A review of droplet bouncing behaviors on superhydrophobic surfaces: Theory, methods, and applications

Abstract

The phenomenon of droplet bouncing on superhydrophobic surfaces has received extensive attention in the academic and industrial fields, as it is critical for various engineering applications such as anti-icing, spray cooling and metal quenching. In this review, the research of droplet bouncing behaviors are comprehensively introduced from the bouncing mechanism, research methods and potential applications. The bouncing mechanism is related to three aspects: droplet properties, surface characteristics and ambient conditions. Among them, droplet size, impact velocity, gas film, surface morphology, surface temperature and applied electric field are frequently concerned. Surface wettability is critical for droplet bouncing behaviors, which affects the droplet movement on the surface. Momentum and mass distribution are essential to reduce contact time, which can be achieved through surface morphology design. The manipulation of solid-liquid contact lines and surface tension can achieve directional droplet transportation. In addition, typical droplet bouncing experiments are presented, and experimental studies of single and successive droplets in recent decades are collated. Volume of fluid, lattice Boltzmann method and molecular dynamics are described, which are typical simulation methods for droplet bouncing dynamics at different scales. Potential engineering applications such as surface self-cleaning, digital microfluidics, and enhanced heat transfer have been developed through theoretical foundations and research methods. Finally, the conclusions and the possible future research directions are outlined. The durability of superhydrophobic surfaces becomes a bottleneck for engineering applications. The life cycle research perspective may be applied to future studies.

Ferroelectricity of ice nanotube forests grown in three-dimensional graphene: the electric field effect

“…[1][2][3] Although the structure of the water molecule is very simple (only composed of oxygen and hydrogen atoms), its complex behavior and peculiar properties make our understanding of it always limited. [4][5][6] Water has many different phases under various conditions. 7,8 The characteristics of water in different phases are also very colorful.…”

“…1–3 Although the structure of the water molecule is very simple (only composed of oxygen and hydrogen atoms), its complex behavior and peculiar properties make our understanding of it always limited. 4–6…”

Coalescence-Induced Jumping of Nanodroplets in a Perpendicular Electric Field: A Molecular Dynamics Study

“…19 Surface wettability is a key factor affecting droplet bouncing behaviors. [17][18][19]24 The application of the designed superhydrophobic surface can not only reduce the adhesion work but also accelerate the retraction of the liquid bridge during the jumping process, resulting in a higher energy conversion efficiency. 13,16,18 Besides, both the application of the electric field on the dropwise condensation experimentally and the insight into the electrowetting-induced one droplet detachment promote the jumping performance of droplets.…”

“…Recently, it has been reported that jumping can be promoted by increasing the hydrophobicity of the substrate − or applying external energy like an electric field. ,,, To achieve an optimal jumping performance, ultralow adhesion and extra-large contact angles need to be pursued during coalescence . Surface wettability is a key factor affecting droplet bouncing behaviors. − , The application of the designed superhydrophobic surface can not only reduce the adhesion work but also accelerate the retraction of the liquid bridge during the jumping process, resulting in a higher energy conversion efficiency. ,, Besides, both the application of the electric field on the dropwise condensation experimentally and the insight into the electrowetting-induced one droplet detachment promote the jumping performance of droplets. − , The researchers focus on the heat-transfer performance of jumping droplets on superhydrophobic surfaces during electric-field-enhanced condensation. − , By applying a constant electric field in the experiment of dropwise condensation, the jumping frequency and height will be raised due to the charge separation of the electric double layer at the hydrophobic coating. , Traipattanakul et al focus on one jumping water droplet on a superhydrophobic surface with various gap widths and electric fields . The electric field threshold related to the gap width and the droplet charge required to remove a macro-sized droplet from a superhydrophobic surface is reported experimentally .…”

Dynamics of Droplet Coalescence on Hydrophobic Fibers in Oil: Morphology and Liquid Bridge Evolution

“…Droplet jumping behavior can be influenced not only by the microstructures of hydrophobic surfaces − and the characteristic of droplets − but also by the bulk fluids surrounding the droplets. − However, most of the work was limited to studying the behavior of water droplet coalescence and jumping in the air, and few mention the effects of bulk fluids on the droplet coalescence and jumping behavior. It has been reported that the properties of the bulk fluid can affect the merged behaviors of droplets.…”