Control of Drop Impact and Proposal of Pseudo-superhydrophobicity Using Electrostatics

Abstract

The phenomenon of droplet collision with a charged substrate is investigated numerically by a coupled electro-hydrodynamic model. A charge conservation equation and Poisson equation are solved to obtain the transient electric field. The divergence of Maxwell stress (due to the electric field) is included in the transient momentum equation as a volumetric force to couple the electrostatic force with the hydrodynamics. The interface between the two phases is tracked by volume of fluid method. The motion of the contact line on the solid substrate is controlled by concentric ring shaped charged regions. The electric stress in the vicinity of the contact line restrains its motion in the desired direction, which changes the impact behavior substantially. A hydrophilic surface shows superhydrophobic characteristics when actuated by a sufficient magnitude of electric potential. The phenomenon is analyzed with different parametric variations like electric potential, wetting nature of the substrate, and velocity of collision as it is governed by the mutual interaction between the inertia, electrostatic, and capillary forces. The present method can be used to develop engineering surfaces with tunable wetting nature.

Drop impact on viscous liquid films

“…Interfacial processes such as Marangoni flow (Geri et al 2017) or the generation of vapour below a drop deposited on a superheated substrate (the Leidenfrost effect, where the liquid levitates on a cushion of its own vapour; Leidenfrost 1756;Quéré 2013;Chantelot & Lohse 2021) can further stabilize the sandwiched air/vapour layer to facilitate levitation, even for the dynamic case of drop impact (Chandra & Avedisian 1991;Tran et al 2012;Shirota et al 2016). Drops can also defy gravity and levitate thanks to the so-called inverse Leidenfrost effect (Adda-Bedia et al 2016;Gauthier et al 2019) or electromagnetic forces (Pal et al 2017;Singh, Das & Das 2018).…”

Bouncing drops over liquid surfaces

“…Interfacial processes such as Marangoni flow [43] or the generation of vapor below a drop deposited on a superheated substrate [the Leidenfrost effect where the liquid levitates on a cushion of its own vapor, 72, 101, 22] can further stabilize the sandwiched air/vapor layer to facilitate levitation, even for the dynamic case of drop impact [20,135,123]. Drops can also defy gravity and levitate thanks to the so-called inverse Leidenfrost effect [1,41], or electromagnetic forces [90,124].…”