Artificial microswimmers formed by liquid crystal droplets

我们的实验项目的目的是研究在表面活性剂水溶液中的自推进液晶液滴及其仿生能力。浮游生物和单细胞生物等游动微生物的推进机制，如趋化性、自趋化性信号和螺旋游动等，引起了人们的高度兴趣。例如，在一个实施例中，对于精子，与界面和土壤等受限几何形状的相互作用，以及生物对流等集体过程，特别是海洋浮游生物动力学。在第一个资助期内，我们已经证明，即使在非常简单的三组分液滴系统中，其中许多特征也可以被观察和调整。我们能够大规模生产单分散液滴，具有可重复的速度和长的运行时间，其显示可切换的螺旋游泳由于其螺旋各向异性，遵循表面活性剂胶束的趋化和自趋化梯度，与直的和弯曲的表面相互作用，可以通过重水的混合物从沉降到自由浮力游泳进行调整，并且其特征在于限制和重力依赖于大型集体合奏中的对流。我们观察到这些液滴在微流控细胞在光学显微镜下再现复杂的和受限的几何形状，并开发了一种荧光片显微镜观察浮力液滴和大对流合奏下真实的三维条件。我们能够通过粒子图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液滴结构。在第二个资助期内，我们与优先计划的理论合作者合作，旨在解决开放问题，进一步应用和基本系统的变化。我们希望定量地了解游泳行为如何取决于液滴的内部结构，这可能会受到混合其他致伸缩剂或手性掺杂剂，包含水滴以创建伸缩壳和外部磁场的影响。螺旋轨迹的形态在很大程度上取决于负自趋化性，这抑制了自交叉，我们的目标是建模和量化的效果。游泳者的壁相互作用，取决于由移动液滴产生的流体动力学和泳动场，将被量化在从准二维到三维几何形状的过渡和壁曲率的变化下。最重要的目的是彻底了解导致对流模式和集群形成的集体行为。使用我们的光片显微镜，我们将研究不同的有效重力和游泳者速度下的大型游泳者合奏的动力学，成像单个液滴的动力学和在体相中的流场。

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.