When does an impacting drop stop bouncing?

Abstract

Non-wetting substrates allow impacting liquid drops to spread, recoil and take-off, provided they are not too heavy (Biance et al., J. Fluid Mech., vol. 554, 2006, pp. 47–66) or too viscous (Jha et al., Soft Matt., vol. 16, no. 31, 2020, pp. 7270–7273). In this article, using direct numerical simulations with the volume of fluid method, we investigate how viscous stresses and gravity oppose capillarity to inhibit drop rebound. Close to the bouncing to non-bouncing transition, we evidence that the initial spreading stage can be decoupled from the later retraction and take-off, allowing us to understand the rebound as a process converting the surface energy of the spread liquid into kinetic energy. Drawing an analogy with coalescence-induced jumping, we propose a criterion for the transition from the bouncing to the non-bouncing regime, namely by the condition ${Oh}_{c} + {Bo}_{c} \sim 1$ , where ${Oh}_{c}$ and ${Bo}_{c}$ are the Ohnesorge number and Bond number at the transition, respectively. This criterion is in excellent agreement with the numerical results. We also elucidate the mechanisms of bouncing inhibition in the heavy and viscous drop limiting regimes by calculating the energy budgets and relating them to the drop's shape and internal flow.

Droplet jumping by modulated electrowetting

“…Nevertheless, our study may serve as a strong basis for wider use of electrowetting in applications requiring precise actuation of droplets such as tissue engineering, digital microfluidics and three-dimensional (3-D) printing. Our results also provide key insights to mechanistic understanding of related phenomena such as coalescence-induced jumping of droplets (Boreyko & Chen 2009;Liu et al 2014;Farokhirad et al 2015) or droplet bouncing on solid substrates (Sanjay, Chantelot & Lohse 2023).…”

Jetting Dynamics of Viscous Droplets on Superhydrophobic Surfaces

“…Subsequently, the air−water−solid three-phase contact line (TPCL) starts retracting back from its maximum position, which is governed by the capillary forces, as seen in Figure 3c, d. Toward the end of the retraction phase, depending on the available kinetic energy, 29 the droplet either lifts off from the surface entirely (Figure 3e) or partially (Figure 3f) or get deposited (Figure 3g) as shown by both schematic illustrations (blue-filled images) as well as experimental images (greyscale). When a droplet completely lifts off from the surface at the end of the retraction stage, we call it a "complete rebound" event.…”

“…The studies suggest that the hydrodynamics of droplet rebound, high-speed singular jet, columnar jet, corona splash, prompt splash, cavity expansion and collapse, ejecta sheet, or liquid crown are influenced by several parameters, namely, wettability and stiffness of the underlying substrate, impact velocity, angle-of-impact, liquid properties, and surrounding conditions. For example, high viscosity and large size of the impacting droplets prohibit droplet rebounding . Similarly, while superhydrophobic surfaces favor splashing of impacting droplets, the same is suppressed if the impacting droplet has high viscosity or the impacted substrate is highly compliant .…”

“…For example, high viscosity and large size of the impacting droplets prohibit droplet rebounding. 29 Similarly, while superhydrophobic surfaces favor splashing of impacting droplets, 20 the same is suppressed if the impacting droplet has high viscosity 30 or the impacted substrate is highly compliant. 15 In this regard, the formation of very high-speed jets and columnar jets has grabbed enormous attention in the past decades.…”

Universality of Scaling Laws Governing Contact and Spreading Time Spans of Bouncing Liquid Marbles and its Physical Origin

“…Bouncing of droplets gives rise to an amazing diversity of physical events. − A broad range of physical phenomena is associated with the flow in the drop, initiated by its impact onto a solid substrate. − The scenarios of drop impact depend on the impact velocity, its direction relative to the surface, the drop radius, the physical properties of the liquid (its density, surface tension, viscosity, and viscoelasticity), − the topography of the surface and its wettability, ,, isothermal effects, and air entrapment . Droplet impact plays a key role in a variety of technological situations, including the building industry, development of anti-icing surfaces, painting/coating, spray technology, corrosion of turbine blades and aircraft, oil separation, heat transfer, and electricity generation. , Naturally occurring impact of rain droplets with leaves and soil is also of great interest. , Rapid progress in understanding the complicated interplay of processes occurring during droplet impact came with the development of rapid imaging experimental techniques …”