Bubbles are commonly found in the world around us, from industrial products to carbonated beverages. This thesis will discuss three processes involving of bubbles, from applications to fundamental phenomena. In the first portion of this thesis, I describe the use of bubbles to prevent the formation of marine biofilms and other colonizing organisms onto built structures, collectively referred to as biofouling. Biofouling detrimentally affects the structures upon which they grow, increasing drag and fuel consumption of moving vessels, reducing performance of acoustic sensors, and enhancing degradation of static structures. With recent international bans placed on common biocidal coatings, there is a demand for environmentally friendly antifouling technologies with strong performance. Bubbles rising along a submerged surface have been shown to inhibit biofouling growth, but little work has been done to determine the primary mechanisms responsible for their antifouling behavior. In this thesis I discuss a combination of field and laboratory experiments as well as a theoretical approach used to gain insight into the dominant mechanisms at play, thus laying a foundation for optimization of this antifouling technique. We find that biofouling is inhibited by shear stresses generated throughout the flow, and the degree of biofouling prevention relates to the distribution of bubbles which locally alters the shear stress. Inspired by the potential for direct interactions between bubbles and biofouling, the second topic of this thesis considers the process by which a bubble dewets, or "sticks to", a solid surface. As a bubble approaches a solid surface, the liquid between the gas and solid begins to drain until it resembles a thin film. Upon rupture of this thin film, the air dewets the surface as a contact line is formed and expands. Previous work regarding this contact line motion assumes viscous effects dominate the spreading dynamics while inertial effects are neglected. Studying the early-time dynamics of dewetting bubbles, we find viscosity to be negligible while inertia and capillarity govern the motion of a newly established contact line, suggesting early stages of dewetting are more rapid than anticipated. In the final portion of this thesis, I discuss the fundamental stability of bubbles in volatile liquids. When a bubble arrives at a free surface, we typically expect the film of the bubble cap to thin over some period of time until it ruptures. Traditionally, the drainage of this film has been considered inevitable with evaporation only hastening the film rupture. Here I show air bubbles at the free surface of liquids which appear to defy traditional drainage rules and can avoid rupture, persisting for hours until dissolution. Using pure, volatile liquids free of any surfactants, we highlight and model a thermocapillary phenomenon in which liquid surrounding the bubble is continuously drawn into the bubble cap, effectively overpowering the drainage effects. / 2020-09-28T00:00:00Z

<div>In many natural and industrial processes, bubbles are exposed to surface-active contaminants (surfactants) that may cover the whole or part of the bubble interface. A partial coverage of the bubble interface results in a spontaneous self-propulsion mechanism, which is yet poorly understood.</div><div>The main goal of this study is to enhance the understanding of the flow and interfacial mechanisms underlying the self-propulsion of small surfactant contaminated bubbles. The focus is on characterizing the self-propulsion regimes generated by the presence of surface-active species, and the influence of surfactant activity and surface coverage on the active bubble motion. </div><div>The study was developed by simultaneously solving the full system of partial differential equations governing the free-surface flow physics and the surfactant transport on the deforming bubble interface using multi-scale numerical simulation. </div><div>Results show in microscopic detail how surface tension gradients (Marangoni stresses) induced by the uneven interfacial coverage produce spontaneous hydrodynamics flows (Marangoni flows) on the surrounding liquid, leading to bubble motion. Results also establish the influence of both surfactant activity and interfacial coverage on total displacement and average bubble velocity at the macroscale. </div><div>Findings from this research improve the fundamental understanding of the free-surface dynamics of self-propulsion and the associated transport of surface-active species, which are critical to important natural and technological processes, ranging from the Marangoni propulsion of microorganisms to the active motion of bubbles and droplets in microfluidic devices. Overall, the findings advance our understanding of active matter behavior; that is, the behavior of material systems with members able to transduce surface energy and mass transport into active movement.</div>