Rational Design of Smectic Liquid Crystals for Electro-Optical Applications

手征性是人类和几乎所有生物都具有的一种性质。手性对象以右手和左手形式存在（例如，手套、高尔夫球杆），并且在它们的镜像上是不可重叠的。手性在分子尺度上也很明显。(e.g.,氨基酸，碳水化合物）;这些手性结构单元自然组装形成较大的手性结构（例如，蛋白质、核酸），其本身形成具有手性形貌的晶体结构。这种分子手性在宏观水平上的表现，首先由巴斯德用酒石酸铵钠晶体认识到，在层状（近晶）液晶相中通过形式手性和自发极化来揭示。例如，手性近晶C（SmC*）相的特征在于螺旋结构，其中分子倾斜取向围绕层法线旋进;它还表现出自发极化（PS），其可以耦合到电场E以产生用于高分辨率铁电液晶（FLC）微显示器的电光光快门。非倾斜的手性近晶A（SmA*）相表现出由分子响应于施加的电场E而倾斜所描述的电斜效应（ECE）;诱导的倾斜角与E成比例，这使得能够在显示器中在时间尺度上产生灰度，该时间尺度比LCD快几个数量级。 PS和ECE都是手性整体性质，其分别取决于SmC* 和SmA* 相中手性组分的结构。 我的研究项目侧重于了解分子结构和液晶相的整体性质之间的关系，作为铁电和电液晶混合物的手性和非手性（非手性）组分的合理设计的基础。本研究的一个方面集中在近晶相的手性诱导，以及如何轴向手性分子可以传播他们的手性最有效地通过分子间相互作用在SmC* 液晶相，以最大限度地提高自发极化。该计划的另一个方面侧重于液晶的合理设计，经历了从非倾斜SmA* 相到倾斜SmC* 相的过渡，具有最小的层收缩。这些所谓的“de Vries类”材料为在投影仪和大型平板显示器中使用铁电液晶（FLC）技术的主要障碍之一提供了解决方案：在将FLC混合物从SmA* 冷却到SmC* 相时，近晶层的屈曲导致形成锯齿形缺陷。这些材料也被称为具有最小的光学条纹缺陷，表现出明显的电诊所效应，我们正在利用我们的设计专业知识，开发新的SmA* 液晶材料，超过目前的电诊所开关标准。**

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. **