Grazing Incidence X-ray Scattering and Its Utilization on Nanostructural Details of Brush Polymer Thin Films

Doctor스침각 입사산란(GIXS) 방법 및 이를 이용한 연구를 통하여 브러쉬 고분자의 다양한 나노구조체가 연구되었다. 기존의 독립적 산란 부분(independent scattering terms)으로 정리된 GIXS 공식에 대하여 상호작용 부분(cross terms)을 고려하여 완전한 GIXS 공식을 유도하였다. 특정 크기의 분포를 가지는 구형의 나노크기의 구멍(nanopore)이 박막내부에서 방향성없이 분포되어 있는 고분자 박막 모델 시스템에 대하여 위 공식을 적용하였다. 상호작용 부분(cross terms)은 전체산란강도에 기여하는바가 작기 때문에 기존의 독립적 산란 부분만을 이용하여 구조 인자(structural parameters)를 성공적으로 제공 할수 있다. 하지만 박막의 두께, 전반사각, 굴절률, 흡수계수등의 박막특성 분석을 위해서 상호작용부분을 포함하는 완전한 2차원적 산란 데이터 분석이 필요하며, 완전한 GIXS 공식을 이용하여 나노크기의 구멍(nanopore)을 가지는 고분자 박막 모델 시스템을 성공적으로 분석하였다.GIXS를 이용하여 poly(n-hexyl isocyanate) (PHIC) 박막의 용매 선택성에 의한 conformation 변화 연구를 수행하였다. PHIC 고분자 박막은 Carbon disulfide 용매 어닐링 조건에서 박막내부에서 잘 정렬된 벌집구조(hexagonal close packing structure) 형태의 구조체를 형성하며, 이 때 고분자는 83 helical conformation를 가진다. 동일 박막시료에 대하여 추가적인 toluene 용매 어닐링 처리를 통한 정렬된 -sheet conformation로 고분자 구조가 변화하는 것을 관찰하였다. 또 Carbon disulfide 용매 어닐링 처리를 다시 해주어 잘 정렬된 벌집구조 형태로 되돌아가는 것을 확인하였다. 본 실험을 통하여 용매 조건을 변화시켜 박막내의 가역적인 구조 변화를 유도하고 성공적으로 구조분석을 시행하였다.두가지 폴리티오펜(polythiophene) 유도체 Regioregular poly(3-(4’-(3”,7”-dimethyloctoxy) phenyl)thiophene) (P3PhT) 과 poly(3-(4’-(3”,7”-dimethyloctoxy)-3’-pyridinyl) thiophene) (P3PyT) 에 대하여 GIXS 분석을 수행하였다. 두 경우 모두 박막 내에서 다층상 구조가 필름의 수직한 방향으로 생성되는 것을 알수 있었다. 이러한 다층상 구조는 잘 정렬된 층(ordered sublayer)와 그렇지 않은 층(amorphous sublayer)으로 이루어 지며, P3PhT의 경우 페닐(phenyl)을 포함하는 폴리티오펜 주쇄 영역의 잘 정렬된 층이 형성되지만 P3PyT의 경우 폴리티오펜 주쇄 영역까지만 잘 정렬된 층이 형성된다. 이러한 P3PhT의 잘 정렬된 층의 증가는 π-conjugation lengths를 증가시키며, 광학적, 전기적 특성을 향상시킨다.각각의 블록이 액정 기능기를 가지는 블록 공중합체를 박막으로 제조하고, GIXS를 이용하여 고분자 박막의 실시간 상변이를 관찰하였다. poly(methyl 4'-(11-(4-vinylphenylcarbonyloxy)undecanoyloxy)biphenyl-4-carboxylate)-b -poly(undecyl 4'-(4-vinylbenzoyloxy)biphenyl-4-carboxylate) (P1-b-P2)의 박막은 두 도메인의 상분리를 통하여 라멜라 구조를 형성하며, 각각의 도메인은 그 내부에 다층상 구조를 형인성한다. 실시간 가열 및 냉각 실험을 통해 각각의 도메인 내부에서 액정의 변화와 블록 공중합체의 상분리에 의한 나노구조체의 변화를 관찰하였다.Grazing Incidence X-ray Scattering (GIXS) measurements and detailed analyses were performed for various nanostructures in the thin films.First, a complete grazing incidence X-ray scattering (GIXS) formula was derived for nanopores buried in a polymer dielectric thin film supported by a substrate. By using the full power of the scattering formula, the GIXS data from nanoporous polymethylsilsesquioxane dielectric thin films, a model nanoporous system, were successfully analyzed. The nanopores were found to be spherical and had a certain level of size distribution but randomly dispersed in the film. In the film GIXS was confirmed to arise predominantly via the first scattering process in which the incident X-ray beam scatters without reflectionthe other scattering processes and their contributions were significantly dependent on the grazing angle. This study also confirmed that GIXS scattering can be analyzed by using only independent scattering terms, but this simple approach can only provide structural parameters. The cross-terms were found to make a relatively small contribution to the intensity of the overall scattering but were required for the complete characterization of the measured 2D scattering data, in particular the extracted out-of-plane scattering data, and their inclusion in the analysis enabled film properties such as film thickness, critical angle (i.e., electron density), refractive index, and the absorption term to be determined. Second, fully reversible conformational change and structural details of poly(n-hexyl isocyanate) (PHIC), in the solid state were studied in detail using GIXS. A well-ordered hexagonal close packing structure of PHIC with 83 helical conformation was nicely demonstrated in the films annealed selectively with carbon disulfide. A well-ordered multibilayer structure of the polymer with -sheet conformation was also nicely formed in the films annealed selectively with toluene. Moreover, a fully reversible transformation between these two self-assembled structures was demonstrated by consecutive annealing with carbon disulfide and toluene. Third, regioregular poly(3-(4’-(3”,7”-dimethyloctoxy)phenyl)thiophene) (P3PhT) and poly(3-(4’-(3”,7”-dimethyloctoxy)-3’-pyridinyl)thiophene) (P3PyT) were prepared with reasonably high molecular weight and low polydispersity. Both the polymers in films revealed a molecularly multilayer structure (i.e., lamellar structure) whose layers stacked normal to the film planeeach lamella consists of two sublayers, namely ordered and amorphous layers by GIXS measurements. The amorphous sublayer was composed of a bilayer formed from the bristles. The ordered sublayer in P3PhT consisted of laterally stacked 3-phenylthiophene backbone chains, whereas that of P3PyT consisted of thiophene backbone chains without pyridinyl linker. These ordered sublayer formations led π-conjugation length longer. The enhanced π-conjugation lengths were reflected in the optical and electronical properties, showing that both P3PhT and P3PyT exhibit lower HOMO level and lower energy band gap, compared to those of poly(3-hexyltiophene) (P3HT). Overall the structure and properties of P3PhT and P3PyT make them a promising material for advanced polymer solar cells with excellent performance.Fourth, Temperature-dependent phase transition behavior of novel double liquid crystalline brush type block copolymer in the thin film was investigated using GIXS. The thin film analysess of poly(methyl 4'-(11-(4-vinylphenylcarbonyl-oxy)undecanoyloxy)biphenyl-4-carboxylate)-b-poly(undecyl 4'-(4-vinylbenzoyloxy)bi-phenyl-4-carboxylate)(P1-b-P2) provide detailed information about the hierarchical nanostructure of phase-separated domain and molecular structures in each domain during heating and cooling runs. In addition, we propose molecules and their hierarchical structure models of the diblock polymer in the thin fil

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