Slippery damper of an overlay for arresting and manipulating droplets on nonwetting surfaces

Abstract

In diverse processes, such as fertilization, insecticides, and cooling, liquid delivery is compromised by the super-repellency of receiving surfaces, including super-hydro-/omni-phobic and superheated types, a consequence of intercalated air pockets or vapor cushions that promote droplet rebounds as floating mass-spring systems. By simply overlaying impacting droplets with a tiny amount of lubricant (less than 0.1 vol% of the droplet), their interfacial properties are modified in such a way that damper-roller support is attached to the mass-spring system. The overlayers suppress the out-of-plane rebounds by slowing the departing droplets through viscous dissipation and sustain the droplets’ in-plane mobility through self-lubrication, a preferential state for scenarios such as shedding of liquid in spray cooling and repositioning of droplets in printing. The footprint of our method can be made to be minimal, circumventing surface contamination and toxification. Our method enables multifunctional and dynamic control of droplets that impact different types of nonwetting surfaces.

Droplet Bouncing: Fundamentals, Regulations, and Applications

“…The method is beneficial to the applications like spraying or coating. [105] The specific live-oligomeric surfactant in the impacting droplet can even induce its uniform spreading Oppositely charged polyelectrolytes Water Hydrophobic surface [18] Aerosol OT surfactant Water Superhydrophobic surface [103] A live-oligomeric surfactant Water Superhydrophobic surface [104] Surfactant and polymer Water Wired and curved superhydrophobic surface [105] Shape distortion Electric field Water Hydrophobic surface [107,108] Electromagnetic field Ferrofluid Solid surface [109] Hot droplet Heating Water Superhydrophobic surface [110][111][112][113] Overlayer Low surface tension liquid Water, oil Superhydrophobic surface, superomniphobic surface, superheated surface [15] on the superhydrophobic surface by jamming at the contact line between the droplet and the superhydrophobic surface, which is desirable for high-requirement printing. [104] Shape Distortion: In the nature, raindrops may oscillate before the impact due to the droplet collisions, which would cause the distortion of the millimeter-sized droplet shape.…”

“…Han et al first used a micro/nanothickness (from ≈300 nm to ≈300 μm) overlayer as a damper to help millimeter-scale droplet deposit on superrepellent surfaces. [15] The overlaying can be achieved via microfluidics [115][116][117][118][119][120][121][122][123][124] or counter spraying [15] etc. The overlayer first contacts and pins the super-repellent surface, and then consumes the kinetic energy of the impacting compound droplet via viscous dissipation inside the compound droplet.…”

“…The bouncing of compound droplets would be also different from pure droplets, while intensive investigations are mainly on the pure droplets bouncing. The compound droplets [12,15,94,[240][241][242][243] may bring more opportunities for the applications due to their richness and various combinations: the wetting overlaying liquid can be beneficial to the deposition of the high-surface-tension core droplet; the environmental overlaying liquid can be a chemical shield for chemical droplet; the sacrificial overlaying liquid can protect the core liquid droplet under extreme conditions.…”

“…The developed and commonly-used technologies for the experiments include high-speed photography. [15] The high-speed photography can record the temporal and spatial information of the bouncing, including the wetting parameters of the droplet on the surface, the original diameter of the droplet, the deformation of the droplet during the bouncing and contact time of the bouncing. With the help of image processing software like ImageJ, the bouncing process can be analyzed.Droplet impact is a ubiquitous phenomenon in nature, daily life, and industrial processes.…”

Non‐Hookean Droplet Spring for Enhancing Hydropower Harvest

“…Inspired by lotus leaves and beetles, wettability, especially heterogeneous wettability, provides an effective way to manipulate droplet behaviors. [19][20][21][22][23][24][25] In this work, we fabricate droplet-based springs using two parallel plates with heterogeneous wettability, and investigate their non-Hookean elastic mechanics under pressing and stretching. We demonstrate that the nonlinear behaviors of the spring can be well manipulated by the droplet volume, droplet number, and especially the wettability patterns on the parallel plates.…”