Gas-phase microdroplets have recently demonstrated exceptional chemical properties via suspected mechanisms such as contact electrification and surface charge pinning, producing high surface electric fields. Here, microdroplets are injected into a low-temperature atmospheric-pressure plasma and exposed to an excess free-electron flux. We report the first measurements of droplet charge in a fully collisional plasma, with averages up to 2.5 $\times 10^{ 5}$ electrons for 15 $\mu$m droplets, dependent on absorbed power. Simulations indicate solid particles under similar conditions acquire $\sim$40\% less charge, likely due to low-mobility water cluster ion formation around evaporating droplets, and predict surface electric fields up to $10^{ 7}$ V m$^{ -1}$ for the smallest droplets (3 $\mu$m). Plasma exposure also produces H$_{ 2}$O$_{ 2}$ in the liquid, with concentrations up to 33 mM, corresponding to remarkable generation rates exceeding 275 M s$^{ -1}$. The system involves complex, not yet fully elucidated mechanisms. A controlled plasma environment enables defined charge levels and exposure times, allowing systematic study and enhancing droplet properties.
Categories: physics.plasm-ph