臺灣博碩士論文加值系統

本研究主要設計並合成兩系列非旋光燕尾液晶2-propylpentyl 4-(4'-alkyloxybiphenyl-4-carbonyloxy) benzoates，簡稱 PPmBCB(m=8~12)及2-ethylbutyl 4-(4'-alkyloxybiphenyl-4-carbonyloxy)benzoates，簡稱 EBmBCB (m=8~12)，來探討結構對液晶相的影響。
研究結果發現此兩系列非旋光燕尾液晶皆具有SA及Scalt液晶相。其中Scalt液晶相由DSC所量測到SA-Scalt 之first order transition及偏光顯微鏡下所觀察到具 two brushes 的 schlieren紋理圖證實。兩系列液晶的實驗結果顯示，隨著末端烷鏈m的增加澄清點會隨著下降、SA液晶相的熱穩定性大致相同而除了PP10BCB及EB11BCB具有較寬廣的Scalt液晶相，其餘的液晶材料熱穩定性則大致相同。
再者，分別將PP10BCB及EB11BCB與標準反誘電性液晶(S)-4-(1-methylheptyloxy)-carbonylpheny 4′-octyloxy-4-biphenylcarboxylate，簡稱(S)-MHPOBC，作不同比例的混合來探討其對液晶相及物理性質的
影響。由介電量測、電流轉換行為及光電感應性質的量測得到混合液晶p15/m85 (15wt% PP10BCB和85wt% (S)-MHPOBC)及p5/m95 (5wt% PP10BCB和95wt% (S)-MHPOBC)之相轉移順序為SA-SC*-SCA*，而混合液晶p85/m15 (85wt% PP10BCB和15wt% (S)-MHPOBC)之相轉移順序為SA-SCA*。同時，混合液晶p15/m85的SC* 液晶相溫度範圍比p5/m95的SC* 液晶相溫度範圍寬廣。而且，混合液晶p85/m15 (85wt% PP10BCB和15wt% (S)-MHPOBC)不具SC*液晶相。由此可推論，似乎在某特定的混合比例下(S)-MHPOBC 的SC*液晶相會被誘導成SCA*液晶相。
混合液晶p15/m85及p5/m95在反誘電性液晶相中進行光電感應的量測可得到雙遲滯；混合液晶p85/m15在反誘電性液晶相中進行光電感應的量測可得到V型態的轉換。同樣的現象也可分別在混合液晶e15/m85及e85/m15中觀察得到。
混合液晶之光電感應量測結果顯示頻率、溫度及液晶試片的厚度對光電感應結果有很大的影響。

Two series of achiral swallow-tailed materials; 2-propylpentyl 4-(4'-alkyloxybiphenyl-4-carbonyloxy) benzoates, PPmBCB(m=8~12), and 2-ethylbutyl 4-(4'-alkyloxybiphenyl-4-carbonyloxy)benzoates, EBmBCB (m=8~12) were designed and synthesized for the investigation of the structure-property relationship of the mesophases.
The results obtained from the study of these two series achiral swallow-tailed materials (PPmBCB and EBmBCB) showed that all materials have enantiotropic SA and Scalt phases. The Scalt phase was confirmed by the first order characterization of SA-Scalt transition in the DSC thermograms and by the schlieren texture showing two-brush and four-brush singularities. Both series of materials showed that the clearing point gradually decreases and the thermal stability of SA phase has no significant variation as the terminal alkyl chain, m, is varied. The thermal stability of SCalt phases is relatively larger for compounds PP10BCB and EB11BCB, while the rest of materials are nearly the same.
The study of binary mixtures were conducted by mixing PP10BCB and EB11BCB separately with the standard antiferroelectric liquid crystal (S)-4-[(1-methylheptyloxy)-carbonyl]pheny 4′-octyloxy-4-biphenyl-carboxylate, (S)-MHPOBC, by various weight percentages to observed the influence of mesophases and physical properties.
The results showed that the binary mixture of (S)-MHPOBC as a host doped with achiral materials (PP10BCB and EB11BCB) displayed a phase sequence of SA-SC*-SCA*, while that of the achiral materials (PP10BCB and EB11BCB) as host doped with (S)-MHPOBC displayed a phase sequence of SA-SCA*. The temperature range of SC* phase for p15/m85 (15wt% PP10BCB doped with 85wt% (S)-MHPOBC), is larger than that for p5/m95 (5wt% PP10BCB doped with 95wt% (S)-MHPOBC), and the SC* phase disappears in the mixture p85/m15 (85wt% PP10BCB doped with 15wt% (S)-MHPOBC). It seems that ferroelectric phase in (S)-MHPOBC can be induced to form antiferroelectric phase by doping with specific ratio of hosts, PP10BCB and EB11BCB.
The electro-optical responses in the SCA* phase of the mixture p15/m85 and p5/m95 show double hysteresis switching behavior, whereas, that of host achiral materials p85/m15 show V-shaped switching in the cell with 5μm thickness. Similar results were also found in the binary mixtures of e15/m85 and e85/m15 correspondingly.
The study of electro-optical response for the binary mixture indicated that the electro-optical response critically depended on the frequency, temperature and thickness of cell.

TABLE OF CONTENTS
ACKNOWLEDGMENTS.....................................................................................................................................................................iii
ABSTRACT...........................................................................................................................................................................................iv
中文摘要...............................................................................................................................................................................................vi
TABLE OF CONTENTS......................................................................................................................................................................viii
LIST OF SCHEME.................................................................................................................................................................................xi
LIST OF TABLES..................................................................................................................................................................................xii
LIST OF FIGURES...............................................................................................................................................................................xiii
CHAPTER 1
INTRODUCTION....................................................................................................................................................................................1
1.1 Smectic A phase..................................................................................................................................................................................2
1.2 Ferroelectric phase...............................................................................................................................................................................2
1.3 Antiferroelectric phase.........................................................................................................................................................................9
1.4 Motivation of study...........................................................................................................................................................................16
CHAPTER 2
EXPERIMENTAL..................................................................................................................................................................................18
2.1 Preparation of materials.....................................................................................................................................................................18
2.1.1 Synthesis of 4-alkyloxy-4-biphenylcarboxylic acids, 1....................................................................................................18
2.1.2 Synthesis of 4-methoxycarbonyloxybenzoic acid, 2.............................................................................................................20
2.1.3 Synthesis of 2-propylpentyl 4-methoxycarbonyloxybenzoate, 3...........................................................................................21
2.1.4 Synthesis of 2-propylpentyl 4-hydroxybenzoate, 4...............................................................................................................21
2.1.5 Synthesis of 2-propylpentyl 4-(4'-alkyloxybiphenyl-4-carbonyloxy) benzoates, PPmBCB (m=8~12)................................21
2.1.6 Preparation of the binary mixture.........................................................................................................................................22
2.2 Physical properties...............................................................................................................................................................22
2.2.1 Chemical structure identification..........................................................................................................................................22
2.2.2 Mesophase identification......................................................................................................................................................23
2.2.3 Measurements of spontaneous polarization (Ps)..................................................................................................................23
2.2.4 Optical response measuremet..............................................................................................................................................26
2.2.5 Measurement of dielectric constant......................................................................................................................................28
CHAPTER 3
RESULTS AND DISCUSSION..........................................................................................................................................................29
3.1 Chemical structure identification......................................................................................................................................................29
3.2 Mesomorphic phases and their corresponding phase transition temperatures of a homologous series of PPmBCB (m=8~12).....32
3.3 Mesomorphic phases and their corresponding phase transition temperatures of a homologous series of EBmBCB (m=8~12).....38
3.4 The effect of molecular pairing of chiral and achiral materials on the formation of antiferroelectric phase.......................................48
3.4.1 Mesomorphic phases and their corresponding phase transition temperatures................................................................................48
3.4.2 Physical properties of binary mixtures...........................................................................................................................................56
3.4.2.1 Switching behavior.....................................................................................................................................................................56
3.4.2.2 Spontaneous polarization............................................................................................................................................................59
3.4.2.3 Dielectric properties....................................................................................................................................................................59
3.4.2.4 Electro-optical responses.............................................................................................................................................................64
CHAPTER 4
CONCLUSION......................................................................................................................................................................................74
REFERENCES.......................................................................................................................................................................................76
APPENDIX............................................................................................................................................................................................80

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