Glassy Liquid Crystals for Reflective Coloration and Optical Storage

玻璃传统上被归类为具有各向同性性质的非晶态材料。作为非晶态固体的一类，玻璃液晶以单轴、片状、螺旋或柱状分子排列为液晶介晶的基本特征。由于光学各向异性和器件的坚固性，玻璃液晶非常适合用于光学、光子学和光电子学。然而，大多数液晶在从熔体冷却时倾向于结晶，从而失去所需的有序，并产生散射光和限制电荷传输的晶界。在先前的NSF支持下，根据经验方法，液晶基团被化学键合到不包括体积的中心核，从而产生了一组确定的材料。玻璃液晶的独特特征包括：具有明确的低至中等分子量的分子结构，优异的化学纯度和成膜能力，以及良好的流变性，便于加工成大面积单域薄膜。此外，还证明了锁存电光器件的可行性，如光开关、衰减器和可调滤光器；高效圆偏振器和偏振光发射器；以及高性能光学陷波滤光器和反射器。为了迎接新的智力和技术挑战，国际和平研究所建议开发具有高玻璃化转变温度(80至150摄氏度)和宽介晶流体温度范围的玻璃向列相和胆甾相；从分子水平上理解液晶的玻璃化而不是结晶；使玻璃液晶具有可热结晶和耐疲劳的光响应部分的功能化；并展示反射着色和图案化的可逆可调性以及可重写光学数据存储的概念。玻璃液晶特别有希望，因为它们能够在很宽的温度范围内(通过玻璃化转变温度)经历重复的加热-冷却循环，而不会遇到结晶。该项目包括实施多功能材料的确定性合成策略；有序固体薄膜的制备和表征；抗热激活结晶的材料稳定性分析；用X射线结晶学和粉末衍射仪确定晶格结构；以及通过光诱导二芳基乙烯部分开环闭环对光学性质的可逆调制。这项拟议的研究旨在培养对发展新型光学材料至关重要的新知识，与全球正在快速增长的光学信息技术高度相关。通过与政府和工业实验室的合作和伙伴关系，将促进学术研究向民用和国防应用的过渡。从教育的角度来看，参与该项目的学生将通过在多学科环境中进行论文研究来发展独特的技能，在具有战略重要性的研究和开发领域获得广阔的视角。

Glasses are traditionally classified as amorphous materials having isotropic properties. As a class of noncrystalline solids, glassy liquid crystals are characterized by a uniaxial, lamellar, helical, or columnar molecular arrangement underlying liquid crystalline mesomorphism. Thanks to optical anisotropy and device robustness, glassy liquid crystals are well suited for optics, photonics, and optoelectronics. However, most liquid crystals tend to crystallize on cooling from melts, thereby losing the desired order and yielding grain boundaries that scatter light and limit charge transport. Under prior NSF support, a definitive set of materials has been generated following an empirical approach in which liquid crystalline groups are chemically bonded to a volume-excluding central core. Unique features of glassy liquid crystals include: a well-defined molecular structure with a low to medium molecular weight, superior chemical purity and film-forming ability, and favorable rheological properties that facilitate processing into large area monodomain thin films. In addition, feasibility has been demonstrated for latching electro-optic devices, such as optical switches, attenuators and tunable filters; efficient circular polarizers and polarized light emitters; and high-performance optical notch filters and reflectors. To take on new intellectual and technological challenges, the PI's propose to develop glassy nematics and cholesterics with a high glass transition temperature (80 to 150 C) and a wide mesomorphic fluid temperature range; to furnish molecular-level understanding of vitrification, as opposed to crystallization, of liquid crystals; to functionalize glassy liquid crystals with photoresponsive moieties that are thermallystable and fatigue resistant; and to demonstrate concepts for reversible tunability of reflective coloration and patterning as well as rewritable optical data storage. Glassy liquid crystals are particularly promising because of their ability to undergo repeated heating-cooling cycles across a wide temperature range (through the glass transition temperature) without encountering crystallization. The project involves implementation of deterministic synthesis strategies for multifunctional materials; preparation and characterization of ordered solid films; analysis of material stability against thermally activated crystallization; determination of crystalline lattice structures with x-ray crystallography and powder diffractometry; and reversible modulation of optical properties through photoinduced ring closure ring opening of diarylethene moieties. Aimed at cultivating new knowledge crucial to the development of novel optical materials, the proposed research is highly relevant to optical information technology that is undergoing a rapid growth worldwide. Transition of academic research to civilian and defense applications will be facilitated through collaboration and partnership with government and industry laboratories. From an educational perspective, students participating in the project will develop unique skills from conducting their thesis research in a multidisciplinary environment, gaining a broad perspective in a strategically important area of research and development.