Plasma bubbles: a route to sustainable chemistry

Atmospheric plasma discharges are finding increased applications in addressing environmental challenges including water purification, chemical synthesis and biotechnology. An effective means of interfacing the reactivity of plasma gas discharges with liquids is needed to enhance liquid phase chemical reactions. Plasma discharges in bubbles has been considered as an innovative solution for achieving this goal potentially offering electrically driven, sustainable chemistry with low energy consumption and the unique benefit of maintaining a large volume discharge under the liquid surface. Here we provide a concise review on the state-of-art for research on plasma-bubble interactions and a perspective for future research.

Cavitation Dynamics and Inertial Cavitation Threshold of Lipid Coated Microbubbles in Viscoelastic Media with Bubble–Bubble Interactions

Encapsulated microbubbles combined with ultrasound have been widely utilized in various biomedical applications; however, the bubble dynamics in viscoelastic medium have not been completely understood. It involves complex interactions of coated microbubbles with ultrasound, nearby microbubbles and surrounding medium. Here, a comprehensive model capable of simulating the complex bubble dynamics was developed via taking the nonlinear viscoelastic behaviors of the shells, the bubble–bubble interactions and the viscoelasticity of the surrounding medium into account simultaneously. For two interacting lipid-coated bubbles with different initial radii in viscoelastic media, it exemplified that the encapsulating shell, the inter-bubble interactions and the medium viscoelasticity would noticeably suppress bubble oscillations. The inter-bubble interactions exerted a much stronger suppressing effect on the small bubble within the parameters examined in this paper, which might result from a larger radiated pressure acting on the small bubble due to the inter-bubble interactions. The lipid shells make the microbubbles exhibit two typical asymmetric dynamic behaviors (i.e., compression or expansion dominated oscillations), which are determined by the initial surface tension of the bubbles. Accordingly, the inertial cavitation threshold decreases as the initial surface tension increases, but increases as the shell elasticity and viscosity increases. Moreover, with the distance between bubbles decreasing and/or the initial radius of the large bubble increasing, the oscillations of the small bubble decrease and the inertial cavitation threshold increases gradually due to the stronger suppression effects caused by the enhanced bubble–bubble interactions. Additionally, increasing the elasticity and/or viscosity of the surrounding medium would also dampen bubble oscillations and result in a significant increase in the inertial cavitation threshold. This study may contribute to both encapsulated microbubble-associated ultrasound diagnostic and emerging therapeutic applications.

A Rational Interpretation of the Role of Turbulence in Particle-Bubble Interactions

Interactions between particles and bubbles have been cornerstone for the successful applications of froth flotation to the beneficiations of minerals or coal. Particle-bubble interactions are highly physio-chemical processes on the basis of surface science and hydrodynamics. Though these two aspects are deeply interwoven, we focus on the discussions of the effects of turbulence on the interactions between particles and bubbles, i.e., collision, attachment and detachment. It has to be mentioned this effect is not working in one direction and can affect flotation performance in a complicated way. Only when turbulence effects are well understood, flotation processes can be optimised by suitably changing equipment structure or operating parameters. The aim of this paper is to review the most recent progresses in this aspect and to identify the future development in successfully considering turbulence effects on flotation processes.

Inter-Bubble Interactions in Ultrasonically Excited Microbubble Clusters

Microbubbles (MBs) have been utilized in a variety of applications ranging from medicine to chemistry. There have been extensive studies on many aspects of microbubble dynamics. The majority of previous theoretical studies examine the oscillations of single microbubbles. In most applications multiple microbubbles form clusters. Oscillating microbubbles generate secondary pressure waves in the medium which have been shown to modify the dynamics of neighboring MBs. Large microbubble clusters have not been studied due to the complexity of solving many coupled differential equations governing the dynamics of a large number of microbubbles. This work expands on previous works conducted on the study of multiple bubble interactions. Two approaches are introduced to simulate large clusters. Inter-bubble interactions are classified and used to explain and predict collective behavior within large polydisperse clusters. This work shows that even identical MBs within a monodisperse cluster do not necessarily exhibit identical behavior.

Inter-Bubble Interactions in Ultrasonically Excited Microbubble Clusters

Microbubbles (MBs) have been utilized in a variety of applications ranging from medicine to chemistry. There have been extensive studies on many aspects of microbubble dynamics. The majority of previous theoretical studies examine the oscillations of single microbubbles. In most applications multiple microbubbles form clusters. Oscillating microbubbles generate secondary pressure waves in the medium which have been shown to modify the dynamics of neighboring MBs. Large microbubble clusters have not been studied due to the complexity of solving many coupled differential equations governing the dynamics of a large number of microbubbles. This work expands on previous works conducted on the study of multiple bubble interactions. Two approaches are introduced to simulate large clusters. Inter-bubble interactions are classified and used to explain and predict collective behavior within large polydisperse clusters. This work shows that even identical MBs within a monodisperse cluster do not necessarily exhibit identical behavior.