Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Department of Chemical Engineering, Columbia University, New York, New York 10027, USA.
Phys Rev E. 2017 Oct;96(4-1):043101. doi: 10.1103/PhysRevE.96.043101. Epub 2017 Oct 2.
We describe a simple microfluidic system that enables the steady generation and efficient transport of aqueous drops using only a constant voltage input. Drop generation is achieved through an electrohydrodynamic dripping mechanism by which conductive drops grow and detach from a grounded nozzle in response to an electric field. The now-charged drops are transported down a ratcheted channel by contact charge electrophoresis powered by the same voltage input used for drop generation. We investigate how the drop size, generation frequency, and transport velocity depend on system parameters such as the liquid viscosity, interfacial tension, applied voltage, and channel dimensions. The observed trends are well explained by a series of scaling analyses that provide insight into the dominant physical mechanisms underlying drop generation and ratcheted transport. We identify the conditions necessary for achieving reliable operation and discuss the various modes of failure that can arise when these conditions are violated. Our results demonstrate that simple electric inputs can power increasingly complex droplet operations with potential opportunities for inexpensive and portable microfluidic systems.
我们描述了一种简单的微流控系统，仅使用恒定电压输入即可实现稳定的水相液滴生成和高效传输。通过电动力学液滴生长和脱离接地喷嘴的机理实现液滴生成，该机理响应电场生长和脱离。现在带电荷的液滴通过接触电荷电泳沿着棘轮通道传输，接触电荷电泳由用于液滴生成的相同电压输入供电。我们研究了液滴尺寸、生成频率和传输速度如何取决于系统参数，如液体粘度、界面张力、施加电压和通道尺寸。观察到的趋势很好地解释了一系列缩放分析，这些分析提供了对液滴生成和棘轮传输的主导物理机制的深入了解。我们确定了实现可靠操作的必要条件，并讨论了当违反这些条件时可能出现的各种故障模式。我们的结果表明，简单的电输入可以为日益复杂的液滴操作提供动力，为廉价和便携式微流控系统提供了潜在的机会。
