Drop detachment modes in microfluidics devices

美国国家科学基金会-化学与运输系统分部-颗粒与多相过程项目（1415）提案号：0651035主要研究人员：Stebe， KathleenAffiliation: Johns Hopkins university提案题目：微流体装置中的液滴分离模式知识成果液滴被连续相包围，在微流体装置中形成，以隔离蛋白质，脂质，细胞碎片，材料制造试剂等。单个滴液可以最大限度地减少交叉污染，并提供小型“反应器”，可以在其中进行分析或制作产品。液滴通常在表面活性剂存在的情况下形成，要么是为了防止易碎试剂（如蛋白质）的吸附，要么是为了减少产生液滴连续相界面所需的功。在表面活性剂存在的情况下，通过简单地调整液滴和连续流体的相对流速，可以在流动聚焦装置中形成大范围的液滴。表面活性剂可能在决定液滴脱离的机制方面起着重要作用。然而，这还没有以定量的方式与表征良好的表面活性剂建立。我们打算研究三种表面活性剂传质方式下流动聚焦装置中的液滴形成和脱离；吸附-解吸控制表面活性剂、扩散控制表面活性剂和混合动力学-扩散控制表面活性剂在微流体中与液滴脱落相关的流场中的作用。问题自然出现了——为什么要研究这三个极限？此外，您如何知道哪个极限适用，以及它如何取决于与表面活性剂相关的热力学或动力学参数？最后，对于微流控装置中表面活性剂的质量通量，采用什么样的模型比较合适？本文的主要工作重点是在数值和实验中解决这些问题。我们打算建立体积扩散通量和吸附/解吸动力学通量作为液滴长度尺度函数的相对重要性。我们假设动力学应该在与微流体相关的长度尺度上占主导地位。如果这可以建立，这将大大简化在10微米及以下长度范围内的滴动力学分析。我们建议在表面活性剂热力学和输运动力学常数方面使用表征良好的表面活性剂进行实验，以比较我们的数值预测。(表面活性剂将通过垂滴分析来表征，PI在这方面有丰富的经验。更广泛的影响多相芯片实验室设备几乎总是含有故意添加的表面活性剂，以减少产生液滴所需的工作量。他们通常使用滴剂来隔离具有表面活性的试剂（如蛋白质、肽和片段）。目前，尚无指导表面活性剂配方、注入方式和剥离条件之间关系的选择规则。同时，从破裂模式的相图来看，负载表面活性剂的液滴的丰富行为的实验证据揭示了具有许多转变的复杂行为。通过开发对这些系统的改进控制，我们支持扩大多相流微流体设备在诊断、筛选和制造方面的使用。PI定期欢迎本科生和高中生进入她的实验室，在过去的12年里，她已经指导了超过24名这样的学生。这些学生中有9名是女性，3名是非裔美国人。这些学生来自各种渠道，包括在JHU注册的感兴趣的本科生，jhumrsc - reu和高中外展项目。PI经常被邀请在拓展活动中发言，如怀廷学校工程开放日，或为有才华的青年中心做演讲，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.