Rational Design of Smectic Liquid Crystals for Electro-Optical Applications

手性是人造生物和几乎所有生物都拥有的一种财产。手性物体以右手和左手的形式存在(例如，手套、高尔夫球杆)，并且不能在其镜像上叠加。手性也在分子水平上表现出来。(例如，氨基酸、碳水化合物)；这些手性构建块在自然界中组装成更大的手性结构(例如，蛋白质、核酸)，这些结构本身形成具有手性拓扑结构的晶体结构。这种分子手性在宏观水平上的表现是由巴斯德首先用酒石酸铵晶体认识到的，它通过形成手性和自发极化在片状(近晶)液晶中被揭示出来。例如，手性近晶C(SMC*)相具有螺旋结构，其中分子的倾斜取向在层法线附近进行；它还表现出自发极化(PS)，可以耦合到电场E来产生用于高分辨率铁电液晶(FLC)微显示器的电光快门。未倾斜的手性近晶A(SMA*)相表现出电倾斜效应(ECA)，由分子对外加电场E的响应来描述；诱导倾斜角与E成比例，这使得能够在比向列相LCD快一个数量级的时间尺度上在显示器中产生灰度级。PS和ECES都是手性主体性质，分别依赖于SMC*和SMA*相中手性组分(S)的结构。我的研究重点是了解分子结构和液晶相体积性质之间的关系，作为合理设计铁电和电倾斜液晶混合物的手性和非手性(非手性)组分的基础。这项研究的一个方面集中在近晶相中手性的诱导，以及轴向手性分子如何通过SMC*液晶相中的分子间相互作用最有效地传播它们的手性，以使自发极化最大化。该计划的另一个方面侧重于液晶的合理设计，这种液晶经历了从非倾斜的SMA*相到倾斜的SMC*相的转变，层收缩最小。这些所谓的“De Vries类”材料为铁电液晶(FLC)技术在投影仪和大型平板显示器中的应用提供了一个主要障碍的解决方案：当FLC混合物从SMA*冷却到SMC*相时，由于近晶层的弯曲而导致的锯齿状缺陷的形成。众所周知，这些材料还具有显著的电倾斜效应和最小的光学条纹缺陷，我们正在利用我们的设计专业知识开发新的SMA*液晶材料，在电倾斜开关方面超过当前标准。**

Chirality is a property that man-made and almost all living things possess. Chiral objects exist in right- and left-handed forms (e.g., gloves, golf clubs) and are non-superposable on their mirror images. Chirality is also manifest at the molecular scale. (e.g., amino acids, carbohydrates); these chiral building blocks are assembled by nature to form larger chiral structures (e.g., proteins, nucleic acids), which themselves form crystalline structures with chiral topographies. This manifestation of molecular chirality at the macroscopic level, which was first recognized by Pasteur with crystals of sodium ammonium tartrate, is revealed in lamellar (smectic) liquid crystal phases by form chirality and spontaneous polarization. For example, the chiral smectic C (SmC*) phase is characterized by a helical structure in which the molecular tilt orientation precesses about the layer normal; it also exhibits a spontaneous polarization (PS) that can be coupled to an electric field E to produce an electro-optical light shutter that is used in high-resolution ferroelectric liquid crystal (FLC) microdisplays. The non-tilted chiral smectic A (SmA*) phase exhibits an electroclinic effect (ECE) described by molecules tilting in response to an applied electric field E; the induced tilt angle scales with E, which enables the generation of a gray scale in displays on a time scale that is orders of magnitude faster than nematic LCDs. Both PS and ECE are chiral bulk properties that depend on the structure of the chiral constituent(s) in the SmC* and SmA* phases, respectively. My research program focuses on understanding the relationship between molecular structure and the bulk properties of liquid crystal phases as a foundation for the rational design of chiral and non-chiral (achiral) components of ferroelectric and electroclinic liquid crystal mixtures. One aspect of this research focuses on the induction of chirality in smectic phases, and how axially chiral molecules can propagate their handedness most effectively via intermolecular interactions in a SmC* liquid crystal phase in order to maximize the spontaneous polarization. Another aspect of this program focuses on the rational design of liquid crystals that undergo a transition from the non-tilted SmA* phase to the tilted SmC* phase with minimal layer contraction. These so-called 'de Vries-like' materials provide a solution to one of the main roadblocks to the use of ferroelectric liquid crystal (FLC) technology in projectors and large flat panel displays: the formation of zigzag defects caused by the buckling of smectic layers upon cooling a FLC mixture from the SmA* to the SmC* phase. These materials are also known to exhibit pronounced electroclinic effects with minimal optical stripe defects and we are leveraging our design expertise to develop new SmA* liquid crystal materials that exceed current standards in electroclinic switching. **