We characterize the motility of athermal swimming droplets within the framework of a persistent random walk. Just like active colloids, their trajectories can be modeled with a constant velocity $V$ and a slow angular diffusion, but the random changes in direction are not thermally driven. Instead, $V$ is determined by the interfacial tension gradient along the droplet surface, while reorientation of the surfactant gradient leads to changes in direction with a persistence time $\tau$. We show that the origin of locomotion is the difference in the critical micellar concentration $\Delta$CMC in the front and the back of the droplet. Tuning this parameter by salt controls $V$ from $3-15$ diameters $d/s$. Surfactant concentration has little effect on speed, but leads to a dramatic decrease in $\tau$ over four orders of magnitude. The corresponding range of the persistence length $\ell =V\tau$ extends beyond the realm of synthetic or living swimmers, in which $V$ is limited by fuel consumption and $\tau$ is set by thermal fluctuations or biological activity, respectively. Our tunable swimmers are ideal candidates for the study of the departure from equilibrium to high levels of activity. We show that their collective behavior exhibits the formation of active clusters of a well-defined size.

中文翻译：

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可调式持续随机游走于飞沫中

我们表征了持续随机行走的框架内无热游泳液滴的运动。就像活性胶体一样，它们的轨迹可以以恒定速度建模$V$和缓慢的角度扩散，但方向的随机变化不会受到热驱动。代替，$V$ 由沿着液滴表面的界面张力梯度确定，而表面活性剂梯度的重新定向导致方向随持久时间的变化 $\tau$。我们显示运动的起源是临界胶束浓度的差异$\Delta$CMC位于液滴的正面和背面。通过盐控件调整此参数$V$ 从 $3-15$ 直径 $d/s$。表面活性剂浓度对速度影响不大，但会导致表面活性剂浓度急剧下降。$\tau$超过四个数量级 持续时间的对应范围$\ell =V\tau$ 超越了人工合成游泳者或现役游泳者的境界 $V$ 受油耗限制， $\tau$分别由热波动或生物活性设定。我们的可调游泳者是研究从平衡到高水平活动的理想人选。我们表明，他们的集体行为表现出良好定义的大小的活动集群的形成。