Microswimmers typically move near walls, which can strongly influence their motion. However, direct experimental measurements of swimmer-wall separation remain elusive to date. Here, we determine this separation for model catalytic microswimmers from the height dependence of the passive component of their mean-squared displacement. We find that swimmers exhibit “ypsotaxis,” a tendency to assume a fixed height above the wall for a range of salt concentrations, swimmer surface charges, and swimmer sizes. Our findings indicate that ypsotaxis is activity induced, posing restrictions on future modeling of their still-debated propulsion mechanism.

中文翻译：

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基于扩散的高度分析揭示了稳健的微掠壁分离

微游泳者通常会在墙壁附近移动，这会极大地影响其运动。然而，迄今为止，对游泳者-墙壁分离的直接实验测量仍然难以捉摸。在这里，我们从模型均方根位移的被动分量的高度依赖性中确定模型催化微泳者的分离程度。我们发现，游泳者表现出“趋态性”，即在一定范围的盐浓度，游泳者表面电荷和游泳者体型的假设下，壁面高度呈固定高度。我们的研究结果表明，yypsotaxis是活动诱导的，对他们仍然争论不休的推进机制的未来建模提出了限制。