Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, Nam-Gu, Pohang, Gyeongbuk, 37673, South Korea.
Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, Nam-Gu, Pohang, Gyeongbuk, 37673, South Korea.
Sci Rep. 2016 Aug 18;6:31901. doi: 10.1038/srep31901.
The dispensing of tiny droplets is a basic and crucial process in a myriad of applications, such as DNA/protein microarray, cell cultures, chemical synthesis of microparticles, and digital microfluidics. This work systematically demonstrates droplet dispensing into immiscible fluids through electric charge concentration (ECC) method. It exhibits three main modes (i.e., attaching, uniform, and bursting modes) as a function of flow rates, applied voltages, and gap distances between the nozzle and the oil surface. Through a conventional nozzle with diameter of a few millimeters, charged droplets with volumes ranging from a few μL to a few tens of nL can be uniformly dispensed into the oil chamber without reduction in nozzle size. Based on the features of the proposed method (e.g., formation of droplets with controllable polarity and amount of electric charge in water and oil system), a simple and straightforward method is developed for microparticle synthesis, including preparation of colloidosomes and fabrication of Janus microparticles with anisotropic internal structures. Finally, a combined system consisting of ECC-induced droplet dispensing and electrophoresis of charged droplet (ECD)-driven manipulation systems is constructed. This integrated platform will provide increased utility and flexibility in microfluidic applications because a charged droplet can be delivered toward the intended position by programmable electric control.
微小液滴的分配是许多应用中的基本且关键的过程，例如 DNA/蛋白质微阵列、细胞培养、微颗粒的化学合成和数字微流控。这项工作通过电荷集中（ECC）方法系统地展示了向不混溶流体中分配液滴。它展示了三种主要模式（即附着、均匀和爆裂模式），作为流速、施加电压和喷嘴与油面之间的间隙距离的函数。通过具有几毫米直径的常规喷嘴，可以将体积从几微升至几十纳升的带电液滴均匀地分配到油室中，而不会减小喷嘴尺寸。基于所提出方法的特点（例如，在水和油系统中形成具有可控极性和电荷量的液滴），开发了一种简单直接的用于微颗粒合成的方法，包括胶体囊泡的制备和具有各向异性内部结构的 Janus 微颗粒的制造。最后，构建了由 ECC 诱导的液滴分配和带电液滴电泳（ECD）驱动的操控系统组成的组合系统。由于可以通过可编程的电控将带电液滴输送到预定位置，因此这个集成平台将在微流控应用中提供更高的实用性和灵活性。
