ISS: A Microgravity Microfluidic Study of Packing and Particle Stabilization of Foams and Emulsions

该项目涉及泡沫和乳液，它们出现在许多可食用食品中，如沙拉酱和冰淇淋，以及消费者和个人护理产品，如剃须膏、化妆品和洗涤剂。此外，它们是许多技术和行业的核心，如蒸馏、石油回收和从环境介质中去除污染物。在许多这些产品和工艺中，泡沫和乳液的微观结构和稳定性在决定其性能和性能方面起着关键作用。然而，一些基本问题，如“非常干燥”的泡沫和乳剂中最有效的结构是什么，一个多世纪以来一直是一个长期未解决的问题。此外，随着环保纳米颗粒作为稳定剂替代传统表面活性剂的出现，这些颗粒如何帮助稳定泡沫和乳液仍不清楚。该项目旨在通过消除重力影响因素的微重力环境下泡沫和乳剂的高分辨率成像来回答这些问题。本项目的目标是了解(a)接近干燥极限的单分散泡沫和乳液在连续相分数为零的情况下的堆积结构；(b)使用胶体颗粒代替表面活性剂对泡沫和乳液的微观结构和稳定性的影响。微重力环境特别适合这些研究，因为1)气泡/液滴可以自由聚集而不受容器的限制，2)聚结可以消除，粗化过程可以被隔离和研究。拟议的微重力实验包括微流体产生单分散气泡和液滴，泡沫和乳液的收集，以及泡沫/乳液样品的显微镜成像。在ISS上收集的显微镜图像将使用Imaris、ImageJ、内部Matlab程序和Surface Evolver程序进行分析和解释。所提出的实验和数据分析将为理解长期存在的开尔文问题提供重要见解，该问题涉及将三维空间划分为具有最小表面积的等体积，以及阐明颗粒，特别是具有粗糙表面的颗粒，在抑制粗化方面的作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The project is concerned with foams and emulsions, which appear in many edible food products, such as salad dressing and ice cream, as well as consumer and personal care products, such as shaving creams, cosmetics, and detergents. In addition, they are central to many technologies and industries like distillation, oil recovery, and removal of pollutants from environmental media. In many of these products and processes, microstructure and stabilization of foams and emulsions play critical roles in determining their properties and performance. However, some fundamental questions such as what the most efficient structure is in "very dry" foams and emulsions has been a long-lasting, unsolved problem for over a century. Moreover, as eco-friendly nanoparticles emerge as an alternative stabilizing agent to replace traditional surfactants, how these particles help stabilize foams and emulsions remains unclear. The project aims to answer these questions by imaging foams and emulsions at high resolution in microgravity environment in which gravity-induced influencing factors can be eliminated. The goal of this project is to understand (a) the packing structure of monodisperse foams and emulsions close to the dry limit with zero-fraction of continuous phase and (b) the impact of using colloidal particles instead of surfactant on microstructure and stabilization of foams and emulsions. Microgravity environment is especially suitable for these studies because 1) bubbles/drops can freely assemble without being confined by a container, and 2) coalescence can be eliminated and the coarsening process can be isolated and studied. Proposed microgravity experiments include microfluidic generation of monodisperse bubbles and drops, collection of foams and emulsions, and microscopy imaging of foam/emulsion samples. The resultant microscopy images to be collected on ISS will then be analyzed and interpreted using Imaris, ImageJ, in-house Matlab program, and Surface Evolver program. The proposed experiments plus data analysis will provide important insights on understanding the long-lasting Kelvin problem regarding 3D space partition into equal volumes with the least surface area, as well as elucidate the role of particles, especially those with rough surfaces, in suppressing coarsening.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.