Rebounding Droplet‐Droplet Collisions on Superhydrophobic Surfaces: from the Phenomenon to Droplet Logic

Abstract

When water droplets impact each other while traveling on a superhydrophobic surface, we demonstrate that they are able to rebound like billiard balls. We present elementary Boolean logic operations and a flip-flop memory based on these rebounding water droplet collisions. Furthermore, bouncing or coalescence can be easily controlled by process parameters. Thus by the controlled coalescence of reactive droplets, here using the quenching of fluorescent metal nanoclusters as a model reaction, we also demonstrate an elementary operation for programmable chemistry.

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

“…Liquid flowing partly over the trapped air exhibits macroscopic viscous slip, that is, non-zero flow at the apparent solid-liquid boundary 15 . The slip can reduce viscous drag 16,17 and thus enhance flow in micro-and nanochannels 15 as well as in sessile droplets [19][20][21] . Combining the reduced drag with the guidance of the droplets by gravitational 18 , electric 18 or magnetic fields 19,20 opens platforms for novel functional droplet devices performing, for example, logic operations or programmable chemistry 21 .…”

Temperature-Induced Coalescence of Colliding Binary Droplets on Superhydrophobic Surface

“…All previous studies of collision between binary droplets focused on droplets set at a fixed temperature123456789, and there is no report, to the best of our knowledge, of the temperature effect on the outcome of collision between droplets. Under appropriate collision conditions, the incoming droplet can rebound as it hits the stationary droplet on the superhyrodphobic surfaces10. This study shows that when there is an increase in temperature for both droplets or one of the droplets, there is increased possibility of coalescence after collision.…”

“…Through both experimental work and theoretic modeling, Graham et al investigated the coalescence of two droplets on a solid surface with various wetting properties to study the dynamics of droplet coalescence with increased hydrophobicity30. Mertaniemi et al explored a droplet logic with rebounding droplet-droplet interaction on the superhydrophobic surface for future bio-computer10. Farhangi et al studied coalescence of a falling droplet with a stationary droplet on a superhydrophobic surface to characterize the kinetic energy needed for the detachment of the droplets from the surfaces31.…”

“…Farhangi et al studied coalescence of a falling droplet with a stationary droplet on a superhydrophobic surface to characterize the kinetic energy needed for the detachment of the droplets from the surfaces31. Compared to the collision under free flying condition, the collision of binary droplets on solid surfaces has slightly different collision regions1015. At low impacting velocities, as reported by Zhao et al32, the head-on collision of the binary liquid droplets on a solid surface can be categorized into four regions: coalescence, complete rebound, partial rebound after conglutination, and coalescence accompanied by conglutination.…”

One- and two-particle dynamics in microfluidic T-junctions

“…However, additional focusing may be needed for serial gate configurations. As the device does not rely on instantaneous collisions, e.g., those of water droplets on superphobic surfaces [30], the phase diagram of Fig. 3 and thus the binary operations should exhibit tolerances to focusing error in both quantities d/R and s/(W/2).…”