In this experimental study, we report on the mixing properties of interfacial colloidal floaters (glass bubbles) by chemical and hydrodynamical currents generated by self-propelled camphor disks swimming at the air-water interface. Despite reaching a statistically stationary state for the glass bubbles distribution, those floaters always remain only partially mixed. This intermediate state results from a competition between (i) the mixing induced by the disordered motion of many camphor swimmers and (ii) the unmixing promoted by the chemical cloud attached to each individual self-propelled disk. Mixing/unmixing is characterized globally using the standard deviation of concentration and spectra, but also more locally by averaging the concentration field around a swimmer. Besides the demixing process, the system develops a “turbulentlike” concentration spectra, with a large-scale region, an inertial regime, and a Batchelor region. We show that unmixing is due to the Marangoni flow around the camphor swimmers, and is associated to compressible effects.

中文翻译：

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活性樟脑颗粒引起的混合与分解

在这项实验研究中，我们报告了由自驱动樟脑盘在空气-水界面处游动而产生的化学和流体动力流对界面胶体漂浮物（玻璃气泡）的混合特性。尽管玻璃泡分布达到统计上的静止状态，但这些漂浮物始终仅保持部分混合。这种中间状态是由（i）由许多樟脑游泳者的不规则运动引起的混合与（ii）由于附着在每个独立的自推进盘上的化学云所促进的解开之间的竞争导致的。混合/未混合的特征是使用浓度和光谱的标准偏差来全局表征，但也可以通过平均游泳者周围的浓度场来更局部地表征。除了混合过程 该系统开发了一个“湍流状”浓度谱，具有一个大范围区域，一个惯性区域和一个Batchelor区域。我们表明，解混是由于樟脑游泳者周围的Marangoni流引起的，并且与可压缩的效果相关。