How Superhydrophobic Grooves Drive Single-Droplet Jumping

Abstract

Rapid shedding of microdroplets enhances the performance of self-cleaning, anti-icing, water-harvesting, and condensation heat-transfer surfaces. Coalescence-induced droplet jumping represents one of the most efficient microdroplet shedding approaches and is fundamentally limited by weak fluid–substrate dynamics, resulting in a departure velocity smaller than 0.3u, where u is the capillary-inertia-scaled droplet velocity. Laplace pressure-driven single-droplet jumping from rationally designed superhydrophobic grooves has been shown to break conventional capillary-inertia energy transfer paradigms by squeezing and launching single droplets independent of coalescence. However, this interesting droplet shedding mechanism remains poorly understood. Here, we investigate single-droplet jumping from superhydrophobic grooves by examining its dependence upon surface and droplet configurations. Using a volume of fluid (VOF) simulation framework benchmarked with optical visualizations, we verify the Laplace pressure contrast established within the groove-confined droplet that governs single-droplet jumping. An optimal departure velocity of 1.13u is achieved, well beyond what is currently available using condensation on homogeneous or hierarchical superhydrophobic structures. We further develop a jumping/non-jumping regime map in terms of surface wettability and initial droplet volume and demonstrate directional jumping under asymmetric confinement. Our work reveals key fluid–structure interactions required for the tuning of droplet jumping dynamics and guides the design of interfaces and materials for enhanced microdroplet shedding for a plethora of applications.

Enhanced condensation heat transfer by water/ethanol binary liquids on polydimethylsiloxane brushes

“…We anticipate that other binary liquids, for example, water/ isopropanol, water/glycol, and so on, can also promote heat transfer when the latent heat and liquid surface tension are carefully adjusted. Future development could go a step further by implementing this strategy to the condensing surfaces with textures or gradient wettabilities, [48][49][50][51][52] which may break the limit of heat transfer performance. Meanwhile, although the PDMS brushes show good durability after ultrasonic washing, the durability for sustaining dropwise condensation in the long term is still needed to be considered in the future.…”

Particulate–Droplet Coalescence and Self-Transport on Superhydrophobic Surfaces

“…Although demonstrated here to enable self-cleaning of both artificial and natural superhydrophobic surfaces, the role of surface adhesion , and surface structuring − need further quantification. Structuring the surface with rationally designed grooves can significantly enhance droplet jumping kinetics, , promising an alternate pathway for promoting particle–droplet coalescence-based self-cleaning. The reported observation and developed understanding of particle–droplet jumping not only provide guidelines for the design of artificial passive self-cleaning surfaces but also provide rich insights into spore discharge and transport, ,− filtration of humid-air entrained particulates, and deposition and resuspension of virus aerosols …”

Superhydrophobic Strategy for Nature-Inspired Rotating Microfliers: Enhancing Spreading, Reducing Contact Time, and Weakening Impact Force of Raindrops

“…The simulation is based on the interFoam solver on the OpenFOAM platform. In this solver, the VOF is used to track the liquid–gas interface by setting the volume fraction in each grid, and the continuum surface force model is coupled with the VOF method to calculate the surface tension. , See Supporting Information S4 for more details about the simulation, such as the governing equations, the computational domain, and the boundary conditions. In addition, the numerical simulation is well validated by the experimental results (Figures S5 and S6).…”