Fabrications of Photonic Crystals with Various Microstructures in Polystyrene-block- Poly(2-vinylpyridine) Block Copolymer Thin Films

• Main Authors: En-Li Lin, 林恩立
• Other Authors: Yeo-Wan Chiang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/16578759266082284441

碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 101 === In this study, the fabrication of block copolymer (BCP) photonic crystals with different microstructures including lamella, cylinder, gyroid and hexagonally perforated layer are conducted from the self-assembly of polystyrene-b-poly (2-vinyl pyridine) (PS-P2VP) BCP thin films. Transmission electron microscope (TEM) micrograph of high-molecular-weight PS-P2VP shows cylinder morphology from 1, 2-dichloroethane whereas low-molecular-weight PS-P2VP exhibits gyroid morphology form dichloromethane in bulk. Owing to the difference of solvent selectivity for PS and P2VP, various morphologies are obtained in as-spun PS-P2VP BCP thin films. Owing to poor solubility for P2VP resulted from strong interaction among pendent pyridines, the P2VP chains easily form micelles in the PS matrix in the as-spun PS-P2VP BCP thin films from PGMEA, THF, and chlorobenzene. Interestingly, the chloride-containing solvents such as chloroform, 1,1,2-trichloroethane, and 1, 2-dichloroethane may form protonation with pyridine so as to enhance the solubility for P2VP, such that microphase-separated gyroid morphology can be observed in the as-spun BCP thin films as evidenced by TEM and the grazing-incidence ultra-small angle X-ray scattering. By solvent annealing, interesting phase behaviors of the PS-P2VP BCP thin films can be found. After solvent annealing by toluene, P2VP micelles in the PS matrix can be obtained due to poor solubility for P2VP. By contrast, phase transitions from the as-spun micelle or gyroid to lamellae can be found after solvent annealing by PS-selective solvents such as 1, 1, 2-trichloroethane (TCE) or chloroform. Accordingly, large-area lamellar microstructures with parallel orientation to glass substrate can be accomplished due to substrate- and solvent-induced microstructural orientation. Most interestingly, a phase transition from the as-spun gyroid to well-oriented hexagonally perforated layer (HPL) phase can be obtained in the PS-P2VP BCP thin film after solvent annealing by TCE. By absorption of ethanol, the selective swelling of the P2VP microdomian in the PS-P2VP BCP thin film may give significant red shift of the reflective wavelength, such that photonic bandgaps in visible spectrum can be carried out. The UV-Vis spectra of the gyroid-forming PS-P2VP photonic crystal exhibits unique solvatochromic behavior by absorption of ethanol, as evidenced by the characteristic reflective wavelength ratio of √6 ∶ √8 . Surprisingly, the HPL-forming BCP photonic crystal reveals that the multiple reflectivity bands cover whole visible spectrum with the accompanying decrease of reflective intensity, resulting in white reflective color mixed with purple. As a result, the BCP photonic reflectors with various microstructures can be fabricated from the self-assembly of the PS-P2VP BCP thin films. The significantly different optical properties associated with the microstructural shapes are promising to be applied in various applications.