Novel Molar Design Concept for Low Molar Mass Glass-Forming Liquid Crystals

提案号：液晶已经在各种光学和光电技术中找到了潜在的应用。除了基于分子取向变化响应于应用领域的活性成分外，液晶的实际应用受到固有的流体性质和结晶倾向的限制。为了提供中间相稳定性和环境耐久性，鉴于玻璃化转变温度高于环境温度的玻璃化潜力，液晶聚合物已被探索作为一种替代方案。然而，聚合物材料本身就很难加工成均匀的薄膜，因为通常熔体粘度很高。最理想的是将这两类材料的属性结合起来，即材料加工的便利性和在玻璃环境中保持高度的亚胚有序的能力。为了实现这一最终目标，提出了一个为期两年的计划，研究低摩尔质量玻璃形成液晶。原则上，在足够快的冷却速度下，所有液体都应玻璃化。然而，为什么一些材料比其他材料更容易形成玻璃的问题至今仍未得到解答。由于理论或计算方法似乎无法在可预见的未来提供合理的分子设计工具，因此建议从经验的角度来追求分子设计概念。从本质上讲，低摩尔质量液晶代表了两个看似相反的因素之间的微妙平衡：一个促进液晶的中晶化，另一个阻碍结晶。提出了两种截然不同的结构特征，介源部分和排除体积核心，通过一个柔性间隔剂相互化学结合。这个想法是使化学组合的系统能够形成光学各向异性、形态稳定的玻璃，即使介生部分和排除体积核心都可能自行结晶。我们的技术方法包括分子设计、化学合成和相关表征，包括形态学、神学和热激活相变动力学。此外，还将进行与实际应用直接相关的表征。所提出的研究结果将为玻璃化、液态结晶度、形貌和低摩尔质量化合物的加工提供新的见解。此外，通过明智的分子设计，有望出现具有光学和光电子应用功能的多功能材料。具体的例子可能包括光偏振、非线性光学活性、光致变色和电致发光，它们构成了新兴显示、成像和通信技术的广泛基础。

ABSTRACT Proposal NO. CTS-9500737 University of Rochester Shaw H. Chen Liquid crystals have found potential applications to various optical and optelectronic technologies. With the exception of active components based on the change in molecular orientation in response to an applied field, practical applications of liquid crystals are limited by the intrinsic fluid nature and tendency to crystallize. To provide mesophase stability and environmental durability, liquid crystalline polymers have been explored as an alternative in view of the potential for vitrification with a glass transition temperature above the ambient. However, polymeric materials are inherently difficult to process into uniform films because of a generally high melt viscosity. It is most desirable to combine the attributes of these two classes of materials, i.e., ease of material processing and ability to preserve a high degree of mesomorphic ordering in a glassy environment. To achieve this ultimate goal, a two-year program is proposed for research on low molar mass glass-forming liquid crystals. In principle, all liquids should vitrify given a sufficiently rapid cooling rate. Nevertheless, the question of why some materials are more prone to glass formation than others has remained unanswered to date. Since theoretical or computational approaches do not appear to promise a rational molecular design tool in the foreseeable future, it is proposed that a molecular design concept be pursued from an empirical standpoint. In essence, low molar mass liquid crystals represent a subtle balance between two seemingly opposing factors: one to encourage liquid crystal mesomorphism and the other to discourage crystallization. It is proposed that two diametrically different structural features, mesogenic moiety and excluded-volume core, be chemically bonded to each other via a flexible spacer. The idea is to enable the chemically combined system to form and optically anisotropic, morphologically stable glass, even though both mesogenic moiety and excluded-volume core may crystallize on their own. Our technical approach consists of molecular design, chemical synthesis, and relevant characterizations including morphology, theology, and the kinetics of thermally activated phase transformation. In addition, characterizations with a direct bearing on practical applications will also be performed. Results from the proposed research will furnish new insight into vitrification, liquid crystallinity, morphology and processing of low molar mass compounds. In addition, through judicious molecular design, multifunctional materials capable of optical and optoelectronic applications are expected to come forth. Specific examples may include light polarization, nonlinear optical activity, photochromizm, and electroluminescence, which constitute a broad base for emerging display, imaging, and communications technologies.