Self-mixing Active Fluids

活性物质是软物质科学中最令人兴奋的前沿领域之一。与典型的流体不同，活性流体并不处于平衡状态。相反，它们在当地消耗能量，将这些能量转化为内部流动和自发混合。在这个项目中，将使用由微管和动蛋白组成的流体来研究活性流体中的质量传输和混沌混合，这些都是细胞中发现的生物分子。由于耦合的运动蛋白分子马达，致密堆积的微管以受控的速度相互反平行滑动。这项工作的一个令人兴奋的结果可能是开发出一类新的自混合活性溶剂。这种溶剂可以彻底改变我们对质量传输和化学反应动力学的理解。目前的提议涉及比标准溶剂大得多的长度尺度，因此将作为这些新想法的实验模型，有助于建立管理活性物质行为的基本定律。由于生物细胞的内容物是高度复杂的活性物质，远离平衡，这项工作有望对活性材料在生物学中的作用产生新的见解。拟议中的Telluride关于活性流体中传输的研讨会将有助于将液晶、生物流体和非线性动力学等相对不同的领域聚集在一起。这项工作将对加州大学默塞德分校的教育产生重大影响，这是一所位于加州社会经济最贫困地区之一的新大学。这项研究将为几篇本科生论文提供基础，PIS将利用这项工作的见解将尖端材料引入他们的研究生和本科生教学。这个项目的重点是在生物启发的可伸展活动向列相中的运输和混合。利用粒子跟踪、粒子图像测速和标记示踪剂的荧光成像等实验工具，可以在不同的长度尺度上测量致密堆积的微管在运动蛋白分子马达的作用下以可控的速度反向平行滑动，并由此产生的混沌平流。实验数据将使用非线性和拓扑动力学工具进行理论解释，从而将混沌平流和液晶领域融合为一种独特的合作努力。拓扑熵将在这项研究中发挥核心、统一的作用。拓扑熵在混沌平流的研究中是众所周知的，但在活动向列学的研究中却被忽视了。具体目标是：1)使用珠子跟踪和速度重建，以及来自非线性动力学的工具，测量活动向列相混合的拓扑熵；2)测量宏观尺度上活动向列相因混沌平流而增强的有效扩散率；以及3)通过不同的系统参数调查分子尺度动力学、中尺度混合和宏观扩散之间的相关性。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。

Active matter is one of the most exciting frontiers in soft matter science. Unlike typical fluids, active fluids are not in equilibrium. Instead, they consume energy locally, translating this energy into internal flows and spontaneous mixing. In this project, mass transport and chaotic mixing in active fluids will be investigated using a fluid consisting of microtubules and kinesin, biological molecules found in the cell. Densely packed microtubules slide antiparallel to each other at a controlled rate due to coupled kinesin molecular motors. An exciting outcome of this work could be the development of a new class of self-mixing active solvents. Such a solvent could revolutionize our understanding of the kinetics of mass transport and chemical reactions. The present proposal concerns much larger length scales than that of standard solvents and will thus serve as an experimental model for these new ideas, helping to establish fundamental laws that govern the behavior of active matter. Since the contents of biological cells are highly complex active materials, far from equilibrium, this work is expected to yield new insights into the role of active materials in biology. A proposed Telluride workshop on transport in active fluids will help to bring together the relatively disparate fields of liquid crystals, biological fluids and nonlinear dynamics. This work will have a significant educational impact at UC Merced, a new university in one of California's most socio-economically disadvantaged areas. This research will provide the basis for several undergraduate theses and the PIs will use insights from this work to introduce cutting edge materials to their graduate and undergraduate teaching. This project focuses on transport and mixing in a biologically inspired extensile active nematic. Densely packed microtubules slide antiparallel to each other at a controlled rate due to kinesin molecular motors and the resulting chaotic advection will be measured on different length scales, using the experimental tools of particle tracking, particle image velocimetry, and fluorescence imaging of labeled tracers. Experimental data will be theoretically interpreted using the tools of nonlinear and topological dynamics, thereby merging the fields of chaotic advection and liquid crystals in a unique collaborative effort. Topological entropy will play a central, unifying role in this study. Topological entropy is well known in studies of chaotic advection, but has been thus far overlooked in studies of active nematics. Specific aims are to: 1) use bead tracking and velocity reconstruction, together with tools from nonlinear dynamics, to measure the topological entropy of active nematic mixing; 2) measure the effective diffusivity, enhanced by chaotic advection, of the active nematic on the macroscale; and 3) investigate correlations between molecular-scale dynamics, mesoscale mixing, and macroscale diffusion by varying system parameters.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.