Activity-induced instability of phonons in 1D microfluidic crystals†,Soft Matter

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Activity-induced instability of phonons in 1D microfluidic crystals†
Soft Matter ( IF 2.9 ) Pub Date : 2018-01-02 00:00:00 , DOI: 10.1039/c7sm01335c
Alan Cheng Hou Tsang _{1,

2,

3,

4,

5} , Michael J. Shelley _{4,

6,

7,

8,

9} , Eva Kanso _{1,

2,

3,

4,

6}

Affiliation

One-dimensional crystals of passively-driven particles in microfluidic channels exhibit collective vibrational modes reminiscent of acoustic ‘phonons’. These phonons are induced by the long-range hydrodynamic interactions among the particles and are neutrally stable at the linear level. Here, we analyze the effect of particle activity – self-propulsion – on the emergence and stability of these phonons. We show that the direction of wave propagation in active crystals is sensitive to the intensity of the background flow. We also show that activity couples, at the linear level, transverse waves to the particles' rotational motion, inducing a new mode of instability that persists in the limit of large background flow, or, equivalently, vanishingly small activity. We then report a new phenomenon of phonons switching back and forth between two adjacent crystals in both passively-driven and active systems, similar in nature to the wave switching observed in quantum mechanics, optical communication, and density stratified fluids. These findings could have implications for the design of commercial microfluidic systems and the self-assembly of passive and active micro-particles into one-dimensional structures.

中文翻译：

一维微流体晶体中声子的活动性诱导的不稳定性†

微流体通道中被动驱动粒子的一维晶体表现出集体振动模式，让人联想到声学“声子”。这些声子是由粒子之间的长距离流体动力相互作用引起的，并且在线性水平上是中性稳定的。在这里，我们分析了粒子活动-自推进-对这些声子的出现和稳定性的影响。我们表明，在活性晶体中波的传播方向对背景流的强度很敏感。我们还表明，活动在线性水平上将横向波耦合到粒子的旋转运动，从而引发了一种新的不稳定性模式，这种不稳定性模式一直存在于大背景流量或同等程度的小活动消失的极限中。然后，我们报告了一种新的声子在无源驱动和有源系统中的两个相邻晶体之间来回切换的新现象，其本质类似于在量子力学，光通信和密度分层流体中观察到的波切换。这些发现可能对商业微流体系统的设计以及将被动和主动微粒自组装成一维结构具有影响。

更新日期：2018-01-02

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