The Synthesis and Evaluation of Novel Bent-core Liquid Crystals Designed to Generate a Biaxial Nematic Phase

人们普遍认为，物质可以以三种状态存在，固体，液体和气体，然而，一些材料，特别是那些由棒状分子组成的材料，可以额外显示一个或多个“液晶”相。液晶相是物质的不同相，其具有介于常见液态的分子排序和常见结晶固态的分子排序之间的分子排序。近晶相（已知有几种）是非常粘稠的液体，因为分子有序度接近固体。双相是非常流动的，因为唯一的分子排序是分子的统计平行排列。正是这种流动液晶被用于广泛可用的平板液晶显示器，该平板液晶显示器现在被用于手表、计算器、移动的电话、照相机、膝上型计算机、台式监视器以及最近的大面积平板电视。在这些装置中，棒状液晶分子通过施加小电场来切换其取向（几伏），并且虽然切换时间相当快，大约50微秒，但更快的切换将是有利的，并且开辟了显示器、电信和光学器件中的快速切换应用的全新领域。杆状分子具有统计学上平行的分子排列，并且在这种排列中，只有一个轴（光轴），偏振光以相等的速度穿过该轴，因此该相位被称为单轴的。弯芯（但不要太弯曲）分子也可以表现出向列相液晶相，然而，弯芯分子结构可以产生双轴向列相，顾名思义，其中有两个光轴。双轴晶型相具有基本的科学意义，另外，它具有技术意义，因为在这种双轴晶型相中的转换将快得多，从而能够实现上述有利的器件，并且可能促进新的高技术应用的开发。并且这些仅在约200 ℃的温度和相对较短的温度范围内表现出来;这显然使得评估困难，并且不可能用于应用中。这项拟议的研究旨在通过合成和评估新型材料设计，彻底研究双轴晶相生成过程中晶核分子结构的结构-性能关系，以期在更宽的温度范围内，在室温或接近室温的温度下提供晶相;从而促进物理性能的评估，并使其能够用于上述应用。

It is commonly recognised that matter can exist in three states, solid, liquid and gas, however, some materials, notably those that consist of rod-shaped molecules, can additionally show one or more 'liquid crystal' phase(s). Liquid crystal phases are distinct phases of matter that have molecular orderings intermediate between those of the common liquid state and those of the common crystalline solid state. The smectic phases (several are known) are liquids that are quite viscous because the degree of molecular ordering is close that of solids. The nematic phase is very fluid because the only molecular ordering is a statistically parallel arrangement of molecules. It is this fluid nematic liquid crystal that is used in the widely available flat-panel liquid crystal displays that are now used for watches, calculators, mobile telephones, cameras, lap-top computers, desk-top monitors and more recently large area flat-panel televisions. In these devices, the rod-like liquid crystal molecules have their orientation switched by the application of a small electric field (a few volts), and although switching times are quite fast, around 50 microseconds, faster switching would be advantageous, and open up a whole new area of fast switching applications in displays, telecommunications and optical devices.In the nematic phase, the rod-like molecules have a statistically parallel arrangement of the molecules and in this arrangement there is only one axis (the optic axis) through which polarised light travels through with equal velocity, hence the phase is termed uniaxial. Bent-core (but not too bent) molecules can also exhibit the nematic liquid crystal phase, however, the bent-core molecular structure can give rise to a biaxial nematic phase, in which, as the name implies, there are two optic axes. A biaxial nematic phase is of fundamental scientific interest, and additionally it is of technological interest because switching in such a biaxial nematic phase would be much faster enabling the advantageous devices mentioned above, and possibly facilitate the development of novel high technology applications.So far, very few compounds have been proven to generate a biaxial nematic phase, and these are only exhibited at temperatures of around 200 C, and over a relatively short temperature range; which obviously makes evaluation difficult, and use in applications impossible. This proposed research is designed to thoroughly investigate the structure-property relationships of bent-core molecular structures in the generation of the biaxial nematic phase, through the synthesis and evaluation of novel material designs, with a view to providing the phase over a wider temperature range, at or close to room temperature; thus facilitating the evaluation of physical properties and enabling use in applications discussed above.