Cooperative properties of thermophoretic microswimmers

由于其与生物系统的相似性及其潜在的实际应用，例如在芯片实验室设备中，合成微泳者正迅速受到越来越多的关注。自发光效应已被证明是设计这种人工微泳器的一种有效和有前途的策略。潜水游泳者的表面加热不均匀，因此在存在外部加热的情况下，由于自身产生的局部温度梯度的存在，例如通过激光照明或磁刺激，他们会向前推进。我们已经开发的、目前起作用的微泳者模拟模型是微二聚体、Janus胶体和微齿轮。溶剂与微泳者表面相互作用的细节决定了磷光力的嗜热或憎热特征，这一特征将是决定微泳者行为以及颗粒大小和形状的关键。通过这种方式，不同的微二聚体表现出类似于推进器、拉动器或中性粒子的流体动力学行为；这是为了在周围流体的驱动下产生吸引、排斥或中性的粒子间相互作用。这些流体动力相互作用将与磷相互作用共存，后者可能具有相同或不同的方向。这些不同机制之间的相互作用，以及由此产生的行为的多样性，在很大程度上仍未得到探索。本项目的主要目的是通过介观模拟来研究多个游泳者的溶液的性质以及游泳者与被动粒子的混合物的性质。这项研究将主要使用Janus胶体、二聚体、三聚体，并最终使用其他游泳运动员的形状。特别令人感兴趣的是三聚体，考虑到珠子的大小和三个珠子的组成，它提供了高度可能的不对称性。这可能导致游泳运动员具有大的持续运动，不同的不对称相互作用，以及以椭圆轨道运动和大范围的手性相互作用。对这些游泳者集体行为的调查将显示出聚集、成群和各种类型的同步运动等重要现象。一些自组装结构预计将在仍未确定的情况下使用很长时间。具有重要潜在应用的现象的例子是磷化游泳者的定向运动，以及游泳者聚集在被动磷化粒子周围，这将使货物能够运输和运送到指定的区域。

Due to their similitude with biological systems and their potential practical applications, for example in lab-on-a-chip devices, synthetic microswimmers are receiving rapidly increasing attention. Self-phoretic effects have shown to be an effective and promising strategy to design such artificial microswimmers. Thermophoretic swimmers account for inhomogeneous surface heating, such that they propel due to the presence of self-generated local temperature gradients in the presence of external heating, for example by laser illumination or magnetic stimulation. The microswimmer simulation models that we have already developed and that are currently functional are microdimers, Janus colloids, and microgears. The details of the solvent interactions with the microswimmer surface determines the thermophilic or thermophobic character of the phoretic forces, and this character will be crucial to determine the microswimmer behavior, together with the particle size and shape. In this way, different microdimers have shown to hydrodynamically behave like pushers, pullers, or neutral particles; this is to generate attractive, repulsive, or neutral interparticle interactions driven by the surrounding fluid. These hydrodynamic interactions will coexist with the phoretic interactions which can have the same or different directions. The interplay of these different mechanisms, and the variety of resulting behaviors is still largely unexplored. The main purpose of this project is to investigate, by means of mesoscopic simulations the properties of solutions with multiple swimmers and of mixtures of swimmers with passive particles. This research will be performed mainly with Janus colloids, dimers, trimers, and eventually other swimmers shapes. Of particular interest are the trimers, which offer a high possible degree of asymmetry, considering the bead sizes and composition of the three beads. These might result in swimmers with a large persistent motion, different asymmetric interactions, and also moving with elliptical orbits, and with large range of chiral interactions. The investigation of the collective behavior of these swimmers will display important phenomena like clustering, swarming, and various types of synchronized motion. Some of the self-assembled structures are expected to be long-lived, under circumstances still to be identified. Examples of phenomena with important potential applications are the directed motion of phoretic swimmers, and the assembly of swimmers around a passive phoretic particle, which would enable to transport and deliver cargo to designated areas.