Title: Chemically active colloids near osmotic-responsive walls with surface-chemistry gradients Show Chinese title

Title: 化学活性胶体靠近渗透响应壁面，具有表面化学梯度

Abstract: Chemically active colloids move by creating gradients in the composition of the surrounding solution and by exploiting the differences in their interactions with the various molecular species in solution. If such particles move near boundaries, e.g., the walls of the container confining the suspension, gradients in the composition of the solution are also created along the wall. This give rise to chemi-osmosis (via the interactions of the wall with the molecular species forming the solution), which drives flows coupling back to the colloid and thus influences its motility. Employing an approximate "point-particle" analysis, we show analytically that -- owing to this kind of induced active response (chemi-osmosis) of the wall -- such chemically active colloids can align with, and follow, gradients in the surface chemistry of the wall. In this sense, these artificial "swimmers" exhibit a primitive form of thigmotaxis with the meaning of sensing the proximity of a (not necessarily discontinuous) physical change in the environment. We show that the alignment with the surface-chemistry gradient is generic for chemically active colloids as long as they exhibit motility in an unbounded fluid, i.e., this phenomenon does not depend on the exact details of the propulsion mechanism. The results are discussed in the context of simple models of chemical activity, corresponding to Janus particles with "source" chemical reactions on one half of the surface and either "inert" or "sink" reactions over the other half. Show Chinese abstract

Abstract: 通过在周围溶液的组成上创建梯度，并利用它们与溶液中各种分子物种的相互作用差异，化学活性胶体能够移动。 如果这些粒子靠近边界，例如限制悬浮液的容器壁，溶液的组成也会在壁上产生梯度。 这会引起化学渗透（通过壁与形成溶液的分子物种的相互作用），从而驱动流体回流到胶体，进而影响其运动性。 通过近似的“点粒子”分析，我们通过解析证明——由于壁的这种诱导主动响应（化学渗透）——这样的化学活性胶体可以与壁表面化学的梯度对齐并跟随。 从这个意义上说，这些人工“游泳者”表现出一种原始形式的触地性，即感知环境中（不一定连续的）物理变化的接近程度。 我们表明，只要化学活性胶体在无限流体中表现出运动性，与表面化学梯度对齐就是普遍现象，即这一现象不依赖于推进机制的精确细节。 结果在简单的化学活性模型背景下进行讨论，这些模型对应于在表面一半上有“源”化学反应的Janus粒子，而在另一半上为“惰性”或“汇”反应。