Abstract

The interactions of autonomous microswimmers play an important role for the formation of collective states of motile active matter. We study them in detail for the common microswimmer-design of two-faced Janus spheres with hemispheres made from different materials. Their chemical and physical surface properties may be tailored to fine-tune their mutual attractive, repulsive or aligning behavior. To investigate these effects systematically, we monitor the dynamics of a single gold-capped Janus particle in the external temperature field created by an optically heated metal nanoparticle. We quantify the orientation-dependent repulsion and alignment of the Janus particle and explain it in terms of a simple theoretical model for the induced thermoosmotic surface fluxes. The model reveals that the particle’s angular velocity is solely determined by the temperature profile on the equator between the Janus particle’s hemispheres and their phoretic mobility contrast. The distortion of the external temperature field by their heterogeneous heat conductivity is moreover shown to break the apparent symmetry of the problem.

Graphic abstract

中文翻译：

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Janus粒子的热趋性

摘要

自主微型游泳者的相互作用对于运动活性物质的集体状态的形成起着重要作用。我们对它们进行了详细研究，以了解具有由不同材料制成的半球的双面 Janus 球体的常见微型游泳器设计。可以调整它们的化学和物理表面特性，以微调它们的相互吸引、排斥或排列行为。为了系统地研究这些影响，我们在由光学加热的金属纳米粒子产生的外部温度场中监测单个金帽 Janus 粒子的动力学。我们量化了 Janus 粒子的取向依赖性排斥和排列，并用诱导热渗透表面通量的简单理论模型对其进行了解释。该模型表明，粒子的角速度完全取决于 Janus 粒子半球之间赤道上的温度分布及其泳动迁移率对比。此外，由于其异质热导率造成的外部温度场失真被证明打破了问题的明显对称性。

图形摘要