Microscopic active droplets are able to swim autonomously in viscous flows. This puzzling feature stems from solute exchanges with the surrounding fluid via surface reactions or their spontaneous solubilization and from the interfacial flows resulting from these solutes’ gradients. Contrary to asymmetric active colloids, these isotropic droplets swim spontaneously by exploiting the nonlinear coupling of solute transport with self-generated Marangoni flows; such coupling is also responsible for secondary transitions to more complex individual and collective dynamics. Thanks to their simple design and their sensitivity to physico-chemical signals, these droplets are fascinating to physicists, chemists, biologists, and fluid dynamicists alike in analyzing viscous self-propulsion and collective dynamics in active-matter systems, developing synthetic cellular models, or performing targeted biomedical or engineering applications. I review here the most recent and significant developments of this rapidly growing field, focusing on the mathematical and physical modeling of these intriguing droplets, together with their experimental design and characterization.

中文翻译：

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化学活性液滴的自推进


微小的活性液滴能够在粘性流中自主游动。这种令人费解的特征源于通过表面反应或其自发增溶与周围流体进行的溶质交换，以及这些溶质梯度产生的界面流动。与不对称活性胶体相反，这些各向同性液滴通过利用溶质运输与自生马兰戈尼流的非线性耦合而自发游动；这种耦合还导致了向更复杂的个人和集体动态的二次转变。由于其简单的设计和对物理化学信号的敏感性，这些液滴对物理学家、化学家、生物学家和流体动力学家来说很有吸引力，他们可以分析活性物质系统中的粘性自推进和集体动力学，开发合成细胞模型，或执行有针对性的生物医学或工程应用。我在这里回顾了这个快速发展的领域的最新和重大发展，重点关注这些有趣的液滴的数学和物理建模，以及它们的实验设计和表征。