标题: 含卤素之强诱电性液晶单体及其侧链液晶高分子之合成与性质之探讨
Studies on the Synthesis and Properties of Halogen Containing Ferroelectric Liquid Crystals and Side Chain Liquid Crystalline Polymers
作者: 谢始荣
Shih-Jung Hsieh
庄祚敏
薛敬和
Dr. Tzuoh-Miin Juang
Dr. Ging-ho Hsiue
应用化学系硕博士班
关键字: 强诱电性液晶;双稳定状想;可擦拭光碟;自发极化值;应答时间;X-ray绕射;介电分析;Ferroelectric liquid crystal;FLC;bistable states;Goldstone mode
公开日期: 1998
摘要: 液晶聚合物因有多元化之光电用途,深具研究之潜力;而液晶中的SC*相因具有强诱电性性质,而显得格外重要。强诱电性液晶(Ferroelectric liquid crystal, FLC)具双稳定状想(bistable states),在电场下可控制其在稳定状态间切换,由于切换的时间相当短(μs),比向列相液晶的切换时间快了好几次方,因此强诱电性液晶可用于高画质电视之显示上;而强诱电性液晶高分子则可应用于可擦拭光碟的记录媒体材料,可以有效的提高其应答速度。
本研究归纳实验室数年来研究之成果,设计出以MDn12Cl为蓝本,改变末端基旋光中心取代基,将氟原子及溴原子取代氯原子。因MDn12Cl液晶分子结构之液晶基坚硬度适当,末端基之部份为双旋光中心。最重要的是,在MDn12Cl液晶单体系列中,MD112Cl拥有高自发极化值389nC/cm2,以及MD312Cl在SC*相中有数十μs 至1ms的应答时间。以卤素原子之阴电性趋势(F>Cl>Br)将氟原子及溴原子取代氯原子,可观察出偶极矩的变化对液晶分子之热运动的影响,以及对液晶分子光电特性之影响。
研究分成两部份:
第一部份为新型液晶单体之合成、液晶相行为之探讨。合成二系列之新型液晶单体MDn12F、MDn12Br,以及合成MD312Cl作为比较之基准。液晶相热行为经由热微差扫瞄卡计、偏光显微镜以及粉末x-ray绕射加以鉴定液晶相的种类与排列结构,探讨不同末端旋光基对液晶相行为之影响。
结果显示,含氟原子及溴原子之液晶单体之液晶相种类与含氯原子之液晶单体类似,其差异点在于各个液晶相温度之分布。
第二部份为强诱电性侧链液晶均聚合物之合成、鉴定与介电测试。选择第一部份所合成之液晶单体进行与聚矽氧烷之矽氢化接枝反应,。其液晶相的鉴定与分析亦以热微差扫瞄卡计、偏光显微镜以及粉末X-ray绕射来分析液晶相的种类与液晶分子在聚合物中的排列结构。并介电分析讨论含不同卤素偶极之强诱电性侧链均聚合物对液晶相行为的影响,将此结果作为液晶光电测试之参考。
结果显示,高分子聚矽氧烷主链的导入,不仅扩展了整体液晶相的温度范围,并也扩展了Sc*相可达约100℃的范围。并且由介电分析得知,具较强偶极之含氟强诱电性液晶侧链均聚合物PS312F在电场之作用下,其Goldstone mode缓和强度在SC*相中随温度之升高而加强,且其介电缓和与损失常数均大于含氯强诱电性液晶侧链均聚合物PS312Cl。此结果表示,若于相同机制之光电测试,也必将有相同之结果。
Liquid-crystalline polymers possess versatile optical-electric applications and therefore are potential research subjects. The Sc* phase of liquid crystals is extremely important because of its ferroelectric property. The ferroelectric liquid crystals (FLC) have bistable states and can be switched between them by controlling the electric field. The switch time is so short (μs) that it is several times order faster than the nematic liquid crystal phase, hence the FLC is applicable in high-fidelity televisions. The FLC polymers can also be adopted as a recording material in the erasable compact discs to elevate the response rate significantly.
This research concluded the results over recent years. It was to design molecules based upon MDn12Cl from which the terminal chiral center had been changed by substituting fluorine or bromine atoms for chlorine. The terminal group of MDn12Cl molecule is a two-chiral center due to the appropriate hardness of its liquid crystalline segment. Among the series of the MDn12Cl liquid crystalline monomers, MD112C has high spontaneous polarization (389 nC/cm2) and MD312Cl has fast response time between tens ofμs to 1 ms. According to the electronegativity of halogens (F>Cl>Br), effects of substitution of Cl by F and Br atoms were observed. Both the thermal movement and the electro-optical properties of liquid crystalline molecules are influenced by the change of the dipole moment.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT870500066
http://hdl.handle.net/11536/64842
显示于类别:Thesis