Bithi Swastika S, Vanapalli Siva A
Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409, USA.
Soft Matter. 2015 Jul 7;11(25):5122-32. doi: 10.1039/c5sm01077b.
We study the complex collective dynamics mediated by flow resistance interactions when trains of non-coalescing and coalescing confined drops are introduced into a microfluidic parking network (MPN). The MPN consists of serially connected loops capable of parking arrays of drops. We define parking modes based on whether drops park without breakage or drop fragments are parked subsequent to breakage or drops park after coalescence. With both non-coalescing and coalescing drops, we map the occurrence of these parking modes in MPNs as a function of system parameters including drop volume, drop spacing and capillary number. We find that the non-coalescing drops can either park or break in the network, producing highly polydisperse arrays. We further show that parking due to collision induced droplet break-up is the main cause of polydispersity. We discover that collisions occur due to a crowding instability, which is a natural outcome of the network topology. In striking contrast, with coalescing drops we show that the ability of drops to coalesce rectifies the volume of parked polydisperse drops, despite drops breaking in the network. We find that several parking modes act in concert during this hydrodynamic self-rectification mechanism, producing highly monodisperse drop arrays over a wide operating parameter space. We demonstrate that the rectification mechanism can be harnessed to produce two-dimensional arrays of microfluidic drops with highly tunable surface-to-volume ratios, paving the way for fundamental investigations of interfacial phenomena in emulsions.
当将非聚并和聚并的受限液滴序列引入微流体停车网络（MPN）时，我们研究了由流动阻力相互作用介导的复杂集体动力学。MPN由能够停放液滴阵列的串联回路组成。我们根据液滴是否完整停放、破碎后停放液滴碎片还是聚并后停放液滴来定义停车模式。对于非聚并和聚并液滴，我们将MPN中这些停车模式的出现情况映射为系统参数的函数，这些参数包括液滴体积、液滴间距和毛细管数。我们发现非聚并液滴在网络中可能停放或破碎，从而产生高度多分散的阵列。我们进一步表明，由碰撞诱导的液滴破碎导致的停车是多分散性的主要原因。我们发现碰撞是由于拥挤不稳定性而发生的，这是网络拓扑结构的自然结果。与之形成鲜明对比的是，对于聚并液滴，我们表明尽管液滴在网络中会破碎，但液滴聚并的能力会校正停放的多分散液滴的体积。我们发现，在这种流体动力学自校正机制中，几种停车模式协同作用，在很宽的操作参数空间内产生高度单分散的液滴阵列。我们证明，可以利用这种校正机制来生产具有高度可调表面积与体积比的二维微流体液滴阵列，为乳液界面现象的基础研究铺平道路。
