The reason why the plasma sheath is essential in plasma-liquid interaction

What is it about?

This perspective article presents several theoretical and application-related arguments on why the plasma sheath is essential in the interaction of plasmas with liquids. A plasma sheath can be understood as a space charge region that naturally gets formed when a plasma comes in contact with a condensed material. This region is characterized by a strong electric field that accelerates the charged plasma species and that influences the particle transport and local chemistry between the plasma and the surface. Plasma sheaths have traditionally been investigated for solid surfaces. Despite the rapidly increasing interest in plasma-liquid interaction for various applications, the plasma sheath at liquid surfaces has largely been disregarded or treated on a superficial level (pun intended) in research up to now. We argue why sheath models for solid surfaces may need to be adjusted for liquids, and why more fundamental research is required to obtain a more profound understanding of the underlying physics and chemistry. We do this on a general level, as well as by means of examples related to biomedical applications, nuclear fusion, nanomaterial synthesis and chemical synthesis. Doing so, we also discuss several fundamental mechanisms related to the electrical coupling, mass transport, sheath chemistry, electron emission from the liquid surface and droplet formation at the liquid surface.

Featured Image

Photo by Savvas Kalimeris on Unsplash

Photo by Savvas Kalimeris on Unsplash

Why is it important?

For now, research on the fundamentals and applications of plasma-liquid interaction largely focus on the chemical and biochemical aspects. In contrast, the underlying physics has received much less attention, which also counts for the plasma sheath in particular. This perspective article is the first publication that puts the plasma sheath in the spotlight for plasma-liquid interaction in general. Apart from bringing more awareness of its importance, we also explore the current knowledge on specific aspects of the plasma sheath at a liquid surface, such as field penetration into the liquid, mass transport, unique chemical mechanisms, droplet formation and electron emission from the liquid surface.

Perspectives