Active colloids with tunable interactions in liquid crystals

非技术摘要：人类越来越依赖于交通技术。几个世纪以来，推动力一直在发展宏观装置，如汽车，飞机，船舶，比人类更大。新的挑战是开发微型系统，可以将环境能量转化为微米级的定向运动。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，提供微量的药物或其他有用的化学品，作为能量采集器，响应致动器，微型混合器和分离器。电场被认为是在微尺度上为物质输运提供动力的最有效手段之一。 大多数微动力学的研究都是在各向同性的环境中进行的，比如水，这并不能为电动微系统提供清晰的方向感。 该项目的目标是学习如何通过各向异性流体控制微粒的动力学，其特性取决于空间方向。这些液体被称为液晶。 液晶在电场作用下的各向异性已经用于现代计算机，智能手机和电视机的信息显示器。该项目将探索如何使用液晶作为一种媒介，使和命令的动力学和相互作用的微粒。该项目将推进在微观尺度上定义软物质动力学的机制的知识，并可能有助于未来的微机械技术。 技术摘要：所谓的活性物质中微观粒子的集体非平衡时空动力学是一个令人着迷的密集研究领域。根据相互作用的类型，活性物质会发展出各种各样的行为，从协调的集体单向运动到顺从的流动。 该项目将探索电场如何控制胶体颗粒的动力学及其在微观尺度上的相互作用，使用光学显微镜，共聚焦显微镜和粒子测速等方法。该项目将回答一个问题，即活性物质的看似混乱的动力学是否以及如何可以通过液晶的有序环境来控制。 潜在的变革价值在于理解取向顺序可以指挥电动活性粒子集合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弹性和流体动力学相互作用以及各向同性流体中不存在的推进模式。该项目将推进LC和胶体的电流体动力学，非平衡活性物质物理学的知识。 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，图案化的光对准和电光将确保新的知识是基于坚实的实验背景。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体，这在现有技术的领域具有巨大的社会效益。（如改进的电泳显示器）到未来的技术，这将利用活性胶体的独特能力，将环境中的能量转化为系统的运动，控制物质的流动，作为微型机械的重要元件。 该项目将教育新一代的科学家，他们在软物质和活性物质方面具有基础和技术专长。该奖项反映了NSF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 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.