Hydrodynamically bound states of a pair of microrollers: A dynamical system insight
Hydrodynamically bound states of a pair of microrollers: A dynamical system insight
复制标题
DOI：
10.1103/physrevfluids.4.044302
复制
发表时间：
2019-04-05
影响因子：
2.7
通讯作者：
Delmotte, Blaise
中科院分区：
文献类型：
--
作者：
Delmotte, Blaise
最近的工作已经确定了持久的簇状态，这些簇状态被证明仅通过流体动力学相互作用组装和保持在一起[Drivel et al. Nat. Phys. 13，375（2017）]。这些状态出现在胶体微辊系统中;微辊是围绕平行于地板的轴旋转的胶体颗粒，并产生强烈的，缓慢衰减的平流。为了理解这些束缚态，我们研究了一个简单而丰富的两个微辊模型系统。在这里，我们表明，对microrollers可以表现出流体动力学的束缚态，其性质取决于一个无量纲数，表示为B，比较引力和外部扭矩的相对强度。使用动力系统框架，我们在相空间中描述这些不同的状态，并分析了系统的分支作为B变化。特别是，我们表明，有一个临界值，B*，以上的活动流可以击败重力，并导致稳定的运动轨道，或“蛙跳”，轨迹，让人想起的自组装的运动结构，称为“生物”，观察到的Drivel等人。我们确定的条件，这些轨迹的出现，并研究他们的吸引力盆地。这项工作表明，各种各样的稳定的束缚态，可以得到只有两个粒子。我们的研究结果有助于理解导致流体动力学系统中自发自组装的机制，如微辊悬浮液，以及如何优化这些系统的颗粒传输。
Recent work has identified persistent cluster states which were shown to be assembled and held together by hydrodynamic interactions alone [Driscoll et al. Nat. Phys. 13, 375 (2017)]. These states were seen in systems of colloidal microrollers; microrollers are colloidal particles which rotate about an axis parallel to the floor and generate strong, slowly decaying, advective flows. To understand these bound states, we study a simple, yet rich, model system of two microrollers. Here we show that pairs of microrollers can exhibit hydrodynamic bound states whose nature depends on a dimensionless number, denoted B, that compares the relative strength of gravitational forces and external torques. Using a dynamical system framework, we characterize these various states in phase space and analyze the bifurcations of the system as B varies. In particular, we show that there is a critical value, B*, above which active flows can beat gravity and lead to stable motile orbiting, or "leapfrog," trajectories, reminiscent of the self-assembled motile structures, called "critters," observed by Driscoll et al. We identify the conditions for the emergence of these trajectories and study their basin of attraction. This work shows that a wide variety of stable bound states can be obtained with only two particles. Our results aid in understanding the mechanisms that lead to spontaneous self-assembly in hydrodynamic systems, such as microroller suspensions, as well as how to optimize these systems for particle transport.