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

该项目涉及泡沫和乳剂，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，它们还是许多技术和工业的核心，如蒸馏、石油回收和从环境介质中去除污染物。在许多此类产品和工艺中，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，一些基本的问题，如在“非常干燥”的泡沫和乳液中，什么是最有效的结构，一直是一个长达一个多世纪的长期悬而未决的问题。此外，随着环保纳米颗粒作为替代传统表面活性剂的稳定剂出现，这些颗粒如何帮助稳定泡沫和乳液仍不清楚。该项目旨在通过在微重力环境中以高分辨率成像泡沫和乳剂来回答这些问题，在微重力环境中可以消除重力诱导的影响因素。本项目的目标是了解(A)连续相含量为零的单分散泡沫和乳液接近干燥极限的堆积结构，以及(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于这些研究，因为1)气泡/液滴可以自由聚集而不受容器限制，2)可以消除聚结，可以分离和研究粗化过程。拟议的微重力实验包括单分散气泡和液滴的微流控生成、泡沫和乳状液的收集以及泡沫/乳状液样品的显微成像。然后将使用Imaris、ImageJ、内部MatLab程序和Surface Evolver程序对在ISS上收集的显微图像进行分析和解释。拟议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的见解，该问题涉及以最小的表面积将3D空间划分为相等的体积，并阐明粒子，特别是那些具有粗糙表面的粒子在抑制粗糙方面的作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.