2006-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/712415摘要：自然界中物質熔化的現象雖然都具有一般性，但其中有很多複雜的相變機制，仍不是瞭解得很清楚，尤其是低維度系統的相變過程與三維物體的相變行為仍有很大的不同，因此吸引了大量學術上的興趣和實際用途上的關注。利用液晶材料在其smectic相位下可以形成有層狀結構的懸浮液晶超薄膜，我們可以藉此來研究低維度系統下的相變行為以及其臨界現象，同時研究中實驗所得數據亦可用來檢驗許多統計力學上不同的物理模型，並可藉此對低維度系統的物理機制有更深入的瞭解。 本計畫是擬使用高解析液晶薄膜比熱儀，光反射儀，光學紋理觀測系統以及改裝型穿透式電子顯微鏡來研究諸多種類之液晶薄膜的熔化現象，前期計畫已成功建造以上量測儀器並使其運轉正常，同時亦有豐富的研究成果出現。此次申請的研究計畫中將承續並展開下列研究： (1) 進行二維液晶晶體結構分析與電子繞射實驗以瞭解造成完美晶格次序在二維液 晶薄膜系統下存在的原因，並同時確認其薄膜層間之作用力大小。 (2) 檢驗二維液晶薄膜系統內所含之熵是否與其體積平方成正相關，同時並檢驗其相變序列之SmA-HexB臨界行為是否符合coupled XY模型的描述。 (3) 研究旋光型鐵電<br> Abstract: In nature, the melting phenomena of materials are common but not fully understood. To understand the melting process in reduced dimensions and near surfaces is of great academic and practical interest. Smectic liquid crystals (LCs) are uniquely suited for studying the phenomenon of melting in reduced dimensions, because of their ability to form stable free-standing films with uniform thickness consisting of two or more molecular layers. To date, the studies of smectic liquid-crystal systems have proven to be among the most fruitful to test the current models and theories in the physics of reduced dimensions and near surfaces. This project is planned to use high-resolution ac calorimeter, optical reflectometer, polarized optical microscope, and transmission electron microscope to study the phenomena of melting in LC thin film system. In this project, we are going to conduct and develop following research topics: 1. Conduct electron-diffraction experiments on ultrathin LC films to realize the cause of the existence of a perfect ordering in 2D system; Confirm the molecular interactions in LC films from reflectivity and diffraction data. 2. Check if the system entropy of a LC film is proportional to its volume square in reduced dimensions; Examine if the critical behavior of the SmA-HexB transition of ultrathin LC films can be well described by coupled XY model. 3. Study the phase-transitional behavior of the SmA-SmC*，SmC*-SmCα*以及SmCα*-SmCFI* transitions in chiral ferroelectric and atiferroelectric LC films using optical textures and high-resolution ac calorimeter. 4. Confirm the existence of the locked liquid phase in bent-like LC films; To conduct experiments on the structural analysis of frontier LC materials in order to develop future new LC compounds. 5. Conduct optical textural and heat capacity experiments on tilted hexatic LC thin films. Free-standing smectic LC films represent an unusual system to study melting in which the spatial dimension can be varied continuously from three to two without the extraneous effects of substrates. Our goal in this project is to discover new frontier LC phase and to establish some related models that can explain how the structure, the thermal property, and type of optical textures of studied LC films are affected by the geometry of the LC molecule, the magnitude of spontaneous polarization, and the location and number of chiral center on the LC molecule. The obtained experimental data can not only provide us further realization on the critical behaviors of different phase transitions in some LC thin films, but also help us for the understanding of the physical mechanism of reduced-dimensional system. In addition, our experimental result can be used to check many different exisiting physical models on critical phenomenon.液晶薄膜低維度系統臨界行為AC比熱與光反射量測電子繞射結構分析液晶光學紋理分析前瞻型液晶材料liquid crystal (LC) filmsreduced dimensionsLC optical texturesfrontier LCs