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스침각 입사 엑스선 산란 및 이를 이용한 기능성 고분자 및 블록 공중합체 박막의 나노구조 연구

Title
스침각 입사 엑스선 산란 및 이를 이용한 기능성 고분자 및 블록 공중합체 박막의 나노구조 연구
Authors
안병철
Date Issued
2013
Publisher
포항공과대학교
Abstract
스침각 입사 산란법 (GIXS) 과 유도된 산란 방정식을 이용하여 기능성 고분자 박막 내의 다양한 나노구조가 연구되었다. 대다수의 고분자 물질은 박막 형태로 제작되기 때문에, 박막 형태의 고분자 물질에 대한 구조 분석 방법이 요구되는 실정이다. 이런 점을 고려할 때, GIXS은 박막 형태의 고분자에 대해 가장 적합한 방법이라 할 수 있다. 성공적인 분석을 위해서 distorted-wave Born 가정 (approximation) 및 굴절, 반사현상을 포함하는 GIXS에 대한 산란 방정식을 유도하였다. 또한 산란 방정식은 형태항 (form factor) 과 구조항 (structure factor) 로 구성되어 있다. 구조항을 기술함에 있어서, decoupling 가정 (DA) 과 local monodisperse 가정 (LMA), 그리고 size-spacing correlation 가정 (SSCA) 의 세 가지 구조항 가정을 이용하였으며, 이를 산란 방정식에 대입함으로써 비교하였다. 구형의 기공을 가지는 다공성 고분자인 PMSSQ박막을 구 (sphere) 형태항의 예시로 이용하였다. 구 형태항 및 세 가지 구조항 가정을 산란 방정식에 대입함으로써, GIXS 실험 결과와 분석 결과를 서로 비교하였다. 본 경우에는 DA 및 LMA 구조항 가정을 도입한 경우에 실험 결과와 잘 일치하며, 구조의 불규칙성이 크다는 사실을 알 수 있었다. 또한 수직 배향 원통 구조를 가지는 Poly(styrene-b-methyl methacrylate) (PS-b-PMMA) 고분자 박막을 원통 형태항의 사례로 이용하였다. 원통 형태항 및 세 가지 구조항 가정을 산란 방정식에 대입하여 계산된 산란 정보를 서로 비교함으로써 구조변수에 따른 산란 정보를 비교하였다. 그리고 실험을 통해 얻어진 산란 정보를 산란 방정식을 이용하여 분석한 결과, LMA 구조항 가정을 이용한 경우에 실험 결과와 가장 잘 일치하였다. 스침각 입사 산란법 및 얻어진 산란 방정식을 기능성 고분자 박막의 구조 분석에 적용하였다. 메모리 특성을 보이는Poly(n-nonyl 4'-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,1'-biphenyl]-4-carboxylate acrylate) (PPOXBPA) 박막을 정량적으로 분석함으로써, 고분자 주쇄는 3.56 nm의 주기를 가지는 수평 배향의 층상 구조를 가지고 있으며, 곁가지들은 서로 간에 파이 쌓임 구조를 가지고 있음을 알 수 있었다. 또한 승온, 강온 실험을 수행함으로써, 형성된 구조는 온도가 높아짐에 따라 부서지지만, 온도가 내려감에 따라 가역적으로 다시 형성되는 것을 확인할 수 있었다. 부피 비율이 각각 29:71, 50:50, and 75:25에 해당하는 Poly[4-di(9,9-dihexylfluoren-2-yl)styrene]-b-poly(2-vinyl pyridine) (P(St-Fl2)-b-P2VP) 공중합체 박막에 대한 분석을 수행하였다. 용매 처리, 열 처리 방법을 통해 부피 비율에 따라 각각 적층된 수평 배향의 라멜라 구조, 수평 배향의 원통 구조, 육각 격자 구조로 쌓인 구형 구조를 축조할 수 있었다. 이를 스침각 입사 산란법 및 산란 방정식을 이용하여 분석함으로써 정량적인 구조 정보를 얻을 수 있었다. 유기-무기 공중합체인 Poly(styrene-b-methacrylate grafted with polyhedral oligomeric silsesquioxane) (PS-b-PMAPOSS) 박막을 정량적으로 분석함으로써, 상 분리에 의해서 수직 배향의 라멜라 구조를 가짐과 동시에 PMAPOSS 영역 내부에 실린더 형태의PMAPOSS 고분자 주쇄가 사방정계 (orthorhombic) 의 격자 구조를 가지는 계층적 (hierarchical) 나노 구조를 형성한다는 사실을 알 수 있었다. 결정-비정질 공중합체Polyethylene-b-poly(methyl methacrylate) (PE-b-PMMA) 박막을 분석함으로써 PE에 의해 수직 배향의 원통 구조가 형성됨을 알 수 있었다. 그리고 원통 내부의 PE에 의한 결정구조는 고분자 주쇄가 수평 배향을 가지나 넓은 분포를 가지고 있으며, 원통 내부에 갇힘 효과에 의해서 PE 단독중합체와 비교할 때, 10%에 해당하는 결정성을 보임을 알 수 있었다.
Grazing incidence X-ray scattering (GIXS) measurements and analysis with derived GIXS equations were performed with various nanostructures in thin films of functional polymer materials. Since many kinds of functional polymer materials are fabricated in thin films for various applications, there are essential needs of analysis method for structure characterization with polymer thin films. Taking this fact into consideration, GIXS is one of most appropriate methods having several advantages. For successful analysis, GIXS equations were derived on the basis of distorted-wave Born approximation including refraction and reflection effects. And GIXS equations are composed of form factor and structure factor. There are three kinds of approximations about handling structure factor to scattering intensity, namely, decoupling approximation (DA), local monodisperse approximation (LMA), and size-spacing correlation approximation (SSCA). To take into account for three approximations, GIXS equations with sphere form factor and cylinder form factor were adopted for comparison. The porous polymer material system, thin films of nanoporous PMSSQ embedded with mPCL6 as thermal degradable porogen was prepared for sphere form factor system. The sphere form factor are used to explain scattering data from porous thin films, and three kinds of structure factor approximations are included in GIXS equations to explain correlation between spherical pores. The analysis results are categorized with respect to three kinds of structure factor, and are compared each other. Among three kinds of structure factor approximations, decoupling approximation and local monodisperse approximation match well with real case, but quantitative analysis with porous thin films using GIXS equations reveals that they exhibit high degree of disorder in structure parameters. GIXS analyses with respect to DA, LMA, and SSCA were also done with vertically oriented cylinder structure. The vertically oriented cylinder system was constructed with spin-casted thin film of mixture of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and PMMA homopolymer, followed by selective etching of PMMA domains with ultraviolet light exposure. The cylinder form factor and three kinds of structure factor approximations are included in GIXS equations to explain correlation between vertical cylinders. The in-plane and out-of-plane scattering profiles are generated to demonstrate the differences among the scattering profiles with respect to changes of structure parameters, such as cylinder radius, cylinder height, or distributions of those parameters. Then the experimental results were analyzed with GIXS equation and approximations. The analysis results show that the fitted scattering profiles using LMA is the best matched with experimental data among three kinds of structure factor approximations. Structural analyses of nanostructures in functional polymer thin films were carried out with other functional polymer thin films using GIXS equations acquired above. It was revealed that the layer structure, stacked along out-of-plane direction, was developed via thermal annealing process with thin films of novel functional brush polymer, poly(n-nonyl 4'-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,1'-biphenyl]-4-carboxylate acrylate) (PPOXBPA) containing oxdiazole moieties at the end of brush side chains. Quantitative GIXS analyses reveals that the layer structure was formed with 3.56 nm of long period and brush side chains are stacked each other to form π-π stacking of phenyl substituted oxadiazole groups. Also, in-situ GIXS measurements were done during heating and subsequent cooling, showing reversible transitions. The melting behavior of brush side chains and breakdown of the layer structure occurred stepwise during heating. During subsequent cooling, the transitions were observed reversely and the layer structure was recovered reversibly. Interesting diblock copolymers, poly[4-di(9,9-dihexylfluoren-2-yl)styrene]-b-poly(2-vinyl pyridine) (P(St-Fl2)-b-P2VP) with various volume fractions were prepared and the thin films of diblock copolymers are annealed with solvent and heat to build up nano-scale morphological structures. Relative volume ratios between two blocks are 29/71, 50/50, and 75/25, showing lamellar, hexagonally packed cylinder, and hexagonally packed sphere structures, respectively. Quantitative structure analyses with the collected scattering patterns were done with GIXS equations to get structural information and parameters. It is quite interesting that P(St-Fl2)-b-P2VP diblock copolymer possesses lamellar, cylinder, and sphere morphologies at the volume ratio with 29/71, 50/50, and 75/25, which is different from cylinder, lamellar, and cylinder structure were expected with other general diblock copolymers. This difference is originated from the fact that P(St-Fl2) chains become rigid due to bulky and solid grafted fluorene units, and enhanced immiscibility between P(St-Fl2) and P2VP blocks. In addition, structural changes during heating and subsequent cooling process were traced. The morphological structures in thin films of organic-inorganic diblock copolymer, poly(styrene-b-methacrylate grafted with polyhedral oligomeric silsesquioxane) (PS-b-PMAPOSS) and their temperature-dependent changes were investigated. The quantitative structure analysis found that the diblock copolymer in the thin films forms hierarchical nanostructures
phase separation into PS and PMAPOSS domains, a vertically ordered lamellar structure, and the PMAPOSS chains have helical conformations and thus are present as molecular cylinders to build up orthorhombic lattice. The thin films of crystalline-amorphous diblock copolymer composed of a polyethylene block and a poly(methyl methacrylate) block, PE69-b-PMMA92 were prepared and annealed to develop micro phase separated domain structure and induce crystallization within PE domains. The morphological structures in thin films were investigated by using GIXS and GIXS equations. The cylinder PE domains are aligned along out-of-plane direction in thin films. PE crystals in diblock copolymer exhibit more distributed orientation and mainly oriented parallel to substrate and the relative crystallinity of PE in diblock copolymer exhibits 10% with respect to that of homopolymer, with comparisons between thermal annealed PE homopolymer.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001623644
http://oasis.postech.ac.kr/handle/2014.oak/1975
Article Type
Thesis
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