Ray Swarnak, Roy Arun
Soft Condensed Matter Group, Raman Research Institute, Bangalore 560080, India.
Phys Rev E. 2023 Sep;108(3-2):035102. doi: 10.1103/PhysRevE.108.035102.
We propose a simple active hydrodynamic model for the self-propulsion of a liquid droplet suspended in micellar solutions. The self-propulsion of the droplet occurs by spontaneous breaking of isotropic symmetry and is studied using both analytical and numerical methods. The emergence of self-propulsion arises from the slow dissolution of the inner fluid into the outer micellar solution as filled micelles. We propose that the surface generation of filled micelles is the dominant reason for the self-propulsion of the droplet. The flow instability is due to the Marangoni stress generated by the nonuniform distribution of the surfactant molecules on the droplet interface. In our model, the driving parameter of the instability is the excess surfactant concentration above the critical micellar concentration, which directly correlates with the experimental observations. We consider various low-order modes of flow instability and show that the first mode becomes unstable through a supercritical bifurcation and is the only mode contributing to the swimming of the droplet. The flow fields around the droplet for these modes and their combined effects are also discussed.
我们提出了一个简单的主动流体动力学模型，用于研究悬浮在胶束溶液中的液滴的自推进。液滴的自推进是由各向同性对称性的自发破缺引起的，并使用解析和数值方法进行研究。自推进的出现源于内部流体作为填充胶束缓慢溶解到外部胶束溶液中。我们认为填充胶束的表面生成是液滴自推进的主要原因。流动不稳定性是由表面活性剂分子在液滴界面上的不均匀分布产生的马兰戈尼应力引起的。在我们的模型中，不稳定性的驱动参数是高于临界胶束浓度的过量表面活性剂浓度，这与实验观察结果直接相关。我们考虑了各种低阶流动不稳定性模式，并表明第一模式通过超临界分岔变得不稳定，并且是唯一有助于液滴游动的模式。还讨论了这些模式下液滴周围的流场及其综合影响。
