The role of boundaries in 2D active nematics

活性物质旨在描述在纳米尺度上消耗化学能导致宏观尺度上运动的材料。例子包括活细胞的运动。最近的理论表明，活细胞的运动受到物理定律的限制，只有特定的特征行为，这些理论提出了一种有趣的可能性，即有可能设计出具有迄今为止只在活生物体中发现的功能的新材料。目前，缺乏定量实验来检验理论阻碍了进步。本研究旨在通过在受限二维活性液晶中提供理论和实验的定量比较来纠正这种不平衡。这些理论测试和新现象的发现将推动该领域向前发展，导致新材料的创造，如自组织发动机和自泵流体。活性物质研究处于软物质领域的前沿，但缺乏定量实验来检验理论，阻碍了研究的进展。这项建议旨在纠正这种不平衡。本文将对受限二维活性向列液晶进行实验研究，以阐明边界条件在影响结构和动力学方面的作用。一个模型系统，可伸缩微管束，将被采用，因为他们相对简单和高度可控性。一个重点将是建立微管束延伸和产生流动的微观机制。这将完成使用联合荧光和二次谐波产生显微镜。第二个重点将是通过创建各种各样的受限结构和定量测量比较理论和实验所需的量来研究边界条件对主动向列线的作用。这将完成使用光刻和微流体制造方法和定量光显微镜。第三个推动力将是利用有限元计算将实验与理论进行比较，第四个推动力将是设计基于受限主动向列式的软机器，这些软机器可以自组织执行工作，比如泵送流体。该奖项反映了美国国家科学基金会的法定使命，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。

PART 1: NON-TECHNICAL SUMMARY Active matter seeks to describe materials in which chemical energy is consumed at the nanoscale resulting in motion at the macro scale. Examples include the motion of living cells. Recent theories suggest that the motions of living cells are constrained by physical laws to certain characteristic behaviors, and these same theories raise the intriguing possibility that it is possible to engineer new materials with functionalities that heretofore are only found in living organisms. Currently, a lack of quantitative experiments to test theory is hampering progress. This proposal seeks to rectify this imbalance by providing quantitative comparison between theory and experiment in confined two-dimensional active liquid crystals. These tests of theory and discovery of new phenomena will propel the field forward leading to the creation of novel materials, such as self-organizing engines and self-pumping fluids. PART 2: TECHNICAL SUMMARY Active matter research is at the forefront of the field of soft matter, but a lack of quantitative experiments to test theory is hampering progress. This proposal seeks to rectify this imbalance. Experimental studies of confined 2D active nematic liquid crystals will be performed with the goal to elucidate the role of boundary conditions in influencing structure and dynamics. A model system, extensile microtubule bundles, will be employed because of their relative simplicity and high degree of controllability. One thrust will be to establish the microscopic mechanism by which microtubule bundles extend and produce flow. This will be accomplished using combined fluorescence and second harmonic generation microscopy. A second thrust will be to investigate the function of boundary conditions on active nematics by creating a wide variety of confined structures and quantitatively measure the quantities necessary to compare theory and experiment. This will be accomplished using photolithographic and microfluidic manufacturing methods and quantitative light microscopy. A third thrust will be to compare experiment to theory using finite element computation and a fourth thrust will be to engineer soft machines based on confined active nematics that self-organize to perform work, such as pumping of fluids.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.