Quantitative measurements of non-equilibrium interactions of catalytic microswimmers with dual colloidal tracers

Celso CarrascoUC San Diego, Quentin MartinetIST Austria, Zaiyi ShenLOMA, Juho S. LintuvuoriLOMA, Jérémie PalacciIST Austria, Antoine AubretLOMA
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Abstract

Catalytic microswimmers convert the chemical energy of a fuel into motion, sustaining spatial chemical gradients and fluid flows that drive their propulsion. This leads to unconventional individual behavior and the emergence of collective dynamics, absent in equilibrium. The characterization of the nonequilibrium interactions driven by those concentration gradients and flows around microswimmers is challenging owing to the importance of fluctuations at the microscale. Previous experiments have focused on large Janus microspheres attached to a surface, and did not investigate non-equilibrium interactions for freely moving microswimmers of various shapes. Here we show a massive dependence of the non-equilibrium interactions on the shape of small catalytic microswimmers. We perform tracking experiments at high troughput to map non-equilibrium interactions between swimmers and colloidal tracers in 2D, accurate down to tracer velocity of 100nm/s. In addition, we devise a novel experimental method combining two types of tracers with differing phoretic mobility to disentangle phoretic interactions in concentration gradients from hydrodynamic flows. We benchmark the method with experiments on a single chemically active site and on a catalytic microswimmer tethered to a surface. We further investigate the activity-driven interactions of freely moving catalytic dimers as microswimmers, for a wide range of aspect ratio between the active and passive part. We confront our results with standard theoretical models of microswimmers near surfaces and show poor agreement, ruling out phoresis as the main interaction for catalytic swimmers. Our findings provide robust quantitative measurements of the non-equilibrium interactions of catalytic microswimmers of various geometry with their environment. The work notably indicates the need for theoretical development, and lays the groundwork for the quantitative description of collective behavior in suspensions of phoretically-driven colloidal suspensions.
定量测量催化微泳道与双胶体示踪剂的非平衡相互作用
催化微型游泳者将燃料的化学能转化为运动,维持空间化学梯度和流体流动,从而推动其前进。这导致了非传统的个体行为,并出现了在平衡状态下不存在的集体动力学。由于微尺度波动的重要性,要描述这些浓度梯度和流体在微型游泳器周围驱动的单平衡相互作用具有挑战性。以前的实验主要针对附着在表面上的大型 Janus 微球,并没有研究自由运动的各种形状的微泳体的非平衡相互作用。在这里,我们展示了非平衡相互作用对小型催化微泳体形状的质量依赖性。我们进行了高通量跟踪实验,绘制了泳体与胶体示踪剂之间的二维非平衡相互作用图,精确到 100nm/s 的示踪剂速度。此外,我们还设计了一种新颖的实验方法,将两种具有不同游动性的示踪剂结合在一起,将浓度梯度中的游动相互作用与水动力流相分离。我们通过对单一化学活性位点和系在表面的催化微泳杆的实验,对该方法进行了基准测试。我们进一步研究了自由移动的催化二聚体作为微泳杆的活性驱动相互作用,以及活性和被动部分之间宽广的长宽比范围。我们将研究结果与表面附近微游子的标准理论模型进行了对比,结果表明两者的一致性很差,这就排除了游离是催化游子主要相互作用的可能性。我们的研究结果提供了对各种几何形状的催化微泳体与其环境的非平衡相互作用的定量测量。这项研究指出了理论发展的必要性,并为定量描述光学驱动胶体悬浮液中的集体行为奠定了基础。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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