Design and Synthesis of New Non-fluorinated and Fluorinated Chiral Alcohols for the Development of Ferroelectric and Antiferroelectric Liquid Crystal Materials

Autor:	Cho-Ying Lin, 林卓瑩
Rok vydání:	2007
Druh dokumentu:	學位論文 ; thesis
Popis:	95 AFLCD display with such good characteristics as: wide screen, high resolution, excellent image quality and full color have been developed. However, so far, display manufacturers have been unable to commercialize AFLC display devices despite continuous efforts. It seems that the appearance of the SmCA* phase and structure-property relationship of AFLC materials are still understood well enough to optimize the material parameters. Thus, in order to ascertain the structure-property correlations and the practical application in electro-optical services, in this work, we attempt to elucidate the structure-property correlation in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-propylene oxide has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by the (i) the structure of the non-fluorunated, fluorinated alkoxy chain length and chiral swallow-tailed structure (ii) lateral halogen substituents in the core and (iii) different core structure of the molecules of the chiral molecules for the study. Chiral non-fluorinated materials, I(m, n; m=8-12, n=0-3) displayed enantiotropic mesophases of the SmA* and SmC* phases; however, chiral semi-fluorinated materials, II(m, n; m=8-12, n=1-3), exhibited SmA*, SmC* and SmCA* phases. These results demonstrate that the presence of the semi-fluorinated alkyl chain in the chiral tail of the material induces an antiferroelectric SmCA* phase. Chiral swallow-tailed materials, III(m, p; p=0, m=8-12), displayed enantiotropic mesophases of the SmA*, SmC* and SmCA* phases. The materials increasing methylene chain lengths n, III(m, p; m=8-12, p=1), the SmCA* was disappeared and only exhibited SmA* and SmC* phase. In addition, the antiferroelectric liquid crystal materials, II(m, n) and III(m, 0), have higher Ps and θ values than ferroelectric liquid crystal materials, I(m, n) and III(m, 1). The electro-optical response in the series of chiral materials, I(10, 2) and III(10, 1), in the SmC* phase displayed V-shaped switching property; however, in the series of chiral materials, II(10, 2) and III(10, 0), in the SmCA* phase displayed typical antiferroelectric tri-stable state of double hysteresis loop switching behavior. Chiral semi-fluorinated materials, IV(m, X, Y) and V(m, X, Y), were synthesized and investigating the influence of lateral halogen substituents in the core. The SmCA* phase was generally occurred in the alkyl chain length from m=8 to m=10 of the materials. The materials with lateral substitutents in the core could depress the formation of mesophase, lowering the transition temperature, melting point and Ps values but increasing θ values. Comparing with the materials of different atom substitution, it is seen that the materials with lateral chloro substituents in the core of molecular was most decreasing transition temperature and Ps values. The materials with halogens substuted at 2-position on the ring of the molecule were sterically shielded so that possessed higher transition temperature than that materials at 3-position; however, the materials with halogens substuted at 2-position on the ring of the molecules also enhanced Ps and θ values. In chiral semi-fluorinated materials, VI(m) and VII(m), the SmCA* phase was also occurred in the alkyl chain length from m=8 to m=10 of the materials. Comparing with different core structure of three series materials, II(m, 2), VI(m), VII(m), it can be found the materials, III(m, 2), with PhPhCOOPh as the core structure of the molecule were favorable for the formation of antiferroelectric SmCA* phase; however, the materials have highest Ps values in those materials. In chiral materials, VIII(m)-XIII(m) which derived firm cinnamatic acid can be found two ring core materials only exhibit ferroelectric SmC* phase; however, three ring core materials favor the formation of antiferroelectric SmCA* phase. Changing the core structure of molecule exhibited some sub-phases such as SmCα* and SmCγ* phases. Binary mixture study shows that the antiferroelectric mixtures with ambient temperature can be obtained by two antiferroelectric liquid crystals. The response of the optical transmission obtained from the antiferroelectric mixture of 80% V(8, H, Cl) and 20% XIV(10) in SSFLC cell by driving at 60Hz and 26V square wave at 25℃ show that the raise time is 586.7 μs and fall time is 109.5μs. In conclusion, the chiral swallow-tailed and semi-fluorinated alcohol groups can be prepared by the optically pure (S)-propylene oxide treating with semi-fluorinated or swallow-tailed alcohols. These chiral alcohols are then developed large amount of antiferroelectric liquid crystals, and subsequently, the structure-property correlation for the formation of antiferroelectric liquid crystals is established. The establishment of this correction will be beneficial for the future design and synthesis of more antiferroelectric liquid crystals. A large amount of antiferroelectric liquid crystals developed in the present work demonstrates that there is a potential for the preparation of suitable antiferroelectric mixtures for the display devices.
Databáze:	Networked Digital Library of Theses & Dissertations
Externí odkaz:	http://ndltd.ncl.edu.tw/handle/2z8rhf Zobrazit plný text záznamu