液晶薄膜之比熱,光反射及光學條紋的相變研究

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羅健榮(Chien-Jung Lo) 查詢紙本館藏

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物理學系

論文名稱

液晶薄膜之比熱,光反射及光學條紋的相變研究
(Calorimetric, Optical Reflectivity and Texture Studies on Phase Transitions in Free-Standing Liquid-Crystal Films)

相關論文

★ 液晶薄膜比熱與光反射相變研究	★ 液晶薄膜光學條紋分析及比熱量測
★ 懸浮液晶薄膜表面張力之研究	★ 液晶薄膜相位光學鑑定分析與研究
★ 反鐵電液晶薄膜光電特性研究	★ 鐵電型液晶(Half-V)配向與光電特性研究

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摘要(中)

在另一個有手徵的液晶材料上 (MDW1397)，我研究薄膜Smectic-A — Smectic-C* —Smectic-CA* 的相變過程。利用偏光型顯微鏡下的觀察，我們提出了一個多重相變模型。此外溫度及外加電場都能使表層分子傾斜結構有所變化。在比熱及光反射量測上，此材料上的Smectic-A — Smectic-C* 相變是一階相變。同時我們在六到二十一層的比熱訊號上發現到一個有趣的比熱訊號外型的轉變現象。

摘要(英)

The phase transitions in reduced-dimensional system have attracted great attention because it involves the research of fundamental physics and technical applications. Free-standing liquid crystal films (FSLCFs) provide an ideal experimental system for the research of reduced-dimension. I have investigated the Sm-A — Hex-B phase transitions of 64COOBC FSLCFs using simultaneous heat-capacity and optical-reflectivity measurements. This observed transition is not of KT-type phase transition but weakly first order that disagree with the KTHNY theory. The heat-capacity anomaly associated with this transition can be well described by a power law with critical exponent a=0.38+-0.02 . For the thicker films (N≧7) undergo an incomplete wetting transition. Unusual highly suppression of the heat capacity at the third transition has been found in 7-, 8-, and 9-layer 64COOBC films. This novel phenomenon is possibly due to the existence of a strong Hex-B surface anchoring field which suppresses the fluctuation of the interior Sm-A layers.
We have also studied the phase transition of one chiral liquid-crystal compound — MDW1397. Base on many observations on its optical textures using the depolarized optical microscope, we propose a suitable model involving multi-step Sm-A — Sm-C* phase transitions. Both thermal and external electric field can induce anticlinic—synclinic transitions. And the heat-capacity and optical-reflectivity measurements both confirm the Sm-A to Sm-C* transition to be the first order. The heat-capacity anomaly exhibits a novel layer-dependent crossover behavior for films from 6 to 21 layers.

關鍵字(中)

★ 液晶
★ 相變
★ 比熱
★ 光反射
★ 懸浮液晶薄膜
★ 手徵

關鍵字(英)

★ Liquid Crystal
★ Phase Transition
★ Heat Capacity
★ Optical Reflectivity
★ Free-Standing Liquid-Crystal Film
★ Chiral

論文目次

Abstracti
List of Figuresii
List of Tablesv
Chapter 1 : Introduction1
Chapter 2 : Background and Theories6
2.1 Classification of Liquid-Crystal Mesophases7
2.2 Free-Standing Liquid-Crystal Films13
2.3 Phase Transitions16
Chapter 3 : Experimental Approach25
3.1 AC Calorimetry26
3.2 Optical Reflectivity30
3.3 Simultaneous Measurement32
3.4 Depolarized Optical Microscope36
Chapter 4 : Phase Transitions in 64COOBC Films44
4.1 Two-Layer 64COOBC Free-Standing Film45
4.2 Layer-by-Layer Sm-A — Hex-B Transition50
Chapter 5 : Phase Transitions in MDW1397 62
5.1 Phase Sequence63
5.2 Anticlinic to Synclinic Transition73
5.3 Heat-Capacity and Optical-Reflectivity Results76
Chapter 6 : Conclusion84
References :89

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指導教授

趙治宇(Chih-Yu Chao)

審核日期

2000-6-22

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