Stability and dynamics at non-aqueous fluid-fluid interfaces
- Fluid-fluid interfaces are common in nature and in various industrial processes and products, including personal care, lubricating oils, wildfire fighting, and food science. Understanding the stability of these interfaces is crucial to their morphology and dynamics, and can enable engineering of interfaces towards an end application. Aqueous liquids are ubiquitous and their interfacial behavior has been reasonably well studied. There is much less known about interfaces involving non-aqueous liquids. In this thesis, we are concerned with two classes of phenomena that are constructed of fluid-fluid interfaces with a non-aqueous liquid component: non-aqueous foams and emulsions. Non-aqueous foams are dispersions of air in liquid, and therefore comprised of many air - non-aqueous liquid interfaces. We explore various mechanisms by which the interfaces are stabilized and destabilized, subsequently influencing the resulting foams. These mechanisms can also be engineered to intentionally control stability of foams, stabilizing beneficial and destabilizing disadvantageous foams. Here, we primarily examine systems where foaming is detrimental, with the aim to destabilize the foam by destabilizing the component interfaces. Diesel fuels are one such system, with unique characteristics that make antifoaming additives challenging. Using custom single bubble interferometry, we show experimental validation of conventional antifoams in diesel and, importantly, demonstrate that a globally viable ash-free alternative is effective. Additionally, we present experimental evidence illustrating the likely physical mechanisms behind each antifoam. Widely used antifoam additives are insoluble and present challenges in implementation and robust function over time. Inspired by evaporation-induced stabilization observed in multi-component mixtures such as diesel and lubricant oils, we introduce a novel miscible antifoam mechanism. By strategically inverting the surface tension gradient and thus the direction of induced flows, this mechanism leverages solutocapillary Marangoni flows to destabilize a foam. Emulsions are dispersions of aqueous liquid in non-aqueous liquid or vice versa, and are built of non-aqueous - aqueous interfaces. We focus on double emulsions (DEs) (water-in-oil-in-water 2-interface emulsions), generated via microfluidics. We conduct a systematic characterization of DE size and shell thickness across a wide range of flow rates, fluid composition and properties, and stability and instability. Understanding interface stability in double emulsions allows better control of DE size, uniformity, and robustness, essential for applications in biomedical research. This dissertation corroborates that fluid-fluid interfaces are key to understanding factors influencing the stability and dynamics of numerous foams and emulsions and their applications, illuminating areas of great potential.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Calhoun, Suzanne Grace
|Degree committee member
|Degree committee member
|Stanford University, School of Engineering
|Stanford University, Department of Chemical Engineering
|Statement of responsibility
|Suzanne Grace Karlson Calhoun.
|Submitted to the Department of Chemical Engineering.
|Thesis Ph.D. Stanford University 2023.
- © 2023 by Suzanne Grace Calhoun
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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