The fabrication of one-dimensional (1-D) polymeric photonic crystals from the self-assembly of ultra-high-Mw polystyrene-b-polyisoprene (PS-PI) block copolymers (BCPs) were conducted in this study. Well-ordered microphase-separated lamellar structures can be observed in the ultra-high-Mw PS-PI BCPs in the bulk by transmission electron microscopy (TEM) and ultra-small angle X-ray scattering (USAXS). To fabricate large-area and well-oriented lamellar microstructures with parallel orientation to the substrate, substrate-induced microstructural orientation with the accompanying solvent annealing method (i.e., solvent-induced orientation) was carried out in the PS-PI film. By grazing-incidence ultra-small angle X-ray scattering (GIUSAXS), scanning probe microscope (SPM) and cross-sectional TEM morphological observation, identification of the microstructural orientation in the PS-PI film can be achieved.
A disordered wormlike morphology is observed in the as-spun PS-PI thin film from toluene on the PS-grafting substrate and on neat glass or wafer. This is attributed to the fast solidification of the disordered microstructure due to fast evaporation rate of the toluene solvent. After solvent annealing by the PS-selective or PI-selective solvents such as divinylbenzene (DVB) (neutral but highly PS-selective), benzene (PS-selective) and cyclohexane (PI-selective), parallel lamellar microstructures can be obtained in the PS-PI films on the PS-grafting substrate. By contrast, the coexistence of parallel and perpendicular lamellar microstructures is obtained in the PS-PI film from toluene after solvent annealing by neutral toluene on the PS-grafting substrate or by PS-selective benzene on the neat glass or wafer. This indicates that the formation of the parallel lamellar microstructures is mainly determined by both solvent-induced and substrate-induced orientation.
In contrast to the as-spun disordered morphology from toluene, well-ordered parallel lamellar microstructures with few defects was found in the as-spun PS-PI film from DVB on the PS-grafting substrate, whereas parallel lamellar microstructures with many defects was observed in the as-spun PS-PI film from DVB on the neat glass or wafer. This further demonstrates that the PS-grafting substrate indeed plays an important role on the fabrication of well-ordered parallel lamellar microstructures. Interestingly, once the initial morphology of the PS-PI BCP reaches a relative stable state (i.e., parallel lamellar microstructures versus disordered wormlike morphology), it is hardly to trigger the microstructural reorientation by the subsequent solvent annealing. We suggest that the stable initial morphology in the PS-PI film may create high energy barrier for microstructural reorientation.
With the controllable microstructural orientation, a PS-PI thick film having large-area and well-oriented parallel lamellar microstructures can be successfully carried out. Therefore, 1-D polymeric photonic crystals from the self-assembly of the lamella-forming PS-PI BCPs can be achieved. The in-situ UV reflectance spectra show that the reflective band shifts from ultraviolet wavelength to visible wavelength was observed in the lamella-forming PS-PI thick film with elapse of time by solvent annealing. Notably, the band gap can be recovered to the initial state once the solvent is removed, indicating the reversible process. As the results, the solvatochromic BCP photonic crystals can be successfully carried out by the manipulation of the solvent swelling in the large-area and well-oriented lamella-forming PS-PI BCP film.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0806112-155520 |
| Date | 06 August 2012 |
| Creators | Chou, Chung-Yi |
| Contributors | Shiao-Wei Kuo, Ching-I Huang, Jing-Cherng Tsai, Rong-Ming Ho, Yeo-Wan Chiang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0806112-155520 |
| Rights | user_define, Copyright information available at source archive |
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