臺灣博碩士論文加值系統

影響誘電性SmC*液晶相性質的因素有很多, 像是旋光中心、硬核構造、連接基、末端烷鏈的長度和光學純度等等. 本研究的目的是將液晶分子由棒狀改變成曲棍形而進一步了解分子結構與液晶性質的關係.
　　本實驗以(S)-(-)-propylene oxide為起始物, 合成四系列新型曲棍形旋光性液晶材料, 第一部分(I、II、III系列) 將不同的旋光末端烷鏈, 在末端苯環meta位置上進行酯化反應而形成曲棍形結構；第二部分(IV系列) 則是於末端苯環meta位置上進行醚化反應而形成曲棍形結構.
液晶相及相轉移溫度是由偏光紋理圖及DSC來鑑定. 實驗結果指出：未氟化液晶材料具有SmA*以及SmC*液晶相, 而半氟化液晶材料會提高層列液晶相的熱穩定性. 除此之外, 隨著旋光末端之半氟化烷鏈長度由-CF3增加至 -CF2CF2CF3, 有利於誘電性液晶相的生成.
然而, 實驗結果也指出化合物IV(m=8-12)在m=12時生成SmA*以及一未知的 SmX1*相；在m=8-11時生成SmA*以及未知的SmX1*及SmX2*相. 電場效應的實驗發現, 化合物IV(m)於SmX1*及SmX2*相時可以被直流電驅動；而電流轉換行為及介電常數的量測結果, 均無法證明SmX1*及SmX2*相是否具有誘電或反誘電之特性.
在物理性質量測方面結果顯示：化合物I(m=8-12)、II(m=8-12)和III(m=7,10,12)自發性極化的最大值範圍介於12.02-18.30 nC/cm2之間. 曲棍形與棒狀液晶材料相比較, 未氟化曲棍形液晶材料具有相近於棒狀液晶材料的自發性極化值, 而半氟化曲棍形液晶材料之自發性極化值則明顯的小於棒狀液晶材料. 將連結基由酯基換成醚基, 其自發性極化值則被抑制.
化合物I(m=8-12)、II(m=8-12)和 III(m=7,10,12)光學傾斜角的最大值範圍介於26-38°. 實驗結果指出, 未氟化以及半氟化的化合物, 具有相似的光學傾斜角最大值；而曲棍形與棒狀液晶材料相比較, 曲棍形液晶材料具有較大的光學傾斜角.
總而言之, 本研究實驗結果顯示半氟化之曲棍形液晶材料可提升層列液晶相的熱穩定性, 尤其是誘電性液晶相. 且很有趣地在化合物IV(m=8-12)發現兩個旋光性層列相：SmX1*及SmX2*相, 但實驗結果無法證實SmX1*及 SmX2*相是否具有誘電或反誘電之特性.

There are many factors affect the properties of ferroelectric chiral smectic C phase such as chiral group, core structure, linking group, terminal chain length and optical purity in rod-like chiral liquid crystals. The purpose of this research is looking for a better understanding the relationship between molecular structure and mesomorphic properties by changing the molecular architecture from rod-like to hockey-stick.
Thus, new non-fluorinated and semi-fluorinated chrial alcohols, (S)-1-butyloxy-2-propanol, (S)-1-(2,2,3,3,4,4,4-heptafluorobutyloxy)-1-propanol, and (S)-1-(2,2,2- trifluoroethoxy)-2-propanol, were designed and synthesized by the reaction of (S)-(-)-propylene oxide with alcohols under the base condition. These alcohols were then connected to the meta-position of phenyl ring in the compounds by the ester linkage to form compounds I(m,CH2CH2CH3), II(m, CF2CF2CF3) and III(m, CF3). (S)-1-(2,2,3,3,4,4,4-Heptafluorobutyloxy)-1-propanol was connected to the meta-position of phenyl ring in the compounds by the ether linkage to produce compounds IV(m, CF2CF2CF3).
The mesomorphic phases and their corresponding phase transition temperatures were determined by the polarizing microscopic texture and DSC thermograms. The results show the non-fluorinated liquid crystal materials posses SmA* and SmC* phases, and the semi-fluorinated liquid crystal materials enhance the thermal stability of smectic phases. In addition, as the semi-fluorinated chiral alkyl chain at chiral tail extending from -CF3 to -CF2CF2CF3 favors the formation and thermal stability of SmC* phase.
The results also show that compounds having ether linkage (IV(m=8-12)) at m=12 posses SmA* and unidentified SmX1* phases, and at m=8-11 posses SmA* and unidentified SmX1* and SmX2* phases. The electric field driven activities show that compounds IV(m) can be switched in SmX1* and SmX2* phases by the dc field, but the measurements of switching behavior and dielectric constants ε′ can not provide evidence for the existing ferroelectricity or antiferroelectricity in SmX1* and SmX2* phases.
The physical properties such as switching current, dielectric constant, spontaneous polarization, and optical tilt angle in the ferroelectric SmC* phase of chiral compounds were measured. The maximum magnitudes of the spontaneous polarization for compounds I(m=8-12), II(m=8-12), and III(m=7,10,12) are approximately in a range of 12.02-18.30 nC/cm2. Comparing rod-like compounds to hockey-stick compounds that possessing the same non-fluorinated chiral group show that there have nearly the same magnitudes of the maximum Ps value. But when comparing rod-like compounds to hockey-stick compounds that possessing the same semi-fluorinated chiral group show that the hokey-stick compounds have much lower magnitudes of the maximum Ps value. Changing the linking group from ester to ether, the Ps value was suppressed.
The maximum optical tilt angle of compounds I(m=8-12), II(m=8-12), and III(m=7,10,12) are approximately in a range of 26-38°. The results show that compounds in non-fluorinated and semi-fluorinated chiral group have nearly the same maximum optical tilt angle of chiral group. Comparing rod-like compounds to hockey-stick compounds show that the maximum apparent tilt angle of hockey-stick compounds are larger than that of rod-like compounds.
In conclusion, our results indicate that the hockey-stick chiral compounds having fluorinated chiral alkyl chain enhance the thermal stability of smectic phase, especially SmC* phase. It is interesting to find that two chiral smectic phases: SmX1* and SmX2* phases in compounds IV(m=8-12). There has no evidence to prove the existence of ferroelectricity or antiferroelectricity in SmX1* and SmX2* phase.

ACKNOWLEDGEMENTS
ABSTRACT
中文摘要
TABLE OF CONTENTS
LIST OF SCHEME
LIST OF TABLES
LIST OF FIGURES
CHAPTER 1
INTRODUCTION
1.1. Overview
1.2. Chiral smectic phases
1.2.1. Chiral smectic A phase (SmA*)
1.2.2. Chiral smectic C phase (Ferroelectric phase, SmC*)
1.3 Motivation of study
CHAPTER 2
EXPERIMENTAL
2.1. Preparation of materials
2.1.1. Synthesis of 4-(4’-alkoxyphenyl)benzoic acids, I-1(m=8-12)
2.1.2. Synthesis of 3-(methoxycarbonyloxy)benzoic acid, I-2
2.1.3. Synthesis of (S)-1-butyloxy-2-propanol, I-3
2.1.4. Synthesis of (S)-1-(2,2,3,3,4,4,4-heptafluorobutyloxy)-1-propanol, II-3, (S)-1-(2,2,2- trifluoroethoxy)-2-propanol, III-3
2.1.5. Synthesis of (R)-2-butyloxy-1-methylethyl 3-(methoxycarbonyloxy) benzoate, I-4
2.1.6. Synthesis of (R)-2-(2,2,3,3,4,4,4-heptafluorobutyloxy)-1-methylethyl 3-(methoxycarbonyloxy)benzoate, II-4 and (R)-2-(2,2,2–trifluoroethyloxy)-1-methylethyl 3-(methoxycarbonyloxy)benzoate, III-4
2.1.7. Synthesis of (R)-2-butyloxy-1-methylethyl 3-hydroxybenzoate, I-5 26
2.1.8. Synthesis of (R)-2-(2,2,3,3,4,4,4–heptafluorobutyloxy)-1-methylethyl
3–hydroxylbenzoate, II-5 and (R)-2-(2,2,2-trifluoroethyloxy)-1-methylethyl- 3–hydroxylbenzoate, III-5 27
2.1.9. Synthesis of (R)-1-butyloxy-2-propyl 3-[4-(4-alkyloxyphenyl)phenyl- carbonyloxy]benzoates, I(m=8-12)
2.1.10. Synthesis of (R)-3-[1-methyl-2-(2,2,3,3,4,4,4-heptafluorobutyloxy)ethyloxycarbonyl]phenyl 4’-alkyloxybiphenyl-4-carboxylates , II(m=8-12)
2.1.11. Synthesis of (R)-3-[1-methyl-2-(2,2,2-trifluoroethyloxy)ethyloxycarbonyl] phenyl 4’-alkyloxybiphenyl-4-carboxylates, III(m=7,10,12)
2.1.12. Synthesis of 4'-(undecyloxy)biphenyl-4-carbonyl chloride, IV-2(m=8-12)
2.1.13. Synthesis of 3-hydroxyphenyl 4'-(undecyloxy)biphenyl-4-carboxylate, IV-3(m=8-12)
2.1.14. Synthesis of (R)-3-[1-methyl-2-(2,2,3,3,4,4,4-heptafluorobutyloxy)ethyloxy]phenyl 4’-alkyloxybiphenyl-4-carboxylates , IV(m=8-12)
2.2. Characterization of Materials
2.2.1. Chemical structure identification
2.2.2. Mesophase identification
2.2.3. Preparation of homogenous cells
2.2.4. Alignment of liquid crystals in SSFLC Cells
2.2.5. Switching behavior measurement
2.2.6. Dielectric constant measurement
2.2.7. The spontaneous polarization (Ps) measurement
2.2.8. Optical tilt angle measurement
CHAPTER 3
RESULTS AND DISCUSSION
3.1. Mesophase studies
3.2. The effect of achiral and chiral chain length on the mesomorphic properties of chiral compounds I(m=8-12), II(m=8-12), and III(m=7,10,12)
3.2.1. Optical microscopy observations and phase transition behaviors of chiral compounds I(m=8-12), II(m=8-12), and III(m=7,10,12)
3.2.2. Switching current behavior
3.2.3. Dielectric property measurements
3.2.4. Spontaneous polarization (Ps)
3.2.5. Optical tilt angle (θ)
3.3. The effect of achiral chain length on the mesomorphic properties of chiral compounds with ether linkage on the phenylene ring IV(m=8-12)
3.3.1. Optical microscopy observations and phase transition behavior of compounds IV(m=8-12)
3.3.2. Switching current behavior
3.3.3. Dielectric property measurements
3.3.4. The electric field driven activities
3.4. The effect of molecular architecture changing form rod-like to hockey-stick and electro-optical properties
3.4.1. The comparison of transition temperatures and mesophase behaviors between rod-like compounds (i(m),ii(m),iii(m)) and hockey-stick compounds (I(m),II(m),III(m))
The phase diagrams of the phase transition temperature versus achiral terminal aliphatic chain length (m) for i(m, CH2CH2CH3) and I(m, CH2CH2CH3) are shown in figure 3.4.1. The results show that all compounds i(m, CH2CH2CH3) and I(m, CH2CH2CH3) exhibit the same phase sequence: Iso.-SmA*-SmC*-Cr.. It is seen that the melting point and all transition temperatures of I(m, CH2CH2CH3) are much lower than that of i(m, CH2CH2CH3). Furthermore, the temperature ranges of mesophases of I(m, CH2CH2CH3) are much shorter than that of i(m, CH2CH2CH3)
3.4.2. The comparison of spontaneous polarization (Ps) between rod-like compounds (i(m),ii(m),iii(m)) and hockey-stick compounds (I(m),II(m),III(m))
3.4.3. The comparison of optical tilt angle (θ) between rod-like compounds (i(m),ii(m),iii(m)) and hockey-stick compounds (I(m),II(m),III(m))
CHAPTER 4
CONCLUSIONS
REFERENCES
APPENDIX

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