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Towards fundamental understanding of bulk nanobubble metastability and the influence of external fields

English title Towards fundamental understanding of bulk nanobubble metastability and the influence of external fields
Applicant Schutzius Thomas
Number 208097
Funding scheme Project funding
Research institution Institut für Energietechnik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Mechanical Engineering
Start/End 01.05.2022 - 31.12.2025
Approved amount 393'153.00
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Keywords (4)

Nucleation Thermodynamics; Interfacial Phenomena; Nanobubble; Thermofluidics

Lay Summary (German)

Lead
Nanoblasen sind Gasblasen in Flüssigkeiten mit Durchmessern von unter einem Mikrometer, die sich laut Theorie innerhalb kürzester Zeit auflösen sollten. Jüngste experimentelle Entdeckungen und theoretische Arbeiten sprechen jedoch für die Existenz von Langzeit-stabilen Nanoblasen in Flüssigkeiten, auch wenn eindeutige Beweise noch fehlen.
Lay summary

Etliche Stabilitäts-Mechanismen wurden vorgeschlagen, jedoch ist bisher keiner akzeptiert. Experimente, welche die Existenz von Nanoblasen beweisen sowie Nano-Verunreinigungen im Testaufbau ausschliessen können, stehen noch aus. Auch der Einfluss von externen Feldern auf deren Stabilität und Transport ist weitgehend unerforscht, jedoch notwendig, um unser Verständnis über die Entstehung und die Existenz von Nanoblasen zu verbessern. Dies ist insbesondere von Bedeutung, weil das Potenzial von Nanoblasen für viele natürliche, wissenschaftliche und technologische Anwendungen in den Bereichen Pharmazie, Wasseraufbereitung und Energieumwandlung, unbestritten ist. Ziel dieses interdisziplinären Projekts ist es daher, durch experimentelle und theoretische Untersuchungen eine wissenschaftliche Grundlage für ein tieferes Verständnis dafür zu schaffen, wie Gas-Übersättigung/Untersättigung und externe Felder die Bildung, Metastabilität, Auflösung und den Transport von Mikro- und Nanoblasen auf der Ebene einzelner Blasen beeinflussen. Diese Arbeit wird unser grundlegendes Verständnis der Stabilität kleiner Gasphasen erheblich erweitern und neue Strategien für die Stabilisierung und den Transport von Nanoblasen hervorbringen. Dies würde Technologien in den Bereichen Antifouling, diagnostische Sonographie und die Verabreichung von Medikamenten bedeutend voranbringen, es könnte aber auch zu unvorhergesehenen Innovationen führen.

Direct link to Lay Summary Last update: 27.04.2022

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Associated projects

Number Title Start Funding scheme
179062 On the fundamental role of substrate compliance and enhanced light absorption on droplet condensation and evaporation 01.10.2018 Project funding

Abstract

Nanobubbles on surfaces (surface nanobubbles) and in bulk liquids (bulk nanobubbles, diameters < 100 nm) are expected to dissolve quickly due to the fast kinetics of gas dissolution, which is driven by high Laplace pressures. Despite this, previous work has shown how surface nanobubbles can overcome this obstacle and be stabilized by contact line pinning, which can result from intrinsic nanoscale physical roughness or chemical heterogeneity of the substrate, allowing the curvature of the nanobubble to decrease while outgassing and reducing the Laplace pressure. Recent experimental evidence and theoretical work support the existence of nanobubbles in bulk liquids, although the evidence is not definitive. Furthermore, absent a surface, the mechanism of bulk nanobubble metastability must be very different from surface nanobubbles. Various mechanisms of stability and metastability have been proposed including the skin, electrostatic repulsion, many body, and dynamic equilibrium models. None of these mechanisms for bulk nanobubble metastability are currently accepted though; experimental evidence definitively proving the existence of nanobubbles and their composition is lacking with significant contamination issues; and knowledge, experimental evidence, and insight into the influence of external electrical and stress fields on stability and transport is absent, but is needed, in order to significantly improve our mechanistic understanding. This is the case despite its clear importance and ability to advance the state-of-the-art to many natural, scientific, and technological applications spanning drug delivery, water treatment, and energy conversion. Therefore, the aim of this interdisciplinary project is to create an integrated science-base for how supersaturation/undersaturation and external electric and stress fields affect bulk microbubble and nanobubble formation, metastability, dissolution, and transport at the single bubble-level through experimental and theoretical investigations. Our strategy will be based on the following fundamental aspects: - Nucleation: Guided by relevant thermofluidic theories, we will study the effect of gas supersaturation and external electric field strength on nanobubble nucleation, growth, and stability with single-bubble resolution. Such nucleated bubbles will be formed within microfluidic channels in a high-pressure compression-decompression setup and detected with laser light scattering and at the necessary optical resolution allowing us to track individual nanobubbles. The use of a compression-decompression method for bubble formation and in situ observations at their formation and growth allows us to drastically minimize contamination issues associated with other nanobubble generation methods. Re-compression also allows us to confirm its gaseous nature.- Dissolution: Guided by fluidic theories, we will generate monodisperse microbubbles whose composition is known a priori on microfluidic chips in water-based fluids having a range of viscosity and viscoelasticity and observe their dissolution behavior down to nanoscopic sizes. We will image the microbubble to nanobubble transition by simultaneously using HILO (high angle laser illumination) and digital holography microscopy, allowing us to quantify the stability of nanobubbles with single bubble resolution. Importantly, the gases and liquids will have high purity and their composition known a priori avoiding contamination effects. By varying the concentration and molecular weight of water-soluble polymers, we can probe to what extent viscoelasticity can inhibit further dissolution of microbubbles and stabilize nanobubbles with a novel mechanism. This work will add significantly to our fundamental understanding on the metastability of nanoscopic gas phases, and, it will develop novel strategies for stabilizing and transporting bulk nanobubbles with implications for antifouling, diagnostic sonography, and drug delivery and also for unforeseen ones.
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