Materials World Network: Electric Field Induced Microfluidic Manipulation

这项NSF材料世界网络奖支持德国哥廷根的马克斯普朗克动力学和自组织研究所（MPI）与堪萨斯州曼哈顿的堪萨斯州立大学之间的国际合作研究。这两个小组将合作研究微流体在地形结构微通道中的静力学和动力学。随着芯片上的化工厂、快速可变焦距光学液体透镜和高可视性视频速度电子纸的出现，微流体，即在封闭通道或衬底表面控制微升或纳升液体或液体溶液的操作，在技术上的重要性日益增加。这种液体操作通常通过使用电场来控制，特别是通过电润湿效应来控制表面上液滴的接触角。目前尚不清楚电场效应、润湿层、表面滑移、衬底表面形貌和液体形态不稳定性的相互作用如何共同控制地形结构通道中液体的时间动力学。在堪萨斯州将研究润湿层和表面滑移对平面表面的影响，以及电场和/或液体剪切的存在如何改变它们。据预测，在足够大的电场中，均匀的润湿层会经历电流体动力学不稳定性（并分解成纳米液滴），其中液体剪切的附加效应起着未知的作用。均匀的润湿层、表面纳米液滴或电场诱导的表面有序有望影响在固/液界面发现的滑移行为。Goettingen的MPI小组将研究电润湿过程中表面形貌的相互作用，以及这种形貌如何影响随时间变化的液体细丝沿着微流体通道扩散，以及这些通道内从液体细丝到液滴的液体形态不稳定性。由于湿层和滑移（在堪萨斯州研究）的存在将在控制微流体通道（在哥廷根研究）中扩散和形态破裂的时间依赖性方面发挥主要作用，因此两组之间将经常进行人员交流。这些交流将加强和促进两个群体之间的教育、文化和国际合作。所提出的研究将为更好地理解地形结构微流控装置中液体的静态和动态电操纵提供基础。这些信息有望在微流控装置设计的许多不同领域具有重要的实际用途。对应项目由德国国家科学基金会（DFG）资助。

This NSF Materials World Network award supports international collaborative research between the Max Planck Institute (MPI) for Dynamics and Self-organization in Goettingen, Germany and Kansas State University in Manhattan, KS. The two groups will collaborate in studying the statics and dynamics of microfluidics in topographically structured microchannels. Microfluidics, the controlled manipulation of microliters or nanoliters of liquid or liquid solution in closed channels or on a substrate surface is gaining increasing technological importance with the creation of chemical factories on a chip, fast variable focal length optical liquid lenses and high visibility video speed electronic paper. This liquid manipulation is frequently controlled via the use of electric fields and in particular via the electrowetting effect, which controls the contact angle of droplets on surfaces. Currently it is not well understood how the interplay of electric field effects, wetting layers, surface slip, surface topography of the substrate and liquid morphological instabilities combine to govern the time dynamics of liquids in topographically structured channels. The influence of wetting layers and surface slip on planar surfaces and how they are changed by the presence of an electric field and/or liquid shear will be studied in Kansas. Uniform wetting layers are predicted to undergo an electrohydrodynamic instability (and break up into nanodroplets) for sufficiently large electric fields where the additional effects of liquid shear play an unknown role. Uniform wetting layers, surface nanodroplets or electric field induced surface ordering is expected to influence the slip behavior found at solid/liquid interfaces. The MPI group in Goettingen will study the interplay of surface topography during electrowetting and how this topography influences the time dependent liquid filament spreading down microfluidic channels, as well as, liquid morphological instabilities from liquid filaments to liquid droplets within these channels. There will be frequent exchanges of personnel between the two groups because the presence of wetting layers and slip (studied in Kansas) will play a major role in governing the time dependence of both the spreading and morphological break up in microfluidic channels (studied in Goettingen). These exchanges will strengthen and enhance the educational, cultural and international cooperation between the two groups. The proposed research will provide the fundamental foundations for a better understanding of the static and dynamic electrical manipulation of liquids in topographically structured microfluidic devices. This information is expected to be of significant practical use for many different fields in microfluidic device design. The counterpart project is funded by the German National Science Foundation (DFG).