Microfluidics to probe partial coalescence in emulsions containing interfacial crystals

微流体探测含有界面晶体的乳液中的部分聚结

• 批准号: 0967172
• 负责人: Siva Vanapalli
• 金额: $ 27万
• 依托单位: Texas Tech University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-15 至 2014-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0967172&HistoricalAwards=false
• 关键词: Microfluidics; probe; partial; coalescence; emulsions

0967172VanapalliIn applications such as foods and consumer products, emulsions are often employed because of their remarkable ability to form a wide variety of materials ranging from low-viscosity fluids, to gels to highly elastic pastes. In some of these applications emulsions containing crystallizable oils are tempered and sheared to form bicontinuous gels by exploiting a phenomenon known as partial coalescence. Unlike coalescence in liquid droplets, partial coalescence occurs when the interfacial crystals of semi-crystalline droplets penetrate neighboring droplets. The mechanical strength of the crystalline network linking the droplets is capable of overcoming the Laplace pressure and maintains the integrity of the non-spherical aggregates. Despite prior investigations, partial coalescence remains a poorly understood convolution of two non-equilibrium and stochastic phenomena - nucleation and aggregation in emulsions. Emerging technologies such as topical drugs and phase change materials also rely on partial coalescence. Thus, fundamental understanding of partial coalescence in oil-in-water emulsions would broadly impact the technological development in these applications. Currently partial coalescence has confounded scientific understanding because of polydispersity in emulsions, shear and additives such as surfactants - all of which affect both the nucleation rates and the probability of partial coalescence. In addition, current methods such as X-ray diffraction and differential scanning calorimetry are top-down approaches and are inadequate to probe the stochastic nature of nucleation and partial coalescence at the level of individual droplets. To address these scientific challenges, the investigators deploy microfluidic technology and direct visualization methods to (1) Quantify nucleation kinetics in exceptionally monodisperse droplets and test the validity of current nucleation theories (2) Directly measure the kinetics of partial coalescence and test the applicability of kinetic theories of aggregation and (3) Directly quantify the probability of shear-induced coalescence in crystalline droplets. The intellectual merit of this work is an integrated experimental effort combining microfluidics and microscopy to address a technological need to fundamentally understand nucleation and partial coalescence in emulsions. Novel aspects of the work include routing droplet traffic in a microfluidic network to control individual droplet parking in well-defined spots on a microfluidic device. Generating such large-scale single droplet arrays enables repeated crystallization-melting cycles to be performed to quantify the heterogeneity in the dynamics of nucleation. In addition, by manipulating the parking space available for droplets, the investigators will generate microfluidic doublets and hexagonally-packed monodisperse droplet arrays for direct visualization of the microscopic dynamics of partial coalescence. To probe shear-induced coalescence, we will generate two microfluidic trains of droplets and induce repeated head-on collisions between individual droplets. The ability to create such large statistical ensembles and perform measurements at the level of individual droplets is essential to discriminate the various mechanisms causing nucleation and will yield a never-before-available picture of the stochastic nature of nucleation and partial coalescence. Thus, this potentially transformative research moves beyond current top-down methods by introducing bottom-up approaches to investigate the non-equilibrium thermodynamics of nucleation and partial coalescence in emulsions. This fundamental investigation of crystallization and partial coalescence in emulsions will broadly impact the technology and engineering in areas as diverse as foods, cosmetics, drug delivery and phase change materials. Furthermore, this study may catalyze the development of an entirely new class of droplet-based fluidic devices for rapid assessment of crystallization and emulsion stability. This work will also impact other engineering areas that rely on fundamental understanding of emulsion crystallization and stability such as oil recovery. The educational component of the project includes drawing graduate and undergraduate students to the visually striking microfluidics research and providing state-of-the-art training in microfluidics, emulsion science, non-equilibrium thermodynamics and microscopy. The PI will pursue outreach activities to high school students by developing a weeklong hands-on-activities and lectures on the theme "Bubbles on Chips"

0967172Vanapalliin的应用，例如食品和消费产品，乳液通常被使用，因为它们具有出色的形成各种材料的能力，从低粘度液，再到凝胶到高弹性糊。在其中一些应用中，含有可结晶的油的乳液被调节并剪切形成双连续凝胶，通过利用一种称为部分聚结的现象。与液滴中的聚结不同，当半晶液滴的界面晶体穿透相邻的液滴时，会发生部分聚结。连接液滴的结晶网络的机械强度能够克服拉普拉斯压力并保持非球形骨料的完整性。尽管事先进行了研究，但部分合并仍然是两个非平衡和随机现象的卷积 - 乳液中的成核和聚集。局部药物和相变材料等新兴技术也依赖于部分合并。因此，对石油乳液中部分合并的基本了解将广泛影响这些应用中的技术发展。目前，由于乳液，剪切和添加剂（例如表面活性剂）中的多分散性，部分合并已经混淆了科学的理解 - 所有这些都会影响成核率和部分聚结的可能性。此外，当前的方法（例如X射线衍射和差异扫描量热法）是自上而下的方法，并且不足以探测单个液滴水平上成核和部分合并的随机性质。 To address these scientific challenges, the investigators deploy microfluidic technology and direct visualization methods to (1) Quantify nucleation kinetics in exceptionally monodisperse droplets and test the validity of current nucleation theories (2) Directly measure the kinetics of partial coalescence and test the applicability of kinetic theories of aggregation and (3) Directly quantify the probability of shear-induced coalescence in结晶液滴。这项工作的智力优点是将微流体和显微镜结合在一起的综合实验努力，以解决从根本上了解乳液中成核和部分合并的技术需求。这项工作的新方面包括微流体网络中的路由液滴流量，以控制微流体设备上定义明确的斑点中的单个液滴停车。产生如此大规模的单液滴阵列，可以进行重复的结晶融化循环，以量化成核动力学中的异质性。此外，通过操纵可用于液滴的停车位，调查人员将产生微流体双线和六角形包装的单分散液滴阵列，以直接可视化部分聚结的显微镜。为了探测剪切诱导的聚结，我们将生成两种微流体列车的液滴，并在单个液滴之间引起重复的正面碰撞。创建如此大的统计合奏并在单个液滴水平上进行测量的能力对于区分引起成核的各种机制至关重要，并且将产生对成核和部分合并的随机性质的不可用的图片。因此，这项潜在的变革研究通过引入自下而上的方法来研究乳液中成核和部分合并的非平衡热力学，超越了当前自上而下的方法。对乳液中结晶和部分聚结的基本研究将广泛影响食品，化妆品，药​​物输送和相变材料等多样性的技术和工程。此外，这项研究可能会促进一类全新的基于液滴的流体设备的发展，以快速评估结晶和乳液稳定性。这项工作还将影响其他依赖对乳液结晶和稳定性（例如回油等稳定性）的工程领域。该项目的教育组成部分包括绘画毕业生和本科生，以示意视觉上引人注目的微流体研究，并提供微流体，乳液科学，非平衡热力学和显微镜的最先进培训。 PI将通过为主题“筹码泡沫”开发为期一周的动手活动和讲座，向高中生开展外展活动。