Artificial microswimmers formed by liquid crystal droplets

由液晶液滴形成的人造微型游泳器

• 批准号: 253358262
• 负责人: Dr. Christian Bahr
• 金额: --
• 依托单位: Physics of Fluids
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/253358262?language=en
• 关键词: Artificial; microswimmers; formed; liquid; crystal

The aim of our experimental project is the study of self-propelled liquid crystal droplets in an aqueous surfactant solution and their biomimetic capabilities. Swimming microorganisms like plankton and single-cell organisms are of high interest with regard to their propulsion mechanisms, as in chemotaxis, autochemotactic signalling and helical swimming, as observed, e. g., for sperm, interactions with interfaces and confined geometries like soil, and collective processes like bioconvection, especially with respect to oceanic plankton dynamics. During the first funding period, we have shown that even in a very simple three component droplet system, many of these characteristics can be observed and tuned. We are able to mass produce monodisperse droplets with reproducible speed and long running times, which show switchable helical swimming due to their nematic anisotropy, follow chemotactic and autochemotactic gradients of surfactant micelles, interact with straight and curved surfaces, can be tuned from sedimented to free buoyant swimming by admixture of heavy water and which feature to confinement and gravity dependent convective flows in large collective ensembles. We observed these droplets in microfluidic cells under light microscopy to reproduce complex and confined geometries and developed a fluorescence light sheet microscope for the observation of buoyant droplets and large convective ensembles under real three dimensional conditions. We were able to image flow fields inside and around the droplets via particle image velocimetry and gained insight into the nematic structure via polarised microscopy. During the second funding period, in collaboration with theory collaborators from the priority programme, we aim to address open questions, further applications and variations of the basic system. We want to understand quantitatively how the swimming behaviour depends on the internal structure of the droplets, which can be affected by admixing other nematogens or chiral dopants, inclusion of water droplets to create nematic shells, and external magnetic fields. The morphology of the helical trajectories strongly depends on negative autochemotaxis, which inhibits self-crossing, an effect we aim to model and quantify. The wall interaction of the swimmers, depending on hydrodynamic and phoretic fields generated by the moving droplet, will be quantified at the transition from quasi two dimensional to three dimensional geometries and under variation of wall curvature. The most important aim is a thorough understanding of the collective behaviour resulting in the formation of convective patterns and clusters. Using our light sheet microscope, we will study the dynamics of large swimmer ensembles under varying effective gravity and swimmer velocity, imaging both individual droplet dynamics and the flow fields in the bulk phase.

本实验项目的目的是研究表面活性剂水溶液中自走式液晶液滴及其仿生性能。浮游生物和单细胞生物等游动微生物的推进机制引起了人们的高度关注，如趋化性、自趋化信号和螺旋游动，如观察到的精子、与界面和受限几何形状（如土壤）的相互作用，以及生物对流等集体过程，特别是海洋浮游生物动力学。在第一个资助期间，我们已经证明，即使在一个非常简单的三组分液滴系统中，也可以观察和调整许多这些特征。我们能够大规模生产具有可重复速度和长运行时间的单分散液滴，由于它们的向列各向异性，它们表现出可切换的螺旋游动，遵循表面活性剂胶束的趋化和自趋化梯度，与直线和弯曲表面相互作用，可以通过重水的混合物从沉积调节到自由浮力游动，并且具有限制和重力依赖的大型集体对流流动的特征。我们在光学显微镜下观察这些微流体细胞中的液滴，以重现复杂和受限的几何形状，并开发了一种荧光光板显微镜，用于观察真实三维条件下的浮力液滴和大对流集合。我们能够通过颗粒成像测速仪对液滴内部和周围的流场进行成像，并通过偏振显微镜深入了解向列结构。在第二个资助期内，我们将与优先计划的理论合作者合作，探讨基本系统的开放性问题、进一步应用和变化。我们想定量地了解游泳行为是如何依赖于水滴的内部结构的，这可能受到其他线虫或手性掺杂剂的混合、水滴的包含以产生向列壳和外部磁场的影响。螺旋轨迹的形态强烈依赖于负的自趋化性，这抑制了自交，我们的目标是建模和量化这一效应。在准二维几何向三维几何过渡以及壁面曲率变化的情况下，游泳者的壁面相互作用依赖于运动液滴产生的流体动力场和电泳场，将被量化。最重要的目标是彻底了解导致对流模式和群集形成的集体行为。利用我们的薄片显微镜，我们将研究在不同的有效重力和游泳速度下的大型游泳者群的动力学，同时成像单个液滴动力学和体相中的流场。