Colloidal Dynamics in Fluids with Spatiotemporally Modulated Nematic Order

液晶是由棒状分子组成的流体。分子的排列比普通液体更有序，但比结晶固体更不有序。向列液晶就是这方面的一个重要例子。向列图中的分子都沿着一个共同的方向运动。杂质，如小颗粒，可以破坏这个秩序，并引入重要的新影响。这些可能包括重要的新光学和磁性能，它们有可能使新技术成为可能。当流体中的顺序是空间模式或随时间变化时，行为变得更加丰富。本项目将实验研究几种时空变化的向列液晶。它们包括“主动”向列线，这种向列线经历内部驱动的永久流动，并带有磁性粒子；还有一种向列线，它具有有序的条纹图案，应该会使粒子按照大小自发地进行排序。该项目的更广泛影响将是研究生和本科生的研究培训和教育。该项目还将与当地一所少数族裔占多数的磁体科学高中建立伙伴关系，为巴尔的摩市有才华的学生提供研究实习机会。技术摘要：对悬浮在液晶中的包裹体的研究可以对这些材料的粘弹性和界面特性产生重要的新见解，并可以进一步通过流体产生的独特的各向异性相互作用为操纵胶体创造新的平台。此外，颗粒分散的液晶作为复合材料具有技术前景，由于颗粒与液晶顺序的耦合而增强了性能。这项工作将寻求实质性地推进对液晶材料动力学性质的理解，以及动力学与胶体运输的关系。特定的目标将是询问从平衡状态驱动的具有向列顺序的流体，无论是在主动向列的情况下由内部产生的流动还是由外部施加的电场或应力场驱动，并研究这种驱动的时空响应如何与粒子运动耦合。研究将集中在三个主题相关的项目上：(i)含有磁驱动纳米和微粒子的活性向列膜，这将为活性物质在关键的内在长度尺度和时间尺度上的粘弹性和流体动力学特性提供新的见解；（ii）图案和动态调制液晶中的胶体动力学，这些液晶配置用于测试在这种环境中胶体传输的惊人预测；(3)剪切诱导向列序流体中的纳米颗粒动力学，其中新的x射线散射技术可以从微观角度研究这种非平衡驱动系统的结构动力学。这项工作的更广泛影响将包括对物理学研究生和本科生的研究培训，为他们在学术界和工业界的职业生涯做好准备。该项目还将与当地一所少数族裔占多数的磁体科学高中建立伙伴关系，为巴尔的摩市有才华的学生提供研究实习机会。

Non-technical abstractLiquid crystals are fluids composed of rod-shaped molecules. The molecules arrange themselves to be more ordered than in an ordinary liquid but less so than in a crystalline solid. Nematic liquid crystal are an important example of this. The molecules in nematics all orient along a common direction. Impurities, like small particles, can disrupt this order and introduce important new effects. These can include important new optical and magnetic properties that potentially enable new technologies. The behavior becomes even richer when the order in the fluid is spatially patterned or changes with time. This project will investigate experimentally several classes of spatially or temporally varying nematic liquid crystals. They include 'active' nematics that undergo internally driven perpetual flow and that are seeded with magnetic particles and nematics with a striped pattern of ordering that should cause particles to sort themselves spontaneously by size. Among the broader impacts of the project will be research training and education for graduate and undergraduate students. The project will also enable a partnership with a local majority-minority magnet science high school to provide talented Baltimore City students with opportunities for research internships.Technical AbstractThe study of inclusions suspended in liquid crystals can lead to important new insight about the viscoelastic and interfacial properties of these materials and can further create novel platforms for manipulation of colloids through unique anisotropic interactions engendered by the fluids. Further, particle-dispersed liquid crystals hold technological promise as composite materials with enhanced properties deriving from coupling of the particles to the liquid crystalline order. This work will seek to advance substantially the understanding of the nature of dynamics in liquid crystalline materials and how the dynamics relates to colloidal transport. The particular goal will be to interrogate fluids with nematic order that are driven from equilibrium, either by internally generated flows in the case of active nematics or by externally imposed electric or stress fields, and to investigate how the spatiotemporal response to this driving couples to the particle motion. The research will focus on three thematically linked projects: (i) active nematic films containing magnetically actuated nano- and micro-particles that will provide new insights into the viscoelastic and hydrodynamic properties of active matter on key intrinsic lengthscales and timescales; (ii) colloidal dynamics in patterned and dynamically modulated liquid crystals configured to test striking predictions for colloidal transport in such environments; and (iii) nanoparticle dynamics in fluids with shear-induced nematic order, where new x-ray scattering techniques can enable novel microscopic perspectives on the structural dynamics of such out-of-equilibrium, driven systems. Broader impacts of the work will include research training for graduate and undergraduate students in physics that will prepare them for careers in academia and industry. The project will also enable a partnership with a local majority-minority magnet science high school to provide talented Baltimore City students with opportunities for research internships.