Drop detachment modes in microfluidics devices

美国国家科学基金会-化学运输系统分部颗粒多相过程计划（1415）提案编号：0651035主要研究者：Stebe，Kathleen所属机构： 约翰霍普金斯大学提案标题：微流体装置中的液滴分离模式智力优点在微流体装置中形成被连续相包围的液滴，以隔离蛋白质、脂质、细胞碎片、用于材料制造的试剂等。单个液滴允许交叉污染最小化，并提供小的“反应器”，其中可以进行测定或可以制造产品。液滴通常在表面活性剂存在下形成，以防止易碎试剂（例如蛋白质）的吸附并减少产生液滴-连续相界面所需的功。在表面活性剂的存在下，通过简单地调节液滴和连续流体的相对流速，可以在流动聚焦装置中形成宽范围的液滴。表面活性剂可能在确定液滴脱离状态中起重要作用。然而，这还没有建立在一个定量的方式与良好的表征surfactors.We打算研究液滴的形成和分离在流动聚焦装置的表面活性剂的质量转移的三个制度;吸附-解吸控制的表面活性剂，扩散控制的表面活性剂和混合动力学扩散控制的表面活性剂在流场相关的微流体中的液滴分离。问题自然出现了--为什么要研究这三个极限？此外，你如何知道哪个极限适用，它如何取决于表面活性剂相关的热力学或动力学参数？最后，微流体装置中表面活性剂的质量通量应采用什么样的模型？这项工作的一个主要重点是解决这些问题的数字和实验。我们打算建立体扩散通量和吸附/解吸动力学通量作为液滴长度尺度的函数的相对重要性。我们假设，动力学应该占主导地位的长度尺度相关的微流体。如果这可以建立，这将大大简化在10微米及以下的长度尺度上的液滴动力学分析。我们建议进行实验，使用良好的表征表面活性剂的表面活性剂的热力学和运输动力学常数比较，我们的数值预测。(The表面活性剂将通过悬滴分析来表征，PI在这方面具有丰富的经验。更广泛的影响多相芯片实验室设备几乎总是包含故意添加的表面活性剂，以减少产生液滴所需的功。它们通常使用液滴来螯合具有表面活性的试剂（例如蛋白质、肽和片段）。目前，没有选择规则来指导表面活性剂配方、注入方式和脱离条件之间的关系。同时，实验证据的丰富行为的表面活性剂负载的下降方面的相图的破裂模式揭示了复杂的行为与一些过渡。通过开发对这些系统的改进控制，我们支持多相流微流体设备在诊断，筛选和制造中的扩展使用。PI定期欢迎本科生和高中生进入她的实验室，并在过去12年中指导了超过24名这样的学生。这些学生中有9名妇女，3名非裔美国人。这些学生来自各种渠道，包括在JHU就读的感兴趣的本科生，以及JHUMRSEC-REU和高中外展计划。PI经常被邀请在外展活动中发言，如怀汀学校工程开放日，或为天才青年中心做演讲，以吸引学生进入科学和工程领域。

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)Proposal Number: 0651035Principal Investigators: Stebe, KathleenAffiliation: Johns Hopkins UniversityProposal Title: Drop detachment modes in microfluidics devicesIntellectual MeritDrops surrounded by a continuous phase are formed in microfluidics devices to sequester proteins, lipids, cellular fragments, reagents for materials manufacture, etc. The individual drops allow cross contamination to be minimized, and provide small "reactors" in which assays can be performed or products can be made. The drops are often formed in the presence of surfactants, either to prevent the adsorption of fragile reagents (e.g. proteins) and to reduce the work required to produce the drop-continuous phase interface. In the presence of surfactants, a wide range of drops can be formed in a flow focusing device by simply tuning the relative flow rates of the drop and continuous fluids. Surfactants likely play a strong role in determining the regime of drop detachment. However, this has not been established in a quantitative fashion with well characterized surfactants.We intend to study drop formation and detachment in a flow focusing device for three regimes of surfactant mass transfer; adsorption-desorption controlled surfactants, diffusion controlled surfactants and mixed kinetic-diffusion controlled surfactants in flow fields relevant to drop detachment in microfluidics. The question naturally arises- why study all three limits? Furthermore, how do you know which limit applies, and how does it depend on the surfactant related thermodynamic or kinetic parameters? Finally, what is the appropriate model to adopt for the mass flux of surfactant in a microfluidics device? A major focus of this work is to address these questions in numerics and experiment. We intend to establish the relative importance of bulk diffusion flux and adsorption/desorption kinetic fluxes as a function of drop length scale. We hypothesize that kinetics should dominate on length scales relevant to microfluidics. If this can be established, this would greatly simplify the analysis of drop dynamics in the length scale of ten microns and below. We propose to perform experiments using well characterized surfactants in terms of the surfactant thermodynamics and transport kinetic constants to compare to our numerical predictions. (The surfactants will be characterized by pendant drop analysis, in which the PI has extensive experience.Broader ImpactsMultiphase lab-on-a-chip devices nearly always contain deliberately added surfactant to reduce the work required to produce drops. They typically use drops to sequester reagents (e.g. proteins, peptides and fragments) that are surface active. At present, there are no selection rules to guide the relationship between surfactant formulations, injection modes and detachment conditions. Meanwhile, experimental evidence for the rich behavior of surfactant-laden drops in terms of phase diagrams of break up modes reveal complex behavior with a number of transitions. By developing improved control over these systems, we support expanded use of multiphase flow microfluidics devices for diagnostics, screening and manufacturing.The PI regularly welcomes undergraduate and high school students into her laboratories, and has directed more than 24 such students over the past 12 years. Of these students 9 were women, and 3 were African American. These students have been drawn from various channels, including interested undergraduates enrolled at JHU, and the JHUMRSEC-REU and high school outreach programs. The PI is regularly invited to speak at outreach events, such as the Whiting School Engineering Open House, or presentations for the Center for Talented Youth to draw students into the science and engineering fields.