Gas-Bubble Mixing Improves Liquid Treatment with Cold Atmospheric Plasma

This research addresses the treatment uniformity of liquid (TUL) treated with cold atmospheric plasma (CAP), a key challenge in plasma-liquid interactions. In CAP treatment of liquids, it is crucial to render the effects of CAP on all parts of a liquid sample such as protein solutions. Existing methods have limited effectiveness due to the restricted liquid diffusion of short-lived reactive species into liquid, complexities of liquid samples and their interface with plasma, and variations in plasma parameters. Consequently, either the liquid surface is overtreated, or its bottom part is rarely modified, resulting in undesirable outcomes. In this work, we used the controlled hydrodynamics of gas bubbles rising in the liquid as a method to improve liquid mixing for enhanced TUL treated with CAP generated on the liquid surface. Proof-of-concept experiments were performed using various liquids containing organic molecules, including bromophenol blue, terephthalic acid, coumarin, and myoglobin. We employed our CAP technology called Plasma-Induced Modification of Biomolecules (PLIMB) [1,2] and integrated it with a gas-bubble mixing system to treat these benchmark liquids. Our preliminary results demonstrated that TUL was significantly improved with this mixing process. Furthermore, the mixing facilitated faster modification of these molecules with PLIMB, substantially reducing treatment time. Overall, we anticipate that the coupling of any CAP device and gas-bubble mixing presents an innovative approach [3] to enhance CAP-based liquid treatment, with potential applications to both engineering and basic research on plasma-liquid interactions, shedding light on transport phenomena of multiple phases.