Active colloids with tunable interactions in liquid crystals

非技术摘要：人类越来越依赖交通技术。几个世纪以来，推动力一直放在汽车、飞机、轮船等比人类更大的宏观设备的发展上。新的挑战是开发能够将环境能量转化为微米级定向运动的微型系统。在未来，这些微型机器有望与生物组织和单个细胞相互作用，作为软微型机器人的基本单元，输送微量药物或其他有用的化学品，用作能量收集器、响应性执行器、微型混合器和分离器。电场被认为是微尺度物质输运的最有效手段之一。大多数微观动力学研究是在各向同性环境下进行的，例如水，这不能为电力驱动的微系统提供明确的方向感。该项目的目标是学习如何通过各向异性流体控制微粒子的动力学，这些流体的性质取决于空间中的方向。这些液体被称为液晶。液晶在电场作用下的各向异性已经被用于现代计算机、智能手机和电视机的信息显示中。该项目将探索如何使用液晶作为媒介，启用和控制微粒子的动力学和相互作用。该项目将促进在微观尺度上定义软物质动力学的机制的知识，并可能对未来的微型机器技术做出贡献。技术摘要：微观粒子在所谓的活性物质中的集体非平衡时空动力学是一个引人入胜的密集研究领域。根据相互作用的类型，活性物质会产生不同的行为场景，从协调的集体单向运动到湍流状的流动。该项目将利用光学显微镜、共聚焦显微镜和粒子测速仪等方法，探索电场如何在微观尺度上控制胶体颗粒的动力学及其相互作用。该项目将回答一个问题，即活性物质看似混乱的动力学能否以及如何被液晶的有序环境控制。潜在的变革性价值在于理解取向序可以控制带电活性粒子系综中的相互作用和集体运动的机制。所提出的LC环境的取向顺序施加了各向异性的长程弹性和流体动力相互作用以及各向同性流体中所不存在的推进模式。该项目将促进对液晶和胶体的电流体动力学、非平衡活性物质的物理学的了解。应用已经测试过的方法，如三维共聚焦显微镜、粒子成像测速、图案化光排列和电光学，将确保新知识建立在坚实的实验背景基础上。该项目将提供一个新的平台来设计和控制活性粒子的集合，这可能在从现有技术(如改进的电泳显示器)到未来技术的各个领域产生巨大的社会效益，这些技术将利用活性胶体的独特能力，将环境中的能量转化为系统运动，控制物质的流动，作为微型机械的重要元件。该项目将培养新一代在软性和主动领域具有基础和技术专长的科学家。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical abstract:Mankind is increasingly dependent on technologies of transportation. Over centuries, the thrust has been on development of macroscopic devices such as cars, planes, ships that are larger than the human beings. The new challenge is to develop miniature systems that could rectify the energy of environment into directed motion at the scale of micrometers. In the future, these micromachines are expected to interact with biological tissues and individual cells, serve as elementary units of soft microrobots, deliver microscopic quantities of drugs or other useful chemicals, work as energy harvesters, responsive actuators, microscale mixers and separators. Electric field is considered as one of the most effective means in powering the transport of matter at microscale. Most of the studies of microdynamics are performed for an isotropic environment, such as water, which does not provide a clear sense of direction for electrically powered microsystems. The goal of the project is to learn how one can control dynamics of microparticles by anisotropic fluids, with properties that depend on the direction in space. These fluids are known as liquid crystals. Anisotropy of liquid crystals under the action of the electric field is already used in informational displays of modern computers, smartphones and TV sets. The project will explore how to use liquid crystals as a medium that enables and commands dynamics and interactions of microparticles. The project will advance the knowledge of mechanisms defining dynamics of soft matter at microscopic scales and potentially contribute to the technologies of future micromachines. Technical abstract:Collective out-of-equilibrium spatiotemporal dynamics of microscopic particles in the so-called active matter is a fascinating area of intense studies. Depending on the type of interactions, active matter develops various scenarios of behavior, from coordinated collective unidirectional motion to turbulent-like flows. The project will explore how the electric field controls dynamics of colloidal particles and their interactions at microscale, using methods such as optical microscopy, confocal microscopy and particle velocimetry. The project will answer a question whether and how the seemingly chaotic dynamics of active matter can be controlled by an ordered environment of a liquid crystal. The potential transformative value is in understanding the mechanisms by which the orientational order can command interactions and collective motion in ensembles of electrically powered active particles. The orientational order of the proposed LC environment imposes long-range anisotropic elastic and hydrodynamic interactions and propulsion modes that are absent in isotropic fluids. The project will advance the knowledge of electro-hydrodynamics of LCs and colloids, physics of out-of-equilibrium active matter. Application of already tested methods such as three-dimensional confocal microscopy, particle imaging velocimetry, patterned photo-alignment and electro-optics will ensure that the new knowledge is based on a solid experimental background. The project will provide a new platform to design and control ensembles of active particles, which has the potential for enormous societal benefits in areas ranging from existing technologies (such as improved electrophoretic displays) to the technologies of the future, which would exploit the unique ability of active colloids to transduce energy from the environment into systematic movement, to control the flow of matter, to serve as important elements of micromachines. The project will educate a new and diverse generation of scientists with fundamental and technological expertise in soft and active matter.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.