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Description
Electrical discharges generated at the interface of immiscible liquids (e.g., oil-water) drive rapid emulsification through the formation of cavitation bubbles and re-entrant liquid jets. While the electrical parameters (voltage, pulse width) are commonly used to modulate this interaction, the role of hydrodynamic confinement remains unexplored in organic-aqueous systems. This work presents an experimental investigation into the dynamics of nanosecond pulsed discharges at the heptane-water interface under variable ambient pressure ($P_{\infty} = 10 - 101$ kPa) and applied voltage. Using synchronized high-speed shadowgraphy (up to 100 kfps) and electrical diagnostics, we characterize the complete life cycle of the plasma-induced bubble. We demonstrate that ambient pressure acts as a critical tuning parameter for the dimensionless standoff distance ($\gamma = d/R_{max}$). Reducing $P_{\infty}$ significantly enhances the maximum bubble radius ($R_{max}$), effectively forcing a transition from stable oscillation to violent inertial jetting without altering the injected electrical energy. We analyze the trade-off between the increased jet penetration depth at low pressures and the reduced collapse intensity (shockwave amplitude) resulting from the lower driving pressure gradient ($\Delta P = P_{\infty} - P_v$). Experimental radius-time curves are validated against the Keller-Miksis formulation to quantify the thermodynamic efficiency of the discharge. The results indicate that optimizing $P_{\infty}$ allows for the control of emulsification regimes—balancing droplet size distribution against mixing depth—offering a novel, non-intrusive control method for plasma-liquid processing applications.
| Keyword-1 | Plasma-liquid interactions |
|---|---|
| Keyword-2 | Bubble dynamics |
| Keyword-3 | Heptane-water interface |