Network-Structured Block Copolymer Photonic Crystals for Template Applications
| Autor: | Po-yu Tsai, 蔡博宇 |
|---|---|
| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 Owing to various potential applications in light emission, sensor, solar cell, and display fields, amorphous photonic crystals (APCs) featuring interconnected network microstructure have been drawn much attention recently. Self-assembled morphologies were manipulated using a weak-incompatible high-Mw polystyrene-b-poly(methyl methacrylate) (PS-PMMA) block copolymer (BCP) so as to generate one-dimensional (1D) or three-dimensional (3D) polymer-based photonic reflectors. To acquire APCs exhibiting angle-dependent optical properties, interconnected short-range-order network microstructures with isotropic orientation were prepared. As evidenced by transmission electron microscopy (TEM) and 2D fast Fourier transform (FFT) pattern, the long-range-order lamellar microstructure with iridescent coloration could be observed in the as-cast PS-PMMA bulk film from 1,1,2-trichloroethane (TCE) or chloroform. By blending with a compatible PS homopolymer, a phase transition from the long-range-order lamellae to the short-range-order network morphologies could be carried out. Also, the network-structured microstructures with isotropic orientation were prepared in the as-spun thin film from TCE, due to the insufficient time for self-ordering process. Owing to the short-range order and the isotropic orientation of the network microstructure, the network-structured PS-PMMA thin film exhibited angle-independent reflectivity, indicating the successful fabrication of the APCs. Also, the PS-PMMA APC exhibited red-shifting reflectivity during solvent fuming, namely, solvatochromism. Using FFT method allowed us to precisely calculate the average distance of the isotropic network microstructure, which is critical for the calculation of the bandgap wavelength of the APC by modified Bragg’s law for coherent scattering. After the degradation of the PMMA segment by UV irradiation, the nanoporous PS-network template was prepared for subsequent infiltration and backfilling of the inorganic materials with different refractive indices. With the introduction of sol-gel process, inorganic SiO2- and TiO2-network microstructures with high porosity were obtained after calcination. Notably, the nanoporous network microstructures with high refractive index contrast in the APC thin films could significantly enhance the intensity and bandwidth of the angle-independent pseudogaps. To manipulate the reflected wavelength in the PS-PMMA APC thin film, the control of the microdomain thickness was conducted by the introduction of supercritical carbon dioxide (scCO2) or additive homopolymers. With the increase of the homopolymer contents, red-shifting bandgap could be obtained progressively in the PS-PMMA/PS/PMMA ternary blends due to the increase of the microdomain thickness. For the application in optical communication, the network-structured APCs composed of different inorganic materials were also demonstrated in a capillary tube, namely, an APC straw. As a result, this provides a novel means for the fabrication of polymer-based APCs with tunable refractive index contrast. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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