블록 공중합체 미셀과 온도기울기 용매처리법을 이용한 높은 종횡 비를 가지는 수직배향 박막구조 제어 및 응용
- 블록 공중합체 미셀과 온도기울기 용매처리법을 이용한 높은 종횡 비를 가지는 수직배향 박막구조 제어 및 응용
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- Block copolymers have been widely attracted as one of the bottom-up approaches in nanotechnology due to their self-assembled characteristics. The segregation of block components because of thermodynamic incompatibility and a connectivity of two chains in a block copolymer can reveal various ordered nanostructures in tens nanometer scale, such as lamellae, cylinders, spheres, and bicontinuous gyroids, depending on the composition of one block and the interaction parameter between the two blocks. Many literatures have provided to control the orientation of microdomains and long-range lateral ordering by using various methods. Solvent vapor annealing has been found very useful and effective means in the fabrication of highly ordered cylindrical microdomains oriented vertically to the substrate with long-range lateral ordering.
Block copolymers containing poly(2-vinylpyridine) (P2VP) or poly(4-vinylpyridine) (P4VP) have been widely employed to develop functional nanomaterials because the organic and inorganic materials have been coordinated having hydrogen bonding or ionic interaction with a nitrogen atom in the pyridine ring. But the fabrication of high aspect ratio of P4VP (or P2VP) cylindrical microdomains oriented vertically to a substrate remains great challenge because of high repulsion between P4VP (or P2VP) and the other block (for example, PS block). In this dissertation, the high aspect ratio cylindrical microdomains oriented vertically on a substrate in PS-b-P4VP thick films were investigated and then using these templates, a high density array of high aspect ratio of gold/polymer nanocomposite nanorods was investigated.
In chapter 2, we report a simple, but novel, method for the preparation of high aspect ratio of cylindrical microdomains oriented vertically on the substrate by using block copolymer micelles and temperature-gradient solvent vapor annealing. For this purpose, multilayered spherical micelles were prepared by spin-coating of polystyrene-block-poly(4-vinylpyridine) copolymer (PS-b-P4VP) in toluene solution on a silicon wafer. All the samples were first annealed at a starting temperature to assure full swelling of the films. When temperature-gradient solvent vapor annealing was performed, the micelle cores consisting of P4VP chains were transformed into vertically oriented cylindrical microdomains spanning the entire film thickness up to several hundred nanometers.
In chapter 3, we have prepared a high density array of high aspect ratio of gold/polymer nanocomposite nanorods oriented vertically on a substrate in asymmetric PS-b-P4VP block copolymers since nitrogen in the P4VP block could be easily coordinated with many metal precursors such as HAuCl4. Using temperature-gradient solvent vapor annealing and block copolymer micelles, high aspect ratio cylindrical microdomains oriented vertically to the substrate in thick films are prepared. It is easily confirmed that an equilibrium precursor loading time and fully reduced Au NPs by the changes of FTIR absorption spectra of PS-b-P4VP thick films with both HAuCl4 and Au NPs. Through the UV-Vis-near IR experiments, the spectral features of a high density array of high aspect ratio of Au nanoparticles/polymer composite nanorods show similar optical response as Au anoparticles/SU8 composite nanoarrays in an AAO themselves. Since this method precludes the need of template (AAO), it can be directly applied to the several substrates for biosensing and optical device, etc.
In appendix chapter I, we studied the microstructural changes of ITO during the annealing process. ITO nanoparticles were prepared by the sol-gel method using indium tin hydroxide as the precursor. The prepared sample was investigated using TEM, powder XRD, XPS, DRIFT, and 2D correlation analysis. The O 1s XPS spectra suggested that the microstructural changes during the annealing process are closely correlated with the oxygen sites of the ITO nanoparticles. The temperature-dependent in situ DRIFT spectra suggested that In-OH in the terminal sites is firstly decomposed and, then, Sn-O-Sn is produced in the ITO nanoparticles during the thermal annealing process. Based on the 2D correlation analysis, we deduced the following sequence of events: 1483 (due to In-OH bending mode) -> 2268, 2164 (due to In-OH stretching mode) -> 1546 (due to overtones of Sn-O-Sn modes) -> 1412 (due to overtones of Sn-O-Sn modes) cm-1
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