively birefringent polymers DPΔn > 1 only when |Δnth| > ∼0.003. Below this critical value, DPΔn < 1, i.e., the polymer is reverse-dispersive. The results are explained in terms of the Cauchy coefficients for the corresponding polymers, and they suggest that the dispersion of birefringence cannot be controlled independently of the birefringence of the polymer film.