Design of Ice-free Nanostructured Surfaces Based on Repulsion of Impacting Water Droplets

Abstract

Materials that control ice accumulation are important to aircraft efficiency, highway and powerline maintenance, and building construction. Most current deicing systems include either physical or chemical removal of ice, both energy and resource-intensive. A more desirable approach would be to prevent ice formation rather than to fight its build-up. Much attention has been given recently to freezing of static water droplets resting on supercooled surfaces. Ice accretion, however, begins with the droplet/substrate collision followed by freezing. Here we focus on the behavior of dynamic droplets impacting supercooled nano- and microstructured surfaces. Detailed experimental analysis of the temperature-dependent droplet/surface interaction shows that highly ordered superhydrophobic materials can be designed to remain entirely ice-free down to ca. -25 to -30 °C, due to their ability to repel impacting water before ice nucleation occurs. Ice accumulated below these temperatures can be easily removed. Factors contributing to droplet retraction, pinning and freezing are addressed by combining classical nucleation theory with heat transfer and wetting dynamics, forming the foundation for the development of rationally designed ice-preventive materials. In particular, we emphasize the potential of hydrophobic polymeric coatings bearing closed-cell surface microstructures for their improved mechanical and pressure stability, amenability to facile replication and large-scale fabrication, and opportunities for greater tuning of their material and chemical properties.

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…The subcooled water drop can instantly bounce off, and it has a residence time (≈13 ms) far smaller than the freezing time. [106][107][108] Even a continuously poured subcooled water flow (−20 °C) is also fully nonsticky at the CMDSP surface, instantly shedding off upon contact, as shown on the left of Figure 7d. In sharp contrast, the subcooled water can instantly freeze and form an ice layer on a common flat hydrophobic metal surface (right of Figure 7d).…”

The challenge of removing snow downfall on photovoltaic solar cell roofs in order to maximize solar energy efficiency—Research opportunities for the future

“…Insets show the corresponding experimental images (scale bars are 2 mm). Red lines in panel E highlight the small remaining capillary bridge between the droplet and the substrate at the pinning transition (Mishchenko et al [54]). …”

“…Anti-icing coating design cases with various roughness scales are illustrated in fig.25 (Xiao and Chaudhuri [78]). Schematics for modeling of droplet freezing on superhydrophobic surfaces, using classical heterogeneous nucleation theory and analysis of dynamic wetting behavior, are given in fig.26 (Mishchenko et al [54]), where further details are given in the figure caption. ; the critical pinning transition occurs when the retraction force becomes zero at the time when R = 0 (E); when the retraction force reaches zero before the droplet fully retracts, the contact line pins at that location and the droplet eventually freezes (F).…”

The superhydrophobicity of polymer surfaces: Recent developments

“…Where structure has been investigated, polymeric complex topographies have come out on top. 71 Even surfaces that do not reduce adhesion of ice can depress the nucleation point significantly by increasing the free energy of nucleation. 72,73 Research has so far concentrated on treatments that can be easily applied to large technical surfaces and on PTFE, which has shown the lowest ice adhesion on flat surfaces, due to its low polarizability.…”