The Dynamics of Static Bubbles:

THE DRAINAGE AND RUPTURE OF QUIESCENT BUBBLES CAN ENRICH, AEROSOLIZE, AND STRESS SUSPENDED MICROORGANISMS

Peter Lee Lafleur Walls | Boston University, College of Engineering, 2017 | Research Advisor: James C. Bird

Abstract: Bubbles are ubiquitous influencing a multitude of biological processes in natural and industrial environments; this influence is especially relevant during and after bubble rupture. Indeed, the influence of a bubble can extend well beyond its lifetime via the droplets produced when it ruptures. These droplets are known to effectively transport nearby particulates including bacteria and viruses into the surroundings, which in addition to affecting human health can influence global climate by acting as cloud condensation nuclei. Further, the bubble’s rupture is a violent event that has been linked to decreased cell viability in bioreactors. However, in all these applications many oft the  studies have taken an empirical approach, making the results difficult to generalize.

Here we combine theory and experiment to investigate the static and dynamic interactions be- tween bubbles and the surrounding microorganisms at a free interface.  Our first study focuses on the enrichment of particulates in the cap of a bursting bubble. As a bubble rises to a free surface, particulates in the bulk liquid are frequently transported to the surface by  attaching to the bubble’s interface. When the bubble ruptures, a portion of these particulates are often ejected into the surroundings as film droplets with particulate concentrations higher than the liquid from which originate. However, the precise mechanisms responsible for this enrichment are unclear. By simultaneously recording the drainage and rupture events with high-speed and standard photography,  we directly measure the concentrations in a thin bubble film. Based on our results, we develop a physical model and provide evidence that the enrichment is due to a combination of scavenging and film drainage. Our next study focuses on the conditions necessary for a jet droplet to be produced. Past research shows that droplet production is halted when either gravitational or viscous effects are significant. Through systematic experimentation we uncover an intermediate region where both effects are significant leading to an early end of droplet production. By numerically decoupling the gravitational effects into before and after rupture, we find that the equilibrium shape is responsible for the existence of this intermediate region. Our last study focuses on quantifying the localized stresses produced during spontaneous bubble bursting. Directly simulating each bubble and its effect on the suspended cells in a bioreactor is currently infeasible. Here we illustrate how the results  of past works, which disagree by several orders of magnitude for similarly sized bubbles, are primarily a result of the chosen numerical mesh, not the underlying physics. By implementing a particle tracking method, we eliminate this mesh dependence and quantify the extent or volume effected by a single bubble bursting event. Based on our results, we develop a generalizable framework that could be integrated into existing models as a parameterization removing the need to simulate both phases.

Our PhD Best Dissertation Honorable Mention and Finalists

COLLEGE OF ENGINEERING SOCIETAL IMPACT DISSERTATION AWARD:

Lauren Cantley
Biomimetic Nanopores from Atomically Thin Membranes
Research Advisor: Scott Bunch

HONORABLE MENTION:

Mohammad Amin Alibakhshi 
Characterization of Molecule and Particle Transport through Nanoscale Conduits
Research Advisor: Chuanhua Duan

FINALISTS:

Steven Scherr
Disposable Cartridge Based Platform for Real-Time Detection of Single Viruses in Solution  
Research Advisor: Selim Unlu

Yunjie Wang
Arterial Mechanics Considering the Structural, Mechanical, and Biochemical Contributions of Elastin
Research Advisor: Katherine Zhang

Xiaoguang Zhao
Active Metamaterial Devices at Terahertz Frequencies
Research Advisor: Xin Zhang