Dynamics and applications inspired by bubble bursting at a compound interface

Abstract

Interfaces between two distinct phases typically include complex molecular and particulate structures. The properties of a complex interface are crucial to the response of many natural and practical systems, and also strongly govern the behaviors of particles near the interface. Therefore, the complex interface plays a key role in a wide range of phenomena involving mass and energy transport, and understanding the underlying physics remains a canonical problem. Inspired by bubble bursting at such a compound interface, this dissertation explores related dynamics and potential applications of the system, and investigates several other examples that highlight the role of the interface.

In particular, we show that bubble bursting at the surface of an aqueous surfactant solution coated by an oil layer can disperse oil nanodroplets in the water. The dispersal results from the detachment of an oil spray from the bubble boundary when the bubble collapses, and the droplet size is set by physicochemical interactions between oil and surfactants. Motivated by this study, we propose a new platform to generate functional nanoemulsions. We demonstrate scaled-up synthesis and the capability of encapsulating functional nanomaterials with nanoemulsions.

To study the hydrodynamic aspects of the system, we consider the stability of a long free film of liquid composed of two immiscible layers. The approach helps to interpret the behaviors of film rupture before a bubble bursts. Furthermore, the dynamics of bubble bouncing at the compound interface before the bubble comes to rest are then investigated with experiments, numerical simulations and a mass-spring-damper model.

To further understand the role of a complex interface in other fluid systems, we use a reciprocal theorem to study the motion of a drop with surfactants immersed in a background flow. In addition, the dynamic response of the interface can be complicated by the surface topography, and an example is shown considering the vibration instability of a liquid film on a rough surface. A side project in which we study the nanoscale interactions between a solid probe and a fluid is also summarized. The above studies add to the understanding of complex interfaces in the multiphase physics.