Droplet impact on plasma surfaces: an interplay of the four states of matter.

Non-thermal plasmas such as dielectric barrier discharges (DBD) in the vicinity of liquids may induce water activation, interfacial deformation, and enhanced evaporation through charge, mass, and energy transport. Complexity increases when a solid surface is introduced into the system. Such multiphase interactions are central to plasma technologies in medicine, disinfection, wastewater treatment, and aerospace applications like flow control and de-icing. We experimentally investigated a water droplet impinging on the plasma-covered dielectric surface of a DBD actuator focusing on droplet dynamics, interfacial processes, and transient plasma response. This study reveals the complex interplay among four states of matter: solid, liquid, gas, and plasma. Key findings include enhanced droplet spreading, the formation of fingerlike structures, and the appearance of localized micro-discharges during droplet-plasma interaction. We also examine plasma discharge behavior, thermal processes during droplet spreading, breakup, and evaporation, and the disruption of ionic wind by droplet impact.