Plasma-liquid interfacial layer detected by in situ Raman light sheet microspectroscopy

Abstract

In situ Raman microscopy has been adapted to study the plasma-water interface by applying a light sheet technique. The Raman modes of the -OO stretch of H2O2, symmetric stretch (v1) of NO3 -, and -OH bend of water were measured simultaneously. By modulating the volume of water under detection, both the bulk liquid and interface regions have been probed with micrometer depth resolution. The plasma was a DC glow discharge generated in atmospheric-pressure air with a water cathode. In the bulk liquid, the molar concentration of aqueous NO3increased at a linear rate of 48 µM/minute, whereas aqueous H2O2 growth stopped at about 5 mM. The concentrations of H2O2 and NO3both increased when measuring at depths less than about 20 µm from the interface. The depth profile of NO3concentration was reconstructed, showing that the interfacial layer of NO3has a depth of 28 µm. The shape of the meniscus may influence the interpretation of this depth. Previous models of plasma-water interfaces have predicted interfacial layers of similar depth for short-lived aqueous species such as OH but not for long-lived species such as NO3 -.

Plasma‐enhanced evaporation and its impact on plasma properties and gaseous chemistry in a pin‐to‐water pulsed discharge

“…Important effects of coupled plasma-liquid surface deformation have been shown on the discharge breakdown and plasma instability, as well as enhanced in-volume mixing, convection, and energy dissipation into the aqueous phase [19][20][21] . Extremely limited penetration of electrons [22,23] and reactive neutral radicals in the plasma-liquid interface was proved by sensitive diagnostic and simulation works [24,25] . Supreme fall of species concentrations, particularly electrons and short-lived radicals like OH and ONOOH, are typically characterized in the thin interface [16] .…”

“…Meanwhile, several researchers applied a plasma jet to the solution and in situ diagnosed and analyzed various important active particles including OH, H, O, H 2 O 2 , and so on above the treated solution surface [34][35][36] . Pai [25] studied the penetration depth of key reactive species in the interfacial layer by Raman light-sheet microspectroscopy. The roadmap work by Bruggeman et al [12] provides an instructive assessment of the state of the art of this multidisciplinary area and identifies the key research challenges.…”

The 2022 Plasma Roadmap: low temperature plasma science and technology

“…Examples include the use of coherent Rayleigh Brillouin scattering to probe nanoparticle formation in plasmas [222] and laser induced fluorescence to measure OH densities in discharges in bubbles in liquid [223]. In addition, the implementation of diagnostics well-established in other research areas provides new insights in plasma science, for example, using second harmonic generation (SHG) to probe the plasmaliquid interface and in situ Raman spectroscopy to measure plasma-produced liquid phase species during plasma-liquid interactions [224].…”

Plasma‐induced formation of coatings on vegetable ivory microparticles immersed in silicone oil: Enhancing surface coverage using natural products

“…[45] These RONS impact the surface of the liquid in addition to electrons, neutrals, and radiation, forming a plasma-liquid interface with a micrometric extent. [19,46] In this interface, reactions between the plasma energetic species and the molecules of the liquid occur. The long-lived species generated by these reactions are further distributed throughout the bulk of the liquid by convective transport [25,47] and, upon reactions on the particle surface, may form the coatings observed by ESEM (Figure 4) and AFM (Figure 5) techniques.…”