Electrified jets in the presence of a co-flowing liquid - A route to fine emulsions

微流控设备对流体的精确操纵正在给许多基于流体的技术带来革命性的变化。特别值得一提的是，微流控技术为成分的受控混合提供了前所未有的可能性，以产生液滴作为新材料的模板。然而，尽管这些小规模的设备前景光明，但可以产生的液滴和颗粒尺寸很少小于~10微米；这不包括具有重大基础和技术价值的胶体领域的材料。该项目的目标是有效地耦合流体动力和电力，以在稳定状态下产生尺寸可以从远低于微米到远高于微米的水滴。智能的优点在于理解和实验控制毛细管基微流控装置在电场存在下产生液滴的机制。特别是，这项研究将阐明电场如何影响同向流动液体流中液滴的形成，其中一种液体通过毛细管注入另一种不混溶液体中，并专注于控制这一过程的基本流体力学。该项目涉及研究电场作用下射流的形成，以及针对静脉曲张、轴对称扰动和离轴、横向不稳定性的增长，研究这些射流的流体动力稳定性。该项目的更广泛影响是利用这一基本知识产生单分散乳液，其液滴大小具有前所未有的可调性；这与工业相关，因为许多日常产品中都使用液滴，包括食品、化妆品、保健和个人护理产品。通过行业合作伙伴的参与，我们还将加强对本科生的教育，他们不仅将学习如何使用与技术相关的仪器，并对液滴形成过程中涉及的相关流体力学有深刻的基本了解，而且还将扩大他们在这些互动中的培训。此外，我们计划进行的研究的视觉吸引力将有助于准备新的课程和讲座。

The precision manipulation of streams of fluids with microfluidic devices is revolutionizing many fluid-based technologies. In particular, microfluidics offers unprecedented possibilities for controlled mixing of components to generate drops as templates for novel materials. However, despite the promise of these small-scale devices, the droplets and particle sizes that can be produced are rarely smaller than ~10 micrometers in diameter; this excludes materials in the colloidal domain of great fundamental and technological value.The objective of this project is to effectively couple hydrodynamic and electric forces to generate, in steady-state, drops with sizes that can be tuned from well below to well above the micron scale. The intellectual merit resides in understanding and experimentally controlling the mechanism by which drops are generated in capillary-based microfluidic devices in the presence of electric fields. In particular, this research will elucidate how electric fields affect drop formation in co-flowing liquid streams, where one liquid is injected through a capillary tube into another immiscible liquid, and focus on the fundamental fluid mechanics controlling the process. The project involves the study of jet formation under the action of electric fields and the study of the hydrodynamic stability of these jets against the growth of both varicose, axisymmetric perturbations and off-axis, lateral instabilities.The broader impact of the project is provided by the use of this fundamental knowledge to generate monodisperse emulsions with an unprecedented tunability of the drop size; this is industrially relevant, as drops are used in many everyday products, including food, cosmetic, heath and personal care products. Through the involvement of industrial partners we will additionally enhance the education of undergraduate students, who will not only learn how to use technologically relevant instrumentation and acquire a deep fundamental understanding of the relevant fluid mechanics involved in drop formation processes, but who will also broaden their training with these interactions. Additionally, the visual appeal of the research we plan to conduct will aid the preparation of new courses and lectures.