Topology Driven Flows in Chromonic Liquid Crystals

该奖项支持关于液晶缺陷的理论和计算研究以及教育。液晶是由杆状分子构成的，它们表现出复杂的空间排列，介于完全有序的晶体和完全无序的液体之间。它们既能像流体一样流动，又能传递方向力，还能像晶体一样具有方向依赖的特性，这使它们适用于广泛的应用。然而，由于其结晶度较弱，在实验室样品中存在大量缺陷。虽然这种性质长期以来被认为对应用有害，但最近的研究发现了这些材料的许多新的和意想不到的性质，这些性质正是由于缺陷的存在和它们的操纵而产生的。例子包括其他分子物种或生物制剂的引导运输，由光或电场激活的机械开关的开发，甚至涉及生物反应的类比。这个项目旨在改进现有的描述有缺陷液晶和任何伴随传输的理论模型。新的模型将详细描述缺陷的结构和运动，包括它们与质量或流体流动的相互作用。目的是开发一个预测框架，描述液晶对操作条件或外部影响的响应。该研究的重点是溶致变色液晶，即通过使用适当的稀释溶剂改变棒状分子的浓度来诱导液晶行为的物质。很长一段时间以来，它们一直被认为是染料（包括食品染料），是肺部表面活性剂的类似物。它们也是生物相容性液晶，目前正在开发用于活细胞导向或分选。这类液晶具有异常大的缺陷特征，使它们易于光学分析和理论比较。这项研究将用于进一步发展和加强物理科学中计算的跨学科课程。参与该项目的学生将受益于明尼苏达超级计算研究所的大量培训和合作机会。该奖项支持理论和计算研究，以及专注于系统研究拓扑缺陷、平衡形态和向列-各向同性液晶中各向同性界面的动态演化的教育。考虑的构型包括纯向列相，或在向列相和各向同性相之间共存的双相区域。这项研究的动机是正在进行的实验表明，色散的特征微观尺度在微米量级，远远大于传统热致液晶的10纳米尺寸。如此大的尺度使得现代光学成像技术能够分辨缺陷核和两相界面，从而提取介观自由能模型的参数，达到前所未有的空间尺度。这一信息打开了关键和定量测试的大门，目前非线性，梯度理论的非平衡向列。此外，由于相互作用的复杂性，包括强各向异性、由拓扑缺陷引起的非局部弹性相互作用和中尺度双轴性，向列域（tactoids）的不寻常形态及其非平衡演化有望导致新的行为。缺陷驱动的流动和生物物质悬浮在慢性动力学是计划的调查。由于在微流体和光生物器件的流动控制、生物医学领域的细胞分选和生物传感方面的潜在应用，这些技术正受到积极的审查。这项研究将用于进一步发展和加强物理科学中计算的跨学科课程。参与该项目的学生将受益于明尼苏达超级计算研究所的大量培训和合作机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research, and education on defects in liquid crystals.Liquid crystals are made of rod like molecules that display complex spatial arrangements, though intermediate between perfectly ordered crystals and completely disordered liquids. Their combined ability to flow like a fluid, while transmitting directional forces and possessing direction dependent properties like a crystal, make them suitable for a wide range of applications. However, because of their weak crystallinity, defects are abundant in laboratory samples. Although this property has long been considered deleterious for applications, recent research has uncovered a host of new and unexpected properties of these materials that follow precisely from the existence of defects, and from their manipulation. Examples include guided transport of other molecular species or biological agents, the development of mechanical switches activated by light or electric fields, and even analogies involving biological response. This project is aimed to improve existing theoretical models that describe defected liquid crystals, and any accompanying transport. New models detailing the structure and motion of defects will be developed, including their interaction with transport of mass or fluid flow. The aim is to develop a predictive framework that describes the response of the liquid crystal to operating conditions or external influences. The specific focus of the research is on lyotropic chromonic liquid crystals, substances in which the liquid crystalline behavior is induced by using an appropriate dilution solvent to change the concentration of the rod like molecules. They have been known for a long time as dyes (including food dyes), and are analogs of lung surfactant agents. They are also bio-compatible liquid crystals, and are currently being developed for live cell steering or sorting. This class of liquid crystals features unusually large defect features that make them amenable to optical analysis, and comparison to theory.The research will be used to further develop and enhance an interdisciplinary course on computation in the physical sciences. Students participating in the project will benefit from substantial training and collaboration opportunities at the Minnesota Supercomputing Institute.TECHNICAL SUMMARYThis award supports theoretical and computational research, and education focused on the systematic study of topological defects, equilibrium morphologies, and dynamical evolution of nematic-isotropic interfaces in lyotropic chromonic liquid crystals. Configurations considered include a pure nematic phase, or the biphasic region of coexistence between nematic and isotropic phases. This study is motivated by ongoing experiments that show that the characteristic microscopic scale of chromonics is on the order of microns, much larger than the 10 nm size in conventional thermotropic liquid crystals. Such large scales allow modern optical imaging techniques to resolve defect cores and two-phase interfaces, and hence to extract the parameters of mesoscopic free energy models down to an unprecedented spatial scale. This information opens the door to critical and quantitative tests of current nonlinear, gradient theories of nonequilibrium for nematics. In addition, the unusual morphology of nematic domains (tactoids), and their nonequilibrium evolution, are expected to lead to novel behavior due to the complexity of interactions at this scale, including strong anisotropy, nonlocal elastic interactions due to topological defects, and mesocale biaxiality. Defect driven flows and the dynamics of biological matter suspended in the chromonic are among planned investigations. These are under active scrutiny because of potential applications in flow control in microfluidics and optobiological devices, in the biomedical field for cell sorting and bio sensing.The research will be used to further develop and enhance an interdisciplinary course on computation in the physical sciences. Students participating in the project will benefit from substantial training and collaboration opportunities at the Minnesota Supercomputing Institute.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.