Calorimetric Study of Smectic Liquid Crystals

9311853加兰 在这个项目中，新的量热计被开发用于潜热和相变前热容的定量测量。 新的量热计可以在很宽的频率范围（10.2 Hz至10.3 Hz）内工作，因为有证据表明，在某些跃迁附近会发生缓慢的动力学，而且热容可能是频率的复杂函数。 有了这些增强的量热能力，将有可能通过研究二元混合物来解决SmC-Sml（倾斜近晶-倾斜六方晶）转变的临界行为，其中转变的性质应该从一阶转变为临界到超临界。 本研究的主要目的是：1）定量测量一级相变的相变潜热和相变前Cp翼，2）确定二级和多临界点的静态热容临界行为，3）表征块体液晶和多孔介质（气凝胶）中液晶的连续非临界演化或有序性，4）研究多孔介质（气凝胶）中液晶的非临界演化或有序性。4）研究液晶相变附近的慢动力学，这引起了复杂的频率依赖热容。 %液晶显示出介于结晶固体和简单液体之间的各种长程有序。 了解这些材料中的相变行为对于液晶显示器和器件技术的不断发展具有重要意义。 一些具有挑战性的问题仍然存在。 几乎没有什么是已知的一些液晶相变附近的慢时间响应，这将是一个新开发的动态量热计进行研究。 手性（右或左手的不对称分子）的影响知之甚少，将探索在键取向有序和新发现的扭曲晶界相的研究。 液晶在气凝胶等随机多孔介质中的行为是一个新的领域，它与液晶在受限几何中的应用密切相关。 将进行广泛的探索性研究，涉及表面效应、有限尺寸限制效应和随机场效应。 ***

9311853 Garland In this project, new calorimeters are developed for quantitative measurements of the latent heat and pre-transitional heat capacity. The new calorimeter can operate over a wide frequency range (10.2 HZ to 10.3 HZ) because there is evidence that slow dynamics occurs near some of the transitions, and because the heat capacity can be a complex function of frequency. With these enhanced calorimetric capabilities, it will be possible to resolve the critical behavior at SmC-Sml (tilted smectic-tilted hexatic) transitions by studying binary mixtures, where the nature of the transition should change from first order to critical to supercritical. The proposed research has the following specific goals: 1) quantitative measurement of latent heats and pre-transitional Cp wings for first-order transitions; 2) determination of critical behavior for the static heat capacity at second-order and multicritical points; 3) characterization of the continuous non-critical evolution or order in bulk liquid crystals and liquid crystals in a porous medium (aerogel); and 4) investigation of the slow dynamics near liquid crystal transitions which give rise to a complex frequency- dependent heat capacity. %%% Liquid crystal, exhibit a variety of long range ordering that is intermediate between that of crystalline solids and simple liquids. Understanding the phase transition behavior in these materials is of importance in view of the growing development of liquid crystal display and device technologies. Several challenging problems remain. Almost nothing is known about the slow time response near some liquid crystal phase transitions, and this will be studied with a newly developed dynamic calorimeter. The effects of chirality (right- or left-handedness in asymmetric molecules) are poorly understood and will be expolored in studies of bond-- orientational ordering and the newly discovered twisted-grain- boundary phases. The behavior of liquid crystals in random por ous media like aerogels is a new field that is closely related to applications involving liquid crystals in restrictive geometries. A wide range of exploratory studies concerned with surface effects, finite size confinement effects, and random field effects will be undertaken. ***