The Role of Hydrodynamics in the Behavior of Active Matter

流体动力学在活性物质行为中的作用

• 批准号: 1803662
• 负责人: John Brady
• 金额: $ 33.5万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1803662&HistoricalAwards=false
• 关键词: Role; Hydrodynamics; Behavior; Active; Matter

A distinguishing feature of many living organisms is their ability to move, to self-propel, to be active. Constituents of "active matter" systems are capable of independent self-propulsion by converting fuel into mechanical motion. Examples of active matter include both microscopic entities like microorganisms and motor proteins within our cells and large bodies like fishes and birds. Inanimate, nonliving bodies can also achieve self-propulsion using mechanisms that are different than living organisms. The outcome of the collective behavior of these nonliving active systems is not necessarily different from living active systems. Indeed, active matter systems of all scales have the tendency to associate together and move collectively, from colonies of bacteria, swarms of insects, flocks of birds, schools of fish, to herds of cattle. The question addressed in this research is the micromechanical, hydrodynamic, origin for living (and nonliving) organisms to exhibit collective and coherent motion and how it can be explained and modeled using simple physical principles. Such insight will enable the prediction, design, and control of active soft matter systems and their exploitation in nature and in industry.The intrinsic activity imparts new behaviors to active matter that distinguish it from equilibrium condensed matter systems. Active matter systems generate their own internal stress, which drives them far from equilibrium and thus frees them from conventional thermodynamic constraints, and by so doing can control and direct their own behavior and that of their surrounding environment. Active matter is always at least a two-component system - the active body and the embedding medium off of which the active body self-propels. In this research fluid-mediated hydrodynamic interactions among self-propelled bodies are incorporated for the first time. Hydrodynamics significantly affect the forces active particles exert on boundaries or other objects and can profoundly affect the phase separation in active systems by modifying the mechanical "swim pressure." The swim pressure provides a pressure-concentration relation for active matter that can quantitatively predict condensation and phase separation in active systems and provides a route for determining the amount of work that can be harvested from the often random motion of active systems. We also show that, in general, the swim stress has off-diagonal or deviatoric contributions, especially when an active system is subject to shearing motion. The swim stress predicts that, under very general conditions, active particles can reduce the suspension effective viscosity to zero, enabling spontaneous flow of active matter. The mechanical swim stress perspective allows one to understand, analyze and exploit a wide class of active soft matter systems, from swimming bacteria to catalytic nanobots to molecular motors that activate the cellular cytoskeleton.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.

许多生物体的一个显着特征是它们移动、自我推进和活跃的能力。 “活性物质”系统的组成部分能够通过将燃料转化为机械运动来独立自推进。活性物质的例子包括我们细胞内的微生物和运动蛋白等微观实体以及鱼和鸟类等大型物体。 无生命体也可以利用与生物体不同的机制实现自我推进。这些非生命活动系统的集体行为的结果不一定与生命活动系统不同。 事实上，各种规模的活性物质系统都倾向于联合在一起并集体移动，从细菌群落、昆虫群、鸟群、鱼群到牛群。 本研究解决的问题是生物体（和非生物体）表现出集体和连贯运动的微机械、流体动力学、起源，以及如何使用简单的物理原理对其进行解释和建模。 这种洞察力将使活性软物质系统的预测、设计和控制及其在自然界和工业中的利用成为可能。内在活性赋予活性物质新的行为，使其有别于平衡凝聚态物质系统。 活性物质系统会产生自己的内应力，使它们远离平衡状态，从而使它们摆脱传统的热力学约束，从而可以控制和指导它们自己的行为以及周围环境的行为。 活性物质始终至少是一个由两部分组成的系统——活性体和活性体自我推进的嵌入介质。 在这项研究中，首次将自推进体之间的流体介导的流体动力相互作用纳入其中。 流体动力学显着影响活性粒子施加在边界或其他物体上的力，并且可以通过改变机械“游动压力”来深刻影响活性系统中的相分离。 游动压力提供了活性物质的压力-浓度关系，可以定量预测活性系统中的凝结和相分离，并提供了确定可以从活性系统的随机运动中获得的功量的途径。 我们还表明，一般来说，游泳应力具有非对角线或偏向贡献，特别是当主动系统受到剪切运动时。 游泳应力预测，在非常一般的条件下，活性颗粒可以将悬浮液的有效粘度降低至零，从而使活性物质能够自发流动。 机械游泳压力视角使人们能够理解、分析和利用一类广泛的活性软物质系统，从游泳细菌到催化纳米机器人，再到激活细胞骨架的分子马达。该奖项反映了 NSF 的法定使命，并被认为值得支持通过使用基金会的智力优点和更广泛的影响审查标准进行评估。

项目成果

Phoretic motion in active matter

活性物质中的泳动

• DOI: 10.1017/jfm.2021.530
• 发表时间: 2021-09
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: Brady; John F.
• 通讯作者: John F.

Reverse osmotic effect in active matter

活性物质的反渗透效应

• DOI: 10.1103/physreve.101.062604
• 发表时间: 2020-06
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Row, Hyeongjoo;Brady, John F.
• 通讯作者: Brady, John F.

Upstream swimming and Taylor dispersion of active Brownian particles

活性布朗粒子的逆流游动和泰勒色散

• DOI: 10.1103/physrevfluids.5.073102
• 发表时间: 2020-07-08
• 期刊: Physical Review Fluids
• 影响因子: 2.7
• 作者: Zhiwei Peng;J. Brady
• 通讯作者: J. Brady