Rational Design of Smectic Liquid Crystals for Electro-Optical Applications

电光应用近晶液晶的合理设计

• 批准号: RGPIN-2016-03614
• 负责人: Lemieux, Robert
• 金额: $ 2.19万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614496
• 关键词: Rational; Design; Smectic; Liquid; Crystals

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.

手性是人造的和几乎所有生物都拥有的属性。手性物体以右手和左手形式存在（例如手套、高尔夫球杆），并且在其镜像上不可叠加。手性也体现在分子尺度上。 （例如，氨基酸、碳水化合物）；这些手性构件自然组装形成更大的手性结构（例如蛋白质、核酸），这些手性结构本身形成具有手性拓扑的晶体结构。这种分子手性在宏观水平上的表现，首先由巴斯德通过酒石酸铵钠晶体认识到，通过形式手性和自发极化在层状（近晶）液晶相中揭示。例如，手性近晶C（SmC*）相的特征是具有螺旋结构，其中分子倾斜取向绕层法线进动；它还表现出自发偏振（PS），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*) 相表现出电斜效应 (ECE)，其描述为分子响应于施加的电场 E 而倾斜； E 引起的倾斜角尺度，这使得在显示器中生成灰度的时间尺度比向列液晶显示器快几个数量级。 PS 和 ECE 都是手性本体性质，分别取决于 SmC* 和 SmA* 相中手性成分的结构。我的研究项目侧重于了解分子结构与液晶相的整体性质之间的关系，作为合理设计铁电和电斜液晶混合物的手性和非手性（非手性）成分的基础。这项研究的一个方面集中于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其手性，从而最大化自发极化。该计划的另一个方面侧重于液晶的合理设计，液晶可以以最小的层收缩从非倾斜 SmA* 相过渡到倾斜 SmC* 相。这些所谓的“类德弗里斯”材料为铁电液晶 (FLC) 技术在投影仪和大型平板显示器中使用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。众所周知，这些材料还表现出显着的电斜效应，并且光学条纹缺陷最小化，我们正在利用我们的设计专业知识来开发新型 SmA* 液晶材料，这些材料超出了电斜开关的当前标准。