探討旋光乳酸衍生之液晶材料中的分子結構與藍相液晶生成的關係

Study on the Relationship Between Molecular Structures of Chiral Liquid Crystals Derived from Optically Active Lactic Acid and the Formation of Blue Phases

楊文菱(Wen-Ling Yang)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/碩士(2012年)

摘要

過去對於藍相(Blue Phase)液晶單一材料的報導並不多見，而且溫度範圍都很狹窄(0.5-2℃)，主要因為藍相(BP)為一種挫敗相(frustrated)，也因此分子結構與藍相(BP)生成的關係從未被建立。因此設計開發具藍相(BP)液晶相的材料並建立分子結構與藍相(BP)生成的關係，近幾年來成為本實驗室研究的方向。所以本研究首先分為二部分，共合成五系列具有旋光乳酸衍生之液晶材料。主要分為三個方向進行探討 (i)非旋光烷鏈長度‘m’、(ii)旋光烷鏈長度‘n’及(iii)非旋光烷鏈以醚基(-O-)連接苯環的化合物與非旋光烷鏈直接連接苯環的化合物。這二部分五系列分子結構如下:
第一部分共二系列，化合物結構如下:

Ia(m=6-9, n=0, X=O)
Ib(m=6-9, n=1, X=O)

第二部分共三系列，化合物結構如下:

IIa(m=6-8, n=0, X= –)
IIb(m=6-8, n=1, X= –)
IIc(m=6-8, n=2, X= –)
第三部分的研究是探討混合液晶對於藍相(BP)液晶的穩定性影響。此部分以BM-I和BM-II的兩混合液晶材料為主要的觀察與探討。將兩化合物依不同重量百分比的比例混合(100/0,75/25,50/50, 25/75,0/100)觀察藍相(BP)液晶相溫度範圍的變化。其相關化合物分子結構如下:
BM-I

BM-II

實驗結果顯示，五系列具有旋光乳酸衍生之液晶材料中，在第一部分化合物Ia和Ib系列中呈現出 BP、N*、TGBA*與 SmA* 液晶相；挫敗相(BP和TGB*)的產生顯示出化合物具有高旋光性。 在 IIa系列化合物中僅觀察到BP 和N* 相，特別在 IIb系列中除 IIb(7, 1, –)具有BP 和N* 相，其餘並無液晶相的存在。證明了化合物由非旋光烷鏈直接連接苯環，而無醚基連接基時，有抑制液晶相生成的現象，特別是對於層列型液晶相的完全抑制。進一步從實驗結果也可觀察到在 IIb 和 IIc 系列中，隨著 n 增加時也不利藍相(BP)液晶生成。
實驗結果也顯示，在第一部分化合物中當旋光末端烷鏈具有支鏈(branched chain)時，有利於藍相(BP)液晶生成。然而，在第二部分化合物中當旋光末端烷鏈具有支鏈(branched chain)時，反而不利於藍相(BP)液晶生成。當比較非旋光烷鏈以醚基(-O-)連接苯環的化合物與非旋光烷鏈直接連接苯環的化合物時，可以觀察到前者有利於藍相(BP)液晶的生成。
在混合液晶實驗證明了液晶的混合對於藍相(BP)液晶的溫度範圍並沒有顯著的影響。
綜合以上研究結果顯示，本次研究中設計和合成出具有旋光乳酸衍生之液晶材料中，最寬廣藍相(BP)溫度範圍在於Ib(7, 1, O)藍相(BP)溫度範圍，但只有5.2℃。在混合液晶材料實驗中，結果顯示混合藍相(BP)液晶材料對於藍相(BP)液晶的溫度範圍並沒有顯著的影響。

關鍵字

藍相液晶 ； 旋光性液晶材料 ； 混合液晶

並列摘要

A few of liquid crystal materials exhibiting blue phases have been reported in a single compound, moreover, the blue phases in the materials possess a very small temperature range (cal. 0.5-2℃), mainly because of the blue phases are frustration phases. Thus, in order to find more of blue phase materials and shed light on the relationship between molecule structure and the formation of blue phases, in this work, we designed and synthesized five series of compounds derive from optically active lactic acid, according to the previous results from our laboratory, for the investigation. The results of the works are divided into two part for discussion, and the results for discussion are in term of the effect of (i) achiral terminal alkyl chain length ‘m’ of the materials, (ii) chiral terminal alkyl chain length 'n' of the materials and (iii) the achiral terminal alkyl chain directly connected to the benzene ring with ether (-O-) linking group, and achiral terminal alkyl chain connected directly to the benzene ring of the materials, on the generation of blue phase liquid crystals.
Five series of the materials for the study with the general formulas are depicted below.

The first part of compounds for second series of the materials:

Ia(m=6-9, n=0, X=O)
Ib(m=6-9, n=1, X=O)

The second part of compounds for third series of the materials:

IIa(m=6-8, n=0, X= –)
IIb(m=6-8, n=1, X= –)
IIc(m=6-8, n=2, X= –)

The third part of the works was to investigate whether the binary mixture of the blue phase materials could enhance the thermal stability of the blue phase. Thus, binary mixtures (BM-I and BM-II) with the weight percentage ratios of 100/0, 75/25, 50/50, 25/75, 0/100 of the compounds were prepared for the investigation. The corresponding molecular structures of the target compounds are depicted below:
The first pairs of compounds for the binary mixture, BM-I

The second pair of compounds for the binary mixture, BM-II

The results from the study of five new series of novel chiral materials derived from optically active (S)-lactic acid show that, chiral compounds Ia(m=6-9, n=0, X=O) and Ib(m=6-9, n=1, X=O), depending on the molecular structure, various mesomorphic phases: BP, N*, TGBA* and SmA* phases can be found. The appearance of frustrated phases (BP and TGB* phases) indicate that all compounds possess high chirality. The results of chiral compounds IIa(m=6-8, n=0, X= –) display only BP and N* phases, indicating that the alkyl group directly attaches to the phenyl ring without ether (-O-) linking group could depress the formation of higher order smectic phases. Similar results also present in the compounds IIb(m=6-8, n=1, X= –) and IIc(m=6-8, n=2, X= –). In general, compounds derived from (S)-lactic acid with oxygen linking group are easier to generate the stable blue phases as compared to that without oxygen linking group.
It is also interested to found that compounds consist of branched chain in the chiral tail favor the formation of the blue phase as compared the corresponding compounds Ia(m=6-9, n=0, X=O), Ib(m=6-9, n=1, X=O) and IIa(m=6-8, n=0, X= –), but it is not feasible to the formation of blue phase as compared the corresponding compounds IIb(m=6-8, n=1, X= –) and IIc(m=6-8, n=2, X= –).
The investigation of the binary mixtures on the formation blue phase demonstrates that the mixtures have no any significant enhancement on the thermal stability of the blue phase.
In conclusion, our results show that the blue phase materials be designed and synthesized, however, the temperature range of blue phase in this work is only reached as large as 5.2℃. The results of binary mixtures of the blue phase materials also indicate that the enhancement of temperature range of blue phase by the mixing method is not feasible.

並列關鍵字

binary mixtures liquid crystal ； blue phase liquid crystal ； chiral liquid crystal material

參考文獻

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