Refractive Index Engineering and Optical Properties Enhancement by Polymer Nanocomposites

The major part of this dissertation discusses the engineering of the refractive index of materials using solution-processable polymer nanocomposites and their applications in building optical components and devices. Three particular polymer nanocomposites have been introduced to achieve materials with tunable refractive indices and enhanced optical properties, which can be used to manipulate the behavior of light or electromagnetic radiations. In the first system, polyhedral oligomeric silsesquioxane (POSS)/polymer nanocomposites are developed. Thin films with tunable, low refractive indicies were fabricated from the composites. The mechanical strength of these films was characterized, and their application in antireflective coatings is discussed. In the second system, a titanium oxide (TiO2)/polymer nanocomposite is developed. For these nanocomposites, a method for fabricating mesoporous TiO2 thin films with tunable refractive indices at room temperature is introduced. The low temperature strategy allows the deposition of mesoporous TiO2 based Bragg mirrors on polymeric substrates. The potential application of the TiO2 Bragg mirror as a gas sensor is discussed. Finally, a zirconium oxide (ZrO2)/polymer nanocomposite with a tunable refractive index is developed. The refractive index of the ZrO2 nanocomposites was tuned to match the index of a rare-earth ion doped nanoparticle. Highly transparent composites containing light emitting nanoparticles with minimum Rayleigh scattering can be achieved by blending the two nanoparticle systems in controlled amounts from solution. This is the first exhibition of the successful employment of hybrid polymer composites as a “refractive index matching” matrix, facilitating fabrication of highly transparent nanocomposites. The second part of this dissertation introduces a light-responsive block copolymer composite. Poly [poly(ethylene glycol) monomethyl ether monomethacrylate]-block-poly(ethyl methacrylate) was prepared using reversible addition-fragmentation chain transfer polymerization (RAFT). This block copolymer is an amorphous, phase mixed system at room temperature. The incorporation of organic additives with multiple carboxylic acid groups, such as mellitic acid, induces phase segregation in this system. Furthermore, the use of additives in which the hydrogen bond donating group is protected with an acid labile group in combination with a photo acid generator enables photo-induced ordering of the composite films. Adjacent disordered/ordered patterns can be obtained using this strategy due to the absence of PEO crystals